BIND 9 Administrator Reference
ManualRelease 9.20.0

Internet Systems Consortium

Jul 23, 2024

CONTENTS

1 Introduction to DNS and BIND 9
1.1 Scope of Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Organization of This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 Conventions Used in This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 The Domain Name System (DNS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.5 DNS Security Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2 Resource Requirements
2.1 Hardware Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 CPU Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Memory Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Name Server-Intensive Environment Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Supported Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 Unsupported Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 Installing BIND 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Configurations and Zone Files
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Authoritative Name Servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Resolver (Caching Name Servers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Zone File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Name Server Operations
4.1 Tools for Use With the Name Server Daemon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Configuring Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Developing Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5 DNSSEC
5.1 Zone Signing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Secure Delegation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3 DNSSEC Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4 Dynamic Trust Anchor Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5 PKCS#11 (Cryptoki) Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6 Advanced Configurations
6.1 Dynamic Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 NOTIFY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3 Incremental Zone Transfers (IXFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6.4
6.5
6.6
6.7
6.8
6.9

Split DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IPv6 Support in BIND 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dynamically Loadable Zones (DLZ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dynamic Database (DynDB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Catalog Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DNS Firewalls and Response Policy Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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7 Security Configurations
7.1 Security Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2 Access Control Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3 Chroot and Setuid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.4 Dynamic Update Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5 TSIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6 SIG(0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8 Configuration Reference87
8.1 Configuration File (named.conf) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.2 Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.3 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
8.4 Statements by Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
8.5 BIND 9 Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
9 Troubleshooting
9.1 Common Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 Incrementing and Changing the Serial Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3 Where Can I Get Help? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10 Building BIND 9
10.1 Required Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2 Optional Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3 macOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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11 Release Notes
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2 Supported Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.3 Download . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.4 Known Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.5 Notes for BIND 9.20.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.6 License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.7 End of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.8 Thank You . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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12 DNSSEC Guide
12.1 Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.4 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.5 Signing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.6 Basic DNSSEC Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.7 Advanced Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.8 Recipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.9 Commonly Asked Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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13 A Brief History of the DNS and BIND

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14 General DNS Reference Information
14.1 Requests for Comment (RFCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3 Internet Drafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15 Manual Pages
15.1 arpaname - translate IP addresses to the corresponding ARPA names . . . . . . . . . . . . . . . . . .
15.2 ddns-confgen - TSIG key generation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3 delv - DNS lookup and validation utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4 dig - DNS lookup utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5 dnssec-cds - change DS records for a child zone based on CDS/CDNSKEY . . . . . . . . . . . . . . .
15.6 dnssec-dsfromkey - DNSSEC DS RR generation tool . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7 dnssec-importkey - import DNSKEY records from external systems so they can be managed . . . . . .
15.8 dnssec-keyfromlabel - DNSSEC key generation tool . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.9 dnssec-keygen: DNSSEC key generation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.10 dnssec-ksr - Create signed key response (SKR) files for offline KSK setups . . . . . . . . . . . . . . .
15.11 dnssec-revoke - set the REVOKED bit on a DNSSEC key . . . . . . . . . . . . . . . . . . . . . . . .
15.12 dnssec-settime: set the key timing metadata for a DNSSEC key . . . . . . . . . . . . . . . . . . . . .
15.13 dnssec-signzone - DNSSEC zone signing tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.14 dnssec-verify - DNSSEC zone verification tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.15 dnstap-read - print dnstap data in human-readable form . . . . . . . . . . . . . . . . . . . . . . . . .
15.16 filter-aaaa.so - filter AAAA in DNS responses when A is present . . . . . . . . . . . . . . . . . . . .
15.17 host - DNS lookup utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.18 mdig - DNS pipelined lookup utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.19 named-checkconf - named configuration file syntax checking tool . . . . . . . . . . . . . . . . . . . .
15.20 named-checkzone - zone file validation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.21 named-compilezone - zone file converting tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.22 named-journalprint - print zone journal in human-readable form . . . . . . . . . . . . . . . . . . . .
15.23 named-nzd2nzf - convert an NZD database to NZF text format . . . . . . . . . . . . . . . . . . . . .
15.24 named-rrchecker - syntax checker for individual DNS resource records . . . . . . . . . . . . . . . . .
15.25 named.conf - configuration file for named . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.26 named - Internet domain name server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.27 nsec3hash - generate NSEC3 hash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.28 nslookup - query Internet name servers interactively . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.29 nsupdate - dynamic DNS update utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.30 rndc-confgen - rndc key generation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.31 rndc.conf - rndc configuration file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.32 rndc - name server control utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.33 tsig-keygen - TSIG key generation tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Index

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CHAPTERONEINTRODUCTION TO DNS AND BIND 9

The Internet Domain Name System (DNS) consists of:• the syntax to specify the names of entities in the Internet in a hierarchical manner,• the rules used for delegating authority over names, and• the system implementation that actually maps names to Internet addresses.
DNS data is maintained in a group of distributed hierarchical databases.

1.1 Scope of Document
The Berkeley Internet Name Domain (BIND) software implements a domain name server for a number of operating systems. This document provides basic information about the installation and maintenance of Internet Systems Consortium(ISC) BIND version 9 software package for system administrators.
This manual covers BIND version 9.20.0.

1.2 Organization of This Document
Introduction to DNS and BIND 9 introduces the basic DNS and BIND concepts. Some tutorial material on The Domain
Name System (DNS) is presented for those unfamiliar with DNS. A DNS Security Overview is provided to allow BIND
operators to implement appropriate security for their operational environment.
Resource Requirements describes the hardware and environment requirements for BIND 9 and lists both the supported
and unsupported platforms.
Configurations and Zone Files is intended as a quickstart guide for newer users. Sample files are included for Authoritative
Name Servers (both primary and secondary), as well as a simple Resolver (Caching Name Servers) and a Forwarding
Resolver Configuration. Some reference material on the Zone File is included.
Name Server Operations covers basic BIND 9 software and DNS operations, including some useful tools, Unix signals,
and plugins.
Advanced Configurations builds on the configurations of Configurations and Zone Files, adding functions and features thesystem administrator may need.
Security Configurations covers most aspects of BIND 9 security, including file permissions, running BIND 9 in a “jail,”and securing file transfers and dynamic updates.
DNSSEC describes the theory and practice of cryptographic authentication of DNS information. The DNSSEC Guide is apractical guide to implementing DNSSEC.

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Configuration Reference gives exhaustive descriptions of all supported blocks, statements, and grammars used in BIND
9’s named.conf configuration file.
Troubleshooting provides information on identifying and solving BIND 9 and DNS problems. Information about bugreporting procedures is also provided.
Building BIND 9 is a definitive guide for those occasions where the user requires special options not provided in thestandard Linux or Unix distributions.
The Appendices contain useful reference information, such as a bibliography and historic information related to BIND
and the Domain Name System, as well as the current man pages for all the published tools.

1.3 Conventions Used in This Document
In this document, we generally use fixed-width text to indicate the following types of information:• pathnames• filenames• URLs• hostnames• mailing list names• new terms or concepts• literal user input• program output• keywords• variables
Text in “quotes,” bold text, or italics is also used for emphasis or clarity.

1.4 The Domain Name System (DNS)This is a brief description of the functionality and organization of the Domain Name System (DNS). It is provided tofamiliarize users with the concepts involved, the (often confusing) terminology used, and how all the parts fit together toform an operational system.
All network systems operate with network addresses, such as IPv4 and IPv6. The vast majority of humans find it easier towork with names rather than seemingly endless strings of network address digits. The earliest ARPANET systems (fromwhich the Internet evolved) mapped names to addresses using a hosts file that was distributed to all entities wheneverchanges occurred. Operationally, such a system became rapidly unsustainable once there were more than 100 networked
entities, which led to the specification and implementation of the Domain Name System that we use today.

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1.4.1 DNS Fundamentals
The DNS naming system is organized as a tree structure comprised of multiple levels and thus it naturally creates a
distributed system. Each node in the tree is given a label which defines its Domain (its area or zone) of Authority. The
topmost node in the tree is the Root Domain; it delegates to Domains at the next level which are generically known as
the Top-Level Domains (TLDs). They in turn delegate to Second-Level Domains (SLDs), and so on. The Top-Level
Domains (TLDs) include a special group of TLDs called the Country Code Top-Level Domains (ccTLDs), in which
every country is assigned a unique two-character country code from ISO 3166 as its domain.
Note: The Domain Name System is controlled by ICANN (https://www.icann.org) (a 501c non-profit entity); theircurrent policy is that any new TLD, consisting of three or more characters, may be proposed by any group of commercial
sponsors and if it meets ICANN’s criteria will be added to the TLDs.
The concept of delegation and authority flows down the DNS tree (the DNS hierarchy) as shown:

Fig. 1: Delegation and Authority in the DNS Name Space
A domain is the label of a node in the tree. A domain name uniquely identifies any node in the DNS tree and is written, left
to right, by combining all the domain labels (each of which are unique within their parent’s zone or domain of authority),
with a dot separating each component, up to the root domain. In the above diagram the following are all domain names:
example.com
b.com
ac.uk
us
org

The root has a unique label of “.” (dot), which is normally omitted when it is written as a domain name, but when it is
written as a Fully Qualified Domain Name (FQDN) the dot must be present. Thus:
example.com
example.com.

# domain name
# FQDN

1.4. The Domain Name System (DNS)

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1.4.2 Authority and Delegation
Each domain (node) has been delegated the authority from its parent domain. The delegated authority includes specificresponsibilities to ensure that every domain it delegates has a unique name or label within its zone or domain of authority,and that it maintains an authoritative list of its delegated domains. The responsibilities further include an operational
requirement to operate two (or more) name servers (which may be contracted to a third party) which will contain theauthoritative data for all the domain labels within its zone of authority in a zone file. Again, the tree structure ensures thatthe DNS name space is naturally distributed.
The following diagram illustrates that Authoritative Name Servers exist for every level and every domain in the DNS
name space:

Fig. 2: Authoritative Name Servers in the DNS Name Space

Note: The difference between a domain and a zone can appear confusing. Practically, the terms are generally usedsynonymously in the DNS. If, however, you are into directed graphs and tree structure theory or similar exotica, a zone
can be considered as an arc through any node (or domain) with the domain at its apex. The zone therefore encompasses
all the name space below the domain. This can, however, lead to the concept of subzones and these were indeed definedin the original DNS specifications. Thankfully the term subzone has been lost in the mists of time.

1.4.3 Root Servers
The root servers are a critical part of the DNS authoritative infrastructure. There are 13 root servers (a.root-servers.net
to m.root-servers.net). The number 13 is historically based on the maximum amount of name and IPv4 data that could bepacked into a 512-byte UDP message, and not a perverse affinity for a number that certain cultures treat as unlucky. The
512-byte UDP data limit is no longer a limiting factor and all root servers now support both IPv4 and IPv6. In addition,
almost all the root servers use anycast, with well over 300 instances of the root servers now providing service worldwide(see further information at https://www.root-servers.org). The root servers are the starting point for all name resolution
within the DNS.

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1.4.4 Name Resolution
So far all the emphasis has been on how the DNS stores its authoritative domain (zone) data. End-user systems use names(an email address or a web address) and need to access this authoritative data to obtain an IP address, which they use tocontact the required network resources such as web, FTP, or mail servers. The process of converting a domain name toa result (typically an IP address, though other types of data may be obtained) is generically called name resolution, andis handled by resolvers (also known as caching name servers and many other terms). The following diagram shows the
typical name resolution process:Fig. 3: Authoritative Name Servers and Name Resolution
An end-user application, such as a browser (1), when needing to resolve a name such as www.example.com, makes aninternal system call to a minimal function resolution entity called a stub resolver (2). The stub resolver (using stored IP
addresses) contacts a resolver (a caching name server or full-service resolver) (3), which in turn contacts all the necessary
authoritative name servers (4, 5, and 6) to provide the answer that it then returns to the user (2, 1). To improve performance, all resolvers (including most stub resolvers) cache (store) their results such that a subsequent request for the samedata is taken from the resolver’s cache, removing the need to repeat the name resolution process and use time-consuming
resources. All communication between the stub resolver, the resolver, and the authoritative name servers uses the DNS
protocol’s query and response message pair.

1.4.5 DNS Protocol and Queries
DNS queries use the UDP protocol over the reserved port 53 (but both TCP and TLS can optionally be used in someparts of the network).
The following diagram shows the name resolution process expressed in terms of DNS queries and responses.
The stub resolver sends a recursive query message (with the required domain name in the QUESTION section of thequery) (2) to the resolver. A recursive query simply requests the resolver to find the complete answer. A stub resolver
only ever sends recursive queries and always needs the service of a resolver. The response to a recursive query can be:
1. The answer to the user’s QUESTION in the ANSWER section of the query response.
2. An error (such as NXDOMAIN - the name does not exist).
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Fig. 4: Resolvers and Queries

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The resolver, on receipt of the user’s recursive query, either responds immediately, if the ANSWER is in its cache, oraccesses the DNS hierarchy to obtain the answer. The resolver always starts with root servers and sends an iterative
query (4, 5, and 6). The response to an iterative query can be:
1. The answer to the resolver’s QUESTION in the ANSWER section of the query response.
2. A referral (indicated by an empty ANSWER section but data in the AUTHORITY section, and typically IP addresses
in the ADDITIONAL section of the response).
3. An error (such as NXDOMAIN - the name does not exist).
If the response is either an answer or an error, these are returned immediately to the user (and cached for future use). If
the response is a referral, the resolver needs to take additional action to respond to the user’s recursive query.
A referral, in essence, indicates that the queried server does not know the answer (the ANSWER section of the responseis empty), but it refers the resolver to the authoritative name servers (in the AUTHORITY section of the response)
which it knows about in the domain name supplied in the QUESTION section of the query. Thus, if the QUESTION
is for the domain name www.example.com, the root server to which the iterative query was sent adds a list of the .com
authoritative name servers in the AUTHORITY section. The resolver selects one of the servers from the AUTHORITY
section and sends an iterative query to it. Similarly, the .com authoritative name servers send a referral containing a list of
the example.com authoritative name servers. This process continues down the DNS hierarchy until either an ANSWER
or an error is received, at which point the user’s original recursive query is sent a response.
Note: The DNS hierarchy is always accessed starting at the root servers and working down; there is no concept of “up”
in the DNS hierarchy. Clearly, if the resolver has already cached the list of .com authoritative name servers and the user’srecursive query QUESTION contains a domain name ending in .com, it can omit access to the root servers. However,that is simply an artifact (in this case a performance benefit) of caching and does not change the concept of top-down
access within the DNS hierarchy.
The insatiably curious may find reading RFC 1034 and RFC 1035 a useful starting point for further information.

1.4.6 DNS and BIND 9
BIND 9 is a complete implementation of the DNS protocol. BIND 9 can be configured (using its named.conf file) as
an authoritative name server, a resolver, and, on supported hosts, a stub resolver. While large operators usually dedicate
DNS servers to a single function per system, smaller operators will find that BIND 9’s flexible configuration features
support multiple functions, such as a single DNS server acting as both an authoritative name server and a resolver.
Example configurations of basic authoritative name servers and resolvers and forwarding resolvers, as well as advanced
configurations and secure configurations, are provided.

1.5 DNS Security Overview
DNS is a communications protocol. All communications protocols are potentially vulnerable to both subversion andeavesdropping. It is important for users to audit their exposure to the various threats within their operational environment
and implement the appropriate solutions. BIND 9, a specific implementation of the DNS protocol, provides an extensive
set of security features. The purpose of this section is to help users to select from the range of available security features
those required for their specific user environment.
A generic DNS network is shown below, followed by text descriptions. In general, the further one goes from the left-handside of the diagram, the more complex the implementation.

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Note: Historically, DNS data was regarded as public and security was concerned, primarily, with ensuring the integrityof DNS data. DNS data privacy is increasingly regarded as an important dimension of overall security, specifically DNS
over TLS.

Fig. 5: BIND 9 Security Overview
The following notes refer to the numbered elements in the above diagram.
1. A variety of system administration techniques and methods may be used to secure BIND 9’s local environment,
including file permissions, running BIND 9 in a jail, and the use of Access Control Lists.
2. The remote name daemon control (rndc) program allows the system administrator to control the operation of a nameserver. The majority of BIND 9 packages or ports come preconfigured with local (loopback address) security preconfigured. If rndc is being invoked from a remote host, further configuration is required. The nsupdate tool uses Dynamic
DNS (DDNS) features and allows users to dynamically change the contents of the zone file(s). nsupdate access andsecurity may be controlled using named.conf statements or using TSIG or SIG(0) cryptographic methods. Clearly, if
the remote hosts used for either rndc or DDNS lie within a network entirely under the user’s control, the security threat
may be regarded as non-existent. Any implementation requirements, therefore, depend on the site’s security policy.
3. Zone transfer from a primary to one or more secondary authoritative name servers across a public network carries
risk. The zone transfer may be secured using named.conf statements, TSIG cryptographic methods or TLS. Clearly, if
the secondary authoritative name server(s) all lie within a network entirely under the user’s control, the security threat
may be regarded as non-existent. Any implementation requirements again depend on the site’s security policy.
4. If the operator of an authoritative name server (primary or secondary) wishes to ensure that DNS responses to userinitiated queries about the zone(s) for which they are responsible can only have come from their server, that the data
received by the user is the same as that sent, and that non-existent names are genuine, then DNSSEC is the only solution.
DNSSEC requires configuration and operational changes both to the authoritative name servers and to any resolver whichaccesses those servers.
5. The typical Internet-connected end-user device (PCs, laptops, and even mobile phones) either has a stub resolver
or operates via a DNS proxy. A stub resolver requires the services of an area or full-service resolver to completely
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answer user queries. Stub resolvers on the majority of PCs and laptops typically have a caching capability to increase
performance. At this time there are no standard stub resolvers or proxy DNS tools that implement DNSSEC. BIND 9
may be configured to provide such capability on supported Linux or Unix platforms. DNS over TLS may be configured toverify the integrity of the data between the stub resolver and area (or full-service) resolver. However, unless the resolver
and the Authoritative Name Server implements DNSSEC, end-to-end integrity (from authoritative name server to stub
resolver) cannot be guaranteed.

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10Chapter 1. Introduction to DNS and BIND 9CHAPTERTWORESOURCE REQUIREMENTS

2.1 Hardware Requirements
DNS hardware requirements have traditionally been quite modest. For many installations, servers that have been retired
from active duty have performed admirably as DNS servers.
However, the DNSSEC features of BIND 9 may be quite CPU-intensive, so organizations that make heavy use of thesefeatures may wish to consider larger systems for these applications. BIND 9 is fully multithreaded, allowing full utilizationof multiprocessor systems for installations that need it.

2.2 CPU Requirements
CPU requirements for BIND 9 range from i386-class machines, for serving static zones without caching, to enterpriseclass machines to process many dynamic updates and DNSSEC-signed zones, serving many thousands of queries per
second.

2.3 Memory Requirements
Server memory must be sufficient to hold both the cache and the zones loaded from disk. The max-cache-size option
can limit the amount of memory used by the cache, at the expense of reducing cache hit rates and causing more DNS
traffic. It is still good practice to have enough memory to load all zone and cache data into memory; unfortunately, thebest way to determine this for a given installation is to watch the name server in operation. After a few weeks, the server
process should reach a relatively stable size where entries are expiring from the cache as fast as they are being inserted.

2.4 Name Server-Intensive Environment Issues
For name server-intensive environments, there are two configurations that may be used. The first is one where clients andany second-level internal name servers query the main name server, which has enough memory to build a large cache;this approach minimizes the bandwidth used by external name lookups. The second alternative is to set up second-levelinternal name servers to make queries independently. In this configuration, none of the individual machines need to haveas much memory or CPU power as in the first alternative, but this has the disadvantage of making many more external
queries, as none of the name servers share their cached data.

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2.5 Supported Platforms
The current support status of BIND 9 versions across various platforms can be found in the ISC Knowledgebase:https://kb.isc.org/docs/supported-platforms
In general, this version of BIND will build and run on any POSIX-compliant system with a modern C11 (or better)compiler, BSD-style sockets with RFC-compliant IPv6 support, POSIX-compliant threads, and the required libraries.
The following C11 features are required to compile BIND 9:• Atomic operations support defined in <stdatomic.h>• Thread Local Storage support defined in <threads.h>
Where it makes sense, BIND 9 uses C-standard fixes introduced by C17 update of the C11 standard.
ISC regularly tests BIND on many operating systems and architectures, but lacks the resources to test all of them. Consequently, ISC is only able to offer support on a “best-effort” basis for some.

2.5.1 Regularly Tested Platforms
Current versions of BIND 9 are fully supported and regularly tested on the following systems:• Debian 11, 12• Ubuntu LTS 20.04, 22.04, 24.04• Fedora 40• Red Hat Enterprise Linux / CentOS / Oracle Linux 8, 9
• FreeBSD 13.3, 14.0
• Alpine Linux 3.20
The amd64 CPU architecture is fully supported and regularly tested.

2.5.2 Best-Effort
The following are platforms on which BIND is known to build and run. ISC makes every effort to fix bugs on theseplatforms, but may be unable to do so quickly due to lack of hardware, less familiarity on the part of engineering staff,
and other constraints. None of these are tested regularly by ISC.
• macOS 10.12+• Solaris 11• NetBSD• OpenBSD• Other Linux distributions still supported by their vendors, such as:– Ubuntu 22.10+– Gentoo– Arch Linux• OpenWRT/LEDE 17.01+• Other CPU architectures (arm, arm64, mips64, ppc64, s390x)

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2.5.3 Community-Maintained
These systems may not all have the required dependencies for building BIND easily available, although it is possible inmany cases to compile those directly from source. The community and interested parties may wish to help with maintenance, and we welcome patch contributions, although we cannot guarantee that we will accept them. All contributions
will be assessed against the risk of adverse effect on officially supported platforms.
• Platforms past or close to their respective EOL dates, such as:– Ubuntu 14.04, 16.04, 18.04 (Ubuntu ESM releases are not supported)– Red Hat Enterprise Linux / CentOS / Oracle Linux 6, 7
– Debian 8 Jessie, 9 Stretch, 10 Buster– FreeBSD 10.x, 11.x
• Less common CPU architectures (i386, i686, mips, mipsel, sparc, ppc, and others)

2.6 Unsupported Platforms
These are platforms on which current versions of BIND 9 are known not to build or run:
• Platforms without at least OpenSSL 1.0.2• Windows• Solaris 10 and older• Platforms that do not support IPv6 Advanced Socket API (RFC 3542)• Platforms that do not support atomic operations (via compiler or library)• Linux without NPTL (Native POSIX Thread Library)• Platforms on which libuv >= 1.34 cannot be compiled or is not available

2.7 Installing BIND 9
Building BIND 9 contains complete instructions for how to build BIND 9.
The ISC Knowledgebase contains many useful articles about installing BIND 9 on specific platforms.

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CHAPTER

THREE

CONFIGURATIONS AND ZONE FILES

3.1 Introduction
BIND 9 uses a single configuration file called named.conf.
/usr/local/etc/namedb.

which is typically located in either /etc/namedb or

Note: If rndc is being used locally (on the same host as BIND 9) then an additional file rndc.conf
may be present, though rndc operates without this file. If rndc is being run from a remote host then an
rndc.conf file must be present as it defines the link characteristics and properties.
Depending on the functionality of the system, one or more zone files is required.
The samples given throughout this and subsequent chapters use a standard base format for both the named.conf andthe zone files for example.com. The intent is for the reader to see the evolution from a common base as features areadded or removed.

3.1.1 named.conf Base File
This file illustrates the typical format and layout style used for named.conf and provides a basic logging service, which
may be extended as required by the user.
// base named.conf file// Recommended that you always maintain a change log in this file as shown here// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)//
logging {channel example_log {// uses a relative path name and the directory statement to(continues on next page)15

BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;// only log info and up messages - all others discarded
severity info;};
category default {example_log;};};

The logging and options blocks and category, channel, directory, file, and severity statements
are all described further in the appropriate sections of this ARM.

3.1.2 example.com base zone file
The following is a complete zone file for the domain example.com, which illustrates a number of common features.
Comments in the file explain these features where appropriate. Zone files consist of Resource Records (RR), which describe
the zone’s characteristics or properties.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
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; base zone file for example.com$TTL 2d; default TTL for zone
$ORIGIN example.com. ; base domain-name; Start of Authority RR defining the key characteristics of the zone (domain)@IN
SOA
ns1.example.com. hostmaster.example.com. (2003080800 ; serial number
12h; refresh
15m; update retry
3w; expiry2h; minimum); name server RR for the domainINNS
ns1.example.com.
; the second name server is external to this zone (domain)INNS
ns2.example.net.
; mail server RRs for the zone (domain)
3w IN
MX 10 mail.example.com.
; the second mail servers is external to the zone (domain)IN
MX 20 mail.example.net.
; domain hosts includes NS and MX records defined above; plus any others required; for instance a user query for the A RR of joe.example.com will
; return the IPv4 address 192.168.254.6 from this zone filens1
INA
192.168.254.2
mail
IN
A
192.168.254.4
joeINA
192.168.254.6
wwwINA
192.168.254.7; aliases ftp (ftp server) to an external domain
ftp
IN
CNAME
ftp.example.net.

This type of zone file is frequently referred to as a forward-mapped zone file, since it maps domain names to someother value, while a reverse-mapped zone file maps an IP address to a domain name. The zone file is called example.com
for no good reason except that it is the domain name of the zone it describes; as always, users are free to use whatever
file-naming convention is appropriate to their needs.

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3.1.3 Other Zone Files
Depending on the configuration additional zone files may or should be present. Their format and functionality are briefly
described here.

3.1.4 localhost Zone FileAll end-user systems are shipped with a hosts file (usually located in /etc). This file is normally configured to map
the name localhost (the name used by applications when they run locally) to the loopback address. It is argued, reasonably, that a forward-mapped zone file for localhost is therefore not strictly required. This manual does use the BIND 9
distribution file localhost-forward.db (normally in /etc/namedb/master or /usr/local/etc/namedb/master) in all
configuration samples for the following reasons:
1. Many users elect to delete the hosts file for security reasons (it is a potential target of serious domain nameredirection/poisoning attacks).
2. Systems normally lookup any name (including domain names) using the hosts file first (if present), followed
by DNS. However, the nsswitch.conf file (typically in /etc) controls this order (normally hosts: file dns),
allowing the order to be changed or the file value to be deleted entirely depending on local needs. Unless the
BIND administrator controls this file and knows its values, it is unsafe to assume that localhost is forward-mappedcorrectly.
3. As a reminder to users that unnecessary queries for localhost form a non-trivial volume of DNS queries on the
public network, which affects DNS performance for all users.
Users may, however, elect at their discretion not to implement this file since, depending on the operational environment,
it may not be essential.
The BIND 9 distribution file localhost-forward.db format is shown for completeness and provides for both IPv4
and IPv6 localhost resolution. The zone (domain) name is localhost.
$TTL 3hlocalhost.

SOA
NS
A
AAAA

localhost.
localhost.
127.0.0.1::1

nobody.localhost. 42

1d

12h

1w

3h

Note: Readers of a certain age or disposition may note the reference in this file to the late, lamented Douglas Noel
Adams.

3.1.5 localhost Reverse-Mapped Zone File
This zone file allows any query requesting the name associated with the loopback IP (127.0.0.1). This file is required toprevent unnecessary queries from reaching the public DNS hierarchy. The BIND 9 distribution file localhost.rev
is shown for completeness:$TTL 1D@IN

SOA

localhost. root.localhost. (2007091701 ; serial
30800; refresh
7200; retry604800; expire
300 ); minimum(continues on next page)

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1

IN
IN

NS
PTR

localhost.
localhost.

3.2 Authoritative Name Servers
These provide authoritative answers to user queries for the zones they support: for instance, the zone data describing thedomain name example.com. An authoritative name server may support one or many zones.
Each zone may be defined as either a primary or a secondary. A primary zone reads its zone data directly from a filesystem. A secondary zone obtains its zone data from the primary zone using a process called zone transfer. Both theprimary and the secondary zones provide authoritative data for their zone; there is no difference in the answer to a queryfrom a primary or a secondary zone. An authoritative name server may support any combination of primary and secondary
zones.
Note: The terms primary and secondary do not imply any access priority. Resolvers (name servers that provide thecomplete answers to user queries) are not aware of (and cannot find out) whether an authoritative answer comes from theprimary or secondary name server. Instead, the resolver uses the list of authoritative servers for the zone (there must be
at least two) and maintains a Round Trip Time (RTT) - the time taken to respond to the query - for each server in the list.
The resolver uses the lowest-value server (the fastest) as its preferred server for the zone and continues to do so until its
RTT becomes higher than the next slowest in its list, at which time that one becomes the preferred server.
For reasons of backward compatibility BIND 9 treats “primary” and “master” as synonyms, as well as “secondary” and“slave.”
The following diagram shows the relationship between the primary and secondary name servers. The text below explains
the process in detail.
The numbers in parentheses in the following text refer to the numbered items in the diagram above.
1. The authoritative primary name server always loads (or reloads) its zone files from (1) a local or networked filestore.
2. The authoritative secondary name server always loads its zone data from a primary via a zone transfer operation.
Zone transfer may use AXFR (complete zone transfer) or IXFR (incremental zone transfer), but only if bothprimary and secondary name servers support the service. The zone transfer process (either AXFR or IXFR) works
as follows:a) The secondary name server for the zone reads (3 and 4) the SOA RR periodically. The interval is defined by
the refresh parameter of the Start of Authority (SOA) RR.
b) The secondary compares the serial number parameter of the SOA RR received from the primary with theserial number in the SOA RR of its current zone data.
c) If the received serial number is arithmetically greater (higher) than the current one, the secondary initiates azone transfer (5) using AXFR or IXFR (depending on the primary and secondary configuration), using TCP
over port 53 (6).
3. The typically recommended zone refresh times for the SOA RR (the time interval when the secondary reads orpolls the primary for the zone SOA RR) are multiples of hours to reduce traffic loads. Worst-case zone change
propagation can therefore take extended periods.
4. The optional NOTIFY (RFC 1996) feature (2) is automatically configured; use the notify statement to turnoff the feature. Whenever the primary loads or reloads a zone, it sends a NOTIFY message to the configured
secondary (or secondaries) and may optionally be configured to send the NOTIFY message to other hosts using thealso-notify statement. The NOTIFY message simply indicates to the secondary that the primary has loaded
or reloaded the zone. On receipt of the NOTIFY message, the secondary respons to indicate it has received the18

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Fig. 1: Authoritative Primary and Secondary Name Servers

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NOTIFY and immediately reads the SOA RR from the primary (as described in section 2 a. above). If the zone
file has changed, propagation is practically immediate.
The authoritative samples all use NOTIFY but identify the statements used, so that they can be removed if not required.

3.2.1 Primary Authoritative Name Server
The zone files are unmodified from the base samples but the named.conf file has been modified as shown:// authoritative primary named.conf file// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";// This is the default - allows user queries from any IP
allow-query { any; };// normal server operations may place items in the cache// this prevents any user query from accessing these items// only authoritative zone data will be returned
allow-query-cache { none; };// Do not provide recursive service to user queries
recursion no;};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)//
logging {channel example_log {// uses a relative path name and the directory statement to// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;// only log info and up messages - all others discarded
severity info;};
category default {example_log;};};// Provide forward mapping zone for localhost// (optional)
zone "localhost" {type primary;file "master/localhost-forward.db";
notify no;};// Provide reverse mapping zone for the loopback// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {type primary;file "localhost.rev";
notify no;(continues on next page)

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zone "example.com" {// this is the primary name server for the zone
type primary;file "example.com";// this is the default
notify yes;// IP addresses of secondary servers allowed to// transfer example.com from this server
allow-transfer {192.168.4.14;
192.168.5.53;};};

The added statements and blocks are commented in the above file.
The zone block, and allow-query, allow-query-cache, allow-transfer, file, notify, recursion, and type statements are described in detail in the appropriate sections.

3.2.2 Secondary Authoritative Name Server
The zone files local-host-forward.db and localhost.rev are unmodified from the base samples. The example.com zone file is not required (the zone file is obtained from the primary via zone transfer). The named.conf filehas been modified as shown:// authoritative secondary named.conf file// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";// This is the default - allows user queries from any IP
allow-query { any; };// normal server operations may place items in the cache// this prevents any user query from accessing these items// only authoritative zone data will be returned
allow-query-cache { none; };// Do not provide recursive service to user queries
recursion no;};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)//
logging {channel example_log {// uses a relative path name and the directory statement to// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;(continues on next page)3.2. Authoritative Name Servers

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severity info;};
category default {example_log;};};// Provide forward mapping zone for localhost// (optional)
zone "localhost" {type primary;file "master/localhost-forward.db";
notify no;};// Provide reverse mapping zone for the loopback// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {type primary;file "localhost.rev";
notify no;};// We are the secondary server for example.com
zone "example.com" {// this is a secondary server for the zone
type secondary;// the file statement here allows the secondary to save// each zone transfer so that in the event of a program restart// the zone can be loaded immediately and the server can start// to respond to queries without waiting for a zone transfer
file "example.com.saved";// IP address of example.com primary server
primaries { 192.168.254.2; };};The statements and blocks added are all commented in the above file.
The zone block, and allow-query, allow-query-cache, allow-transfer, file, primaries, recursion, and type statements are described in detail in the appropriate sections.
If NOTIFY is not being used, no changes are required in this named.conf file, since it is the primary that initiates the
NOTIFY message.
Note: Just when the reader thought they understood primary and secondary, things can get more complicated. A
secondary zone can also be a primary to other secondaries: named, by default, sends NOTIFY messages for every zone
it loads. Specifying notify primary-only; in the zone block for the secondary causes named to only send NOTIFY
messages for primary zones that it loads.

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3.3 Resolver (Caching Name Servers)
Resolvers handle recursive user queries and provide complete answers; that is, they issue one or more iterative queries tothe DNS hierarchy. Having obtained a complete answer (or an error), a resolver passes the answer to the user and places it
in its cache. Subsequent user requests for the same query will be answered from the resolver’s cache until the TTL of thecached answer has expired, when it will be flushed from the cache; the next user query that requests the same information
results in a new series of queries to the DNS hierarchy.
Resolvers are frequently referred to by a bewildering variety of names, including caching name servers, recursive nameservers, forwarding resolvers, area resolvers, and full-service resolvers.
The following diagram shows how resolvers can function in a typical networked environment:

Resolver and Forwarding Resolver
1. End-user systems are all distributed with a local stub resolver as a standard feature. Today, the majority of stub
resolvers also provide a local cache service to speed up user response times.
2. A stub resolver has limited functionality; specifically, it cannot follow referrals. When a stub resolver receives arequest for a name from a local program, such as a browser, and the answer is not in its local cache, it sends arecursive user query (1) to a locally configured resolver (5), which may have the answer available in its cache. If it
does not, it issues iterative queries (2) to the DNS hierarchy to obtain the answer. The resolver to which the local
system sends the user query is configured, for Linux and Unix hosts, in /etc/resolv.conf; for Windows
users it is configured or changed via the Control Panel or Settings interface.
3. Alternatively, the user query can be sent to a forwarding resolver (4). Forwarding resolvers on first glance lookfairly pointless, since they appear to be acting as a simple pass-though and, like the stub resolver, require a fullservice resolver (5). However, forwarding resolvers can be very powerful additions to a network for the following
reasons:a) Cost and Performance. Each recursive user query (1) at the forwarding resolver (4) results in two messages- the query and its answer. The resolver (5) may have to issue three, four, or more query pairs (2) to get
the required answer. Traffic is reduced dramatically, increasing performance or reducing cost (if the linkis tariffed). Additionally, since the forwarding resolver is typically shared across multiple hosts, its cache ismore likely to contain answers, again improving user performance.
b) Network Maintenance. Forwarding resolvers (4) can be used to ease the burden of local administration by
providing a single point at which changes to remote name servers can be managed, rather than having to update
all hosts. Thus, all hosts in a particular network section or area can be configured to point to a forwarding
resolver, which can be configured to stream DNS traffic as desired and changed over time with minimal effort.
c) Sanitizing Traffic. Especially in larger private networks it may be sensible to stream DNS traffic using aforwarding resolver structure. The forwarding resolver (4) may be configured, for example, to handle all
in-domain traffic (relatively safe) and forward all external traffic to a hardened resolver (5).
d) Stealth Networks. Forwarding resolvers are extensively used in stealth or split networks.
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4. Forwarding resolvers (4) can be configured to forward all traffic to a resolver (5), or to only forward selective traffic(5) while directly resolving other traffic (3).
Attention: While the diagram above shows recursive user queries arriving via interface (1), there is nothing to stopthem from arriving via interface (2) via the public network. If no limits are placed on the source IPs that can send suchqueries, the resolver is termed an open resolver. Indeed, when the world was young this was the way things workedon the Internet. Much has changed and what seems to be a friendly, generous action can be used by rogue actors tocause all kinds of problems including Denial of Service (DoS) attacks. Resolvers should always be configured to limit
the IP addresses that can use their services. BIND 9 provides a number of statements and blocks to simplify defining
these IP limits and configuring a closed resolver. The resolver samples given here all configure closed resolvers using
a variety of techniques.

3.3.1 Additional Zone Files
Root Servers (Hint) Zone File
Resolvers (although not necessarily forwarding resolvers) need to access the DNS hierarchy. To do this, they need toknow the addresses (IPv4 and/or IPv6) of the 13 root servers. This is done by the provision of a root server zone file,which is contained in the standard BIND 9 distribution as the file named.root (normally found in /etc/namedb or/usr/local/namedb). This file may also be obtained from the IANA website (https://www.iana.org/domains/root/files).
Note: Many distributions rename this file for historical reasons. Consult the appropriate distribution documentation for the actual file name.
The hint zone file is referenced using the type hint statement and a zone (domain) name of “.” (the generally silent
dot).
Note: The root server IP addresses have been stable for a number of years and are likely to remain stable
for the near future. BIND 9 has a root-server list in its executable such that even if this file is omitted,
out-of-date, or corrupt BIND 9 can still function. For this reason, many sample configurations omit thehints file. All the samples given here include the hints file primarily as a reminder of the functionality of theconfiguration, rather than as an absolute necessity.

Private IP Reverse Map Zone Files
Resolvers are configured to send iterative queries to the public DNS hierarchy when the information requested is not intheir cache or not defined in any local zone file. Many networks make extensive use of private IP addresses (defined by
RFC 1918, RFC 2193, RFC 5737, and RFC 6598). By their nature these IP addresses are forward-mapped in various
user zone files. However, certain applications may issue reverse map queries (mapping an IP address to a name). If
the private IP addresses are not defined in one or more reverse-mapped zone file(s), the resolver sends them to the DNS
hierarchy where they are simply useless traffic, slowing down DNS responses for all users.
Private IP addresses may be defined using standard reverse-mapping techniques or using the empty-zones-enable
statement. By default this statement is set to empty-zones-enable yes; and thus automatically prevents unnecessary DNS traffic by sending an NXDOMAIN error response (indicating the name does not exist) to any request.
However, some applications may require a genuine answer to such reverse-mapped requests or they will fail to function.
Mail systems in particular perform reverse DNS queries as a first-line spam check; in this case a reverse-mapped zone
file is essential. The sample configuration files given here for both the resolver and the forwarding resolver provide areverse-mapping zone file for the private IP address 192.168.254.4, which is the mail server address in the base zone
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file, as an illustration of the reverse-map technique. The file is named 192.168.254.rev and has a zone name of
254.168.192.in-addr.arpa.
; reverse map zone file for 192.168.254.4 only
$TTL 2d ; 172800 seconds$ORIGIN 254.168.192.IN-ADDR.ARPA.
@IN
SOA
ns1.example.com. hostmaster.example.com. (2003080800 ; serial number
3h; refresh
15m; update retry
3w; expiry3h; nx = nxdomain ttl); only one NS is required for this local file; and is an out of zone nameINNS
ns1.example.com.
; other IP addresses can be added as required; this maps 192.168.254.4 as shown
4IN
PTR
mail.example.com. ; fully qualified domain name (FQDN)

3.3.2 Resolver Configuration
The resolver provides recursive query support to a defined set of IP addresses. It is therefore a closed resolver and cannot
be used in wider network attacks.
// resolver named.conf file// Two corporate subnets we wish to allow queries from// defined in an acl clauseacl corpnets {192.168.4.0/24;
192.168.7.0/24;};// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";// this is the default
recursion yes;// recursive queries only allowed from these ips// and references the acl clauseallow-query { corpnets; };// this ensures that any reverse map for private IPs// not defined in a zone file will *not* be passed to the public network// it is the default value
empty-zones-enable yes;};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)(continues on next page)3.3. Resolver (Caching Name Servers)25

BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)//logging {channel example_log {// uses a relative path name and the directory statement to// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;// only log info and up messages - all others discarded
severity info;};
category default {example_log;};};// zone file for the root servers// discretionary zone (see root server discussion above)zone "." {type hint;
file "named.root";};// zone file for the localhost forward map// discretionary zone depending on hosts file (see discussion)zone "localhost" {type primary;file "masters/localhost-forward.db";
notify no;};// zone file for the loopback address// necessary zone
zone "0.0.127.in-addr.arpa" {type primary;file "localhost.rev";
notify no;};// zone file for local IP reverse map// discretionary file depending on requirementszone "254.168.192.in-addr.arpa" {type primary;file "192.168.254.rev";
notify no;};

The zone and acl blocks, and the allow-query, empty-zones-enable, file, notify, recursion, andtype statements are described in detail in the appropriate sections.
As a reminder, the configuration of this resolver does not access the DNS hierarchy (does not use the public network) for
any recursive query for which:
1. The answer is already in the cache.
2. The domain name is localhost (zone localhost).
3. Is a reverse-map query for 127.0.0.1 (zone 0.0.127.in-addr.arpa).
4. Is a reverse-map query for 192.168.254/24 (zone 254.168.192.in-addr.arpa).

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5. Is a reverse-map query for any local IP (empty-zones-enable statement).
All other recursive queries will result in access to the DNS hierarchy to resolve the query.

3.3.3 Forwarding Resolver Configuration
This forwarding resolver configuration forwards all recursive queries, other than those for the defined zones and those forwhich the answer is already in its cache, to a full-service resolver at the IP address 192.168.250.3, with an alternative at
192.168.230.27. The forwarding resolver will cache all responses from these servers. The configuration is closed, in thatit defines those IPs from which it will accept recursive queries.
A second configuration in which selective forwarding occurs is also provided.
// forwarding named.conf file// Two corporate subnets we wish to allow queries from// defined in an acl clauseacl corpnets {192.168.4.0/24;
192.168.7.0/24;};// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";// this is the default
recursion yes;// recursive queries only allowed from these ips// and references the acl clauseallow-query { corpnets; };// this ensures that any reverse map for private IPs// not defined in a zone file will *not* be passed to the public network// it is the default value
empty-zones-enable yes;// this defines the addresses of the resolvers to which queries will be forwarded
forwarders {192.168.250.3;
192.168.230.27;};// indicates all queries will be forwarded other than for defined zones
forward only;};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)//
logging {channel example_log {// uses a relative path name and the directory statement to// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;(continues on next page)3.3. Resolver (Caching Name Servers)27

BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)// only log info and up messages - all others discarded
severity info;};
category default {example_log;};};// hints zone file is not required// zone file for the localhost forward map// discretionary zone depending on hosts file (see discussion)zone "localhost" {type primary;file "masters/localhost-forward.db";
notify no;};// zone file for the loopback address// necessary zone
zone "0.0.127.in-addr.arpa" {type primary;file "localhost.rev";
notify no;};// zone file for local IP reverse map// discretionary file depending on requirementszone "254.168.192.in-addr.arpa" {type primary;file "192.168.254.rev";
notify no;};

The zone and acl blocks, and the allow-query, empty-zones-enable, file, forward, forwarders,
notify, recursion, and type statements are described in detail in the appropriate sections.
As a reminder, the configuration of this forwarding resolver does not forward any recursive query for which:
1. The answer is already in the cache.
2. The domain name is localhost (zone localhost).
3. Is a reverse-map query for 127.0.0.1 (zone 0.0.127.in-addr.arpa).
4. Is a reverse-map query for 192.168.254/24 (zone 254.168.192.in-addr.arpa).
5. Is a reverse-map query for any local IP (empty-zones-enable statement).
All other recursive queries will be forwarded to resolve the query.

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3.3.4 Selective Forwarding Resolver Configuration
This forwarding resolver configuration only forwards recursive queries for the zone example.com to the resolvers at
192.168.250.3 and 192.168.230.27. All other recursive queries, other than those for the defined zones and those forwhich the answer is already in its cache, are handled by this resolver. The forwarding resolver will cache all responses
from both the public network and from the forwarded resolvers. The configuration is closed, in that it defines those IPsfrom which it will accept recursive queries.
// selective forwarding named.conf file// Two corporate subnets we wish to allow queries from// defined in an acl clauseacl corpnets {192.168.4.0/24;
192.168.7.0/24;};// options clause defining the server-wide properties
options {// all relative paths use this directory as a basedirectory "/var";// version statement for security to avoid hacking known weaknesses// if the real version number is revealed
version "not currently available";// this is the default
recursion yes;// recursive queries only allowed from these ips// and references the acl clauseallow-query { corpnets; };// this ensures that any reverse map for private IPs// not defined in a zone file will *not* be passed to the public network// it is the default value
empty-zones-enable yes;// forwarding is not global but selective by zone in this configuration};// logging clause// log to /var/log/named/example.log all events from info UP in severity (no debug)// uses 3 files in rotation swaps files when size reaches 250K// failure messages that occur before logging is established are// in syslog (/var/log/messages)//
logging {channel example_log {// uses a relative path name and the directory statement to// expand to /var/log/named/example.log
file "log/named/example.log" versions 3 size 250k;// only log info and up messages - all others discarded
severity info;};
category default {example_log;};};// zone file for the root servers// discretionary zone (see root server discussion above)(continues on next page)3.3. Resolver (Caching Name Servers)29

BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)

zone "." {type hint;
file "named.root";};// zone file for the localhost forward map// discretionary zone depending on hosts file (see discussion)zone "localhost" {type primary;file "masters/localhost-forward.db";
notify no;};// zone file for the loopback address// necessary zone
zone "0.0.127.in-addr.arpa" {type primary;file "localhost.rev";
notify no;};// zone file for local IP reverse map// discretionary file depending on requirementszone "254.168.192.in-addr.arpa" {type primary;file "192.168.254.rev";
notify no;};// zone file forwarded example.com
zone "example.com" {type forward;// this defines the addresses of the resolvers to// which queries for this zone will be forwarded
forwarders {192.168.250.3;
192.168.230.27;};// indicates all queries for this zone will be forwarded
forward only;};

The zone and acl blocks, and the allow-query, empty-zones-enable, file, forward, forwarders,
notify, recursion, and type statements are described in detail in the appropriate sections.
As a reminder, the configuration of this resolver does not access the DNS hierarchy (does not use the public network) for
any recursive query for which:
1. The answer is already in the cache.
2. The domain name is localhost (zone localhost).
3. Is a reverse-map query for 127.0.0.1 (zone 0.0.127.in-addr.arpa).
4. Is a reverse-map query for 192.168.254/24 (zone 254.168.192.in-addr.arpa).
5. Is a reverse-map query for any local IP (empty-zones-enable statement).
6. Is a query for the domain name example.com, in which case it will be forwarded to either 192.168.250.3 or
192.168.230.27 (zone example.com).

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All other recursive queries will result in access to the DNS hierarchy to resolve the query.

3.4 Load Balancing
A primitive form of load balancing can be achieved in the DNS by using multiple resource records (RRs) in a zone file(such as multiple A records) for one name.
For example, assuming three HTTP servers with network addresses of 10.0.0.1, 10.0.0.2, and 10.0.0.3, a set of records
such as the following means that clients will connect to each machine one-third of the time:
Name
www

TTL
600
600
600

CLASS
IN
IN
IN

TYPE
A
A
A

Resource Record (RR) Data
10.0.0.1
10.0.0.2
10.0.0.3

When a resolver queries for these records, BIND rotates them and responds to the query with the records in a random
order. In the example above, clients randomly receive records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients use
the first record returned and discard the rest.
For more detail on ordering responses, refer to the rrset-order statement in the options block.

3.5 Zone File
This section, largely borrowed from RFC 1034, describes the concept of a Resource Record (RR) and explains how to
use them.

3.5.1 Resource Records
A domain name identifies a node in the DNS tree namespace. Each node has a set of resource information, which may
be empty. The set of resource information associated with a particular name is composed of separate RRs. The order of
RRs in a set is not significant and need not be preserved by name servers, resolvers, or other parts of the DNS. However,sorting of multiple RRs is permitted for optimization purposes: for example, to specify that a particular nearby server be
tried first. See sortlist and RRset Ordering.
The components of a Resource Record are:owner name
The domain name where the RR is found.
RR typeAn encoded 16-bit value that specifies the type of the resource record. For a list of types of valid RRs, including those that have been obsoleted, please refer to https://www.iana.org/assignments/dns-parameters/dnsparameters.xhtml#dns-parameters-4.
TTL
The time-to-live of the RR. This field is a 32-bit integer in units of seconds, and is primarily used by resolvers when
they cache RRs. The TTL describes how long a RR can be cached before it should be discarded.
class
An encoded 16-bit value that identifies a protocol family or an instance of a protocol.
RDATA
The resource data. The format of the data is type- and sometimes class-specific.
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The following classes of resource records are currently valid in the DNS:INThe Internet. The only widely class used today.
CH
Chaosnet, a LAN protocol created at MIT in the mid-1970s. It was rarely used for its historical purpose, but wasreused for BIND’s built-in server information zones, e.g., version.bind.
HS
Hesiod, an information service developed by MIT’s Project Athena. It was used to share information about various
systems databases, such as users, groups, printers, etc.
The owner name is often implicit, rather than forming an integral part of the RR. For example, many name servers
internally form tree or hash structures for the name space, and chain RRs off nodes. The remaining RR parts are the fixed
header (type, class, TTL), which is consistent for all RRs, and a variable part (RDATA) that fits the needs of the resource
being described.
The TTL field is a time limit on how long an RR can be kept in a cache. This limit does not apply to authoritative datain zones; that also times out, but follows the refreshing policies for the zone. The TTL is assigned by the administrator
for the zone where the data originates. While short TTLs can be used to minimize caching, and a zero TTL prohibits
caching, the realities of Internet performance suggest that these times should be on the order of days for the typical host.
If a change is anticipated, the TTL can be reduced prior to the change to minimize inconsistency, and then increased backto its former value following the change.
The data in the RDATA section of RRs is carried as a combination of binary strings and domain names. The domainnames are frequently used as “pointers” to other data in the DNS.
Textual Expression of RRs
RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded
form when stored in a name server or resolver. In the examples provided in RFC 1034, a style similar to that used inprimary files was employed in order to show the contents of RRs. In this format, most RRs are shown on a single line,
although continuation lines are possible using parentheses.
The start of the line gives the owner of the RR. If a line begins with a blank, then the owner is assumed to be the sameas that of the previous RR. Blank lines are often included for readability.
Following the owner are listed the TTL, type, and class of the RR. Class and type use the mnemonics defined above, andTTL is an integer before the type field. To avoid ambiguity in parsing, type and class mnemonics are disjoint, TTLs areintegers, and the type mnemonic is always last. The IN class and TTL values are often omitted from examples in theinterest of clarity.
The resource data or RDATA section of the RR is given using knowledge of the typical representation for the data.
For example, the RRs carried in a message might be shown as:
ISI.EDU.
VENERA.ISI.EDU
VAXA.ISI.EDU

MX
MX
A
A
A
A

10 VENERA.ISI.EDU.
10 VAXA.ISI.EDU
128.9.0.32
10.1.0.52
10.2.0.27
128.9.0.33

The MX RRs have an RDATA section which consists of a 16-bit number followed by a domain name. The address RRs
use a standard IP address format to contain a 32-bit Internet address.
The above example shows six RRs, with two RRs at each of three domain names.
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Here is another possible example:
XX.LCS.MIT.EDU.

IN A
CH A

10.0.0.44
MIT.EDU. 2420

This shows two addresses for XX.LCS.MIT.EDU, each of a different class.

3.5.2 Discussion of MX Records
As described above, domain servers store information as a series of resource records, each of which contains a particularpiece of information about a given domain name (which is usually, but not always, a host). The simplest way to think of
an RR is as a typed pair of data, a domain name matched with a relevant datum and stored with some additional type
information, to help systems determine when the RR is relevant.
MX records are used to control delivery of email. The data specified in the record is a priority and a domain name. The
priority controls the order in which email delivery is attempted, with the lowest number first. If two priorities are thesame, a server is chosen randomly. If no servers at a given priority are responding, the mail transport agent falls back to
the next largest priority. Priority numbers do not have any absolute meaning; they are relevant only respective to otherMX records for that domain name. The domain name given is the machine to which the mail is delivered. It must havean associated address record (A or AAAA); CNAME is not sufficient.
For a given domain, if there is both a CNAME record and an MX record, the MX record is in error and is ignored.
Instead, the mail is delivered to the server specified in the MX record pointed to by the CNAME. For example:
example.com.

mail.example.com.
mail2.example.com.

IN
IN
IN
IN
IN

MX
MX
MX
A
A

10
10
20
10.0.0.1
10.0.0.2

mail.example.com.
mail2.example.com.
mail.backup.org.

Mail delivery is attempted to mail.example.com and mail2.example.com (in any order); if neither of those succeeds,
delivery to mail.backup.org is attempted.

3.5.3 Setting TTLs
The time-to-live (TTL) of the RR field is a 32-bit integer represented in units of seconds, and is primarily used by resolvers
when they cache RRs. The TTL describes how long an RR can be cached before it should be discarded. The following
three types of TTLs are currently used in a zone file.
SOA minimum
The last field in the SOA is the negative caching TTL. This controls how long other servers cache no-such-domain(NXDOMAIN) responses from this server. Further details can be found in RFC 2308.
The maximum time for negative caching is 3 hours (3h).
$TTL
The $TTL directive at the top of the zone file (before the SOA) gives a default TTL for every RR without a specific
TTL set.
RR TTLs
Each RR can have a TTL as the second field in the RR, which controls how long other servers can cache it.
All of these TTLs default to units of seconds, though units can be explicitly specified: for example, 1h30m.

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3.5.4 Inverse Mapping in IPv4
Reverse name resolution (that is, translation from IP address to name) is achieved by means of the in-addr.arpa domain
and PTR records. Entries in the in-addr.arpa domain are made in least-to-most significant order, read left to right. Thisis the opposite order to the way IP addresses are usually written. Thus, a machine with an IP address of 10.1.2.3 would
have a corresponding in-addr.arpa name of 3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose
data field is the name of the machine or, optionally, multiple PTR records if the machine has more than one name. For
example, in the example.com domain:$ORIGIN3

2.1.10.in-addr.arpa
IN PTR foo.example.com.

Note: The $ORIGIN line in this example is only to provide context; it does not necessarily appear in the actual usage.
It is only used here to indicate that the example is relative to the listed origin.

3.5.5 Other Zone File Directives
The DNS “master file” format was initially defined in RFC 1035 and has subsequently been extended. While the format
itself is class-independent, all records in a zone file must be of the same class.
Master file directives include $ORIGIN, $INCLUDE, and $TTL.
The @ (at-sign)
When used in the label (or name) field, the asperand or at-sign (@) symbol represents the current origin. At the start ofthe zone file, it is the <zone_name>, followed by a trailing dot (.).
The $ORIGIN Directive
Syntax: $ORIGIN domain-name [comment]$ORIGIN sets the domain name that is appended to any unqualified records. When a zone is first read, there is an implicit$ORIGIN <zone_name>.; note the trailing dot. The current $ORIGIN is appended to the domain specified in the$ORIGIN argument if it is not absolute.
$ORIGIN example.com.
WWW
CNAME
MAIN-SERVER

is equivalent to
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.

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The $INCLUDE Directive
Syntax: $INCLUDE filename [origin] [comment]This reads and processes the file filename as if it were included in the file at this point. The filename can be an absolutepath, or a relative path. In the latter case it is read from named’s working directory. If origin is specified, the file isprocessed with $ORIGIN set to that value; otherwise, the current $ORIGIN is used.
The origin and the current domain name revert to the values they had prior to the $INCLUDE once the file has been
read.
Note: RFC 1035 specifies that the current origin should be restored after an $INCLUDE, but it is silent on whether
the current domain name should also be restored. BIND 9 restores both of them. This could be construed as a deviationfrom RFC 1035, a feature, or both.

The $TTL Directive
Syntax: $TTL default-ttl [comment]This sets the default Time-To-Live (TTL) for subsequent records with undefined TTLs. Valid TTLs are of the range
0-2147483647 seconds.
$TTL is defined in RFC 2308.

3.5.6 BIND Primary File Extension: the $GENERATE Directive
Syntax: $GENERATE range owner [ttl] [class] type rdata [comment]$GENERATE is used to create a series of resource records that only differ from each other by an iterator.
rangeThis can be one of two forms: start-stop or start-stop/step. If the first form is used, then step is set to 1. “start”,“stop”, and “step” must be positive integers between 0 and (2^31)-1. “start” must not be larger than “stop”.
ownerThis describes the owner name of the resource records to be created.
The owner string may include one or more $ (dollar sign) symbols, which will be replaced with the iterator value
when generating records; see below for details.
ttlThis specifies the time-to-live of the generated records. If not specified, this is inherited using the normal TTL
inheritance rules.
class and ttl can be entered in either order.
class
This specifies the class of the generated records. This must match the zone class if it is specified.
class and ttl can be entered in either order.
type
This can be any valid type.
rdata
This is a string containing the RDATA of the resource record to be created. As with owner, the rdata string may
include one or more $ symbols, which are replaced with the iterator value. rdata may be quoted if there are spacesin the string; the quotation marks do not appear in the generated record.
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Any single $ (dollar sign) symbols within the owner or rdata strings are replaced by the iterator value. To get a $ inthe output, escape the $ using a backslash \, e.g., \$. (For compatibility with earlier versions, $$ is also recognized
as indicating a literal $ in the output.)
The $ may optionally be followed by modifiers which change the offset from the iterator, field width, and base.
Modifiers are introduced by a { (left brace) immediately following the $, as in ${offset[,width[,base]]}. For example, ${-20,3,d} subtracts 20 from the current value and prints the result as a decimal in a zero-padded field ofwidth 3. Available output forms are decimal (d), octal (o), hexadecimal (x or X for uppercase), and nibble (n orN for uppercase). The modfiier cannot contain whitespace or newlines.
The default modifier is ${0,0,d}. If the owner is not absolute, the current $ORIGIN is appended to the name.
In nibble mode, the value is treated as if it were a reversed hexadecimal string, with each hexadecimal digit as aseparate label. The width field includes the label separator.
Examples:$GENERATE can be used to easily generate the sets of records required to support sub-/24 reverse delegations describedin RFC 2317:$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0

is equivalent to0.0.0.192.IN-ADDR.ARPA. NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.

This example creates a set of A and MX records. Note the MX’s rdata is a quoted string; the quotes are stripped when
$GENERATE is processed:$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$$GENERATE 1-127 HOST-$ MX "0 ."is equivalent to
HOST-1.EXAMPLE.
A 1.2.3.1
HOST-1.EXAMPLE.
MX 0 .
HOST-2.EXAMPLE.
A 1.2.3.2
HOST-2.EXAMPLE.
MX 0 .
HOST-3.EXAMPLE.
A 1.2.3.3
HOST-3.EXAMPLE.
MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .

This example generates A and AAAA records using modifiers; the AAAA owner names are generated using nibble mode:$ORIGIN EXAMPLE.
$GENERATE 0-2 HOST-${0,4,d} A 1.2.3.${1,0,d}$GENERATE 1024-1026 ${0,3,n} AAAA 2001:db8::${0,4,x}

is equivalent to:36

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HOST-0000.EXAMPLE.
HOST-0001.EXAMPLE.
HOST-0002.EXAMPLE.
0.0.4.EXAMPLE.
1.0.4.EXAMPLE.
2.0.4.EXAMPLE.

A
A
A
AAAA
AAAA
AAAA

1.2.3.1
1.2.3.2
1.2.3.3
2001:db8::400
2001:db8::401
2001:db8::402

The $GENERATE directive is a BIND extension and not part of the standard zone file format.

3.5.7 Additional File Formats
In addition to the standard text format, BIND 9 supports the ability to read or dump to zone files in other formats.
The raw format is a binary representation of zone data in a manner similar to that used in zone transfers. Since it does
not require parsing text, load time is significantly reduced.
For a primary server, a zone file in raw format is expected to be generated from a text zone file by thenamed-compilezone command. For a secondary server or a dynamic zone, the zone file is automatically generated when named dumps the zone contents after zone transfer or when applying prior updates, if one of these formats is
specified by the masterfile-format option.
If a zone file in raw format needs manual modification, it first must be converted to text format by thenamed-compilezone command, then converted back after editing. For example:
named-compilezone -f raw -F text -o zonefile.text <origin> zonefile.raw[edit zonefile.text]
named-compilezone -f text -F raw -o zonefile.raw <origin> zonefile.text

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CHAPTER

FOUR

NAME SERVER OPERATIONS

4.1 Tools for Use With the Name Server Daemon
This section describes several indispensable diagnostic, administrative, and monitoring tools available to the system administrator for controlling and debugging the name server daemon.

4.1.1 Diagnostic Tools
The dig, host, and nslookup programs are all command-line tools for manually querying name servers. They differ
in style and output format.
dig
dig is the most versatile and complete of these lookup tools. It has two modes: simple interactive mode for asingle query, and batch mode, which executes a query for each in a list of several query lines. All query options areaccessible from the command line.
For more information and a list of available commands and options, see dig - DNS lookup utility.
host
The host utility emphasizes simplicity and ease of use. By default, it converts between host names and Internet
addresses, but its functionality can be extended with the use of options.
For more information and a list of available commands and options, see host - DNS lookup utility.
nslookupnslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query name servers
for information about various hosts and domains, or to print a list of hosts in a domain. Non-interactive mode isused to print just the name and requested information for a host or domain.
Due to its arcane user interface and frequently inconsistent behavior, we do not recommend the use of nslookup.
Use dig instead.

4.1.2 Administrative Tools
Administrative tools play an integral part in the management of a server.
named-checkconf
The named-checkconf program checks the syntax of a named.conf file.
For more information and a list of available commands and options, see named-checkconf - named configuration
file syntax checking tool.

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named-checkzone
The named-checkzone program checks a zone file for syntax and consistency.
For more information and a list of available commands and options, see named-checkzone - zone file validation
tool.
named-compilezone
This tool is similar to named-checkzone but it always dumps the zone content to a specified file (typically in adifferent format).
For more information and a list of available commands and options, see named-compilezone - zone file converting
tool.
rndc
The remote name daemon control (rndc) program allows the system administrator to control the operation of aname server.
See rndc - name server control utility for details of the available rndc commands.
rndc requires a configuration file, since all communication with the server is authenticated with digital signaturesthat rely on a shared secret, and there is no way to provide that secret other than with a configuration file. The
default location for the rndc configuration file is /etc/rndc.conf, but an alternate location can be specified
with the -c option. If the configuration file is not found, rndc also looks in /etc/rndc.key (or whateversysconfdir was defined when the BIND build was configured). The rndc.key file is generated by runningrndc-confgen -a as described in controls.
The format of the configuration file is similar to that of named.conf, but is limited to only three blocks: theoptions, key, server, and the include Directive. These blocks are what associate the secret keys to the servers
with which they are meant to be shared. The order of blocks is not significant.
options
Grammar:options {default-key <string>;
default-port <integer>;default-server <string>;
default-source-address ( <ipv4_address> | * );default-source-address-v6 ( <ipv6_address> | * );};Blocks: topmost
default-server
Grammar: default-server <string>;
Blocks: options
default-server takes a host name or address argument and represents the server that is contacted if no-s option is provided on the command line.
default-key
Grammar: default-key <string>;
Blocks: options
default-key takes the name of a key as its argument, as defined by a key block.
default-port
Grammar: default-port <integer>;
Blocks: options
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default-port specifies the port to which rndc should connect if no port is given on the command line
or in a server block.
default-source-address
Grammar: default-source-address ( <ipv4_address> | * );Blocks: options
default-source-address-v6
Grammar: default-source-address-v6 ( <ipv6_address> | * );Blocks: options
default-source-address and default-source-address-v6 specify the IPv4 and IPv6
source address used to communicate with the server if no address is given on the command line or in aserver block.
key
Grammar server: key <string>;
Grammar topmost:key <string> {algorithm <string>;
secret <string>;}; // may occur multiple times

Blocks: topmost, server
The key block defines a key to be used by rndc when authenticating with named. Its syntax is identical to the
key statement in named.conf. The keyword key is followed by a key name, which must be a valid domain
name, though it need not actually be hierarchical; thus, a string like rndc_key is a valid name. The key block
has two statements: algorithm and secret.
algorithm
Grammar: algorithm <string>;
Blocks: key
While the configuration parser accepts any string as the argument to algorithm, currently only the strings
hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, and hmac-sha512
have any meaning.
secretGrammar: secret <string>;
Blocks: key
The secret is a Base64-encoded string as specified in RFC 3548.
serverGrammar:server <string> {addresses { ( <quoted_string> [ port <integer> ] | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ); ... };key <string>;
port <integer>;source-address ( <ipv4_address> | * );source-address-v6 ( <ipv6_address> | * );}; // may occur multiple times

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Blocks: topmost
The server block specifies connection parameters for a given server. The server can be specified as a host nameor address.
addresses
Grammar: addresses { ( <quoted_string> [ port <integer> ] | <ipv4_address>[ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };Blocks: server
Specifies one or more addresses to use when communicating with this server.
key
Associates a key defined using the key statement with a server.
portGrammar: port <integer>;
Blocks: server
Specifes the port rndc should connect to on the server.
source-address
Grammar: source-address ( <ipv4_address> | * );Blocks: server
source-address-v6
Grammar: source-address-v6 ( <ipv6_address> | * );Blocks: server
Overrides default-source-address and default-source-address-v6 for this specificserver.
A sample minimal configuration file is as follows:
key rndc_key {algorithm "hmac-sha256";secret"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";};
options {default-server 127.0.0.1;
default-key
rndc_key;};

This file, if installed as /etc/rndc.conf, allows the command:rndc reload
to connect to 127.0.0.1 port 953 and causes the name server to reload, if a name server on the local machine isrunning with the following controls statements:
controls {inet 127.0.0.1
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and it has an identical key block for rndc_key.
Running the rndc-confgen program conveniently creates an rndc.conf file, and also displays the corresponding controls statement needed to add to named.conf. Alternatively, it is possible to run
rndc-confgen -a to set up an rndc.key file and not modify named.conf at all.

4.2 Signals
Certain Unix signals cause the name server to take specific actions, as described in the following table. These signals canbe sent using the kill command.
SIGHUPSIGTERM
SIGINT

Causes the server to read named.conf and reload the database.
Causes the server to clean up and exit.
Causes the server to clean up and exit.

4.3 Plugins
Plugins are a mechanism to extend the functionality of named using dynamically loadable libraries. By using plugins,core server functionality can be kept simple for the majority of users; more complex code implementing optional featuresneed only be installed by users that need those features.
The plugin interface is a work in progress, and is expected to evolve as more plugins are added. Currently, only “queryplugins” are supported; these modify the name server query logic. Other plugin types may be added in the future.
The only plugin currently included in BIND is filter-aaaa.so, which replaces the filter-aaaa feature that
previously existed natively as part of named. The code for this feature has been removed from named and can no longer
be configured using standard named.conf syntax, but linking in the filter-aaaa.so plugin provides identical
functionality.

4.4 Configuring Plugins
pluginGrammar: plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur
multiple times
Blocks: topmost, viewTags: server

Configures plugins in named.conf.
A plugin is configured with the plugin statement in named.conf:
plugin query "library.so" {parameters};

In this example, file library.so is the plugin library. query indicates that this is a query plugin.
Multiple plugin statements can be specified, to load different plugins or multiple instances of the same plugin.

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parameters are passed as an opaque string to the plugin’s initialization routine. Configuration syntax differs dependingon the module.

4.5 Developing Plugins
Each plugin implements four functions:• plugin_register to allocate memory, configure a plugin instance, and attach to hook points within named ,• plugin_destroy to tear down the plugin instance and free memory,• plugin_version to check that the plugin is compatible with the current version of the plugin API,• plugin_check to test syntactic correctness of the plugin parameters.
At various locations within the named source code, there are “hook points” at which a plugin may register itself. When ahook point is reached while named is running, it is checked to see whether any plugins have registered themselves there;
if so, the associated “hook action” - a function within the plugin library - is called. Hook actions may examine the runtime
state and make changes: for example, modifying the answers to be sent back to a client or forcing a query to be aborted.
More details can be found in the file lib/ns/include/ns/hooks.h.

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CHAPTERFIVEDNSSECDNS Security Extensions (DNSSEC) provide reliable protection from cache poisoning attacks. At the same time these
extensions also provide other benefits: they limit the impact of random subdomain attacks on resolver caches and authoritative servers, and provide the foundation for modern applications like authenticated and private e-mail transfer.
To achieve this goal, DNSSEC adds digital signatures to DNS records in authoritative DNS zones, and DNS resolvers
verify the validity of the signatures on the received records. If the signatures match the received data, the resolver can be
sure that the data was not modified in transit.
Note: DNSSEC and transport-level encryption are complementary! Unlike typical transport-level encryption like DNSover-TLS, DNS-over-HTTPS, or VPN, DNSSEC makes DNS records verifiable at all points of the DNS resolution chain.
This section focuses on ways to deploy DNSSEC using BIND. For a more in-depth discussion of DNSSEC principles(e.g. How Does DNSSEC Change DNS Lookup?) please see DNSSEC Guide.

5.1 Zone Signing
BIND offers several ways to generate signatures and maintain their validity during the lifetime of a DNS zone:• Fully Automated (Key and Signing Policy) - strongly recommended• Manual Signing - discouraged, use only for debugging

5.1.1 Zone keys
Regardless of the zone-signing method in use, cryptographic keys are stored in files named like Kdnssec.example.
+013+12345.key and Kdnssec.example.+013+12345.private. The private key (in the .private file)is used to generate signatures, and the public key (in the .key file) is used for signature verification. Additionally, theFully Automated (Key and Signing Policy) method creates a third file, Kdnssec.example+013+12345.state,
which is used to track DNSSEC key timings and to perform key rollovers safely.
These filenames contain:• the key name, which always matches the zone name (dnssec.example.),• the algorithm number (013 is ECDSAP256SHA256, 008 is RSASHA256, etc.),• and the key tag, i.e. a non-unique key identifier (12345 in this case).

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Warning: Private keys are required for full disaster recovery. Back up key files in a safe location and protect themfrom unauthorized access. Anyone with access to the private key can create fake but seemingly valid DNS data.

5.1.2 Fully Automated (Key and Signing Policy)
Key and Signing Policy (KASP) is a method of configuration that describes how to maintain DNSSEC signing keys andhow to sign the zone.
This is the recommended, fully automated way to sign and maintain DNS zones. For most use cases users can simply use
the built-in default policy, which applies up-to-date DNSSEC practices:zone "dnssec.example" {type primary;file "dnssec.example.db";
dnssec-policy default;};

The dnssec-policy statement requires dynamic DNS to be set up, or inline-signing to be enabled. In theexample above we use the latter, because the default policy uses inline-signing.
This is sufficient to create the necessary signing keys, and generate DNSKEY, RRSIG, and NSEC records for the zone.
BIND also takes care of any DNSSEC maintenance for this zone, including replacing signatures that are about to expire
and managing Key Rollovers.
Note: dnssec-policy needs write access to the zone. Please see dnssec-policy for more details about implications for zone storage.
The default policy creates one key that is used to sign the complete zone, and uses NSEC to enable authenticated denialof existence (a secure way to tell which records do not exist in a zone). This policy is recommended and typically does
not need to be changed.
If needed, a custom policy can be defined by adding a dnssec-policy statement into the configuration:
dnssec-policy "custom" {dnskey-ttl 600;
keys {
ksk lifetime P1Y algorithm ecdsap384sha384;
zsk lifetime 60d algorithm ecdsap384sha384;};
nsec3param iterations 0 optout no salt-length 0;};This custom policy, for example:• uses a very short DNSKEY TTL (600 seconds),• uses two keys to sign the zone: a Key Signing Key (KSK) to sign the key related RRsets (DNSKEY, CDS, and
CDNSKEY), and a Zone Signing Key (ZSK) to sign the rest of the zone. The KSK is automatically rotated after
one year and the ZSK after 60 days.
Also:• The configured keys have a lifetime set and use the ECDSAP384SHA384 algorithm.
• The last line instructs BIND to generate NSEC3 records for Proof of Non-Existence, using zero extra iterations
and no salt. NSEC3 opt-out is disabled, meaning insecure delegations also get an NSEC3 record.
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For more information about KASP configuration see dnssec-policy.
The Advanced Discussions section in the DNSSEC Guide discusses the various policy settings and may be useful for
determining values for specific needs.
Key Rollover
When using a dnssec-policy, a key lifetime can be set to trigger key rollovers. ZSK rollovers are fully automatic,
but for KSK and CSK rollovers a DS record needs to be submitted to the parent. See Secure Delegation for possible ways
to do so.
Once the DS is in the parent (and the DS of the predecessor key is withdrawn), BIND needs to be told that this event has
happened. This can be done automatically by configuring parental agents:
zone "dnssec.example" {type primary;file "dnssec.example.db";
dnssec-policy default;
parental-agents { 192.0.2.1; };checkds explicit;};

Here one server, 192.0.2.1, is configured for BIND to send DS queries to, to check the DS RRset fordnssec-example during key rollovers. This needs to be a trusted server, because BIND does not validate the response. The checkds option makes BIND use the explicitly configured parental agents, rather than looking them up by
querying for the parent NS records.
If setting up a parental agent is undesirable, it is also possible to tell BIND that the DS is published in the parent with:rndc dnssec -checkds -key 12345 published dnssec.example.. and the DS for the predecessor
key has been removed with: rndc dnssec -checkds -key 54321 withdrawn dnssec.example..
where 12345 and 54321 are the key tags of the successor and predecessor key, respectively.
To roll a key sooner than scheduled, or to roll a key that has an unlimited lifetime, use: rndc dnssec -rollover-key 12345 dnssec.example..
To revert a signed zone back to an insecure zone, change the zone configuration to use the built-in “insecure” policy.
Detailed instructions are described in Reverting to Unsigned.
Multi-Signer Model
Dynamic zones provide the ability to sign a zone by multiple providers, meaning each provider signs and serves the samezone independently, as is described in RFC 8901. BIND 9 is able to support Model 2, where each provider has their own
KSK and ZSK (or CSK). The keys from the other provider can be imported via Dynamic Update. For each active KSK
there must be a corresponding DS record in the parent zone. Key rollovers require coordination in order to update theDS and DNSKEY RRset.

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5.1.3 Manual Signing
There are several tools available to manually sign a zone.
Warning: Please note manual procedures are available mainly for backwards compatibility and should be used only
by expert users with specific needs.
To set up a DNSSEC secure zone manually, a series of steps must be followed. Please see chapter Manual Signing in the
DNSSEC Guide for more information.

5.1.4 Monitoring with Private Type Records
The state of the signing process is signaled by private type records (with a default type value of 65534). When signing iscomplete, those records with a non-zero initial octet have a non-zero value for the final octet.
If the first octet of a private type record is non-zero, the record indicates either that the zone needs to be signed with the
key matching the record, or that all signatures that match the record should be removed. Here are the meanings of thedifferent values of the first octet:• algorithm (octet 1)• key ID in network order (octet 2 and 3)• removal flag (octet 4)• complete flag (octet 5)
Only records flagged as “complete” can be removed via dynamic update; attempts to remove other private type records
are silently ignored.
If the first octet is zero (this is a reserved algorithm number that should never appear in a DNSKEY record), the record
indicates that changes to the NSEC3 chains are in progress. The rest of the record contains an NSEC3PARAM record,
while the flag field tells what operation to perform based on the flag bits:
0x01 OPTOUT
0x80 CREATE
0x40 REMOVE
0x20 NONSEC

5.2 Secure Delegation
Once a zone is signed on the authoritative servers, the last remaining step is to establish chain of trust1 between the parent
zone (example.) and the local zone (dnssec.example.).
Generally the procedure is:• Wait for stale data to expire from caches. The amount of time required is equal to the maximum TTL value used in
the zone before signing. This step ensures that unsigned data expire from caches and resolvers do not get confusedby missing signatures.
• Insert/update DS records in the parent zone (dnssec.example. DS record).
1 For further details on how the chain of trust is used in practice, see The 12-Step DNSSEC Validation Process (Simplified) in the DNSSEC Guide.

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There are multiple ways to update DS records in the parent zone. Refer to the documentation for the parent zone to findout which options are applicable to a given case zone. Generally the options are, from most- to least-recommended:• Automatically update the DS record in the parent zone using CDS/CDNSKEY records automatically generated by
BIND. This requires support for RFC 7344 in either parent zone, registry, or registrar. In that case, configure
BIND to monitor DS records in the parent zone and everything will happen automatically at the right time.
• Query the zone for automatically generated CDS or CDNSKEY records using dig, and then insert these records
into the parent zone using the method specified by the parent zone (web form, e-mail, API, …).
• Generate DS records manually using the dnssec-dsfromkey utility on zone keys, and then insert them into
the parent zone.

5.3 DNSSEC Validation
The BIND resolver validates answers from authoritative servers by default. This behavior is controlled by the configuration
statement dnssec-validation.
By default a trust anchor for the DNS root zone is used. This trust anchor is provided as part of BIND and is kept
up-to-date using Dynamic Trust Anchor Management.
Note: DNSSEC validation works “out of the box” and does not require additional configuration. Additional configuration
options are intended only for special cases.
To validate answers, the resolver needs at least one trusted starting point, a “trust anchor.” Essentially, trust anchors arecopies of DNSKEY RRs for zones that are used to form the first link in the cryptographic chain of trust. Alternative trust
anchors can be specified using trust-anchors, but this setup is very unusual and is recommended only for expert
use. For more information, see Trust Anchors in the DNSSEC Guide.
The BIND authoritative server does not verify signatures on load, so zone keys for authoritative zones do not need to be
specified in the configuration file.

5.3.1 Validation Failures
When DNSSEC validation is configured, the resolver rejects any answers from signed, secure zones which fail to validate,and returns SERVFAIL to the client.
Responses may fail to validate for any of several reasons, including missing, expired, or invalid signatures; a key which
does not match the DS RRset in the parent zone; or an insecure response from a zone which, according to its parent,
should have been secure.
For more information see Basic DNSSEC Troubleshooting.

5.3.2 Coexistence With Unsigned (Insecure) Zones
Zones not protected by DNSSEC are called “insecure,” and these zones seamlessly coexist with signed zones.
When the validator receives a response from an unsigned zone that has a signed parent, it must confirm with the parent
that the zone was intentionally left unsigned. It does this by verifying, via signed and validated NSEC/NSEC3 records, thatthe parent zone contains no DS records for the child.
If the validator can prove that the zone is insecure, then the response is accepted. However, if it cannot, the validator
must assume an insecure response to be a forgery; it rejects the response and logs an error.

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The logged error reads “insecurity proof failed” and “got insecure response; parent indicates it should be secure.”

5.4 Dynamic Trust Anchor Management
BIND is able to maintain DNSSEC trust anchors using RFC 5011 key management. This feature allows named to keep
track of changes to critical DNSSEC keys without any need for the operator to make changes to configuration files.

5.4.1 Validating Resolver
To configure a validating resolver to use RFC 5011 to maintain a trust anchor, configure the trust anchor using
a trust-anchors statement and the initial-key keyword. Information about this can be found in thetrust-anchors statement description.

5.4.2 Authoritative Server
To set up an authoritative zone for RFC 5011 trust anchor maintenance, generate two (or more) key signing keys (KSKs)
for the zone. Sign the zone with one of them; this is the “active” KSK. All KSKs which do not sign the zone are “stand-by”
keys.
Any validating resolver which is configured to use the active KSK as an RFC 5011-managed trust anchor takes note of
the stand-by KSKs in the zone’s DNSKEY RRset, and stores them for future reference. The resolver rechecks the zone
periodically; after 30 days, if the new key is still there, the key is accepted by the resolver as a valid trust anchor for thezone. Anytime after this 30-day acceptance timer has completed, the active KSK can be revoked, and the zone can be“rolled over” to the newly accepted key.
The easiest way to place a stand-by key in a zone is to use the “smart signing” features of dnssec-keygen anddnssec-signzone. If a key exists with a publication date in the past, but an activation date which is unset or in the
future, dnssec-signzone -S includes the DNSKEY record in the zone but does not sign with it:$ dnssec-keygen -K keys -f KSK -P now -A now+2y example.net$ dnssec-signzone -S -K keys example.net

To revoke a key, use the command dnssec-revoke. This adds the REVOKED bit to the key flags and regenerates
the K*.key and K*.private files.
After revoking the active key, the zone must be signed with both the revoked KSK and the new active KSK. Smart signing
takes care of this automatically.
Once a key has been revoked and used to sign the DNSKEY RRset in which it appears, that key is never again accepted
as a valid trust anchor by the resolver. However, validation can proceed using the new active key, which was accepted by
the resolver when it was a stand-by key.
See RFC 5011 for more details on key rollover scenarios.
When a key has been revoked, its key ID changes, increasing by 128 and wrapping around at 65535. So, for example, thekey “Kexample.com.+005+10000” becomes “Kexample.com.+005+10128”.
If two keys have IDs exactly 128 apart and one is revoked, the two key IDs will collide, causing several problems. To
prevent this, dnssec-keygen does not generate a new key if another key which may collide is present. This checking
only occurs if the new keys are written to the same directory that holds all other keys in use for that zone.
Older versions of BIND 9 did not have this protection. Exercise caution if using key revocation on keys that were generated
by previous releases, or if using keys stored in multiple directories or on multiple machines.

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It is expected that a future release of BIND 9 will address this problem in a different way, by storing revoked keys with
their original unrevoked key IDs.

5.5 PKCS#11 (Cryptoki) Support
Public Key Cryptography Standard #11 (PKCS#11) defines a platform-independent API for the control of hardware
security modules (HSMs) and other cryptographic support devices.
PKCS#11 uses a “provider library”: a dynamically loadable library which provides a low-level PKCS#11 interface todrive the HSM hardware. The PKCS#11 provider library comes from the HSM vendor, and it is specific to the HSM to
be controlled.
BIND 9 access PKCS#11 libraries via OpenSSL extensions. The extension for OpenSSL 3 and newer is pkcs11-provider.
And for the older OpenSSL versions engine_pkcs11 from the OpenSC project can be used.
In both cases the extension is dynamically loaded into OpenSSL and the HSM is operated indirectly; any cryptographic
operations not supported by the HSM can be carried out by OpenSSL instead.

5.5.1 Prerequisites
See the documentation provided by the HSM vendor for information about installing, initializing, testing, and troubleshooting the HSM.

5.5.2 Building SoftHSMv2
SoftHSMv2, the latest development version of SoftHSM, is available from https://github.com/opendnssec/SoftHSMv2.
It is a software library developed by the OpenDNSSEC project (https://www.opendnssec.org) which provides a PKCS#11
interface to a virtual HSM, implemented in the form of an SQLite3 database on the local filesystem. It provides less security than a true HSM, but it allows users to experiment with native PKCS#11 when an HSM is not available. SoftHSMv2
can be configured to use either OpenSSL or the Botan library to perform cryptographic functions, but when using it for
native PKCS#11 in BIND, OpenSSL is required.
By default, the SoftHSMv2 configuration file is prefix/etc/softhsm2.conf (where prefix is configured atcompile time). This location can be overridden by the SOFTHSM2_CONF environment variable. The SoftHSMv2
cryptographic store must be installed and initialized before using it with BIND.
$
$
$
$
$

cd SoftHSMv2
configure --with-crypto-backend=openssl --prefix=/opt/pkcs11/usr
make
make install/opt/pkcs11/usr/bin/softhsm-util --init-token 0 --slot 0 --label softhsmv2

5.5.3 OpenSSL 1.x.x with engine_pkcs11
OpenSSL engine-based PKCS#11 uses engine_pkcs11 OpenSSL engine from libp11 project.
engine_pkcs11 tries to fit the PKCS#11 API within the engine API of OpenSSL. That is, it provides a gateway between
PKCS#11 modules and the OpenSSL engine API. One has to register the engine with OpenSSL and one has to provide
the path to the PKCS#11 module which should be gatewayed to. This can be done by editing the OpenSSL configuration
file, by engine specific controls, or by using the p11-kit proxy module.
It is recommended, that libp11 >= 0.4.12 is used.

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For more detailed howto including the examples, we recommend reading:https://gitlab.isc.org/isc-projects/bind9/-/wikis/BIND-9-PKCS11
When using engine_pkcs11, all BIND binaries potentially need the keys require ‘-E pkcs11’ argument to activate theengine support.
Even though OpenSSL 3 has compatibility support for Engine API it is not recommended to be used due to bugs in
OpenSSL and libp11.
It is not possible to generate new keys via the engine_pkcs11 and therefore it is not recommended to use it in adnssec-policy setup (although it is possible to put previously generated keys in the key-directory and let
the key manager select those keys when a key rollover is started.

5.5.4 Configuring engine_pkcs11
The canonical documentation for configuring engine_pkcs11 is in the libp11/README.md, but here’s copy of working
configuration for your convenience:
We are going to use our own custom copy of OpenSSL configuration, again it’s driven by an environment variable, thistime called OPENSSL_CONF. We are going to copy the global OpenSSL configuration (often found in etc/ssl/
openssl.conf) and customize it to use engines_pkcs11.
cp /etc/ssl/openssl.cnf /opt/bind9/etc/openssl.cnf

and export the environment variable:
export OPENSSL_CONF=/opt/bind9/etc/openssl.cnf

Now add the following line at the top of file, before any sections (in square brackets) are defined:
openssl_conf = openssl_init

And make sure there are no other ‘openssl_conf = …’ lines in the file.
Add following lines at the bottom of the file:[openssl_init]
engines=engine_section[engine_section]
pkcs11 = pkcs11_section[pkcs11_section]engine_id = pkcs11
dynamic_path = <PATHTO>/pkcs11.so
MODULE_PATH = <FULL_PATH_TO_HSM_MODULE># if automatic logging to the token is needed, PIN can be specified as below#PIN = 1234
init = 052

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5.5.5 Enabling the OpenSSL Engine in BIND commands
When using OpenSSL Engine-based PKCS#11, the “engine” to be used by OpenSSL can be specified in named andall of the BIND dnssec-* tools by using the -E <engine> command line option. This engine name matches the‘engine_id’ in the openssl.cnf created in previous section.
The zone signing commences as usual, with only one small difference. We need to provide the name of the OpenSSL
engine using the -E command line option.
dnssec-signzone -E pkcs11 -S -o example.net example.net

5.5.6 OpenSSL 3 with pkcs11-provider
OpenSSL provider-based PKCS#11 uses pkcs11-provider project.
pkcs11-provider tries to fit the PKCS#11 API within the Provider API of OpenSSL. That is, it provides a gateway between
PKCS#11 modules and the OpenSSL Provider API. One has to register the engine with OpenSSL and one has to provide
the path to the PKCS#11 module which should be gatewayed to. This can be done by editing the OpenSSL configuration
file, by engine specific controls, or by using the p11-kit proxy module.
It is required to use pkcs11-provider git commit 2e8c26b4157fd21422c66f0b4d7b26cf8c320570 from October 2, 2023
or later.
BIND support for pkcs11-provider is built in and the -E command line option explained above should not be used.

5.5.7 Configuring pkcs11-provider
The canonical documentation for configuring pkcs11-provider is in the provider-pkcs11.7 manual page, but here’s copyof working configuration for your convenience:
We are going to use our own custom copy of OpenSSL configuration, again it’s driven by an environment variable, thistime called OPENSSL_CONF. We are going to copy the global OpenSSL configuration (often found in etc/ssl/
openssl.conf) and customize it to use pkcs11-provider.
cp /etc/ssl/openssl.cnf /opt/bind9/etc/openssl.cnf

and export the environment variable:
export OPENSSL_CONF=/opt/bind9/etc/openssl.cnf

Now add the following line at the top of file, before any sections (in square brackets) are defined:
openssl_conf = openssl_init

And make sure there are no other ‘openssl_conf = …’ lines in the file.
Add following lines at the bottom of the file:[openssl_init]
providers = provider_init[provider_init]
default = default_init
pkcs11 = pkcs11_init[default_init](continues on next page)

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activate = 1[pkcs11_init]
module = <PATHTO>/pkcs11.so
pkcs11-module-path = <FULL_PATH_TO_HSM_MODULE># bind uses the digest+sign api. this is broken with the default load behaviour,# but works with early load. see: https://github.com/latchset/pkcs11-provider/issues/,→266
pkcs11-module-load-behavior = early# no-deinit quirk is needed if you use softhsm2#pkcs11-module-quirks = no-deinit# if automatic logging to the token is needed, PIN can be specified as below# the file referenced should contain just the PIN#pkcs11-module-token-pin = file:/etc/pki/pin.txt
activate = 1

5.5.8 Key Generation
HSM keys can now be created and used. We are going to assume that you already have a BIND 9 installed, either from apackage, or from the sources, and the tools are readily available in the $PATH.
For generating the keys, we are going to use pkcs11-tool available from the OpenSC suite. On both DEB-based andRPM-based distributions, the package is called opensc.
We need to generate at least two RSA keys:
pkcs11-tool --module <FULL_PATH_TO_HSM_MODULE> -l -k --key-type rsa:2048 --label␣,→example.net-ksk --pin <PIN>
pkcs11-tool --module <FULL_PATH_TO_HSM_MODULE> -l -k --key-type rsa:2048 --label␣,→example.net-zsk --pin <PIN>

Remember that each key should have unique label and we are going to use that label to reference the private key.
Convert the RSA keys stored in the HSM into a format that BIND 9 understands. The dnssec-keyfromlabel toolfrom BIND 9 can link the raw keys stored in the HSM with the K<zone>+<alg>+<id> files.
You’ll need to provide the OpenSSL engine name (pkcs11) if using the engine and the algorithm (RSASHA256). The
key is referenced with the PKCS#11 URI scheme and it can contain the PKCS#11 token label (we asume that it has been
initialized as bind9), and the PKCS#11 object label (called label when generating the keys using pkcs11-tool) andthe HSM PIN. Refer to RFC 7512 for the full PKCS#11 URI specification.
Convert the KSK:
dnssec-keyfromlabel -E pkcs11 -a RSASHA256 -l "pkcs11:token=bind9;object=example.net,→ksk;pin-value=0000" -f KSK example.net

and ZSK:dnssec-keyfromlabel -E pkcs11 -a RSASHA256 -l "pkcs11:token=bind9;object=example.net,→zsk;pin-value=0000" example.net

NOTE: you can use PIN stored on disk, by specifying pin-source=<path_to>/<file>, f.e.:(umask 0700 && echo -n 0000 > /opt/bind9/etc/pin.txt)

and then use in the label specification:

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pin-source=/opt/bind9/etc/pin.txt

Confirm that you have one KSK and one ZSK present in the current directory:ls -l K*The output should look like this (the second number will be different):
Kexample.net.+008+31729.key
Kexample.net.+008+31729.private
Kexample.net.+008+42231.key
Kexample.net.+008+42231.private

A note on generating ECDSA keys: there is a bug in libp11 when looking up a key, that function compares keys only on
their ID, not the label. So when looking up a key it returns the first key, rather than the matching key. The workaroundfor this is when creating ECDSA keys, you should specify a unique ID:
ksk=$(echo "example.net-ksk" | openssl sha1 -r | awk '{print $1}')
zsk=$(echo "example.net-zsk" | openssl sha1 -r | awk '{print $1}')
pkcs11-tool --module <FULL_PATH_TO_HSM_MODULE> -l -k --key-type EC:prime256v1 --id,→$ksk --label example.net-ksk --pin <PIN>
pkcs11-tool --module <FULL_PATH_TO_HSM_MODULE> -l -k --key-type EC:prime256v1 --id,→$zsk --label example.net-zsk --pin <PIN>

5.5.9 Running named With Automatic Zone Re-signing
The zone can also be signed automatically by named. Again, we need to provide the name of the OpenSSL engine using
the -E command line option, if using OpenSSL 1.x.x with engine_pkcs11, and this is not needed when using OpenSSL
3.x.x providers.
named -E pkcs11 -c named.conf

and the logs should have lines like:
Fetching example.net/RSASHA256/31729 (KSK) from key repository.
DNSKEY example.net/RSASHA256/31729 (KSK) is now published
DNSKEY example.net/RSA256SHA256/31729 (KSK) is now active
Fetching example.net/RSASHA256/42231 (ZSK) from key repository.
DNSKEY example.net/RSASHA256/42231 (ZSK) is now published
DNSKEY example.net/RSA256SHA256/42231 (ZSK) is now active

For named to dynamically re-sign zones using HSM keys, and/or to sign new records inserted via nsupdate, named musthave access to the HSM PIN. In OpenSSL-based PKCS#11, this is accomplished by placing the PIN into the openssl.
cnf file (in the above examples, /opt/pkcs11/usr/ssl/openssl.cnf).
See OpenSSL extension specific documentation on how to configure the PIN on global level. Doing so allows thednssec-\* tools to access the HSM without PIN entry. (The pkcs11-\* tools access the HSM directly, not via
OpenSSL, so a PIN is still required to use them.)

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6.1 Dynamic Update
Dynamic update is a method for adding, replacing, or deleting records in a primary server by sending it a special form of
DNS messages. The format and meaning of these messages is specified in RFC 2136.
Dynamic update is enabled by including an allow-update or an update-policy clause in the zone statement.
If the zone’s update-policy is set to local, updates to the zone are permitted for the key local-ddns, whichis generated by named at startup. See Dynamic Update Policies for more details.
Dynamic updates using Kerberos-signed requests can be made using the TKEY/GSS protocol, either by setting thetkey-gssapi-keytab option or by setting both the tkey-gssapi-credential and tkey-domain options.
Once enabled, Kerberos-signed requests are matched against the update policies for the zone, using the Kerberos principal
as the signer for the request.
Updating of secure zones (zones using DNSSEC) follows RFC 3007: RRSIG, NSEC, and NSEC3 records affected by
updates are automatically regenerated by the server using an online zone key. Update authorization is based on transaction
signatures and an explicit server policy.

6.1.1 The Journal FileAll changes made to a zone using dynamic update are stored in the zone’s journal file. This file is automatically created by
the server when the first dynamic update takes place. The name of the journal file is formed by appending the extension.jnl to the name of the corresponding zone file unless specifically overridden. The journal file is in a binary format andshould not be edited manually.
The server also occasionally writes (“dumps”) the complete contents of the updated zone to its zone file. This is not done
immediately after each dynamic update because that would be too slow when a large zone is updated frequently. Instead,the dump is delayed by up to 15 minutes, allowing additional updates to take place. During the dump process, transient
files are created with the extensions .jnw and .jbk; under ordinary circumstances, these are removed when the dump
is complete, and can be safely ignored.
When a server is restarted after a shutdown or crash, it replays the journal file to incorporate into the zone any updates
that took place after the last zone dump.
Changes that result from incoming incremental zone transfers are also journaled in a similar way.
The zone files of dynamic zones cannot normally be edited by hand because they are not guaranteed to contain the mostrecent dynamic changes; those are only in the journal file. The only way to ensure that the zone file of a dynamic zone is
up-to-date is to run rndc stop.
To make changes to a dynamic zone manually, follow these steps: first, disable dynamic updates to the zone using rndc
freeze zone. This updates the zone file with the changes stored in its .jnl file. Then, edit the zone file. Finally,
run rndc thaw zone to reload the changed zone and re-enable dynamic updates.
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rndc sync zone updates the zone file with changes from the journal file without stopping dynamic updates; thismay be useful for viewing the current zone state. To remove the .jnl file after updating the zone file, use rndc sync-clean.

6.2 NOTIFYDNS NOTIFY is a mechanism that allows primary servers to notify their secondary servers of changes to a zone’s data.
In response to a NOTIFY message from a primary server, the secondary checks to see that its version of the zone is thecurrent version and, if not, initiates a zone transfer.
For more information about DNS NOTIFY, see the description of the notify and :namedconf:ref`also-notify` statements. The NOTIFY protocol is specified in RFC 1996.
Note: As a secondary zone can also be a primary to other secondaries, named, by default, sends NOTIFY messages forevery zone it loads.

6.3 Incremental Zone Transfers (IXFR)The incremental zone transfer (IXFR) protocol is a way for secondary servers to transfer only changed data, instead of
having to transfer an entire zone. The IXFR protocol is specified in RFC 1995.
When acting as a primary server, BIND 9 supports IXFR for those zones where the necessary change history information
is available. These include primary zones maintained by dynamic update and secondary zones whose data was obtained
by IXFR. For manually maintained primary zones, and for secondary zones obtained by performing a full zone transfer(AXFR), IXFR is supported only if the option ixfr-from-differences is set to yes.
When acting as a secondary server, BIND 9 attempts to use IXFR unless it is explicitly disabled. For more information
about disabling IXFR, see the description of the request-ixfr clause of the server statement.
When a secondary server receives a zone via AXFR, it creates a new copy of the zone database and then swaps it into place;during the loading process, queries continue to be served from the old database with no interference. When receivinga zone via IXFR, however, changes are applied to the running zone, which may degrade query performance during thetransfer. If a server receiving an IXFR request determines that the response size would be similar in size to an AXFR
response, it may wish to send AXFR instead. The threshold at which this determination is made can be configured using
the max-ixfr-ratio option.

6.4 Split DNS
Setting up different views of the DNS space to internal and external resolvers is usually referred to as a split DNS setup.
There are several reasons an organization might want to set up its DNS this way.
One common reason to use split DNS is to hide “internal” DNS information from “external” clients on the Internet.
There is some debate as to whether this is actually useful. Internal DNS information leaks out in many ways (via email
headers, for example) and most savvy “attackers” can find the information they need using other means. However, sincelisting addresses of internal servers that external clients cannot possibly reach can result in connection delays and otherannoyances, an organization may choose to use split DNS to present a consistent view of itself to the outside world.
Another common reason for setting up a split DNS system is to allow internal networks that are behind filters or in RFC
1918 space (reserved IP space, as documented in RFC 1918) to resolve DNS on the Internet. Split DNS can also be used
to allow mail from outside back into the internal network.

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6.4.1 Example Split DNS Setup
Let’s say a company named Example, Inc. (example.com) has several corporate sites that have an internal networkwith reserved Internet Protocol (IP) space and an external demilitarized zone (DMZ), or “outside” section of a network,that is available to the public.
Example, Inc. wants its internal clients to be able to resolve external hostnames and to exchange mail with people on theoutside. The company also wants its internal resolvers to have access to certain internal-only zones that are not available
at all outside of the internal network.
To accomplish this, the company sets up two sets of name servers. One set is on the inside network (in the reserved IP
space) and the other set is on bastion hosts, which are “proxy” hosts in the DMZ that can talk to both sides of its network.
The internal servers are configured to forward all queries, except queries for site1.internal, site2.internal,site1.example.com, and site2.example.com, to the servers in the DMZ. These internal servers have complete sets of information for site1.example.com, site2.example.com, site1.internal, and site2.
internal.
To protect the site1.internal and site2.internal domains, the internal name servers must be configured todisallow all queries to these domains from any external hosts, including the bastion hosts.
The external servers, which are on the bastion hosts, are configured to serve the “public” version of the site1.
example.com and site2.example.com zones. This could include things such as the host records for public
servers (www.example.com and ftp.example.com) and mail exchange (MX) records (a.mx.example.com
and b.mx.example.com).
In addition, the public site1.example.com and site2.example.com zones should have special MX records
that contain wildcard (*) records pointing to the bastion hosts. This is needed because external mail servers have no otherway of determining how to deliver mail to those internal hosts. With the wildcard records, the mail is delivered to thebastion host, which can then forward it on to internal hosts.
Here’s an example of a wildcard MX record:*

IN MX 10 external1.example.com.

Now that they accept mail on behalf of anything in the internal network, the bastion hosts need to know how to deliver
mail to internal hosts. The resolvers on the bastion hosts need to be configured to point to the internal name servers for
DNS resolution.
Queries for internal hostnames are answered by the internal servers, and queries for external hostnames are forwarded
back out to the DNS servers on the bastion hosts.
For all of this to work properly, internal clients need to be configured to query only the internal name servers for DNS
queries. This could also be enforced via selective filtering on the network.
If everything has been set properly, Example, Inc.’s internal clients are now able to:• Look up any hostnames in the site1.example.com and site2.example.com zones.
• Look up any hostnames in the site1.internal and site2.internal domains.
• Look up any hostnames on the Internet.
• Exchange mail with both internal and external users.
Hosts on the Internet are able to:• Look up any hostnames in the site1.example.com and site2.example.com zones.
• Exchange mail with anyone in the site1.example.com and site2.example.com zones.
Here is an example configuration for the setup just described above. Note that this is only configuration information; for
information on how to configure the zone files, see Configurations and Zone Files.

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Internal DNS server config:
acl internals { 172.16.72.0/24; 192.168.1.0/24; };acl externals { bastion-ips-go-here; };options {...
...
forward only;// forward to external servers
forwarders {bastion-ips-go-here;};// sample allow-transfer (no one)allow-transfer { none; };// restrict query accessallow-query { internals; externals; };// restrict recursion
allow-recursion { internals; };
...
...
};
// sample primary zone
zone "site1.example.com" {type primary;file "m/site1.example.com";// do normal iterative resolution (do not forward)
forwarders { };allow-query { internals; externals; };allow-transfer { internals; };};// sample secondary zone
zone "site2.example.com" {type secondary;file "s/site2.example.com";primaries { 172.16.72.3; };forwarders { };allow-query { internals; externals; };allow-transfer { internals; };};zone "site1.internal" {type primary;file "m/site1.internal";
forwarders { };allow-query { internals; };allow-transfer { internals; }};zone "site2.internal" {type secondary;file "s/site2.internal";
primaries { 172.16.72.3; };forwarders { };allow-query { internals };(continues on next page)

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allow-transfer { internals; }};External (bastion host) DNS server configuration:acl internals { 172.16.72.0/24; 192.168.1.0/24; };acl externals { bastion-ips-go-here; };options {...
...
// sample allow-transfer (no one)allow-transfer { none; };// default query accessallow-query { any; };// restrict cache accessallow-query-cache { internals; externals; };// restrict recursion
allow-recursion { internals; externals; };
...
...
};
// sample secondary zone
zone "site1.example.com" {type primary;file "m/site1.foo.com";allow-transfer { internals; externals; };};zone "site2.example.com" {type secondary;file "s/site2.foo.com";primaries { another_bastion_host_maybe; };allow-transfer { internals; externals; }};In the resolv.conf (or equivalent) on the bastion host(s):search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4

6.5 IPv6 Support in BIND 9
BIND 9 fully supports all currently defined forms of IPv6 name-to-address and address-to-name lookups. It also uses
IPv6 addresses to make queries when running on an IPv6-capable system.
For forward lookups, BIND 9 supports only AAAA records. RFC 3363 deprecated the use of A6 records, and client-side
support for A6 records was accordingly removed from BIND 9. However, authoritative BIND 9 name servers still loadzone files containing A6 records correctly, answer queries for A6 records, and accept zone transfer for a zone containing
A6 records.

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For IPv6 reverse lookups, BIND 9 supports the traditional “nibble” format used in the ip6.arpa domain, as well as theolder, deprecated ip6.int domain. Older versions of BIND 9 supported the “binary label” (also known as “bitstring”)
format, but support of binary labels has been completely removed per RFC 3363. Many applications in BIND 9 do notunderstand the binary label format at all anymore, and return an error if one is given. In particular, an authoritative BIND
9 name server will not load a zone file containing binary labels.

6.5.1 Address Lookups Using AAAA Records
The IPv6 AAAA record is a parallel to the IPv4 A record, and, unlike the deprecated A6 record, specifies the entire IPv6
address in a single record. For example:$ORIGIN example.com.
host
3600

IN

AAAA

2001:db8::1

Use of IPv4-in-IPv6 mapped addresses is not recommended. If a host has an IPv4 address, use an A record, not a AAAA,
with ::ffff:192.168.42.1 as the address.

6.5.2 Address-to-Name Lookups Using Nibble Format
When looking up an address in nibble format, the address components are simply reversed, just as in IPv4, and ip6.
arpa. is appended to the resulting name. For example, the following commands produce a reverse name lookup for ahost with address 2001:db8::1:$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400
IN
PTR
host.example.com. )(6.6 Dynamically Loadable Zones (DLZ)
Dynamically Loadable Zones (DLZ) are an extension to BIND 9 that allows zone data to be retrieved directly from anexternal database. There is no required format or schema. DLZ modules exist for several different database backends,
including MySQL and LDAP, and can be written for any other.
The DLZ module provides data to named in text format, which is then converted to DNS wire format by named. This
conversion, and the lack of any internal caching, places significant limits on the query performance of DLZ modules.
Consequently, DLZ is not recommended for use on high-volume servers. However, it can be used in a hidden primaryconfiguration, with secondaries retrieving zone updates via AXFR. Note, however, that DLZ has no built-in support for
DNS notify; secondary servers are not automatically informed of changes to the zones in the database.

6.6.1 Configuring DLZ
dlz
Grammar zone (primary, redirect, secondary): dlz <string>;
Grammar topmost, view:dlz <string> {database <string>;
search <boolean>;}; // may occur multiple times

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Blocks: topmost, view, zone (primary, redirect, secondary)Tags: zone

Configures a Dynamically Loadable Zone (DLZ) database in named.conf.
A DLZ database is configured with a dlz statement in named.conf:
dlz example {database "dlopen driver.so args";
search yes;};This specifies a DLZ module to search when answering queries; the module is implemented in driver.so and is loaded
at runtime by the dlopen DLZ driver. Multiple dlz statements can be specified.
searchGrammar: search <boolean>;
Blocks: dlz, view.dlz
Tags: query

Specifies whether a Dynamically Loadable Zone (DLZ) module is queried for an answer to a query name.
When answering a query, all DLZ modules with search set to yes are queried to see whether they contain an answer
for the query name. The best available answer is returned to the client.
The search option in the above example can be omitted, because yes is the default value.
If search is set to no, this DLZ module is not searched for the best match when a query is received. Instead, zones inthis DLZ must be separately specified in a zone statement. This allows users to configure a zone normally using standard
zone-option semantics, but specify a different database backend for storage of the zone’s data. For example, to implement
NXDOMAIN redirection using a DLZ module for backend storage of redirection rules:
dlz other {database "dlopen driver.so args";
search no;};zone "." {type redirect;
dlz other;};

6.6.2 Sample DLZ Module
For guidance in the implementation of DLZ modules, the directory contrib/dlz/example contains a basic dynamically linkable DLZ module - i.e., one which can be loaded at runtime by the “dlopen” DLZ driver. The example sets up
a single zone, whose name is passed to the module as an argument in the dlz statement:dlz other {database "dlopen driver.so example.nil";};

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In the above example, the module is configured to create a zone “example.nil”, which can answer queries and AXFR
requests and accept DDNS updates. At runtime, prior to any updates, the zone contains an SOA, NS, and a single A
record at the apex:
example.nil.

3600

IN

example.nil.
example.nil.

3600
1800

)
IN
IN

SOA
example.nil. hostmaster.example.nil. (123 900 600 86400 3600
NS
A

example.nil.
10.53.0.1

The sample driver can retrieve information about the querying client and alter its response on the basis of this information.
To demonstrate this feature, the example driver responds to queries for “source-addr.``zonename``>/TXT” with the source
address of the query. Note, however, that this record will not be included in AXFR or ANY responses. Normally, thisfeature is used to alter responses in some other fashion, e.g., by providing different address records for a particular namedepending on the network from which the query arrived.
Documentation of the DLZ module API can be found in contrib/dlz/example/README. This directory also
contains the header file dlz_minimal.h, which defines the API and should be included by any dynamically linkable
DLZ module.

6.7 Dynamic Database (DynDB)
Dynamic Database, or DynDB, is an extension to BIND 9 which, like DLZ (see Dynamically Loadable Zones (DLZ)),
allows zone data to be retrieved from an external database. Unlike DLZ, a DynDB module provides a full-featured BIND
zone database interface. Where DLZ translates DNS queries into real-time database lookups, resulting in relatively poor
query performance, and is unable to handle DNSSEC-signed data due to its limited API, a DynDB module can pre-load
an in-memory database from the external data source, providing the same performance and functionality as zones served
natively by BIND.
A DynDB module supporting LDAP has been created by Red Hat and is available from https://pagure.io/bind-dyndb-ldap.
A sample DynDB module for testing and developer guidance is included with the BIND source code, in the directorybin/tests/system/dyndb/driver.

6.7.1 Configuring DynDB
dyndb
Grammar: dyndb <string> <quoted_string> { <unspecified-text> }; // may occur
multiple times
Blocks: topmost, viewTags: zone

Configures a DynDB database in named.conf.
A DynDB database is configured with a dyndb statement in named.conf:
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The file driver.so is a DynDB module which implements the full DNS database API. Multiple dyndb statements
can be specified, to load different drivers or multiple instances of the same driver. Zones provided by a DynDB module
are added to the view’s zone table, and are treated as normal authoritative zones when BIND responds to queries. Zone
configuration is handled internally by the DynDB module.
The parameters are passed as an opaque string to the DynDB module’s initialization routine. Configuration syntax differs
depending on the driver.

6.7.2 Sample DynDB Module
For guidance in the implementation of DynDB modules, the directory bin/tests/system/dyndb/driver contains a basic DynDB module. The example sets up two zones, whose names are passed to the module as arguments in the
dyndb statement:
dyndb sample "sample.so" { example.nil. arpa. };In the above example, the module is configured to create a zone, “example.nil”, which can answer queries and AXFR
requests and accept DDNS updates. At runtime, prior to any updates, the zone contains an SOA, NS, and a single A
record at the apex:
example.nil.

86400

IN

SOA

example.nil.
example.nil.

86400
86400

IN
IN

NS
A

example.nil. example.nil. (0 28800 7200 604800 86400)
example.nil.
127.0.0.1

When the zone is updated dynamically, the DynDB module determines whether the updated RR is an address (i.e., type
A or AAAA); if so, it automatically updates the corresponding PTR record in a reverse zone. Note that updates are notstored permanently; all updates are lost when the server is restarted.

6.8 Catalog Zones
A “catalog zone” is a special DNS zone that contains a list of other zones to be served, along with their configuration
parameters. Zones listed in a catalog zone are called “member zones.” When a catalog zone is loaded or transferred to asecondary server which supports this functionality, the secondary server creates the member zones automatically. Whenthe catalog zone is updated (for example, to add or delete member zones, or change their configuration parameters), thosechanges are immediately put into effect. Because the catalog zone is a normal DNS zone, these configuration changes canbe propagated using the standard AXFR/IXFR zone transfer mechanism.
Catalog zones’ format and behavior are specified as RFC 9432.

6.8.1 Principle of Operation
Normally, if a zone is to be served by a secondary server, the named.conf file on the server must list the zone, or thezone must be added using rndc addzone. In environments with a large number of secondary servers, and/or where
the zones being served are changing frequently, the overhead involved in maintaining consistent zone configuration on all
the secondary servers can be significant.
A catalog zone is a way to ease this administrative burden: it is a DNS zone that lists member zones that should be servedby secondary servers. When a secondary server receives an update to the catalog zone, it adds, removes, or reconfigures
member zones based on the data received.

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To use a catalog zone, it must first be set up as a normal zone on both the primary and secondary servers that are configured
to use it. It must also be added to a catalog-zones list in the options or view statement in named.conf. Thisis comparable to the way a policy zone is configured as a normal zone and also listed in a response-policy statement.
To use the catalog zone feature to serve a new member zone:• Set up the member zone to be served on the primary as normal. This can be done by editing named.conf or byrunning rndc addzone.
• Add an entry to the catalog zone for the new member zone. This can be done by editing the catalog zone’s zone fileand running rndc reload, or by updating the zone using nsupdate.
The change to the catalog zone is propagated from the primary to all secondaries using the normal AXFR/IXFR mechanism. When the secondary receives the update to the catalog zone, it detects the entry for the new member zone, creates
an instance of that zone on the secondary server, and points that instance to the primaries specified in the catalog
zone data. The newly created member zone is a normal secondary zone, so BIND immediately initiates a transfer of zone
contents from the primary. Once complete, the secondary starts serving the member zone.
Removing a member zone from a secondary server requires only deleting the member zone’s entry in the catalog zone;
the change to the catalog zone is propagated to the secondary server using the normal AXFR/IXFR transfer mechanism.
The secondary server, on processing the update, notices that the member zone has been removed, stops serving the zone,
and removes it from its list of configured zones. However, removing the member zone from the primary server must be
done by editing the configuration file or running rndc delzone.

6.8.2 Configuring Catalog Zones
catalog-zones
Grammar: catalog-zones { zone <string> [ default-primaries [ port <integer>] [ source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port
<integer> ] ) [ key <string> ] [ tls <string> ]; ... } ] [ zone-directory<quoted_string> ] [ in-memory <boolean> ] [ min-update-interval <duration>]; ... };Blocks: options, viewTags: zone

Configures catalog zones in named.conf.
Catalog zones are configured with a catalog-zones statement in the options or view section of named.conf.
For example:
catalog-zones {zone "catalog.example"
default-primaries { 10.53.0.1; }in-memory nozone-directory "catzones"
min-update-interval 10;};

This statement specifies that the zone catalog.example is a catalog zone. This zone must be properly configured in
the same view. In most configurations, it would be a secondary zone.
The options following the zone name are not required, and may be specified in any order.

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default-masters
Synonym for default-primaries.
default-primaries
This option defines the default primaries for member zones listed in a catalog zone, and can be overridden by options
within a catalog zone. If no such options are included, then member zones transfer their contents from the servers
listed in this option.
in-memory
This option, if set to yes, causes member zones to be stored only in memory. This is functionally equivalent toconfiguring a secondary zone without a file option. The default is no; member zones’ content is stored locallyin a file whose name is automatically generated from the view name, catalog zone name, and member zone name.
zone-directoryThis option causes local copies of member zones’ zone files to be stored in the specified directory, if in-memory
is not set to yes. The default is to store zone files in the server’s working directory. A non-absolute pathname inzone-directory is assumed to be relative to the working directory.
min-update-intervalThis option sets the minimum interval between updates to catalog zones, in seconds. If an update to a catalog zone
(for example, via IXFR) happens less than min-update-interval seconds after the most recent update, thechanges are not carried out until this interval has elapsed. The default is 5 seconds.
Catalog zones are defined on a per-view basis. Configuring a non-empty catalog-zones statement in a view automatically turns on allow-new-zones for that view. This means that rndc addzone and rndc delzone also
work in any view that supports catalog zones.

6.8.3 Catalog Zone Format
A catalog zone is a regular DNS zone; therefore, it must have a single SOA and at least one NS record.
A record stating the version of the catalog zone format is also required. If the version number listed is not supported by
the server, then a catalog zone may not be used by that server.
catalog.example.
IN SOA . . 2016022901 900 600 86400 1
catalog.example.
IN NS invalid.
version.catalog.example.
IN TXT "2"

Note that this record must have the domain name version.catalog-zone-name. The data stored in a catalog
zone is indicated by the domain name label immediately before the catalog zone domain. Currently BIND supports catalog
zone schema versions “1” and “2”.
Also note that the catalog zone must have an NS record in order to be a valid DNS zone, and using the value “invalid.”
for NS is recommended.
A member zone is added by including a PTR resource record in the zones sub-domain of the catalog zone. The recordlabel can be any unique label. The target of the PTR record is the member zone name. For example, to add member
zones domain.example and domain2.example:
5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example. IN PTR domain.example.
uniquelabel.zones.catalog.example. IN PTR domain2.example.

The label is necessary to identify custom properties (see below) for a specific member zone. Also, the zone state can bereset by changing its label, in which case BIND will remove the member zone and add it back.

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6.8.4 Catalog Zone Custom Properties
BIND uses catalog zones custom properties to define different properties which can be set either globally for the wholecatalog zone or for a single member zone. Global custom properties override the settings in the configuration file, andmember zone custom properties override global custom properties.
For the version “1” of the schema custom properties must be placed without a special suffix.
For the version “2” of the schema custom properties must be placed under the “.ext” suffix.
Global custom properties are set at the apex of the catalog zone, e.g.:
primaries.ext.catalog.example.

IN AAAA 2001:db8::1

BIND currently supports the following custom properties:• A simple primaries definition:
primaries.ext.catalog.example.

IN A 192.0.2.1

This custom property defines a primary server for the member zones, which can be either an A or AAAA record.
If multiple primaries are set, the order in which they are used is random.
Note: masters can be used as a synonym for primaries.
• A primaries with a TSIG key defined:label.primaries.ext.catalog.example.
label.primaries.ext.catalog.example.

IN A 192.0.2.2
IN TXT "tsig_key_name"

This custom property defines a primary server for the member zone with a TSIG key set. The TSIG key must be
configured in the configuration file. label can be any valid DNS label.
Note: masters can be used as a synonym for primaries.
• allow-query and allow-transfer ACLs:
allow-query.ext.catalog.example.
IN APL 1:10.0.0.1/24
allow-transfer.ext.catalog.example.
IN APL !1:10.0.0.1/32 1:10.0.0.0/24

These custom properties are the equivalents of allow-query and allow-transfer options in a zone declaration in the named.conf configuration file. The ACL is processed in order; if there is no match to any rule,the default policy is to deny access. For the syntax of the APL RR, see RFC 3123.
The member zone-specific custom properties are defined the same way as global custom properties, but in the member
zone subdomain:
primaries.ext.5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example. IN A␣
,→192.0.2.2
label.primaries.ext.5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example.␣
,→IN AAAA 2001:db8::2
label.primaries.ext.5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example.␣
,→IN TXT "tsig_key_name"allow-query.ext.5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example. IN␣
,→APL 1:10.0.0.0/24
primaries.ext.uniquelabel.zones.catalog.example. IN A 192.0.2.3

Custom properties defined for a specific zone override the global custom properties defined in the catalog zone. These inturn override the global options defined in the catalog-zones statement in the configuration file.

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Note that none of the global records for a custom property are inherited if any records are defined for that custom property
for the specific zone. For example, if the zone had a primaries record of type A but not AAAA, it would not inherit
the type AAAA record from the global custom property or from the global option in the configuration file.

6.8.5 Change of Ownership (coo)BIND supports the catalog zones “Change of Ownership” (coo) property. When the same entry which exists in one catalog
zone is added into another catalog zone, the default behavior for BIND is to ignore it, and continue serving the zone using
the catalog zone where it was originally existed, unless it is removed from there, then it can be added into the new one.
Using the coo property it is possible to gracefully move a zone from one catalog zone into another, by letting the catalog
consumers know that it is permitted to do so. To do that, the original catalog zone should be updated with a new record
with coo custom property:
uniquelabel.zones.catalog.example. IN PTR domain2.example.
coo.uniquelabel.zones.catalog.example. IN PTR catalog2.example.

Here, the catalog.example catalog zone gives permission for the member zone with label “uniquelabel” to be transferred into catalog2.example catalog zone. Catalog consumers which support the coo property will then takenote, and when the zone is finally added into catalog2.example catalog zone, catalog consumers will change theownership of the zone from catalog.example to catalog2.example. BIND’s implementation simply deletes
the zone from the old catalog zone and adds it back into the new catalog zone, which also means that all associated state
for the just migrated zone will be reset, including when the unique label is the same.
The record with coo custom property can be later deleted by the catalog zone operator after confirming that all the
consumers have received it and have successfully changed the ownership of the zone.

6.9 DNS Firewalls and Response Policy Zones
A DNS firewall examines DNS traffic and allows some responses to pass through while blocking others. This examination
can be based on several criteria, including the name requested, the data (such as an IP address) associated with that name,or the name or IP address of the name server that is authoritative for the requested name. Based on these criteria, a DNS
firewall can be configured to discard, modify, or replace the original response, allowing administrators more control overwhat systems can access or be accessed from their networks.
DNS Response Policy Zones (RPZ) are a form of DNS firewall in which the firewall rules are expressed within the DNS
itself - encoded in an open, vendor-neutral format as records in specially constructed DNS zones.
Using DNS zones to configure policy allows policy to be shared from one server to another using the standard DNS zonetransfer mechanism. This allows a DNS operator to maintain their own firewall policies and share them easily amongst
their internal name servers, or to subscribe to external firewall policies such as commercial or cooperative “threat feeds,”
or both.
named can subscribe to up to 64 Response Policy Zones, each of which encodes a separate policy rule set. Each rule
is stored in a DNS resource record set (RRset) within the RPZ, and consists of a trigger and an action. There are five
types of triggers and six types of actions.
A response policy rule in a DNS RPZ can be triggered as follows:• by the IP address of the client• by the query name• by an address which would be present in a truthful response• by the name or address of an authoritative name server responsible for publishing the original response

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A response policy action can be one of the following:• to synthesize a “domain does not exist” (NXDOMAIN) response• to synthesize a “name exists but there are no records of the requested type” (NODATA) response• to drop the response• to switch to TCP by sending a truncated UDP response that requires the DNS client to try again with TCP• to replace/override the response’s data with specific data (provided within the response policy zone)• to exempt the response from further policy processing
The most common use of a DNS firewall is to “poison” a domain name, IP address, name server name, or name server
IP address. Poisoning is usually done by forcing a synthetic “domain does not exist” (NXDOMAIN) response. Thismeans that if an administrator maintains a list of known “phishing” domains, these names can be made unreachable bycustomers or end users just by adding a firewall policy into the recursive DNS server, with a trigger for each known“phishing” domain, and an action in every case forcing a synthetic NXDOMAIN response. It is also possible to use adata-replacement action such as answering for these known “phishing” domains with the name of a local web server thatcan display a warning page. Such a web server would be called a “walled garden.”Note: Authoritative name servers can be responsible for many different domains. If DNS RPZ is used to poison all
domains served by some authoritative name server name or address, the effects can be quite far-reaching. Users areadvised to ensure that such authoritative name servers do not also serve domains that should not be poisoned.

6.9.1 Why Use a DNS Firewall?
Criminal and network abuse traffic on the Internet often uses the Domain Name System (DNS), so protection against
these threats should include DNS firewalling. A DNS firewall can selectively intercept DNS queries for known network
assets including domain names, IP addresses, and name servers. Interception can mean rewriting a DNS response to directa web browser to a “walled garden,” or simply making any malicious network assets invisible and unreachable.

6.9.2 What Can a DNS Firewall Do?
Firewalls work by applying a set of rules to a traffic flow, where each rule consists of a trigger and an action. Triggers
determine which messages within the traffic flow are handled specially, and actions determine what that special handlingis. For a DNS firewall, the traffic flow to be controlled consists of responses sent by a recursive DNS server to its end-userclients. Some true responses are not safe for all clients, so the policy rules in a DNS firewall allow some responses to beintercepted and replaced with safer content.

6.9.3 Creating and Maintaining RPZ Rule SetsIn DNS RPZ, the DNS firewall policy rule set is stored in a DNS zone, which is maintained and synchronized using thesame tools and methods as for any other DNS zone. The primary name server for a DNS RPZ may be an internal server,
if an administrator is creating and maintaining their own DNS policy zone, or it may be an external name server (such asa security vendor’s server), if importing a policy zone published externally. The primary copy of the DNS firewall policy
can be a DNS “zone file” which is either edited by hand or generated from a database. A DNS zone can also be edited
indirectly using DNS dynamic updates (for example, using the “nsupdate” shell level utility).
DNS RPZ allows firewall rules to be expressed in a DNS zone format and then carried to subscribers as DNS data. A
recursive DNS server which is capable of processing DNS RPZ synchronizes these DNS firewall rules using the same
standard DNS tools and protocols used for secondary name service. The DNS policy information is then promoted to the
DNS control plane inside the customer’s DNS resolver, making that server into a DNS firewall.
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A security company whose products include threat intelligence feeds can use a DNS Response Policy Zone (RPZ) as adelivery channel to customers. Threats can be expressed as known-malicious IP addresses and subnets, known-malicious
domain names, and known-malicious domain name servers. By feeding this threat information directly into customers’
local DNS resolvers, providers can transform these DNS servers into a distributed DNS firewall.
When a customer’s DNS resolver is connected by a realtime subscription to a threat intelligence feed, the provider canprotect the customer’s end users from malicious network elements (including IP addresses and subnets, domain names,
and name servers) immediately as they are discovered. While it may take days or weeks to “take down” criminal andabusive infrastructure once reported, a distributed DNS firewall can respond instantly.
Other distributed TCP/IP firewalls have been on the market for many years, and enterprise users are now comfortable
importing real-time threat intelligence from their security vendors directly into their firewalls. This intelligence can takethe form of known-malicious IP addresses or subnets, or of patterns which identify known-malicious email attachments,
file downloads, or web addresses (URLs). In some products it is also possible to block DNS packets based on the names
or addresses they carry.

6.9.4 Limitations of DNS RPZ
We’re often asked if DNS RPZ could be used to set up redirection to a CDN. For example, if “mydomain.com” is a normal
domain with SOA, NS, MX, TXT records etc., then if someone sends an A or AAAA query for “mydomain.com”, canwe use DNS RPZ on an authoritative nameserver to return “CNAME mydomain.com.my-cdn-provider.net”?
The problem with this suggestion is that there is no way to CNAME only A and AAAA queries, not even with RPZ.
The underlying reason is that if the authoritative server answers with a CNAME, the recursive server making that querywill cache the response. Thereafter (while the CNAME is still in cache), it assumes that there are no records of any
non-CNAME type for the name that was being queried, and directs subsequent queries for all other types directly to thetarget name of the CNAME record.
To be clear, this is not a limitation of RPZ; it is a function of the way the DNS protocol works. It’s simply not possible
to use “partial” CNAMES to help when setting up CDNs because doing this will break other functionality such as email
routing.
Similarly, following the DNS protocol definition, wildcards in the form of *.example records might behave in unintuitive ways. For a detailed definition of wildcards in DNS, please see RFC 4592, especially section 2.

6.9.5 DNS Firewall Usage Examples
Here are some scenarios in which a DNS firewall might be useful.
Some known threats are based on an IP address or subnet (IP address range). For example, an analysis may show that alladdresses in a “class C” network are used by a criminal gang for “phishing” web servers. With a DNS firewall based on
DNS RPZ, a firewall policy can be created such as “if a DNS lookup would result in an address from this class C network,
then answer instead with an NXDOMAIN indication.” That simple rule would prevent any end users inside customers’
networks from being able to look up any domain name used in this phishing attack – without having to know in advance
what those names might be.
Other known threats are based on domain names. An analysis may determine that a certain domain name or set of domainnames is being or will shortly be used for spamming, phishing, or other Internet-based attacks which all require working
domain names. By adding name-triggered rules to a distributed DNS firewall, providers can protect customers’ end users
from any attacks which require them to be able to look up any of these malicious names. The names can be wildcards(for example, *.evil.com), and these wildcards can have exceptions if some domains are not as malicious as others (if*.evil.com is bad, then not.evil.com might be an exception).
Alongside growth in electronic crime has come growth of electronic criminal expertise. Many criminal gangs now maintain their own extensive DNS infrastructure to support a large number of domain names and a diverse set of IP addressing
resources. Analyses show in many cases that the only truly fixed assets criminal organizations have are their name servers,
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which are by nature slightly less mobile than other network assets. In such cases, DNS administrators can anchor their
DNS firewall policies in the abusive name server names or name server addresses, and thus protect their customers’ end
users from threats where neither the domain name nor the IP address of that threat is known in advance.
Electronic criminals rely on the full resiliency of DNS just as the rest of digital society does. By targeting criminal assets
at the DNS level we can deny these criminals the resilience they need. A distributed DNS firewall can leverage the highskills of a security company to protect a large number of end users. DNS RPZ, as the first open and vendor-neutral
distributed DNS firewall, can be an effective way to deliver threat intelligence to customers.
A Real-World Example of DNS RPZ’s Value
The Conficker malware worm (https://en.wikipedia.org/wiki/Conficker) was first detected in 2008. Although it is nolonger an active threat, the techniques described here can be applied to other DNS threats.
Conficker used a domain generation algorithm (DGA) to choose up to 50,000 command and control domains per day.
It would be impractical to create an RPZ that contains so many domain names and changes so much on a daily basis.
Instead, we can trigger RPZ rules based on the names of the name servers that are authoritative for the command andcontrol domains, rather than trying to trigger on each of 50,000 different (daily) query names. Since the well-known nameserver names for Conficker’s domain names are never used by nonmalicious domains, it is safe to poison all lookups that
rely on these name servers. Here is an example that achieves this result:$ORIGIN rpz.example.com.
ns.0xc0f1c3a5.com.rpz-nsdname
ns.0xc0f1c3a5.net.rpz-nsdname
ns.0xc0f1c3a5.org.rpz-nsdname

CNAME
CNAME
CNAME

*.walled-garden.example.com.
*.walled-garden.example.com.
*.walled-garden.example.com.

The * at the beginning of these CNAME target names is special, and it causes the original query name to be prepended
to the CNAME target. So if a user tries to visit the Conficker command and control domain racaldftn.com.ai (which wasa valid Conficker command and control domain name on 19-October-2011), the RPZ-configured recursive name server
will send back this answer:
racaldftn.com.ai.
CNAME
racaldftn.com.ai.walled-garden.example.com.
racaldftn.com.ai.walled-garden.example.com.
A
192.168.50.3

This example presumes that the following DNS content has also been created, which is not part of the RPZ zone itself
but is in another domain:$ORIGIN walled-garden.example.com.
*
A
192.168.50.3

Assuming that we’re running a web server listening on 192.168.50.3 that always displays a warning message no matter
what uniform resource identifier (URI) is used, the above RPZ configuration will instruct the web browser of any infected
end user to connect to a “server name” consisting of their original lookup name (racaldftn.com.ai) prepended to the walled
garden domain name (walled-garden.example.com). This is the name that will appear in the web server’s log file, andhaving the full name in that log file will facilitate an analysis as to which users are infected with what virus.

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6.9.6 Keeping Firewall Policies Updated
It is vital for overall system performance that incremental zone transfers (see RFC 1995) and real-time change notification(see RFC 1996) be used to synchronize DNS firewall rule sets between the publisher’s primary copy of the rule set andthe subscribers’ working copies of the rule set.
If DNS dynamic updates are used to maintain a DNS RPZ rule set, the name server automatically calculates a streamof deltas for use when sending incremental zone transfers to the subscribing name servers. Sending a stream of deltas –known as an “incremental zone transfer” or IXFR – is usually much faster than sending the full zone every time it changes,
so it’s worth the effort to use an editing method that makes such incremental transfers possible.
Administrators who edit or periodically regenerate a DNS RPZ rule set and whose primary name server uses BIND
can enable the ixfr-from-differences option, which tells the primary name server to calculate the differences
between each new zone and the preceding version, and to make these differences available as a stream of deltas for use
in incremental zone transfers to the subscribing name servers. This will look something like the following:
options {// ...
ixfr-from-differences yes;// ...
};As mentioned above, the simplest and most common use of a DNS firewall is to poison domain names known to be purely
malicious, by simply making them disappear. All DNS RPZ rules are expressed as resource record sets (RRsets), andthe way to express a “force a name-does-not-exist condition” is by adding a CNAME pointing to the root domain (.). In
practice this looks like:$ORIGIN rpz.example.com.
malicious1.org
CNAME .
*.malicious1.org
CNAME .
malicious2.org
CNAME .
*.malicious2.org
CNAME .

Two things are noteworthy in this example. First, the malicious names are made relative within the response policy zone.
Since there is no trailing dot following “.org” in the above example, the actual RRsets created within this response policy
zone are, after expansion:
malicious1.org.rpz.example.com.
*.malicious1.org.rpz.example.com.
malicious2.org.rpz.example.com.
*.malicious2.org.rpz.example.com.

CNAME .
CNAME .
CNAME .
CNAME .

Second, for each name being poisoned, a wildcard name is also listed. This is because a malicious domain name probably
has or may potentially have malicious subdomains.
In the above example, the relative domain names malicious1.org and malicious2.org will match only the real domain names
malicious1.org and malicious2.org, respectively. The relative domain names *.malicious1.org and *.malicious2.org will
match any subdomain.of.malicious1.org or subdomain.of.malicious2.org, respectively.
This example forces an NXDOMAIN condition as its policy action, but other policy actions are also possible.

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6.9.7 Performance and Scalability When Using Multiple RPZs
Since version 9.10, BIND can be configured to have different response policies depending on the identity of the querying
client and the nature of the query. To configure BIND response policy, the information is placed into a zone file whose
only purpose is conveying the policy information to BIND. A zone file containing response policy information is called a
Response Policy Zone, or RPZ, and the mechanism in BIND that uses the information in those zones is called DNS RPZ.
It is possible to use as many as 64 separate RPZ files in a single instance of BIND, and BIND is not significantly slowedby such heavy use of RPZ.
(Note: by default, BIND 9.11 only supports up to 32 RPZ files, but this can be increased to 64 at compile time. All othersupported versions of BIND support 64 by default.)
Each one of the policy zone files can specify policy for as many different domains as necessary. The limit of 64 is on thenumber of independently-specified policy collections and not the number of zones for which they specify policy.
Policy information from all of the policy zones together are stored in a special data structure allowing simultaneous
lookups across all policy zones to be performed very rapidly. Looking up a policy rule is proportional to the logarithm of
the number of rules in the largest single policy zone.

6.9.8 Practical Tips for DNS Firewalls and DNS RPZ
Administrators who subscribe to an externally published DNS policy zone and who have a large number of internal
recursive name servers should create an internal name server called a “distribution master” (DM). The DM is a secondary(stealth secondary) name server from the publisher’s point of view; that is, the DM is fetching zone content from theexternal server. The DM is also a primary name server from the internal recursive name servers’ point of view: they fetch
zone content from the DM. In this configuration the DM is acting as a gateway between the external publisher and theinternal subscribers.
The primary server must know the unicast listener address of every subscribing recursive server, and must enumerate allof these addresses as destinations for real time zone change notification (as described in RFC 1996). So if an enterprisewide RPZ is called “rpz.example.com” and if the unicast listener addresses of four of the subscribing recursive nameservers are 192.0.200.1, 192.0.201.1, 192.0.202.1, and 192.0.203.1, the primary server’s configuration looks like this:zone "rpz.example.com" {type primary;file "primary/rpz.example.com";
notify explicit;
also-notify { 192.0.200.1;
192.0.201.1;
192.0.202.1;
192.0.203.1; };allow-transfer { 192.0.200.1;
192.0.201.1;
192.0.202.1;
192.0.203.1; };allow-query { localhost; };};Each recursive DNS server that subscribes to the policy zone must be configured as a secondary server for the zone, andmust also be configured to use the policy zone for local response policy. To subscribe a recursive name server to a response
policy zone where the unicast listener address of the primary server is 192.0.220.2, the server’s configuration should look
like this:options {// ...
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response-policy {zone "rpz.example.com";};// ...
};
zone "rpz.example.com";type secondary;primaries { 192.0.222.2; };file "secondary/rpz.example.com";allow-query { localhost; };allow-transfer { none; };};Note that queries are restricted to “localhost,” since query access is never used by DNS RPZ itself, but may be useful to
DNS operators for use in debugging. Transfers should be disallowed to prevent policy information leaks.
If an organization’s business continuity depends on full connectivity with another company whose ISP also serves somecriminal or abusive customers, it’s possible that one or more external RPZ providers – that is, security feed vendors –may eventually add some RPZ rules that could hurt a company’s connectivity to its business partner. Users can protect
themselves from this risk by using an internal RPZ in addition to any external RPZs, and by putting into their internal RPZ
some “pass-through” rules to prevent any policy action from affecting a DNS response that involves a business partner.
A recursive DNS server can be connected to more than one RPZ, and these are searched in order. Therefore, to protect a
network from dangerous policies which may someday appear in external RPZ zones, administrators should list the internal
RPZ zones first.
options {// ...
response-policy {zone "rpz.example.com";zone "rpz.security-vendor-1.com";zone "rpz.security-vendor-2.com";};// ...
};

Within an internal RPZ, there need to be rules describing the network assets of business partners whose communications
need to be protected. Although it is not generally possible to know what domain names they use, administrators will beaware of what address space they have and perhaps what name server names they use.
$ORIGIN rpz.example.com.
8.0.0.0.10.rpz-ip
16.0.0.45.128.rpz-nsip
ns.partner1.com.rpz-nsdname
ns.partner2.com.rpz-nsdname

CNAME
CNAME
CNAME
CNAME

rpz-passthru.
rpz-passthru.
rpz-passthru.
rpz-passthru.

Here, we know that answers in address block 10.0.0.0/8 indicate a business partner, as well as answers involving any
name server whose address is in the 128.45.0.0/16 address block, and answers involving the name servers whose names
are ns.partner1.com or ns.partner2.com.
The above example demonstrates that when matching by answer IP address (the .rpz-ip owner), or by name server IP
address (the .rpz-nsip owner) or by name server domain name (the .rpz-nsdname owner), the special RPZ marker (.rpzip, .rpz-nsip, or .rpz-nsdname) does not appear as part of the CNAME target name.
By triggering these rules using the known network assets of a partner, and using the “pass-through” policy action, no later
RPZ processing (which in the above example refers to the “rpz.security-vendor-1.com” and “rpz.security-vendor-2.com”

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policy zones) will have any effect on DNS responses for partner assets.

6.9.9 Creating a Simple Walled Garden Triggered by IP Address
It may be the case that the only thing known about an attacker is the IP address block they are using for their “phishing” webservers. If the domain names and name servers they use are unknown, but it is known that every one of their “phishing”
web servers is within a small block of IP addresses, a response can be triggered on all answers that would include records
in this address range, using RPZ rules that look like the following example:$ORIGIN rpz.example.com.
22.0.212.94.109.rpz-ip*.212.94.109.in-addr.arpa*.213.94.109.in-addr.arpa*.214.94.109.in-addr.arpa*.215.94.109.in-addr.arpa

CNAME
CNAME
CNAME
CNAME
CNAME

drop.garden.example.com.
.
.
.
.

Here, if a truthful answer would include an A (address) RR (resource record) whose value were within the 109.94.212.0/22
address block, then a synthetic answer is sent instead of the truthful answer. Assuming the query is for www.malicious.net,
the synthetic answer is:www.malicious.net.
drop.garden.example.com.

CNAME
A

drop.garden.example.com.
192.168.7.89

This assumes that drop.garden.example.com has been created as real DNS content, outside of the RPZ:
$ORIGIN example.com.
drop.garden

A

192.168.7.89

In this example, there is no “*” in the CNAME target name, so the original query name will not be present in the walled
garden web server’s log file. This is an undesirable loss of information, and is shown here for example purposes only.
The above example RPZ rules would also affect address-to-name (also known as “reverse DNS”) lookups for the unwanted
addresses. If a mail or web server receives a connection from an address in the example’s 109.94.212.0/22 address block,it will perform a PTR record lookup to find the domain name associated with that IP address.
This kind of address-to-name translation is usually used for diagnostic or logging purposes, but it is also common foremail servers to reject any email from IP addresses which have no address-to-name translation. Most mail from such IP
addresses is spam, so the lack of a PTR record here has some predictive value. By using the “force name-does-not-exist”
policy trigger on all lookups in the PTR name space associated with an address block, DNS administrators can give theirservers a hint that these IP addresses are probably sending junk.

6.9.10 A Known Inconsistency in DNS RPZ’s NSDNAME and NSIP Rules
Response Policy Zones define several possible triggers for each rule, and among these two are known to produce inconsistent results. This is not a bug; rather, it relates to inconsistencies in the DNS delegation model.

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DNS Delegation
In DNS authority data, an NS RRset that is not at the apex of a DNS zone creates a sub-zone. That sub-zone’s data isseparate from the current (or “parent”) zone, and it can have different authoritative name servers than the current zone.
In this way, the root zone leads to COM, NET, ORG, and so on, each of which have their own name servers and theirown way of managing their authoritative data. Similarly, ORG has delegations to ISC.ORG and to millions of other“dot-ORG” zones, each of which can have its own set of authoritative name servers. In the parlance of the protocol, these
NS RRsets below the apex of a zone are called “delegation points.” An NS RRset at a delegation point contains a list of
authoritative servers to which the parent zone is delegating authority for all names at or below the delegation point.
At the apex of every zone there is also an NS RRset. Ideally, this so-called “apex NS RRset” should be identical to the“delegation point NS RRset” in the parent zone, but this ideal is not always achieved. In the real DNS, it’s almost always
easier for a zone administrator to update one of these NS RRsets than the other, so that one will be correct and the otherout of date. This inconsistency is so common that it’s been necessarily rendered harmless: domains that are inconsistentin this way are less reliable and perhaps slower, but they still function as long as there is some overlap between each of the
NS RRsets and the truth. (“Truth” in this case refers to the actual set of name servers that are authoritative for the zone.)A Quick Review of DNS Iteration
In DNS recursive name servers, an incoming query that cannot be answered from the local cache is sent to the closest
known delegation point for the query name. For example, if a server is looking up XYZZY.ISC.ORG and it the nameservers for ISC.ORG, then it sends the query to those servers directly; however, if it has never heard of ISC.ORG before,
it must first send the query to the name servers for ORG (or perhaps even to the root zone that is the parent of ORG).
When it asks one of the parent name servers, that server will not have an answer, so it sends a “referral” consisting onlyof the “delegation point NS RRset.” Once the server receives this referral, it “iterates” by sending the same query again,
but this time to name servers for a more specific part of the query name. Eventually this iteration terminates, usually bygetting an answer or a “name error” (NXDOMAIN) from the query name’s authoritative server, or by encountering some
type of server failure.
When an authoritative server for the query name sends an answer, it has the option of including a copy of the zone’s apex
NS RRset. If this occurs, the recursive name server caches this NS RRset, replacing the delegation point NS RRset that it
had received during the iteration process. In the parlance of the DNS, the delegation point NS RRset is “glue,” meaning
non-authoritative data, or more of a hint than a real truth. On the other hand, the apex NS RRset is authoritative data,
coming as it does from the zone itself, and it is considered more credible than the “glue.” For this reason, it’s a little bit
more important that the apex NS RRset be correct than that the delegation point NS RRset be correct, since the former
will quickly replace the latter, and will be used more often for a longer total period of time.
Importantly, the authoritative name server need not include its apex NS RRset in any answers, and recursive name servers
do not ordinarily query directly for this RRset. Therefore it is possible for the apex NS RRset to be completely wrong
without any operational ill-effects, since the wrong data need not be exposed. Of course, if a query comes in for this NS
RRset, most recursive name servers will forward the query to the zone’s authority servers, since it’s bad form to return“glue” data when asked a specific question. In these corner cases, bad apex NS RRset data can cause a zone to become
unreachable unpredictably, according to what other queries the recursive name server has processed.
There is another kind of “glue,” for name servers whose names are below delegation points. If ORG delegates ISC.ORG
to NS-EXT.ISC.ORG, the ORG server needs to know an address for NS-EXT.ISC.ORG and return this address as
part of the delegation response. However, the name-to-address binding for this name server is only authoritative inside
the ISC.ORG zone; therefore, the A or AAAA RRset given out with the delegation is non-authoritative “glue,” which is
replaced by an authoritative RRset if one is seen. As with apex NS RRsets, the real A or AAAA RRset is not automaticallyqueried for by the recursive name server, but is queried for if an incoming query asks for this RRset.

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Enter RPZ
RPZ has two trigger types that are intended to allow policy zone authors to target entire groups of domains based on
those domains all being served by the same DNS servers: NSDNAME and NSIP. The NSDNAME and NSIP rules arematched against the name and IP address (respectively) of the nameservers of the zone the answer is in, and all of its
parent zones. In its default configuration, BIND actively fetches any missing NS RRsets and address records. If, in theprocess of attempting to resolve the names of all of these delegated server names, BIND receives a SERVFAIL response
for any of the queries, then it aborts the policy rule evaluation and returns SERVFAIL for the query. This is technicallyneither a match nor a non-match of the rule.
Every “.” in a fully qualified domain name (FQDN) represents a potential delegation point. When BIND goes searchingfor parent zone NS RRsets (and, in the case of NSIP, their accompanying address records), it has to check every possibledelegation point. This can become a problem for some specialized pseudo-domains, such as some domain name andnetwork reputation systems, that have many “.” characters in the names. It is further complicated if that system also
has non-compliant DNS servers that silently drop queries for NS and SOA records. This forces BIND to wait for thosequeries to time out before it can finish evaluating the policy rule, even if this takes longer than a reasonable client typicallywaits for an answer (delays of over 60 seconds have been observed).
While both of these cases do involve configurations and/or servers that are technically “broken,” they may still “work”
outside of RPZ NSIP and NSDNAME rules because of redundancy and iteration optimizations.
There are two RPZ options, nsip-wait-recurse and nsdname-wait-recurse, that alter BIND’s behavior
by allowing it to use only those records that already exist in the cache when evaluating NSIP and NSDNAME rules,
respectively.
Therefore NSDNAME and NSIP rules are unreliable. The rules may be matched against either the apex NS RRset or the“glue” NS RRset, each with their associated addresses (that also might or might not be “glue”). It’s in the administrator’sinterests to discover both the delegation name server names and addresses, and the apex name server names and authoritative address records, to ensure correct use of NS and NSIP triggers in RPZ. Even then, there may be collateral damage
to completely unrelated domains that otherwise “work,” just by having NSIP and NSDNAME rules.

6.9.11 Example: Using RPZ to Disable Mozilla DoH-by-Default
Mozilla announced in September 2019 that they would enable DNS-over-HTTPS (DoH) for all US-based users of theFirefox browser, sending all their DNS queries to predefined DoH providers (Cloudflare’s 1.1.1.1 service in particular).
This is a concern for some network administrators who do not want their users’ DNS queries to be rerouted unexpectedly. However, Mozilla provides a mechanism to disable the DoH-by-default setting: if the Mozilla-owned domain
use-application-dns.net returns an NXDOMAIN response code, Firefox will not use DoH.
To accomplish this using RPZ:
1. Create a polizy zone file called mozilla.rpz.db configured so that NXDOMAIN will be returned for any
query to use-application-dns.net:$TTL 604800$ORIGIN
mozilla.rpz.
@
IN
SOA
localhost. root.localhost. 1 604800 86400 2419200 604800@
INNS
localhost.
use-application-dns.net CNAME .

2. Add the zone into the BIND configuration (usually named.conf):zone mozilla.rpz {type primary;file "/<PATH_TO>/mozilla.rpz.db";
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3. Enable use of the Response Policy Zone for all incoming queries by adding the response-policy directive
into the options {} section:
options {response-policy { zone mozilla.rpz; } break-dnssec yes;};

4. Reload the configuration and test whether the Response Policy Zone that was just added is in effect:# rndc reload# dig IN A use-application-dns.net @<IP_ADDRESS_OF_YOUR_RESOLVER># dig IN AAAA use-application-dns.net @<IP_ADDRESS_OF_YOUR_RESOLVER>

The response should return NXDOMAIN instead of the list of IP addresses, and the BIND 9 log should contain lines likethis:
09-Sep-2019 18:50:49.439 client @0x7faf8e004a00 ::1#54175 (use-application-dns.net):␣
,→rpz QNAME NXDOMAIN rewrite use-application-dns.net/AAAA/IN via use-application-dns.
,→net.mozilla.rpz
09-Sep-2019 18:50:49.439 client @0x7faf8e007800 127.0.0.1#62915 (use-application-dns.
,→net): rpz QNAME NXDOMAIN rewrite use-application-dns.net/AAAA/IN via use,→application-dns.net.mozilla.rpz

Note that this is the simplest possible configuration; specific configurations may be different, especially for administrators
who are already using other response policy zones, or whose servers are configured with multiple views.

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CHAPTERSEVEN

SECURITY CONFIGURATIONS

7.1 Security Assumptions
BIND 9’s design assumes that access to the objects listed below is limited only to trusted parties. An incorrect deployment,
which does not follow rules set by this section, cannot be the basis for CVE assignment or special security-sensitive
handling of issues.
Unauthorized access can potentially disclose sensitive data, slow down server operation, etc. Unauthorized, unexpected,
or incorrect writes to listed objects can potentically cause crashes, incorrect data handling, or corruption.
• All files stored on disk - including zone files, configuration files, key files, temporary files, etc.
• Clients communicating via controls socket using configured keys
• Access to statistics-channels from untrusted clients• Sockets used for update-policy type external
Certain aspects of the DNS protocol are left unspecified, such as the handling of responses from DNS servers which do
not fully conform to the DNS protocol. For such a situation, BIND implements its own safety checks and limits which
are subject to change as the protocol and deployment evolve.

7.1.1 Authoritative Servers
By default, zones use intentionally lenient limits (unlimited size, long transfer timeouts, etc.). These defaults can bemisused by the source of data (zone transfers or UPDATEs) to exhaust resources on the receiving side.
The impact of malicious zone changes can be limited, to an extent, using configuration options listed in sections Server
Resource Limits and Zone Transfers. Limits should also be applied to zones where malicious clients may potentially beauthorized to use Dynamic Update.

7.1.2 DNS Resolvers
By definition, DNS resolvers act as traffic amplifiers; during normal operation, a DNS resolver can legitimately generate
more outgoing traffic (counted in packets or bytes) than the incoming client traffic that triggered it. The DNS protocol
specification does not currently specify limits for this amplification, but BIND implements its own limits to balanceinteroperability and safety. As a general rule, if a traffic amplification factor for any given scenario is lower than 100
packets, ISC does not handle the given scenario as a security issue. These limits are subject to change as DNS deployment
evolves.
All DNS answers received by the DNS resolver are treated as untrusted input and are subject to safety and correctness
checks. However, protocol non-conformity might cause unexpected behavior. If such unexpected behavior is limited to
DNS domains hosted on non-conformant servers, it is not deemed a security issue in BIND.

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7.2 Access Control Lists
Access Control Lists (ACLs) are address match lists that can be set up and nicknamed for future
use in allow-notify, allow-query, allow-query-on, allow-recursion, blackhole,allow-transfer, match-clients, etc.
ACLs give users finer control over who can access the name server, without cluttering up configuration files with hugelists of IP addresses.
It is a good idea to use ACLs, and to control access. Limiting access to the server by outside parties can help prevent
spoofing and denial of service (DoS) attacks against the server.
ACLs match clients on the basis of up to three characteristics: 1) The client’s IP address; 2) the TSIG or SIG(0) key thatwas used to sign the request, if any; and 3) an address prefix encoded in an EDNS Client-Subnet option, if any.
Here is an example of ACLs based on client addresses:// Set up an ACL named "bogusnets" that blocks// RFC1918 space and some reserved space, which is// commonly used in spoofing attacks.
acl bogusnets {0.0.0.0/8; 192.0.2.0/24; 224.0.0.0/3;
10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;};// Set up an ACL called our-nets. Replace this with the// real IP numbers.
acl our-nets { x.x.x.x/24; x.x.x.x/21; };options {...
...
allow-query { our-nets; };allow-recursion { our-nets; };...
blackhole { bogusnets; };...
};zone "example.com" {type primary;file "m/example.com";allow-query { any; };};This allows authoritative queries for example.com from any address, but recursive queries only from the networks
specified in our-nets, and no queries at all from the networks specified in bogusnets.
In addition to network addresses and prefixes, which are matched against the source address of the DNS request, ACLs
may include key elements, which specify the name of a TSIG or SIG(0) key.
When BIND 9 is built with GeoIP support, ACLs can also be used for geographic access restrictions. This is done byspecifying an ACL element of the form: geoip db database field value.
The field parameter indicates which field to search for a match. Available fields are country, region, city,
continent, postal (postal code), metro (metro code), area (area code), tz (timezone), isp, asnum, anddomain.
value is the value to search for within the database. A string may be quoted if it contains spaces or other special
characters. An asnum search for autonomous system number can be specified using the string “ASNNNN” or the integer
NNNN. If a country search is specified with a string that is two characters long, it must be a standard ISO-3166-1
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two-letter country code; otherwise, it is interpreted as the full name of the country. Similarly, if region is the searchterm and the string is two characters long, it is treated as a standard two-letter state or province abbreviation; otherwise,
it is treated as the full name of the state or province.
The database field indicates which GeoIP database to search for a match. In most cases this is unnecessary, because
most search fields can only be found in a single database. However, searches for continent or country can be
answered from either the city or country databases, so for these search types, specifying a database forces thequery to be answered from that database and no other. If a database is not specified, these queries are first answeredfrom the city database if it is installed, and then from the country database if it is installed. Valid database names
are country, city, asnum, isp, and domain.
Some example GeoIP ACLs:
geoip country US;
geoip country JP;
geoip db country country Canada;
geoip region WA;
geoip city "San Francisco";geoip region Oklahoma;
geoip postal 95062;
geoip tz "America/Los_Angeles";geoip org "Internet Systems Consortium";

ACLs use a “first-match” logic rather than “best-match”; if an address prefix matches an ACL element, then that ACL
is considered to have matched even if a later element would have matched more specifically. For example, the ACL {10/8; !10.0.0.1; } would actually match a query from 10.0.0.1, because the first element indicates that the queryshould be accepted, and the second element is ignored.
When using “nested” ACLs (that is, ACLs included or referenced within other ACLs), a negative match of a nested
ACL tells the containing ACL to continue looking for matches. This enables complex ACLs to be constructed, in which
multiple client characteristics can be checked at the same time. For example, to construct an ACL which allows a query
only when it originates from a particular network and only when it is signed with a particular key, use:allow-query { !{ !10/8; any; }; key example; };Within the nested ACL, any address that is not in the 10/8 network prefix is rejected, which terminates the processing of
the ACL. Any address that is in the 10/8 network prefix is accepted, but this causes a negative match of the nested ACL,
so the containing ACL continues processing. The query is accepted if it is signed by the key example, and rejected
otherwise. The ACL, then, only matches when both conditions are true.

7.3 Chroot and Setuid
On Unix servers, it is possible to run BIND in a chrooted environment (using the chroot() function) by specifying the-t option for named. This can help improve system security by placing BIND in a “sandbox,” which limits the damage
done if a server is compromised.
Another useful feature in the Unix version of BIND is the ability to run the daemon as an unprivileged user (-u user).
We suggest running as an unprivileged user when using the chroot feature.
Here is an example command line to load BIND in a chroot sandbox, /var/named, and to run named setuid touser 202:/usr/local/sbin/named -u 202 -t /var/named

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7.3.1 The chroot Environment
For a chroot environment to work properly in a particular directory (for example, /var/named), the environment
must include everything BIND needs to run. From BIND’s point of view, /var/named is the root of the filesystem;
the values of options like directory and pid-file must be adjusted to account for this.
Unlike with earlier versions of BIND, named does not typically need to be compiled statically, nor do shared libraries
need to be installed under the new root. However, depending on the operating system, it may be necessary to set up
locations such as /dev/zero, /dev/random, /dev/log, and /etc/localtime.

7.3.2 Using the setuid Function
Prior to running the named daemon, use the touch utility (to change file access and modification times) or the chown
utility (to set the user id and/or group id) on files where BIND should write.
Note: If the named daemon is running as an unprivileged user, it cannot bind to new restricted ports if the server isreloaded.

7.4 Dynamic Update Security
Access to the dynamic update facility should be strictly limited. In earlier versions of BIND, the only way to do
this was based on the IP address of the host requesting the update, by listing an IP address or network prefix in theallow-update zone option. This method is insecure, since the source address of the update UDP packet is easily
forged. Also note that if the IP addresses allowed by the allow-update option include the address of a secondary
server which performs forwarding of dynamic updates, the primary can be trivially attacked by sending the update to thesecondary, which forwards it to the primary with its own source IP address - causing the primary to approve it without
question.
For these reasons, we strongly recommend that updates be cryptographically authenticated by means of transaction signatures (TSIG). That is, the allow-update option should list only TSIG key names, not IP addresses or network prefixes.
Alternatively, the update-policy option can be used.
Some sites choose to keep all dynamically updated DNS data in a subdomain and delegate that subdomain to a separate
zone. This way, the top-level zone containing critical data, such as the IP addresses of public web and mail servers, need
not allow dynamic updates at all.

7.5 TSIG
TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS messages, originally specified in RFC 2845. It
allows DNS messages to be cryptographically signed using a shared secret. TSIG can be used in any DNS transaction,
as a way to restrict access to certain server functions (e.g., recursive queries) to authorized clients when IP-based access
control is insufficient or needs to be overridden, or as a way to ensure message authenticity when it is critical to the integrityof the server, such as with dynamic UPDATE messages or zone transfers from a primary to a secondary server.
This section is a guide to setting up TSIG in BIND. It describes the configuration syntax and the process of creating TSIG
keys.
named supports TSIG for server-to-server communication, and some of the tools included with BIND support it for
sending messages to named:

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BIND 9 Administrator Reference Manual, Release 9.20.0• nsupdate - dynamic DNS update utility supports TSIG via the -k, -l, and -y command-line options, or via the
key command when running interactively.
• dig - DNS lookup utility supports TSIG via the -k and -y command-line options.

7.5.1 Generating a Shared Key
TSIG keys can be generated using the tsig-keygen command; the output of the command is a key directive suitablefor inclusion in named.conf. The key name, algorithm, and size can be specified by command-line parameters; thedefaults are “tsig-key”, HMAC-SHA256, and 256 bits, respectively.
Any string which is a valid DNS name can be used as a key name. For example, a key to be shared between servers called
host1 and host2 could be called “host1-host2.”, and this key can be generated using:$ tsig-keygen host1-host2. > host1-host2.key

This key may then be copied to both hosts. The key name and secret must be identical on both hosts. (Note: copying ashared secret from one server to another is beyond the scope of the DNS. A secure transport mechanism should be used:secure FTP, SSL, ssh, telephone, encrypted email, etc.)
tsig-keygen can also be run as ddns-confgen, in which case its output includes additional configuration text for
setting up dynamic DNS in named. See ddns-confgen - TSIG key generation tool for details.

7.5.2 Loading a New Key
For a key shared between servers called host1 and host2, the following could be added to each server’s named.conf
file:
key "host1-host2." {algorithm hmac-sha256;
secret "DAopyf1mhCbFVZw7pgmNPBoLUq8wEUT7UuPoLENP2HY=";};(This is the same key generated above using tsig-keygen.)Since this text contains a secret, it is recommended that either named.conf not be world-readable, or that the key
directive be stored in a file which is not world-readable and which is included in named.conf via the include
directive.
Once a key has been added to named.conf and the server has been restarted or reconfigured, the server can recognize
the key. If the server receives a message signed by the key, it is able to verify the signature. If the signature is valid, theresponse is signed using the same key.

7.5.3 Instructing the Server to Use a Key
A server sending a request to another server must be told whether to use a key, and if so, which key to use.
For example, a key may be specified for each server in the primaries statement in the definition of a secondary zone;
in this case, all SOA QUERY messages, NOTIFY messages, and zone transfer requests (AXFR or IXFR) are signed
using the specified key. Keys may also be specified in the also-notify statement of a primary or secondary zone,
causing NOTIFY messages to be signed using the specified key.
Keys can also be specified in a server directive. Adding the following on host1, if the IP address of host2
is 10.1.2.3, would cause all requests from host1 to host2, including normal DNS queries, to be signed using thehost1-host2. key:

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server 10.1.2.3 {keys { host1-host2. ;};};Multiple keys may be present in the keys statement, but only the first one is used. As this directive does not containsecrets, it can be used in a world-readable file.
Requests sent by host2 to host1 would not be signed, unless a similar server directive were in host2’s configuration file.
When any server sends a TSIG-signed DNS request, it expects the response to be signed with the same key. If a response
is not signed, or if the signature is not valid, the response is rejected.

7.5.4 TSIG-Based Access Control
TSIG keys may be specified in ACL definitions and ACL directives such as allow-query, allow-transfer, andallow-update. The above key would be denoted in an ACL element as key host1-host2.
Here is an example of an allow-update directive using a TSIG key:
allow-update { !{ !localnets; any; }; key host1-host2. ;};This allows dynamic updates to succeed only if the UPDATE request comes from an address in localnets, and if it
is signed using the host1-host2. key.
See Dynamic Update Policies for a discussion of the more flexible update-policy statement.

7.5.5 Errors
Processing of TSIG-signed messages can result in several errors:• If a TSIG-aware server receives a message signed by an unknown key, the response will be unsigned, with the TSIG
extended error code set to BADKEY.
• If a TSIG-aware server receives a message from a known key but with an invalid signature, the response will be
unsigned, with the TSIG extended error code set to BADSIG.
• If a TSIG-aware server receives a message with a time outside of the allowed range, the response will be signed
but the TSIG extended error code set to BADTIME, and the time values will be adjusted so that the response canbe successfully verified.
In all of the above cases, the server returns a response code of NOTAUTH (not authenticated).

7.6 SIG(0)BIND partially supports DNSSEC SIG(0) transaction signatures as specified in RFC 2535 and RFC 2931. SIG(0)uses public/private keys to authenticate messages. Access control is performed in the same manner as with TSIG keys;
privileges can be granted or denied in ACL directives based on the key name.
When a SIG(0) signed message is received, it is only verified if the key is known and trusted by the server. The server
does not attempt to recursively fetch or validate the key.
SIG(0) signing of multiple-message TCP streams is not supported.
The only tool shipped with BIND 9 that generates SIG(0) signed messages is nsupdate.

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CHAPTEREIGHTCONFIGURATION REFERENCE

The operational functionality of BIND 9 is defined using the file named.conf, which is typically located in /etc or/usr/local/etc/namedb, depending on the operating system or distribution. A further file rndc.conf will be present if
rndc is being run from a remote host, but is not required if rndc is being run from localhost (the same system as BIND
9 is running on).

8.1 Configuration File (named.conf)
The file named.conf may contain three types of entities:
Comment
Multiple comment formats are supported.
Block
Blocks are containers for statements which either have common functionality - for example, the definition of acryptographic key in a key block - or which define the scope of the statement - for example, a statement whichappears in a zone block has scope only for that zone.
Blocks are organized hierarchically within named.conf and may have a number of different properties:• Certain blocks cannot be nested inside other blocks and thus may be regarded as the topmost-level blocks: forexample, the options block and the logging block.
• Certain blocks can appear multiple times, in which case they have an associated name to disambiguate them:for example, the zone block (zone example.com { ... };) or the key block (key mykey {... };).
• Certain blocks may be “nested” within other blocks. For example, the zone block may appear within aview block.
The description of each block in this manual lists its permissible locations.
Statement• Statements define and control specific BIND behaviors.
• Statements may have a single parameter (a Value) or multiple parameters (Argument/Value pairs). For
example, the recursion statement takes a single value parameter - in this case, the string yes or no(recursion yes;) - while the port statement takes a numeric value defining the DNS port number(port 53;). More complex statements take one or more argument/value pairs. The also-notify
statement may take a number of such argument/value pairs, such as also-notify port 5353;, where
port is the argument and 5353 is the corresponding value.
• Statements can appear in a single block - for example, an algorithm statement can appear only in a key
block - or in multiple blocks - for example, an also-notify statement can appear in an options block
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overrides any global statement), or even in a view block where it has scope for only that view (and overrides
any global statement).
The file named.conf may further contain one or more instances of the include Directive. This directive is provided
for administrative convenience in assembling a complete named.conf file and plays no subsequent role in BIND 9
operational characteristics or functionality.
Note: Over a period of many years the BIND ARM acquired a bewildering array of terminology. Many of the terms
used described similar concepts and served only to add a layer of complexity, possibly confusion, and perhaps mystiqueto BIND 9 configuration. The ARM now uses only the terms Block, Statement, Argument, Value, and Directive todescribe all entities used in BIND 9 configuration.

8.1.1 Comment Syntax
The BIND 9 comment syntax allows comments to appear anywhere that whitespace may appear in a BIND configuration
file. To appeal to programmers of all kinds, they can be written in the C, C++, or shell/Perl style.
Syntax/* This is a BIND comment as in C */// This is a BIND comment as in C++# This is a BIND comment as in common Unix shells# and Perl

Definition and Usage
Comments can be inserted anywhere that whitespace may appear in a BIND configuration file.
C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.
C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with thefirst */:/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */This is no longer in any comment. */C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They
cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use
the // pair. For example:// This is the start of a comment. The next line// is a new comment, even though it is logically// part of the previous comment.

Shell-style (or Perl-style) comments start with the character # (number/pound sign) and continue to the end of the physicalline, as in C++ comments. For example:

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# is a new comment, even though it is logically# part of the previous comment.

Warning: The semicolon (;) character cannot start a comment, unlike in a zone file. The semicolon indicates theend of a configuration statement.

8.1.2 Configuration Layout Styles
BIND is very picky about opening and closing brackets/braces, semicolons, and all the other separators defined in theformal syntaxes in later sections. There are many layout styles that can assist in minimizing errors, as shown in thefollowing examples:// dense single-line stylezone "example.com" in{type secondary; file "secondary.example.com"; primaries {10.0.0.
,→1;};};// single-statement-per-line stylezone "example.com" in{type secondary;file "secondary.example.com";primaries {10.0.0.1;};};// spot the differencezone "example.com" in{type secondary;file "sec.secondary.com";primaries {10.0.0.1;}; };8.1.3 include Directive
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include Directive Definition and Usage
The include directive inserts the specified file (or files if a valid glob expression is detected) at the point where the include
directive is encountered. The include directive facilitates the administration of configuration files by permitting the reading
or writing of some things but not others. For example, the statement could include private keys that are readable only by
the name server.

8.1.4 Address Match Lists
SyntaxAn address match list is a list of semicolon-separated address_match_element s.
{ <address_match_element>; ... };Each element is then defined as:
address_match_element[ ! ] ( <ip_address> | <netprefix> | key <server_key> | <acl_name> | { address_,→match_list } )Definition and Usage
Address match lists are primarily used to determine access control for various server operations. They are also used in
the listen-on and sortlist statements. The elements which constitute an address match list can be any of thefollowing:• ip_address: an IP address (IPv4 or IPv6)• netprefix: an IP prefix (in / notation)• server_key: a key ID, as defined by the key statement• acl_name: the name of an address match list defined with the acl statement• a nested address match list enclosed in braces
Elements can be negated with a leading exclamation mark (!), and the match list names “any”, “none”, “localhost”, and“localnets” are predefined. More information on those names can be found in the description of the acl statement.
The addition of the key clause made the name of this syntactic element something of a misnomer, since security keys canbe used to validate access without regard to a host or network address. Nonetheless, the term “address match list” is stillused throughout the documentation.
When a given IP address or prefix is compared to an address match list, the comparison takes place in approximately O(1)time. However, key comparisons require that the list of keys be traversed until a matching key is found, and therefore
may be somewhat slower.
The interpretation of a match depends on whether the list is being used for access control, defining listen-on ports,
or in a sortlist, and whether the element was negated.
When used as an access control list, a non-negated match allows access and a negated match denies access. If there isno match, access is denied. The clauses allow-notify, allow-recursion, allow-recursion-on,
allow-query,allow-query-on,
allow-query-cache,allow-query-cache-on,
allow-transfer, allow-update, allow-update-forwarding, and blackhole all use address
match lists. Similarly, the listen-on option causes the server to refuse queries on any of the machine’s addresses
which do not match the list.
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Order of insertion is significant. If more than one element in an ACL is found to match a given IP address or prefix,
preference is given to the one that came first in the ACL definition. Because of this first-match behavior, an elementthat defines a subset of another element in the list should come before the broader element, regardless of whether either
is negated. For example, in 1.2.3/24; ! 1.2.3.13; the 1.2.3.13 element is completely useless because thealgorithm matches any lookup for 1.2.3.13 to the 1.2.3/24 element. Using ! 1.2.3.13; 1.2.3/24 fixes thatproblem by blocking 1.2.3.13 via the negation, but all other 1.2.3.* hosts pass through.

8.1.5 Glossary of Terms Used
Following is a list of terms used throughout the BIND configuration file documentation:
acl_name
The name of an address_match_list as defined by the acl statement.
address_match_list
See Address Match Lists.
booleanEither yes or no. The words true and false are also accepted, as are the numbers 1 and 0.
domain_name
A quoted string which is used as a DNS name; for example: my.test.domain.
duration
A duration in BIND 9 can be written in three ways: as single number representing seconds, as a string of numberswith TTL-style time-unit suffixes, or in ISO 6801 duration format.
Allowed TTL time-unit suffixes are: “W” (week), “D” (day), “H” (hour), “M” (minute), and “S” (second). Examples: “1W” (1 week), “3d12h” (3 days, 12 hours).
ISO 8601 duration format consists of the letter “P”, followed by an optional series of numbers with unit suffixes“Y” (year), “M” (month), “W” (week), and “D” (day); this may optionally be followed by the letter “T”, and anotherseries of numbers with unit suffixes “H” (hour), “M” (minute), and “S” (second). Examples: “P3M10D” (3 months,
10 days), “P2WT12H” (2 weeks, 12 hours), “pt15m” (15 minutes). For more information on ISO 8601 duration
format, see RFC 3339, appendix A.
Both TTL-style and ISO 8601 duration formats are case-insensitive.
fixedpoint
A non-negative real number that can be specified to the nearest one-hundredth. Up to five digits can be specified
before a decimal point, and up to two digits after, so the maximum value is 99999.99. Acceptable values might befurther limited by the contexts in which they are used.
integer
A non-negative 32-bit integer (i.e., a number between 0 and 4294967295, inclusive). Its acceptable value might befurther limited by the context in which it is used.
ip_address
An ipv4_address or ipv6_address.
ipv4_address
An IPv4 address with exactly four integer elements valued 0 through 255 and separated by dots (.), such as 192.
168.1.1 (a “dotted-decimal” notation with all four elements present).
ipv6_address
An IPv6 address, such as 2001:db8::1234. IPv6-scoped addresses that have ambiguity on their scope zones
must be disambiguated by an appropriate zone ID with the percent character (%) as a delimiter. It is strongly
recommended to use string zone names rather than numeric identifiers, to be robust against system configuration
changes. However, since there is no standard mapping for such names and identifier values, only interface names as

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link identifiers are supported, assuming one-to-one mapping between interfaces and links. For example, a link-local
address fe80::1 on the link attached to the interface ne0 can be specified as fe80::1%ne0. Note that on
most systems link-local addresses always have ambiguity and need to be disambiguated.
netprefix
An IP network specified as an ip_address, followed by a slash (/) and then the number of bits in the netmask.
Trailing zeros in an ip_address may be omitted. For example, 127/8 is the network 127.0.0.0 with netmask
255.0.0.0 and 1.2.3.0/28 is network 1.2.3.0 with netmask 255.255.255.240. When specifying aprefix involving an IPv6-scoped address, the scope may be omitted. In that case, the prefix matches packets fromany scope.
percentage
An integer value followed by % to represent percent.
port
An IP port integer. It is limited to 0 through 65535, with values below 1024 typically restricted to use by processes
running as root. In some cases, an asterisk (*) character can be used as a placeholder to select a random highnumbered port.
portrange
A list of a port or a port range. A port range is specified in the form of range followed by two port s, port_low
and port_high, which represents port numbers from port_low through port_high, inclusive. port_low
must not be larger than port_high. For example, range 1024 65535 represents ports from 1024 through65535. The asterisk (*) character is not allowed as a valid port or as a port range boundary.
remote-servers
A named list of one or more ip_address es with optional tls_id, server_key, and/or port. A remote-servers
list may include other remote-servers lists. See primaries block.
server_key
A domain_name representing the name of a shared key, to be used for transaction security. Keys are defined using
key blocks.
size
sizeval
A 64-bit unsigned integer. Integers may take values 0 <= value <= 18446744073709551615, though certain parameters (such as max-journal-size) may use a more limited range within these extremes. In most cases,
setting a value to 0 does not literally mean zero; it means “undefined” or “as big as possible,” depending on thecontext. See the explanations of particular parameters that use size for details on how they interpret its use.
Numeric values can optionally be followed by a scaling factor: K or k for kilobytes, M or m for megabytes, and G
or g for gigabytes, which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.
Some statements also accept the keywords unlimited or default: unlimited generally means “as big as
possible,” and is usually the best way to safely set a very large number. default uses the limit that was in force
when the server was started.
tls_idA named TLS configuration object which defines a TLS key and certificate. See tls block.

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8.2 Blocks
A BIND 9 configuration consists of blocks, statements, and comments.
The following blocks are supported:acl
Defines a named IP address matching list, for access control and other uses.
controls
Declares control channels to be used by the rndc utility.
dnssec-policy
Describes a DNSSEC key and signing policy for zones. See dnssec-policy for details.
keySpecifies key information for use in authentication and authorization using TSIG.
:any:key-store
Describes a DNSSEC key store. See key-store Grammar for details.
loggingSpecifies what information the server logs and where the log messages are sent.
masters
Synonym for primaries.
options
Controls global server configuration options and sets defaults for other statements.
parental-agents
Defines a named list of servers for inclusion in primary and secondary zones’ parental-agentslists.
primaries
Defines a named list of servers for inclusion in stub and secondary zones’ primaries or
also-notify lists. (Note: this is a synonym for the original keyword masters, which can still be
used, but is no longer the preferred terminology.)
serverSets certain configuration options on a per-server basis.
statistics-channels
Declares communication channels to get access to named statistics.
tls
Specifies configuration information for a TLS connection, including a key-file,cert-file, ca-file, dhparam-file, remote-hostname, ciphers, protocols,
prefer-server-ciphers, and session-tickets.
httpSpecifies configuration information for an HTTP connection,
listener-clients, and streams-per-connection.

includingendpoints,

trust-anchors
Defines DNSSEC trust anchors: if used with the initial-key or initial-ds keyword, trust
anchors are kept up-to-date using RFC 5011 trust anchor maintenance; if used with static-key or
static-ds, keys are permanent.
managed-keys
Is identical to trust-anchors; this option is deprecated in favor of trust-anchors with theinitial-key keyword, and may be removed in a future release.
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trusted-keys
Defines permanent trusted DNSSEC keys; this option is deprecated in favor of trust-anchorswith the static-key keyword, and may be removed in a future release.
view
Defines a view.
zone
Defines a zone.
The logging and options statements may only occur once per configuration.

8.2.1 acl Block Grammar
aclGrammar: acl <string> { <address_match_element>; ... }; // may occur multiple
times
Blocks: topmost
Tags: server

Assigns a symbolic name to an address match list.

8.2.2 acl Block Definition and Usage
The acl statement assigns a symbolic name to an address match list. It gets its name from one of the primary uses ofaddress match lists: Access Control Lists (ACLs).
The following ACLs are built-in:anyMatches all hosts.
none
Matches no hosts.
localhostMatches the IPv4 and IPv6 addresses of all network interfaces on the system. When addresses areadded or removed, the localhost ACL element is updated to reflect the changes.
localnets
Matches any host on an IPv4 or IPv6 network for which the system has an interface. When addresses areadded or removed, the localnets ACL element is updated to reflect the changes. Some systems do
not provide a way to determine the prefix lengths of local IPv6 addresses; in such cases, localnets
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8.2.3 controls Block Grammar
controls
Grammar:controls {inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ]␣,→allow { <address_match_element>; ... } [ keys { <string>; ... } ] [ read-only,→<boolean> ]; // may occur multiple times
unix <quoted_string> perm <integer> owner <integer> group <integer> [␣,→keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple times}; // may occur multiple times

Blocks: topmost
Tags: server

Specifies control channels to be used to manage the name server.

8.2.4 controls Block Definition and Usage
The controls statement declares control channels to be used by system administrators to manage the operation of thename server. These control channels are used by the rndc utility to send commands to and retrieve non-DNS resultsfrom a name server.
unix
Grammar: unix <quoted_string> perm <integer> owner <integer> group <integer>[ keys { <string>; ... } ] [ read-only <boolean> ]; // may occur multiple
times
Blocks: controls
Tags: obsolete

Specifies a Unix domain socket as a control channel.
This option has been removed and using it will cause a fatal error.
inetGrammar controls: inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer>| * ) ] allow { <address_match_element>; ... } [ keys { <string>; ... } ] [read-only <boolean> ]; // may occur multiple times
Grammar statistics-channels: inet ( <ipv4_address> | <ipv6_address> | * ) [ port (<integer> | * ) ] [ allow { <address_match_element>; ... } ]; // may occur
multiple times
Blocks: controls, statistics-channels
Tags: server

Specifies a TCP socket as a control channel.
An inet control channel is a TCP socket listening at the specified port on the specified ip_address, which can be
an IPv4 or IPv6 address. An ip_address of * (asterisk) is interpreted as the IPv4 wildcard address; connections
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are accepted on any of the system’s IPv4 addresses. To listen on the IPv6 wildcard address, use an ip_address of::. If rndc is only used on the local host, using the loopback address (127.0.0.1 or ::1) is recommended
for maximum security.
If no port is specified, port 953 is used. The asterisk * cannot be used for port.
The ability to issue commands over the control channel is restricted by the allow and keys clauses.
allow
Connections to the control channel are permitted based on the address_match_list. This is for simple IP
address-based filtering only; any server_key elements of the address_match_list are ignored.
keys
The primary authorization mechanism of the command channel is the list of server_key s. Each listed key
is authorized to execute commands over the control channel. See Administrative Tools for information about
configuring keys in rndc.
read-only
If the read-only argument is on, the control channel is limited to the following set of read-only commands:
nta -dump, null, status, showzone, testgen, and zonestatus. By default, read-only is notenabled and the control channel allows read-write access.
If no controls statement is present, named sets up a default control channel listening on the loopback address
127.0.0.1 and its IPv6 counterpart, ::1. In this case, and also when the controls statement is present but does nothave a keys clause, named attempts to load the command channel key from the file /etc/rndc.key. To create an
rndc.key file, run rndc-confgen -a.
To disable the command channel, use an empty controls statement: controls { };.

8.2.5 key Block Grammar
key
Grammar:key <string> {algorithm <string>;
secret <string>;}; // may occur multiple times

Blocks: topmost, viewTags: security

Defines a shared secret key for use with TSIG or the command channel.

8.2.6 key Block Definition and Usage
The key statement defines a shared secret key for use with TSIG (see TSIG) or the command channel (see controls).
The key statement can occur at the top level of the configuration file or inside a view statement. Keys defined in toplevel key statements can be used in all views. Keys intended for use in a controls statement must be defined at the
top level.
The server_key, also known as the key name, is a domain name that uniquely identifies the key. It can be used in aserver statement to cause requests sent to that server to be signed with this key, or in address match lists to verify that
incoming requests have been signed with a key matching this name, algorithm, and secret.

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algorithm
Grammar: algorithm <string>;
Blocks: key, view.key
Tags: security

Defines the algorithm to be used in a key clause.
The algorithm_id is a string that specifies a security/authentication algorithm. The named server supports
hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, and hmac-sha512 TSIG authentication. Truncated hashes are supported by appending the minimum number of required bits preceded by adash, e.g., hmac-sha1-80.
secretGrammar: secret <string>;
Blocks: key, view.key
Tags: security

Defines a Base64-encoded string to be used as the secret by the algorithm.
The secret_string is the secret to be used by the algorithm, and is treated as a Base64-encoded string.

8.2.7 key-store Block Grammar
key-store
Grammar:key-store <string> {directory <string>;
pkcs11-uri <quoted_string>;}; // may occur multiple times

Blocks: topmost
Tags: dnssec

Configures a DNSSEC key store.

8.2.8 key-store Block Definition and Usage
The key-store statement defines how DNSSEC keys should be stored.
There is one built-in key store named key-directory. Configuring keys to use key-store "key-directory"
is identical to using key-directory.
The following options can be specified in a key-store statement:

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pkcs11-uriGrammar: pkcs11-uri <quoted_string>;
Blocks: key-store
Tags: pkcs11, dnssec
The uri is a string that specifies a PKCS#11 URI Scheme (defined in RFC 7512). When set, named will try tocreate keys inside the corresponding PKCS#11 token. This requires BIND to be built with OpenSSL 3, and havea PKCS#11 provider configured.

8.2.9 logging Block Grammar
logging
Grammar:logging {category <string> { <string>; ... }; // may occur multiple times
channel <string> {buffered <boolean>;file <quoted_string> [ versions ( unlimited | <integer> ) ] [␣,→size <size> ] [ suffix ( increment | timestamp ) ];null;
print-category <boolean>;print-severity <boolean>;print-time ( iso8601 | iso8601-utc | local | <boolean> );severity <log_severity>;stderr;syslog [ <syslog_facility> ];}; // may occur multiple times};

Blocks: topmost
Tags: logging

Configures logging options for the name server.

8.2.10 logging Block Definition and Usage
The logging statement configures a wide variety of logging options for the name server. Its channel phrase associates
output methods, format options, and severity levels with a name that can then be used with the category phrase to
select how various classes of messages are logged.
Only one logging statement is used to define as many channels and categories as desired. If there is no logging
statement, the logging configuration is:
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logging {category default { default_logfile; default_debug; };category unmatched { null; };};The logging configuration is only established when the entire configuration file has been parsed. When the server starts
up, all logging messages regarding syntax errors in the configuration file go to the default channels, or to standard error if
the -g option was specified.
The channel Phrase
channelGrammar:channel <string> {buffered <boolean>;file <quoted_string> [ versions ( unlimited | <integer> ) ] [ size <size>␣
,→] [ suffix ( increment | timestamp ) ];null;
print-category <boolean>;print-severity <boolean>;print-time ( iso8601 | iso8601-utc | local | <boolean> );severity <log_severity>;stderr;syslog [ <syslog_facility> ];}; // may occur multiple times

Blocks: logging
Tags: logging

Defines a stream of data that can be independently logged.
All log output goes to one or more channels; there is no limit to the number of channels that can be created.
Every channel definition must include a destination clause that says whether messages selected for the channel go to a file,
go to a particular syslog facility, go to the standard error stream, or are discarded. The definition can optionally also limit
the message severity level that is accepted by the channel (the default is info), and whether to include a named-generated
time stamp, the category name, and/or the severity level (the default is not to include any).
nullGrammar: null;
Blocks: logging.channel
Tags: logging

Causes all messages sent to the logging channel to be discarded.
The null destination clause causes all messages sent to the channel to be discarded; in that case, other options forthe channel are meaningless.
file
The file destination clause directs the channel to a disk file. It can include additional arguments to specify how
large the file is allowed to become before it is rolled to a backup file (size), how many backup versions of the file
are saved each time this happens (versions), and the format to use for naming backup versions (suffix).
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The size option is used to limit log file growth. If the file ever exceeds the specified size, then named stops
writing to the file unless it has a versions option associated with it. If backup versions are kept, the files arerolled as described below. If there is no versions option, no more data is written to the log until some out-ofband mechanism removes or truncates the log to less than the maximum size. The default behavior is not to limit
the size of the file.
File rolling only occurs when the file exceeds the size specified with the size option. No backup versions are kept
by default; any existing log file is simply appended. The versions option specifies how many backup versionsof the file should be kept. If set to unlimited, there is no limit.
The suffix option can be set to either increment or timestamp. If set to timestamp, then when a log fileis rolled, it is saved with the current timestamp as a file suffix. If set to increment, then backup files are saved withincrementing numbers as suffixes; older files are renamed when rolling. For example, if versions is set to 3 andsuffix to increment, then when filename.log reaches the size specified by size, filename.log.1
is renamed to filename.log.2, filename.log.0 is renamed to filename.log.1, and filename.
log is renamed to filename.log.0, whereupon a new filename.log is opened.
Here is an example using the size, versions, and suffix options:channel an_example_channel {file "example.log" versions 3 size 20m suffix increment;
print-time yes;print-category yes;};syslogGrammar: syslog [ <syslog_facility> ];Blocks: logging.channel
Tags: logging

Directs the logging channel to the system log.
The syslog destination clause directs the channel to the system log. Its argument is a syslog facility as describedin the syslog man page. Known facilities are kern, user, mail, daemon, auth, syslog, lpr, news,
uucp, cron, authpriv, ftp, local0, local1, local2, local3, local4, local5, local6, andlocal7; however, not all facilities are supported on all operating systems. How syslog handles messages sent
to this facility is described in the syslog.conf man page. On a system which uses a very old version of syslog,
which only uses two arguments to the openlog() function, this clause is silently ignored.
severity
Grammar: severity <log_severity>;
Blocks: logging.channel
Tags: logging

Defines the priority level of log messages.
The severity clause works like syslog’s “priorities,” except that they can also be used when writing straight
to a file rather than using syslog. Messages which are not at least of the severity level given are not selected forthe channel; messages of higher severity levels are accepted.
When using syslog, the syslog.conf priorities also determine what eventually passes through. For example, defining a channel facility and severity as daemon and debug, but only logging daemon.warning via
syslog.conf, causes messages of severity info and notice to be dropped. If the situation were reversed,

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with named writing messages of only warning or higher, then syslogd would print all messages it received
from the channel.
stderrGrammar: stderr;
Blocks: logging.channel
Tags: logging

Directs the logging channel output to the server’s standard error stream.
The stderr destination clause directs the channel to the server’s standard error stream. This is intended for use
when the server is running as a foreground process, as when debugging a configuration, for example.
The server can supply extensive debugging information when it is in debugging mode. If the server’s global debug level isgreater than zero, debugging mode is active. The global debug level is set either by starting the named server with the -dflag followed by a positive integer, or by running rndc trace. The global debug level can be set to zero, and debugging
mode turned off, by running rndc notrace. All debugging messages in the server have a debug level; higher debug
levels give more detailed output. Channels that specify a specific debug severity, for example:
channel specific_debug_level {file "foo";
severity debug 3;};

get debugging output of level 3 or less any time the server is in debugging mode, regardless of the global debugging level.
Channels with dynamic severity use the server’s global debug level to determine what messages to print.
print-time
Grammar: print-time ( iso8601 | iso8601-utc | local | <boolean> );Blocks: logging.channel
Tags: logging

Specifies the time format for log messages.
print-time can be set to yes, no, or a time format specifier, which may be one of local, iso8601, or
iso8601-utc. If set to no, the date and time are not logged. If set to yes or local, the date and time arelogged in a human-readable format, using the local time zone. If set to iso8601, the local time is logged in ISO
8601 format. If set to iso8601-utc, the date and time are logged in ISO 8601 format, with time zone set toUTC. The default is no.
print-time may be specified for a syslog channel, but it is usually pointless since syslog also logs the date
and time.
print-category
Grammar: print-category <boolean>;
Blocks: logging.channel
Tags: logging

Includes the category in log messages.
If print-category is requested, then the category of the message is logged as well.

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print-severity
Grammar: print-severity <boolean>;
Blocks: logging.channel
Tags: logging

Includes the severity in log messages.
If print-severity is on, then the severity level of the message is logged. The print- options may be usedin any combination, and are always printed in the following order: time, category, severity.
Here is an example where all three print- options are on:
28-Feb-2000 15:05:32.863 general: notice: runningbufferedGrammar: buffered <boolean>;
Blocks: logging.channel
Tags: logging

Controls flushing of log messages.
If buffered has been turned on, the output to files is not flushed after each log entry. By default all log messages
are flushed.
There are four predefined channels that are used for named’s default logging, as follows. If named is started with the-L option, then a fifth channel, default_logfile, is added. How they are used is described in category.
channel default_syslog {// send to syslog's daemon facility
syslog daemon;// only send priority info and higher
severity info;};
channel default_debug {// write to named.run in the working directory// Note: stderr is used instead of "named.run" if// the server is started with the '-g' option.
file "named.run";// log at the server's current debug level
severity dynamic;};
channel default_stderr {// writes to stderr
stderr;// only send priority info and higher
severity info;};
channel null {// toss anything sent to this channel
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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)channel default_logfile {// this channel is only present if named is// started with the -L option, whose argument// provides the file namefile "...";// log at the server's current debug level
severity dynamic;};

The default_debug channel has the special property that it only produces output when the server’s debug level is
non-zero. It normally writes to a file called named.run in the server’s working directory.
For security reasons, when the -u command-line option is used, the named.run file is created only after named haschanged to the new UID, and any debug output generated while named is starting - and still running as root - is discarded.
To capture this output, run the server with the -L option to specify a default logfile, or the -g option to log to standard
error which can be redirected to a file.
Once a channel is defined, it cannot be redefined. The built-in channels cannot be altered directly, but the default logging
can be modified by pointing categories at defined channels.
The category Phrase
There are many categories, so desired logs can be sent anywhere while unwanted logs are ignored. If a list of channels
is not specified for a category, log messages in that category are sent to the default category instead. If no default
category is specified, the following “default default” is used:category default { default_syslog; default_debug; };If named is started with the -L option, the default category is:category default { default_logfile; default_debug; };As an example, let’s say a user wants to log security events to a file, but also wants to keep the default logging behavior.
They would specify the following:
channel my_security_channel {file "my_security_file";
severity info;};
category security {my_security_channel;
default_syslog;
default_debug;};

To discard all messages in a category, specify the null channel:
category xfer-out { null; };category notify { null; };category
Grammar: category <string> { <string>; ... }; // may occur multiple times
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Tags: logging

Specifies the type of data logged to a particular channel.
The following are the available categories and brief descriptions of the types of log information they contain. Morecategories may be added in future BIND releases.
clientProcessing of client requests.
cname
Name servers that are skipped for being a CNAME rather than A/AAAA records.
configConfiguration file parsing and processing.
database
Messages relating to the databases used internally by the name server to store zone and cache data.
default
Logging options for those categories where no specific configuration has been defined.
dispatch
Dispatching of incoming packets to the server modules where they are to be processed.
dnssecDNSSEC and TSIG protocol processing.
dnstapThe dnstap DNS traffic capture system.
edns-disabled
Log queries that have been forced to use plain DNS due to timeouts. This is often due to the remote servers not
being RFC 1034-compliant (not always returning FORMERR or similar to EDNS queries and other extensions
to the DNS when they are not understood). In other words, this is targeted at servers that fail to respond to DNS
queries that they don’t understand.
Note: the log message can also be due to packet loss. Before reporting servers for non-RFC 1034 compliancethey should be re-tested to determine the nature of the non-compliance. This testing should prevent or reduce thenumber of false-positive reports.
Note: eventually named will have to stop treating such timeouts as due to RFC 1034 non-compliance and start
treating it as plain packet loss. Falsely classifying packet loss as due to RFC 1034 non-compliance impacts
DNSSEC validation, which requires EDNS for the DNSSEC records to be returned.
generalA catch-all for many things that still are not classified into categories.
lame-servers
Misconfigurations in remote servers, discovered by BIND 9 when trying to query those servers during resolution.
network
Network operations.
notifyThe NOTIFY protocol.
nsid
NSID options received from upstream servers.
queries
A location where queries should be logged.
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At startup, specifying the category queries also enables query logging unless the querylog option has been
specified.
The query log entry first reports a client object identifier in @0x<hexadecimal-number> format. Next, it reports
the client’s IP address and port number, and the query name, class, and type. Next, it reports whether the Recursion
Desired flag was set (+ if set, - if not set), whether the query was signed (S), whether EDNS was in use along with
the EDNS version number (E(#)), whether TCP was used (T), whether DO (DNSSEC Ok) was set (D), whether
CD (Checking Disabled) was set (C), whether a valid DNS Server COOKIE was received (V), and whether a DNSCOOKIE option without a valid Server COOKIE was present (K). After this, the destination address the query
was sent to is reported. Finally, if any CLIENT-SUBNET option was present in the client query, it is included insquare brackets in the format [ECS address/source/scope].
client @0x7f91b8005490 127.0.0.1#62536 (www.example.com): query: www.example.com␣
,→IN AAAA +E(0)K (127.0.0.1)
client @0x7f91b4007400 ::1#62537 (www.example.net): query: www.example.net IN␣
,→AAAA +E(0)K (::1)

The first part of this log message, showing the client address/port number and query name, is repeated in all
subsequent log messages related to the same query.
query-errors
Information about queries that resulted in some failure.
rate-limit
Start, periodic, and final notices of the rate limiting of a stream of responses that are logged at info severity inthis category. These messages include a hash value of the domain name of the response and the name itself, except
when there is insufficient memory to record the name for the final notice. The final notice is normally delayed until
about one minute after rate limiting stops. A lack of memory can hurry the final notice, which is indicated by aninitial asterisk (*). Various internal events are logged at debug level 1 and higher.
Rate limiting of individual requests is logged in the query-errors category.
resolver
DNS resolution, such as the recursive lookups performed on behalf of clients by a caching name server.
rpz
Information about errors in response policy zone files, rewritten responses, and, at the highest debug levels, mere
rewriting attempts.
rpz-passthru
Information about RPZ PASSTHRU policy activity. This category allows pre-approved policy activity to be logged
into a dedicated channel.
security
Approval and denial of requests.
serve-stale
Indication of whether a stale answer is used following a resolver failure.
spill
Queries that have been terminated, either by dropping or responding with SERVFAIL, as a result of a fetchlimit
quota being exceeded.
sslkeylog
TLS pre-master secrets (for debugging purposes).
trust-anchor-telemetry
trust-anchor-telemetry requests received by named.
unmatched
Messages that named was unable to determine the class of, or for which there was no matching view. A one-line
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summary is also logged to the client category. This category is best sent to a file or stderr; by default it is sent
to the null channel.
updateDynamic updates.
update-security
Approval and denial of update requests.
xfer-in
Zone transfers the server is receiving.
xfer-out
Zone transfers the server is sending.
zoneload
Loading of zones and creation of automatic empty zones.
The query-errors Category
The query-errors category is used to indicate why and how specific queries resulted in responses which indicate anerror. Normally, these messages are logged at debug logging levels; note, however, that if query logging is active, someare logged at info. The logging levels are described below:
At debug level 1 or higher - or at info when query logging is active - each response with the rcode of SERVFAIL islogged as follows:client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA atquery.c:3880
This means an error resulting in SERVFAIL was detected at line 3880 of source file query.c. Log messages of thislevel are particularly helpful in identifying the cause of SERVFAIL for an authoritative server.
At debug level 2 or higher, detailed context information about recursive resolutions that resulted in SERVFAIL is logged.
The log message looks like this:fetch completed at resolver.c:2970 for www.example.com/A
in 10.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,quota:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]

The first part before the colon shows that a recursive resolution for AAAA records of www.example.com completed in
10.000183 seconds, and the final result that led to the SERVFAIL was determined at line 2970 of source file resolver.
c.
The next part shows the detected final result and the latest result of DNSSEC validation. The latter is always “success”
when no validation attempt was made. In this example, this query probably resulted in SERVFAIL because all nameservers are down or unreachable, leading to a timeout in 10 seconds. DNSSEC validation was probably not attempted.
The last part, enclosed in square brackets, shows statistics collected for this particular resolution attempt. The domain
field shows the deepest zone that the resolver reached; it is the zone where the error was finally detected. The meaning of
the other fields is summarized in the following list.
referral
The number of referrals the resolver received throughout the resolution process. In the above example.com
there are two.
restart
The number of cycles that the resolver tried remote servers at the domain zone. In each cycle, the resolver sends
one query (possibly resending it, depending on the response) to each known name server of the domain zone.

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qrysent
The number of queries the resolver sent at the domain zone.
timeout
The number of timeouts the resolver received since the last response.
lame
The number of lame servers the resolver detected at the domain zone. A server is detected to be lame either by
an invalid response or as a result of lookup in BIND 9’s address database (ADB), where lame servers are cached.
quota
The number of times the resolver was unable to send a query because it had exceeded the permissible fetch quota
for a server.
neterr
The number of erroneous results that the resolver encountered in sending queries at the domain zone. One
common case is when the remote server is unreachable and the resolver receives an “ICMP unreachable” error
message.
badresp
The number of unexpected responses (other than lame) to queries sent by the resolver at the domain zone.
adberrFailures in finding remote server addresses of the``domain`` zone in the ADB. One common case of this is that the
remote server’s name does not have any address records.
findfail
Failures to resolve remote server addresses. This is a total number of failures throughout the resolution process.
valfail
Failures of DNSSEC validation. Validation failures are counted throughout the resolution process (not limited tothe domain zone), but should only happen in domain.
At debug level 3 or higher, the same messages as those at debug level 1 are logged for errors other than SERVFAIL.
Note that negative responses such as NXDOMAIN are not errors, and are not logged at this debug level.
At debug level 4 or higher, the detailed context information logged at debug level 2 is logged for errors other than
SERVFAIL and for negative responses such as NXDOMAIN.

8.2.11 parental-agents Block Grammar
parental-agents
Grammar zone (primary, secondary): parental-agents [ port <integer> ] [ source( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };Grammar topmost: parental-agents <string> [ port <integer> ] [ source (<ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [port <integer> ] ) [ key <string> ] [ tls <string> ]; ... }; // may occur
multiple times
Blocks: topmost, zone (primary, secondary)Tags: zone

Defines a list of delegation agents to be used by primary and secondary zones.

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8.2.12 parental-agents Block Definition and Usage
parental-agents lists allow for a common set of parental agents to be easily used by multiple primary and secondary
zones. A “parental agent” is a trusted DNS server that is queried to check if DS records for a given zones are up-to-date.

8.2.13 primaries Block Grammar
primaries
Grammar zone (mirror, redirect, secondary, stub): primaries [ port <integer> ] [ source( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };Grammar topmost: primaries <string> [ port <integer> ] [ source (<ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [port <integer> ] ) [ key <string> ] [ tls <string> ]; ... }; // may occur
multiple times
Blocks: topmost, zone (mirror, redirect, secondary, stub)Tags: zone

Defines one or more primary servers for a zone.

8.2.14 primaries Block Definition and Usageprimaries lists allow for a common set of primary servers to be easily used by multiple stub and secondary zones
in their primaries or also-notify lists. (Note: primaries is a synonym for the original keyword masters,
which can still be used, but is no longer the preferred terminology.)
To force the zone transfer requests to be sent over TLS, use tls keyword, e.g. primaries { 192.0.2.1 tls
tls-configuration-name; };, where tls-configuration-name refers to a previously defined tls
statement.
Warning: Please note that TLS connections to primaries are not authenticated unless remote-hostname or
ca-file are specified within the tls statement in use (see information on Strict TLS and Mutual TLS for
more details). Not authenticated mode (Opportunistic TLS) provides protection from passive observers but does notprotect from man-in-the-middle attacks on zone transfers.

8.2.15 options Block Grammar
options
Grammar:options {allow-new-zones <boolean>;allow-notify { <address_match_element>; ... };allow-proxy { <address_match_element>; ... }; // experimental
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allow-query { <address_match_element>; ... };allow-query-cache { <address_match_element>; ... };allow-query-cache-on { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-recursion { <address_match_element>; ... };allow-recursion-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };answer-cookie <boolean>;
attach-cache <string>;
auth-nxdomain <boolean>;
automatic-interface-scan <boolean>;
avoid-v4-udp-ports { <portrange>; ... }; // deprecatedavoid-v6-udp-ports { <portrange>; ... }; // deprecatedbindkeys-file <quoted_string>; // test only
blackhole { <address_match_element>; ... };catalog-zones { zone <string> [ default-primaries [ port <integer> ] [␣,→source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (,→<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port,→<integer> ] ) [ key <string> ] [ tls <string> ]; ... } ] [ zone-directory,→<quoted_string> ] [ in-memory <boolean> ] [ min-update-interval <duration> ]; ..
,→. };
check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( primary | master | secondary | slave | response ) ( fail |␣,→warn | ignore ); // may occur multiple times
check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;clients-per-query <integer>;cookie-algorithm ( siphash24 );cookie-secret <string>; // may occur multiple times
deny-answer-addresses { <address_match_element>; ... } [ except-from {,→<string>; ... } ];deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddirectory <quoted_string>;
disable-algorithms <string> { <string>; ... }; // may occur multiple times
disable-ds-digests <string> { <string>; ... }; // may occur multiple times
disable-empty-zone <string>; // may occur multiple times
dns64 <netprefix> {break-dnssec <boolean>;clients { <address_match_element>; ... };exclude { <address_match_element>; ... };mapped { <address_match_element>; ... };recursive-only <boolean>;(continues on next page)8.2. Blocks

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suffix <ipv6_address>;}; // may occur multiple times
dns64-contact <string>;
dns64-server <string>;
dnskey-sig-validity <integer>; // obsolete
dnsrps-enable <boolean>;
dnsrps-library <quoted_string>;
dnsrps-options { <unspecified-text> };dnssec-accept-expired <boolean>;dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-must-be-secure <string> <boolean>; // may occur multiple times,␣
,→deprecateddnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
dnssec-validation ( yes | no | auto );dnstap { ( all | auth | client | forwarder | resolver | update ) [ (␣,→query | response ) ]; ... };dnstap-identity ( <quoted_string> | none | hostname );dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited | <size>␣
,→) ] [ versions ( unlimited | <integer> ) ] [ suffix ( increment | timestamp ) ];dnstap-version ( <quoted_string> | none );dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer>,→ ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ..
,→. };
dump-file <quoted_string>;
edns-udp-size <integer>;
empty-contact <string>;
empty-server <string>;
empty-zones-enable <boolean>;fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
fetches-per-server <integer> [ ( drop | fail ) ];fetches-per-zone <integer> [ ( drop | fail ) ];flush-zones-on-shutdown <boolean>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };fstrm-set-buffer-hint <integer>;fstrm-set-flush-timeout <integer>;fstrm-set-input-queue-size <integer>;fstrm-set-output-notify-threshold <integer>;fstrm-set-output-queue-model ( mpsc | spsc );fstrm-set-output-queue-size <integer>;fstrm-set-reopen-interval <duration>;
geoip-directory ( <quoted_string> | none );heartbeat-interval <integer>; // deprecatedhostname ( <quoted_string> | none );http-listener-clients <integer>;
http-port <integer>;
http-streams-per-connection <integer>;https-port <integer>;interface-interval <duration>;
ipv4only-contact <string>;
ipv4only-enable <boolean>;
ipv4only-server <string>;
ixfr-from-differences ( primary | master | secondary | slave | <boolean>␣
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keep-response-order { <address_match_element>; ... }; // obsolete
key-directory <quoted_string>;lame-ttl <duration>;
listen-on [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http,→<string> ] { <address_match_element>; ... }; // may occur multiple times
listen-on-v6 [ port <integer> ] [ proxy <string> ] [ tls <string> ] [␣,→http <string> ] { <address_match_element>; ... }; // may occur multiple times
lmdb-mapsize <sizeval>;managed-keys-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );match-mapped-addresses <boolean>;max-cache-size ( default | unlimited | <sizeval> | <percentage> );max-cache-ttl <duration>;max-clients-per-query <integer>;max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-ncache-ttl <duration>;max-records <integer>;max-records-per-type <integer>;max-recursion-depth <integer>;max-recursion-queries <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-rsa-exponent-size <integer>;max-stale-ttl <duration>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-udp-size <integer>;max-validation-failures-per-fetch <integer>; // experimental
max-validations-per-fetch <integer>; // experimental
max-zone-ttl ( unlimited | <duration> ); // deprecatedmemstatistics <boolean>;memstatistics-file <quoted_string>;
message-compression <boolean>;min-cache-ttl <duration>;
min-ncache-ttl <duration>;min-refresh-time <integer>;min-retry-time <integer>;minimal-any <boolean>;minimal-responses ( no-auth | no-auth-recursive | <boolean> );multi-master <boolean>;
new-zones-directory <quoted_string>;
no-case-compress { <address_match_element>; ... };nocookie-udp-size <integer>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-rate <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)nta-recheck <duration>;
nxdomain-redirect <string>;
parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );pid-file ( <quoted_string> | none );port <integer>;preferred-glue <string>;
prefetch <integer> [ <integer> ];provide-ixfr <boolean>;qname-minimization ( strict | relaxed | disabled | off );query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );querylog <boolean>;rate-limit {all-per-second <integer>;errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;log-only <boolean>;max-table-size <integer>;min-table-size <integer>;nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;referrals-per-second <integer>;
responses-per-second <integer>;slip <integer>;
window <integer>;};recursing-file <quoted_string>;
recursion <boolean>;recursive-clients <integer>;request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-server-cookie <boolean>;resolver-query-timeout <integer>;
resolver-use-dns64 <boolean>;
response-padding { <address_match_element>; ... } block-size <integer>;
response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [␣,→max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname␣,→| disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only,→<quoted_string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [␣,→nsdname-enable <boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [␣,→break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval,→<duration> ] [ min-ns-dots <integer> ] [ nsip-wait-recurse <boolean> ] [␣,→nsdname-wait-recurse <boolean> ] [ qname-wait-recurse <boolean> ] [ recursive,→only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [␣,→dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text> } ];reuseport <boolean>;root-key-sentinel <boolean>;rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string>␣
,→] <string> <string>; ... };secroots-file <quoted_string>;
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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)serial-update-method ( date | increment | unixtime );server-id ( <quoted_string> | none | hostname );servfail-ttl <duration>;session-keyalg <string>;
session-keyfile ( <quoted_string> | none );session-keyname <string>;
sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
sig0checks-quota <integer>; // experimental
sig0checks-quota-exempt { <address_match_element>; ... }; // experimental
sortlist { <address_match_element>; ... }; // deprecatedstale-answer-client-timeout ( disabled | off | <integer> );stale-answer-enable <boolean>;stale-answer-ttl <duration>;stale-cache-enable <boolean>;stale-refresh-time <duration>;startup-notify-rate <integer>;statistics-file <quoted_string>;
synth-from-dnssec <boolean>;
tcp-advertised-timeout <integer>;
tcp-clients <integer>;
tcp-idle-timeout <integer>;
tcp-initial-timeout <integer>;
tcp-keepalive-timeout <integer>;
tcp-listen-queue <integer>;tcp-receive-buffer <integer>;tcp-send-buffer <integer>;tkey-domain <quoted_string>;
tkey-gssapi-credential <quoted_string>;
tkey-gssapi-keytab <quoted_string>;
tls-port <integer>;transfer-format ( many-answers | one-answer );transfer-message-size <integer>;transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers-in <integer>;transfers-out <integer>;transfers-per-ns <integer>;trust-anchor-telemetry <boolean>;try-tcp-refresh <boolean>;
udp-receive-buffer <integer>;
udp-send-buffer <integer>;
update-check-ksk <boolean>; // obsolete
update-quota <integer>;use-v4-udp-ports { <portrange>; ... }; // deprecateduse-v6-udp-ports { <portrange>; ... }; // deprecatedv6-bias <integer>;validate-except { <string>; ... };version ( <quoted_string> | none );zero-no-soa-ttl <boolean>;zero-no-soa-ttl-cache <boolean>;zone-statistics ( full | terse | none | <boolean> );};Blocks: topmost

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Tags: server

Defines global options to be used by BIND 9.
This is the grammar of the options statement in the named.conf file:

8.2.16 options Block Definition and Usage
The options statement sets up global options to be used by BIND. This statement may appear only once in a configuration file. If there is no options statement, an options block with each option set to its default is used.
attach-cache
Grammar: attach-cache <string>;
Blocks: options, viewTags: view

Allows multiple views to share a single cache database.
This option allows multiple views to share a single cache database. Each view has its own cache database by default,
but if multiple views have the same operational policy for name resolution and caching, those views can share asingle cache to save memory, and possibly improve resolution efficiency, by using this option.
The attach-cache option may also be specified in view statements, in which case it overrides the global
attach-cache option.
The cache_name specifies the cache to be shared. When the named server configures views which are supposed
to share a cache, it creates a cache with the specified name for the first view of these sharing views. The rest of theviews simply refer to the already-created cache.
One common configuration to share a cache is to allow all views to share a single cache. This can be done byspecifying attach-cache as a global option with an arbitrary name.
Another possible operation is to allow a subset of all views to share a cache while the others retain their own
caches. For example, if there are three views A, B, and C, and only A and B should share a cache, specify theattach-cache option as a view of A (or B)’s option, referring to the other view name:view "A" {// this view has its own cache...
};view "B" {// this view refers to A's cacheattach-cache "A";};view "C" {// this view has its own cache...
};

Views that share a cache must have the same policy on configurable parameters that may affectcaching. The current implementation requires the following configurable options be consistent among
these views: check-names, dnssec-accept-expired, dnssec-validation, max-cache-ttl,
max-ncache-ttl, max-stale-ttl, max-cache-size, min-cache-ttl, min-ncache-ttl, andzero-no-soa-ttl.

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Note that there may be other parameters that may cause confusion if they are inconsistent for different views thatshare a single cache. For example, if these views define different sets of forwarders that can return different answers
for the same question, sharing the answer does not make sense or could even be harmful. It is the administrator’s
responsibility to ensure that configuration differences in different views do not cause disruption with a shared cache.
directory
Grammar key-store: directory <string>;
Grammar options: directory <quoted_string>;
Blocks: key-store, options
Tags: server

Sets the server’s working directory.
This sets the working directory of the server. Any non-absolute pathnames in the configuration file are taken as
relative to this directory. The default location for most server output files (e.g., named.run) is this directory. If
a directory is not specified, the working directory defaults to ".", the directory from which the server was started.
The directory specified should be an absolute path, and must be writable by the effective user ID of the named
process.
The option takes effect only at the time that the configuration option is parsed; if other files are being included
before or after specifying the new directory, the directory option must be listed before any other directive(like include) that can work with relative files. The safest way to include files is to use absolute file names.
dnstapGrammar: dnstap { ( all | auth | client | forwarder | resolver | update ) [( query | response ) ]; ... };Blocks: options, viewTags: logging

Enables logging of dnstap messages.
dnstap is a fast, flexible method for capturing and logging DNS traffic. Developed by Robert Edmonds at Farsight
Security, Inc., and supported by multiple DNS implementations, dnstap uses libfstrm (a lightweight highspeed framing library; see https://github.com/farsightsec/fstrm) to send event payloads which are encoded using
Protocol Buffers (libprotobuf-c, a mechanism for serializing structured data developed by Google, Inc.; see
https://developers.google.com/protocol-buffers/).
To enable dnstap at compile time, the fstrm and protobuf-c libraries must be available, and BIND must
be configured with --enable-dnstap.
The dnstap option is a bracketed list of message types to be logged. These may be set differently for each view.
Supported types are client, auth, resolver, forwarder, and update. Specifying type all causes all
dnstap messages to be logged, regardless of type.
Each type may take an additional argument to indicate whether to log query messages or response messages;
if not specified, both queries and responses are logged.
Example: To log all authoritative queries and responses, recursive client responses, and upstream queries sent by
the resolver, use:
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resolver query;};

Note: In the default configuration, the dnstap output for recursive resolver traffic does not include the IP addresses
used by server-side sockets. This is caused by the fact that unless the query source address is explicitly set, thesesockets are bound to wildcard IP addresses and determining the specific IP address used by each of them requires
issuing a system call (i.e. incurring a performance penalty).
Logged dnstap messages can be parsed using the dnstap-read utility (see dnstap-read - print dnstap data inhuman-readable form for details).
For more information on dnstap, see https://dnstap.info.
The fstrm library has a number of tunables that are exposed in named.conf, and can be modified if necessary
to improve performance or prevent loss of data. These are:fstrm-set-buffer-hint
Grammar: fstrm-set-buffer-hint <integer>;
Blocks: options
Tags: logging

Sets the number of accumulated bytes in the output buffer before forcing a buffer flush.
The threshold number of bytes to accumulate in the output buffer before forcing a buffer flush. The minimumis 1024, the maximum is 65536, and the default is 8192.
fstrm-set-flush-timeout
Grammar: fstrm-set-flush-timeout <integer>;
Blocks: options
Tags: logging

Sets the number of seconds that unflushed data remains in the output buffer.
The number of seconds to allow unflushed data to remain in the output buffer. The minimum is 1 second, themaximum is 600 seconds (10 minutes), and the default is 1 second.
fstrm-set-output-notify-threshold
Grammar: fstrm-set-output-notify-threshold <integer>;
Blocks: options
Tags: logging

Sets the number of outstanding queue entries allowed on an input queue before waking the I/O thread.
The number of outstanding queue entries to allow on an input queue before waking the I/O thread. The
minimum is 1 and the default is 32.

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fstrm-set-output-queue-model
Grammar: fstrm-set-output-queue-model ( mpsc | spsc );Blocks: options
Tags: logging

Sets the queuing semantics to use for queue objects.
The queuing semantics to use for queue objects. The default is mpsc (multiple producer, single consumer);the other option is spsc (single producer, single consumer).
fstrm-set-input-queue-sizeGrammar: fstrm-set-input-queue-size <integer>;
Blocks: options
Tags: logging

Sets the number of queue entries to allocate for each input queue.
The number of queue entries to allocate for each input queue. This value must be a power of 2. The minimum
is 2, the maximum is 16384, and the default is 512.
fstrm-set-output-queue-sizeGrammar: fstrm-set-output-queue-size <integer>;
Blocks: options
Tags: logging

Sets the number of queue entries allocated for each output queue.
The number of queue entries to allocate for each output queue. The minimum is 2, the maximum is systemdependent and based on IOV_MAX, and the default is 64.
fstrm-set-reopen-interval
Grammar: fstrm-set-reopen-interval <duration>;
Blocks: options
Tags: logging

Sets the number of seconds to wait between attempts to reopen a closed output stream.
The number of seconds to wait between attempts to reopen a closed output stream. The minimum is 1 second,
the maximum is 600 seconds (10 minutes), and the default is 5 seconds. For convenience, TTL-style time-unit
suffixes may be used to specify the value.
Note that all of the above minimum, maximum, and default values are set by the libfstrm library, and may besubject to change in future versions of the library. See the libfstrm documentation for more information.
dnstap-output
Grammar: dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited |<size> ) ] [ versions ( unlimited | <integer> ) ] [ suffix ( increment |timestamp ) ];Blocks: options
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Tags: logging

Configures the path to which the dnstap frame stream is sent.
This configures the path to which the dnstap frame stream is sent if dnstap is enabled at compile time andactive.
The first argument is either file or unix, indicating whether the destination is a file or a Unix domain socket.
The second argument is the path of the file or socket. (Note: when using a socket, dnstap messages are only sent
if another process such as fstrm_capture (provided with libfstrm) is listening on the socket.)
If the first argument is file, then up to three additional options can be added: size indicates the size to whicha dnstap log file can grow before being rolled to a new file; versions specifies the number of rolled log
files to retain; and suffix indicates whether to retain rolled log files with an incrementing counter as the suffix(increment) or with the current timestamp (timestamp). These are similar to the size, versions, andsuffix options in a logging channel. The default is to allow dnstap log files to grow to any size withoutrolling.
dnstap-output can only be set globally in options. Currently, it can only be set once while named isrunning; once set, it cannot be changed by rndc reload or rndc reconfig.
dnstap-identity
Grammar: dnstap-identity ( <quoted_string> | none | hostname );Blocks: options
Tags: logging

Specifies an identity string to send in dnstap messages.
This specifies an identity string to send in dnstap messages. If set to hostname, which is the default, theserver’s hostname is sent. If set to none, no identity string is sent.
dnstap-version
Grammar: dnstap-version ( <quoted_string> | none );Blocks: options
Tags: logging

Specifies a version string to send in dnstap messages.
This specifies a version string to send in dnstap messages. The default is the version number of the BIND
release. If set to none, no version string is sent.
geoip-directory
Grammar: geoip-directory ( <quoted_string> | none );Blocks: options
Tags: server

Specifies the directory containing GeoIP database files.
When named is compiled using the MaxMind GeoIP2 geolocation API, this specifies the directory containing
GeoIP database files. By default, the option is set based on the prefix used to build the libmaxminddb module;

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for example, if the library is installed in /usr/local/lib, then the default geoip-directory is /usr/
local/share/GeoIP. See acl for details about geoip ACLs.
key-directory
Grammar: key-directory <quoted_string>;
Blocks: options, view, zone (primary, secondary)Tags: dnssec

Indicates the directory where public and private DNSSEC key files are found.
This is the directory where the public and private DNSSEC key files should be found when performing a dynamic
update of secure zones, if different than the current working directory. (Note that this option has no effect on thepaths for files containing non-DNSSEC keys such as rndc.key, or session.key.)lmdb-mapsize
Grammar: lmdb-mapsize <sizeval>;
Blocks: options, viewTags: server

Sets a maximum size for the memory map of the new-zone database in LMDB database format.
When named is built with liblmdb, this option sets a maximum size for the memory map of the new-zone database(NZD) in LMDB database format. This database is used to store configuration information for zones added using
rndc addzone. Note that this is not the NZD database file size, but the largest size that the database may growto.
Because the database file is memory-mapped, its size is limited by the address space of the named process. The
default of 32 megabytes was chosen to be usable with 32-bit named builds. The largest permitted value is 1
terabyte. Given typical zone configurations without elaborate ACLs, a 32 MB NZD file ought to be able to holdconfigurations of about 100,000 zones.
managed-keys-directory
Grammar: managed-keys-directory <quoted_string>;
Blocks: options
Tags: dnssec

Specifies the directory in which to store the files that track managed DNSSEC keys.
This specifies the directory in which to store the files that track managed DNSSEC keys (i.e., those configured
using the initial-key or initial-ds keywords in a trust-anchors statement). By default, this is theworking directory. The directory must be writable by the effective user ID of the named process.
If named is not configured to use views, managed keys for the server are tracked in a single file called
managed-keys.bind. Otherwise, managed keys are tracked in separate files, one file per view; each filename is the view name (or, if it contains characters that are incompatible with use as a file name, the SHA256 hashof the view name), followed by the extension .mkeys.
(Note: in earlier releases, file names for views always used the SHA256 hash of the view name. To ensure compatibility after upgrading, if a file using the old name format is found to exist, it is used instead of the new format.)

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max-ixfr-ratio
Grammar: max-ixfr-ratio ( unlimited | <percentage> );Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Sets the maximum size for IXFR responses to zone transfer requests.
This sets the size threshold (expressed as a percentage of the size of the full zone) beyond which named chooses touse an AXFR response rather than IXFR when answering zone transfer requests. See Incremental Zone Transfers(IXFR).
The minimum value is 1%. The keyword unlimited disables ratio checking and allows IXFRs of any size. The
default is 100%.
new-zones-directory
Grammar: new-zones-directory <quoted_string>;
Blocks: options, viewTags: zone

Specifies the directory where configuration parameters are stored for zones added by rndc addzone.
This specifies the directory in which to store the configuration parameters for zones added via rndc addzone.
By default, this is the working directory. If set to a relative path, it is relative to the working directory. The directorymust be writable by the effective user ID of the named process.
qname-minimization
Grammar: qname-minimization ( strict | relaxed | disabled | off );Blocks: options, viewTags: query

Controls QNAME minimization behavior in the BIND 9 resolver.
When this is set to strict, BIND follows the QNAME minimization algorithm to the letter, as specified in RFC
7816.
Setting this option to relaxed causes BIND to fall back to normal (non-minimized) query mode when it receives either NXDOMAIN or other unexpected responses (e.g., SERVFAIL, improper zone cut, REFUSED) to aminimized query.
In relaxed mode named makes NS queries for <domain> as it walks down the tree.
disabled disables QNAME minimization completely. off is a synonym for disabled.
The current default is relaxed, but it may be changed to strict in a future release.
tkey-gssapi-keytab
Grammar: tkey-gssapi-keytab <quoted_string>;
Blocks: options
Tags: security

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Sets the KRB5 keytab file to use for GSS-TSIG updates.
This is the KRB5 keytab file to use for GSS-TSIG updates.
If this option is set andtkey-gssapi-credential is not set, updates are allowed with any key matching a principal in thespecified keytab.
tkey-gssapi-credential
Grammar: tkey-gssapi-credential <quoted_string>;
Blocks: options
Tags: security

Sets the security credential for authentication keys requested by the GSS-TSIG protocol.
This is the security credential with which the server should authenticate keys requested by the GSS-TSIG protocol.
Currently only Kerberos 5 authentication is available; the credential is a Kerberos principal which the server canacquire through the default system key file, normally /etc/krb5.keytab. The location of the keytab filecan be overridden using the tkey-gssapi-keytab option. Normally this principal is of the form DNS/
server.domain. To use GSS-TSIG, tkey-domain must also be set if a specific keytab is not set withtkey-gssapi-keytab.
tkey-domain
Grammar: tkey-domain <quoted_string>;
Blocks: options
Tags: security

Sets the domain appended to the names of all shared keys generated with TKEY.
This domain is appended to the names of all shared keys generated with TKEY. When a client requests a TKEY
exchange, it may or may not specify the desired name for the key. If present, the name of the shared key isclient-specified part + tkey-domain. Otherwise, the name of the shared key is random hex
digits + tkey-domain. In most cases, the domainname should be the server’s domain name, or an otherwise nonexistent subdomain like _tkey.domainname. If using GSS-TSIG, this variable must be defined,
unless a specific keytab is specified using tkey-gssapi-keytab.
dump-file
Grammar: dump-file <quoted_string>;
Blocks: options
Tags: logging

Indicates the pathname of the file where the server dumps the database after rndc dumpdb.
This is the pathname of the file the server dumps the database to, when instructed to do so with rndc dumpdb.
If not specified, the default is named_dump.db.
memstatistics-fileGrammar: memstatistics-file <quoted_string>;
Blocks: options
Tags: logging

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Sets the pathname of the file where the server writes memory usage statistics on exit.
This is the pathname of the file the server writes memory usage statistics to on exit. If not specified, the default isnamed.memstats.
pid-file
Grammar: pid-file ( <quoted_string> | none );Blocks: options
Tags: server

Specifies the pathname of the file where the server writes its process ID.
This is the pathname of the file the server writes its process ID in. If not specified, the default is /run/named.
pid. The PID file is used by programs that send signals to the running name server. Specifying pid-file none
disables the use of a PID file; no file is written and any existing one is removed. Note that none is a keyword, nota filename, and therefore is not enclosed in double quotes.
recursing-fileGrammar: recursing-file <quoted_string>;
Blocks: options
Tags: server

Specifies the pathname of the file where the server dumps queries that are currently recursing via rndc recursing.
This is the pathname of the file where the server dumps the queries that are currently recursing, when instructed to
do so with rndc recursing. If not specified, the default is named.recursing.
statistics-fileGrammar: statistics-file <quoted_string>;
Blocks: options
Tags: server, logging

Specifies the pathname of the file where the server appends statistics, when using rndc stats.
This is the pathname of the file the server appends statistics to, when instructed to do so using rndc stats. If
not specified, the default is named.stats in the server’s current directory. The format of the file is described in
The Statistics File.
bindkeys-fileGrammar: bindkeys-file <quoted_string>; // test only
Blocks: options
Tags: dnssec

Specifies the pathname of a file to override the built-in trusted keys provided by named.
This is the pathname of a file to override the built-in trusted keys provided by named. See the discussion ofdnssec-validation for details. This is intended for server testing.

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secroots-fileGrammar: secroots-file <quoted_string>;
Blocks: options
Tags: dnssec

Specifies the pathname of the file where the server dumps security roots, when using rndc secroots.
This is the pathname of the file the server dumps security roots to, when instructed to do so with rndc secroots.
If not specified, the default is named.secroots.
session-keyfile
Grammar: session-keyfile ( <quoted_string> | none );Blocks: options
Tags: security

Specifies the pathname of the file where a TSIG session key is written, when generated by named for use by
nsupdate -l.
This is the pathname of the file into which to write a TSIG session key generated by named for use by nsupdate-l. If not specified, the default is /run/session.key. (See Dynamic Update Policies, and in particular the
discussion of the update-policy statement’s local option, for more information about this feature.)session-keyname
Grammar: session-keyname <string>;
Blocks: options
Tags: security

Specifies the key name for the TSIG session key.
This is the key name to use for the TSIG session key. If not specified, the default is local-ddns.
session-keyalg
Grammar: session-keyalg <string>;
Blocks: options
Tags: security

Specifies the algorithm to use for the TSIG session key.
This is the algorithm to use for the TSIG session key. Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, hmac-sha512, and hmac-md5. If not specified, the default is hmac-sha256.
port
Grammar: port <integer>;
Blocks: options
Tags: query, server

Specifies the UDP/TCP port number the server uses to receive and send DNS protocol traffic.
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This is the UDP/TCP port number the server uses to receive and send DNS protocol traffic. The default is 53. This
option is mainly intended for server testing; a server using a port other than 53 is not able to communicate with theglobal DNS.
tls-port
Grammar: tls-port <integer>;
Blocks: options
Tags: query, server

Specifies the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic.
This is the TCP port number the server uses to receive and send DNS-over-TLS protocol traffic. The default is853.
https-port
Grammar: https-port <integer>;
Blocks: options
Tags: query, server

Specifies the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic.
This is the TCP port number the server uses to receive and send DNS-over-HTTPS protocol traffic. The default is443.
http-port
Grammar: http-port <integer>;
Blocks: options
Tags: query, server

Specifies the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP.
This is the TCP port number the server uses to receive and send unencrypted DNS traffic via HTTP (a configurationthat may be useful when encryption is handled by third-party software or by a reverse proxy).
http-listener-clients
Grammar: http-listener-clients <integer>;
Blocks: options
Tags: server

Limits the number of active concurrent connections on a per-listener basis.
This sets a hard limit on the number of active concurrent connections on a per-listener basis. The default value is300; setting it to 0 removes the quota.
http-streams-per-connection
Grammar: http-streams-per-connection <integer>;
Blocks: options
Tags: server

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Limits the number of active concurrent HTTP/2 streams on a per-connection basis.
This sets a hard limit on the number of active concurrent HTTP/2 streams on a per-connection basis. The default
value is 100; setting it to 0 removes the limit. Once the limit is exceeded, the server finishes the HTTP session.
preferred-glue
Grammar: preferred-glue <string>;
Blocks: options, viewTags: query

Controls the order of glue records in an A or AAAA response.
If specified, the listed type (A or AAAA) is emitted before other glue in the additional section of a query response.
The default is to prefer A records when responding to queries that arrived via IPv4 and AAAA when responding
to queries that arrived via IPv6.
disable-algorithms
Grammar: disable-algorithms <string> { <string>; ... }; // may occur multiple
times
Blocks: options, viewTags: dnssec

Disables DNSSEC algorithms from a specified zone.
This disables the specified DNSSEC algorithms at and below the specified name.
Multipledisable-algorithms statements are allowed. Only the best-match disable-algorithms clauseis used to determine the algorithms.
If all supported algorithms are disabled, the zones covered by the disable-algorithms setting are treated as
insecure.
Configured trust anchors in trust-anchors (or managed-keys or trusted-keys) that match a disabledalgorithm are ignored and treated as if they were not configured.
disable-ds-digests
Grammar: disable-ds-digests <string> { <string>; ... }; // may occur multiple
times
Blocks: options, viewTags: zone, dnssec

Disables DS digest types from a specified zone.
This disables the specified DS digest types at and below the specified name. Multiple disable-ds-digests
statements are allowed. Only the best-match disable-ds-digests clause is used to determine the digest
types.
If all supported digest types are disabled, the zones covered by disable-ds-digests are treated as insecure.

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dnssec-must-be-secure

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: dnssec-must-be-secure <string> <boolean>; // may occur multiple
times, deprecated
Blocks: options, viewTags: deprecatedDefines hierarchies that must or may not be secure (signed and validated).
This option is deprecated and will be removed in a future release.
This specifies hierarchies which must be or may not be secure (signed and validated). If yes, then named only
accepts answers if they are secure. If no, then normal DNSSEC validation applies, allowing insecure answers to be
accepted. The specified domain must be defined as a trust anchor, for instance in a trust-anchors statement,
or dnssec-validation auto must be active.
dns64
Grammar:
dns64 <netprefix> {break-dnssec <boolean>;clients { <address_match_element>; ... };exclude { <address_match_element>; ... };mapped { <address_match_element>; ... };recursive-only <boolean>;suffix <ipv6_address>;}; // may occur multiple times

Blocks: options, viewTags: query

Instructs named to return mapped IPv4 addresses to AAAA queries when there are no AAAA records.
This directive instructs named to return mapped IPv4 addresses to AAAA queries when there are no AAAA
records. It is intended to be used in conjunction with a NAT64. Each dns64 defines one DNS64 prefix. Multiple
DNS64 prefixes can be defined.
Compatible IPv6 prefixes have lengths of 32, 40, 48, 56, 64, and 96, per RFC 6052. Bits 64..71 inclusive must be
zero, with the most significant bit of the prefix in position 0.
In addition, a reverse IP6.ARPA zone is created for the prefix to provide a mapping from the IP6.ARPA names tothe corresponding IN-ADDR.ARPA names using synthesized CNAMEs.
dns64-server
Grammar: dns64-server <string>;
Blocks: options, viewTags: server

Specifies the name of the server for dns64 zones.
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dns64-contact
Grammar: dns64-contact <string>;
Blocks: options, viewTags: server

Specifies the name of the contact for dns64 zones.
dns64-server and dns64-contact can be used to specify the name of the server and contact for thezones. These can be set at the view/options level but not on a per-prefix basis.
dns64 will also cause IPV4ONLY.ARPA to be created if not explicitly disabled using
ipv4only-enable.
clients
Grammar: clients { <address_match_element>; ... };Blocks: options.dns64, view.dns64
Tags: query

Specifies an access control list (ACL) of clients that are affected by a given dns64 directive.
Each dns64 supports an optional clients ACL that determines which clients are affected by this directive.
If not defined, it defaults to any;.
mappedGrammar: mapped { <address_match_element>; ... };Blocks: options.dns64, view.dns64
Tags: query

Specifies an access control list (ACL) of IPv4 addresses that are to be mapped to the corresponding A RRset
in dns64.
Each dns64 block supports an optional mapped ACL that selects which IPv4 addresses are to be mappedin the corresponding A RRset. If not defined, it defaults to any;.
excludeGrammar: exclude { <address_match_element>; ... };Blocks: options.dns64, view.dns64
Tags: query

Allows a list of IPv6 addresses to be ignored if they appear in a domain name’s AAAA records in dns64.
Normally, DNS64 does not apply to a domain name that owns one or more AAAA records; these records
are simply returned. The optional exclude ACL allows specification of a list of IPv6 addresses that are
ignored if they appear in a domain name’s AAAA records; DNS64 is applied to any A records the domainname owns. If not defined, exclude defaults to ::ffff:0.0.0.0/96.

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suffixGrammar: suffix <ipv6_address>;
Blocks: options.dns64, view.dns64
Tags: query

Defines trailing bits for mapped IPv4 address bits in dns64.
An optional suffix can also be defined to set the bits trailing the mapped IPv4 address bits. By default
these bits are set to ::. The bits matching the prefix and mapped IPv4 address must be zero.
recursive-onlyGrammar: recursive-only <boolean>;
Blocks: options.dns64, view.dns64
Tags: query

Toggles whether dns64 synthesis occurs only for recursive queries.
If recursive-only is set to yes, the DNS64 synthesis only happens for recursive queries. The default
is no.
break-dnssec
Grammar: break-dnssec <boolean>;
Blocks: options.dns64, view.dns64
Tags: query

Enables dns64 synthesis even if the validated result would cause a DNSSEC validation failure.
If break-dnssec is set to yes, the DNS64 synthesis happens even if the result, if validated, would cause
a DNSSEC validation failure. If this option is set to no (the default), the DO is set on the incoming query,and there are RRSIGs on the applicable records, then synthesis does not happen.
acl rfc1918 { 10/8; 192.168/16; 172.16/12; };dns64 64:FF9B::/96 {clients { any; };mapped { !rfc1918; any; };exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };suffix ::;};resolver-use-dns64
Grammar: resolver-use-dns64 <boolean>;
Blocks: options, viewTags: server

Specifies whether to apply DNS64 mappings when sending queries.
If resolver-use-dns64 is set to yes, then the IPv4-to-IPv6 address transformations specified by the dns64
option will be applied to IPv4 server addresses to which recursive queries are sent. This allows a server to perform
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lookups via a NAT64 connection; queries that would have been sent via IPv4 are instead sent to mapped IPv6
addresses. The default is no.
ipv4only-enable
Grammar: ipv4only-enable <boolean>;
Blocks: options, viewTags: query

Enables automatic IPv4 zones if a dns64 block is configured.
This enables or disables automatic zones ipv4only.arpa, 170.0.0.192.in-addr.arpa, and 171.0.
0.192.in-addr.arpa.
By default these zones are loaded if dns64 is configured.
ipv4only-server
Grammar: ipv4only-server <string>;
Blocks: options, viewTags: query, server

Specifies the name of the server for the IPV4ONLY.ARPA zone created by dns64.
ipv4only-contact
Grammar: ipv4only-contact <string>;
Blocks: options, viewTags: server

Specifies the contact for the IPV4ONLY.ARPA zone created by dns64.
ipv4only-server and ipv4only-contact can be used to specify the name of the server and contact for
the IPV4ONLY.ARPA zone created by dns64.
dnssec-loadkeys-interval
Grammar: dnssec-loadkeys-interval <integer>;
Blocks: options, view, zone (primary, secondary)Tags: dnssec

Sets the frequency of automatic checks of the DNSSEC key repository.
When a zone is configured with dnssec-policy;, its key repository must be checked periodically to see if thenext step of a key rollover is due. The dnssec-loadkeys-interval option sets the default interval of key
repository checks, in minutes, in case the next key event cannot be calculated (for example because a DS record
needs to be published).
The default is 60 (1 hour), the minimum is 1 (1 minute), and the maximum is 1440 (24 hours); any higher value
is silently reduced.
dnssec-policy
This specifies which key and signing policy (KASP) should be used for this zone. This is a string referring
to a dnssec-policy block. The default is none.
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dnssec-update-mode
Grammar: dnssec-update-mode ( maintain | no-resign ); // obsolete
Blocks: options, view, zone (primary, secondary)Tags: obsolete
This option no longer has any effect.
nta-lifetime
Grammar: nta-lifetime <duration>;
Blocks: options, viewTags: dnssec

Specifies the lifetime, in seconds, for negative trust anchors added via rndc nta.
This specifies the default lifetime, in seconds, for negative trust anchors added via rndc nta.
A negative trust anchor selectively disables DNSSEC validation for zones that are known to be failing because of
misconfiguration, rather than an attack. When data to be validated is at or below an active NTA (and above anyother configured trust anchors), named aborts the DNSSEC validation process and treats the data as insecure rather
than bogus. This continues until the NTA’s lifetime has elapsed. NTAs persist across named restarts.
For convenience, TTL-style time-unit suffixes can be used to specify the NTA lifetime in seconds, minutes, orhours. It also accepts ISO 8601 duration formats.
nta-lifetime defaults to one hour; it cannot exceed one week.
nta-recheck
Grammar: nta-recheck <duration>;
Blocks: options, viewTags: dnssec

Specifies the time interval for checking whether negative trust anchors added via rndc nta are still necessary.
This specifies how often to check whether negative trust anchors added via rndc nta are still necessary.
A negative trust anchor is normally used when a domain has stopped validating due to operator error; it temporarily
disables DNSSEC validation for that domain. In the interest of ensuring that DNSSEC validation is turned backon as soon as possible, named periodically sends a query to the domain, ignoring negative trust anchors, to findout whether it can now be validated. If so, the negative trust anchor is allowed to expire early.
Validity checks can be disabled for an individual NTA by using rndc nta -f, or for all NTAs by setting
nta-recheck to zero.
For convenience, TTL-style time-unit suffixes can be used to specify the NTA recheck interval in seconds, minutes,
or hours. It also accepts ISO 8601 duration formats.
The default is five minutes. It cannot be longer than nta-lifetime, which cannot be longer than a week.
max-zone-ttl

Warning: This option is deprecated and will be removed in a future version of BIND.

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Grammar dnssec-policy: max-zone-ttl <duration>;
Grammar options, view, zone (primary, redirect): max-zone-ttl ( unlimited | <duration>); // deprecated
Blocks: dnssec-policy, options, view, zone (primary, redirect)
Tags: deprecatedSpecifies a maximum permissible time-to-live (TTL) value, in seconds.
This should now be configured as part of dnssec-policy. Use of this option in options, view andzone blocks is a fatal error if dnssec-policy has also been configured for the same zone. In zones without dnssec-policy, this option is deprecated, and will be rendered non-operational in a future release.
max-zone-ttl specifies a maximum permissible TTL value in seconds. For convenience, TTL-style time-unit
suffixes may be used to specify the maximum value. When a zone file is loaded, any record encountered with a
TTL higher than max-zone-ttl causes the zone to be rejected.
This is needed in DNSSEC-maintained zones because when rolling to a new DNSKEY, the old key needs to remain
available until RRSIG records have expired from caches. The max-zone-ttl option guarantees that the largest
TTL in the zone is no higher than the set value.
When used in options, view and zone blocks, setting max-zone-ttl to zero is equivalent to “unlimited”.
stale-answer-ttl
Grammar: stale-answer-ttl <duration>;
Blocks: options, viewTags: query

Specifies the time to live (TTL) to be returned on stale answers, in seconds.
This specifies the TTL to be returned on stale answers. The default is 30 seconds. The minimum allowed is 1
second; a value of 0 is updated silently to 1 second.
For stale answers to be returned, they must be enabled, either in the configuration file using
stale-answer-enable or via rndc serve-stale on.
serial-update-method
Grammar: serial-update-method ( date | increment | unixtime );Blocks: options, view, zone (primary)Tags: zone

Specifies the update method to be used for the zone serial number in the SOA record.
Zones configured for dynamic DNS may use this option to set the update method to be used for the zone serial
number in the SOA record.
With the default setting of serial-update-method increment;, the SOA serial number is incremented
by one each time the zone is updated.
When set to serial-update-method unixtime;, the SOA serial number is set to the number of seconds
since the Unix epoch, unless the serial number is already greater than or equal to that value, in which case it issimply incremented by one.

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When set to serial-update-method date;, the new SOA serial number is the current date in the form
“YYYYMMDD”, followed by two zeroes, unless the existing serial number is already greater than or equal to thatvalue, in which case it is incremented by one.
zone-statistics
Grammar: zone-statistics ( full | terse | none | <boolean> );Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)Tags: logging, zone

Controls the level of statistics gathered for all zones.
If full, the server collects statistical data on all zones, unless specifically turned off on a per-zone basis by specifying zone-statistics terse or zone-statistics none in the zone statement. The statistical
data includes, for example, DNSSEC signing operations and the number of authoritative answers per query type.
The default is terse, providing minimal statistics on zones (including name and current serial number, but notquery type counters), and also information about the currently ongoing incoming zone transfers.
These statistics may be accessed via the statistics-channel or using rndc stats, which dumps themto the file listed in the statistics-file. See also The Statistics File.
For backward compatibility with earlier versions of BIND 9, the zone-statistics option can also accept yesor no; yes has the same meaning as full. As of BIND 9.10, no has the same meaning as none; previously, it
was the same as terse.
Boolean Options
automatic-interface-scanGrammar: automatic-interface-scan <boolean>;
Blocks: options
Tags: server

Controls the automatic rescanning of network interfaces when addresses are added or removed.
If yes and supported by the operating system, this automatically rescans network interfaces when the interface
addresses are added or removed. The default is yes. This configuration option does not affect the time-based
interface-interval option; it is recommended to set the time-based interface-interval to 0 when
the operator confirms that automatic interface scanning is supported by the operating system.
The automatic-interface-scan implementation uses routing sockets for the network interface discovery;
therefore, the operating system must support the routing sockets for this feature to work.
allow-new-zones
Grammar: allow-new-zones <boolean>;
Blocks: options, viewTags: server, zone

Controls the ability to add zones at runtime via rndc addzone.
If yes, then zones can be added at runtime via rndc addzone. The default is no.

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Newly added zones’ configuration parameters are stored so that they can persist after the server is restarted. The
configuration information is saved in a file called viewname.nzf (or, if named is compiled with liblmdb, in an
LMDB database file called viewname.nzd). “viewname” is the name of the view, unless the view name contains
characters that are incompatible with use as a file name, in which case a cryptographic hash of the view name isused instead.
Configurations for zones added at runtime are stored either in a new-zone file (NZF) or a new-zone database (NZD),
depending on whether named was linked with liblmdb at compile time. See rndc - name server control utility forfurther details about rndc addzone.
auth-nxdomain
Grammar: auth-nxdomain <boolean>;
Blocks: options, viewTags: query

Controls whether BIND, acting as a resolver, provides authoritative NXDOMAIN (domain does not exist) answers.
If yes, then the AA bit is always set on NXDOMAIN responses, even if the server is not actually authoritative.
The default is no.
memstatistics
Grammar: memstatistics <boolean>;
Blocks: options
Tags: server, logging

Controls whether memory statistics are written to the file specified by memstatistics-file at exit.
This writes memory statistics to the file specified by memstatistics-file at exit. The default is no unless-m record is specified on the command line, in which case it is yes.
dialupWarning: This option is deprecated and will be removed in a future version of BIND.
Grammar: dialup ( notify | notify-passive | passive | refresh | <boolean> );// deprecated
Blocks: options, view, zone (primary, secondary, stub)Tags: deprecatedConcentrates zone maintenance so that all transfers take place once every heartbeat-interval, ideally during a single call.
This option is deprecated and will be removed in a future release.
If yes, then the server treats all zones as if they are doing zone transfers across a dial-on-demand dialup link,
which can be brought up by traffic originating from this server. Although this setting has different effects
according to zone type, it concentrates the zone maintenance so that everything happens quickly, once every
heartbeat-interval, ideally during a single call. It also suppresses some normal zone maintenance traffic. The default is no.

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If specified in the view and zone statements, the dialup option overrides the global dialup option.
If the zone is a primary zone, the server sends out a NOTIFY request to all the secondaries (default). This should
trigger the zone serial number check in the secondary (providing it supports NOTIFY), allowing the secondary toverify the zone while the connection is active. The set of servers to which NOTIFY is sent can be controlled by
notify and also-notify.
If the zone is a secondary or stub zone, the server suppresses the regular “zone up to date” (refresh) queries andonly performs them when the heartbeat-interval expires, in addition to sending NOTIFY requests.
Finer control can be achieved by using notify, which only sends NOTIFY messages; notify-passive,
which sends NOTIFY messages and suppresses the normal refresh queries; refresh, which suppresses normal
refresh processing and sends refresh queries when the heartbeat-interval expires; and passive, which
disables normal refresh processing.
dialup modeno (default)
yes
notifyrefreshpassivenotify-passive

normal refresh
yes
no
yes
no
no
no

heart-beat refresh
no
yes
no
yes
no
no

heart-beat notify
no
yes
yes
no
no
yes

Note that normal NOTIFY processing is not affected by dialup.
flush-zones-on-shutdown
Grammar: flush-zones-on-shutdown <boolean>;
Blocks: options
Tags: zone

Controls whether pending zone writes are flushed when the name server exits.
When the name server exits upon receiving SIGTERM, flush or do not flush any pending zone writes. The default
is flush-zones-on-shutdown no.
root-key-sentinel
Grammar: root-key-sentinel <boolean>;
Blocks: options, viewTags: server

Controls whether BIND 9 responds to root key sentinel probes.
If yes, respond to root key sentinel probes as described in RFC 8509:. The default is yes.
reuseport
Grammar: reuseport <boolean>;
Blocks: options
Tags: server

Enables kernel load-balancing of sockets.

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This option enables kernel load-balancing of sockets on systems which support it, including Linux(SO_REUSEPORT) and FreeBSD (SO_REUSEPORT_LB). This instructs the kernel to distribute incoming socket
connections among the networking threads based on a hashing scheme. For more information, see the receive network flow classification options (rx-flow-hash) section in the ethtool manual page. The default is yes.
Enabling reuseport significantly increases general throughput when incoming traffic is distributed uniformly
onto the threads by the operating system. However, in cases where a worker thread is busy with a long-lasting
operation, such as processing a Response Policy Zone (RPZ) or Catalog Zone update or an unusually large zonetransfer, incoming traffic that hashes onto that thread may be delayed. On servers where these events occur frequently, it may be preferable to disable socket load-balancing so that other threads can pick up the traffic that would
have been sent to the busy thread.
Note: this option can only be set when named first starts. Changes will not take effect during reconfiguration; theserver must be restarted.
message-compression
Grammar: message-compression <boolean>;
Blocks: options, viewTags: query

Controls whether DNS name compression is used in responses to regular queries.
If yes, DNS name compression is used in responses to regular queries (not including AXFR or IXFR, which always
use compression). Setting this option to no reduces CPU usage on servers and may improve throughput. However,it increases response size, which may cause more queries to be processed using TCP; a server with compression
disabled is out of compliance with RFC 1123 Section 6.1.3.2. The default is yes.
minimal-responses
Grammar: minimal-responses ( no-auth | no-auth-recursive | <boolean> );Blocks: options, viewTags: query

Controls whether the server only adds records to the authority and additional data sections when they are required(e.g. delegations, negative responses). This improves server performance.
This option controls the addition of records to the authority and additional sections of responses. Such records may
be included in responses to be helpful to clients; for example, MX records may have associated address records
included in the additional section, obviating the need for a separate address lookup. However, adding these records
to responses is not mandatory and requires additional database lookups, causing extra latency when marshalling
responses.
Responses to DNSKEY, DS, CDNSKEY, and CDS requests will never have optional additional records added.
Responses to NS requests will always have additional section processing.
minimal-responses takes one of four values:• no: the server is as complete as possible when generating responses.
• yes: the server only adds records to the authority and additional sections when such records are required by
the DNS protocol (for example, when returning delegations or negative responses). This provides the best
server performance but may result in more client queries.
• no-auth: the server omits records from the authority section except when they are required, but it may still
add records to the additional section.

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BIND 9 Administrator Reference Manual, Release 9.20.0• no-auth-recursive: the same as no-auth when recursion is requested in the query (RD=1), or thesame as no if recursion is not requested.
no-auth and no-auth-recursive are useful when answering stub clients, which usually ignore the authority
section. no-auth-recursive is meant for use in mixed-mode servers that handle both authoritative andrecursive queries.
The default is no-auth-recursive.
minimal-any
Grammar: minimal-any <boolean>;
Blocks: options, viewTags: query

Controls whether the server replies with only one of the RRsets for a query name, when generating a positive
response to a query of type ANY over UDP.
If set to yes, the server replies with only one of the RRsets for the query name, and its covering RRSIGs if any,
when generating a positive response to a query of type ANY over UDP, instead of replying with all known RRsets
for the name. Similarly, a query for type RRSIG is answered with the RRSIG records covering only one type.
This can reduce the impact of some kinds of attack traffic, without harming legitimate clients. (Note, however,that the RRset returned is the first one found in the database; it is not necessarily the smallest available RRset.)
Additionally, minimal-responses is turned on for these queries, so no unnecessary records are added to theauthority or additional sections. The default is no.
notifyGrammar: notify ( explicit | master-only | primary-only | <boolean> );Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Controls whether NOTIFY messages are sent on zone changes.
If set to yes (the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes;
see using notify. The messages are sent to the servers listed in the zone’s NS records (except the primary server
identified in the SOA MNAME field), and to any servers listed in the also-notify option.
If set to primary-only (or the older keyword master-only), notifies are only sent for primary zones. If set
to explicit, notifies are sent only to servers explicitly listed using also-notify. If set to no, no notifies aresent.
The notify option may also be specified in the zone statement, in which case it overrides the options notify statement. It would only be necessary to turn off this option if it caused secondary zones to crash.
notify-to-soa
Grammar: notify-to-soa <boolean>;
Blocks: options, view, zone (primary, secondary)Tags: transfer

Controls whether the name servers in the NS RRset are checked against the SOA MNAME.
If yes, do not check the name servers in the NS RRset against the SOA MNAME. Normally a NOTIFY message
is not sent to the SOA MNAME (SOA ORIGIN), as it is supposed to contain the name of the ultimate primary

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server. Sometimes, however, a secondary server is listed as the SOA MNAME in hidden primary configurations;in that case, the ultimate primary should be set to still send NOTIFY messages to all the name servers listed in the
NS RRset.
recursion
Grammar: recursion <boolean>;
Blocks: options, viewTags: query

Defines whether recursion and caching are allowed.
If yes, and a DNS query requests recursion, then the server attempts to do all the work required to answer thequery. If recursion is off and the server does not already know the answer, it returns a referral response. The default
is yes. Note that setting recursion no does not prevent clients from getting data from the server’s cache; it
only prevents new data from being cached as an effect of client queries. Caching may still occur as an effect of theserver’s internal operation, such as NOTIFY address lookups.
request-nsidGrammar: request-nsid <boolean>;
Blocks: options, server, view, view.server
Tags: query

Controls whether an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative
name servers during iterative resolution.
If yes, then an empty EDNS(0) NSID (Name Server Identifier) option is sent with all queries to authoritative
name servers during iterative resolution. If the authoritative server returns an NSID option in its response, then its
contents are logged in the nsid category at level info. The default is no.
require-cookie
Grammar: require-cookie <boolean>;
Blocks: server, view.server
Tags: query

Controls whether responses without a server cookie are accepted
The require-cookie clause can be used to indicate that the remote server is known to support DNS COOKIE.
Setting this option to yes causes named to always retry a request over TCP when it receives a UDP response
without a DNS COOKIE from the remote server, even if UDP responses with DNS COOKIE have not been sentby this server before. This prevents spoofed answers from being accepted without a retry over TCP when named
has not yet determined whether the remote server supports DNS COOKIE. Setting this option to no (the default)
causes named to rely on autodetection of DNS COOKIE support to determine when to retry a request over TCP.
Note: If a UDP response is signed using TSIG, named accepts it even if require-cookie is set to yes andthe response does not contain a DNS COOKIE.
The send-cookie clause determines whether the local server adds a COOKIE EDNS option to requests sent tothe server. This overrides send-cookie set at the view or option level. The named server may determine that
COOKIE is not supported by the remote server and not add a COOKIE EDNS option to requests.

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require-server-cookie
Grammar: require-server-cookie <boolean>;
Blocks: options, viewTags: query

Controls whether a valid server cookie is required before sending a full response to a UDP request.
If yes, require a valid server cookie before sending a full response to a UDP request from a cookie-aware client.
BADCOOKIE is sent if there is a bad or nonexistent server cookie.
The default is no.
Users wishing to test that DNS COOKIE clients correctly handle BADCOOKIE, or who are getting a lot of forged
DNS requests with DNS COOKIES present, should set this to yes. Setting this to yes results in a reduced
amplification effect in a reflection attack, as the BADCOOKIE response is smaller than a full response, while also
requiring a legitimate client to follow up with a second query with the new, valid, cookie.
answer-cookie
Grammar: answer-cookie <boolean>;
Blocks: options
Tags: query

Controls whether COOKIE EDNS replies are sent in response to client queries.
When set to the default value of yes, COOKIE EDNS options are sent when applicable in replies to client queries.
If set to no, COOKIE EDNS options are not sent in replies. This can only be set at the global options level, notper-view.
answer-cookie no is intended as a temporary measure, for use when named shares an IP address with otherservers that do not yet support DNS COOKIE. A mismatch between servers on the same address is not expected tocause operational problems, but the option to disable COOKIE responses so that all servers have the same behavior
is provided out of an abundance of caution. DNS COOKIE is an important security mechanism, and should not bedisabled unless absolutely necessary.
send-cookie
Grammar: send-cookie <boolean>;
Blocks: options, server, view, view.server
Tags: query

Controls whether a COOKIE EDNS option is sent along with a query.
If yes, then a COOKIE EDNS option is sent along with the query. If the resolver has previously communicated with the server, the COOKIE returned in the previous transaction is sent. This is used by the server todetermine whether the resolver has talked to it before. A resolver sending the correct COOKIE is assumed not
to be an off-path attacker sending a spoofed-source query; the query is therefore unlikely to be part of a reflection/amplification attack, so resolvers sending a correct COOKIE option are not subject to response rate limiting(RRL). Resolvers which do not send a correct COOKIE option may be limited to receiving smaller responses via
the nocookie-udp-size option.
The named server may determine that COOKIE is not supported by the remote server and not add a COOKIEEDNS option to requests.

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The default is yes.
stale-answer-enable
Grammar: stale-answer-enable <boolean>;
Blocks: options, viewTags: query, server

Enables the returning of “stale” cached answers when the name servers for a zone are not answering.
If yes, enable the returning of “stale” cached answers when the name servers for a zone are not answering and thestale-cache-enable option is also enabled. The default is not to return stale answers.
Stale answers can also be enabled or disabled at runtime via rndc serve-stale on or rndc serve-stale
off; these override the configured setting. rndc serve-stale reset restores the setting to the one specified
in named.conf. Note that if stale answers have been disabled by rndc, they cannot be re-enabled by reloadingor reconfiguring named; they must be re-enabled with rndc serve-stale on, or the server must be restarted.
Information about stale answers is logged under the serve-stale log category.
stale-answer-client-timeout
Grammar: stale-answer-client-timeout ( disabled | off | <integer> );Blocks: options, viewTags: query, server

Defines the amount of time (in milliseconds) that named waits before attempting to answer a query with a stale
RRset from cache.
This option defines the amount of time (in milliseconds) that named waits before attempting to answer the querywith a stale RRset from cache. If a stale answer is found, named continues the ongoing fetches, attempting torefresh the RRset in cache until the resolver-query-timeout interval is reached.
This option is off by default, which is equivalent to setting it to off or disabled. It also has no effect if
stale-answer-enable is disabled.
The minimum value, 0, causes a cached (stale) RRset to be immediately returned if it is available while still
attempting to refresh the data in cache.
When this option is enabled, the only supported value in the current version of BIND 9 is 0. Non-zero values
generate a warning message, and are treated as 0.
stale-cache-enable
Grammar: stale-cache-enable <boolean>;
Blocks: options, viewTags: query, server

Enables the retention of “stale” cached answers.
If yes, enable the retaining of “stale” cached answers. Default no.
stale-refresh-time
Grammar: stale-refresh-time <duration>;
Blocks: options, view

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Tags: query, server

Sets the time window for the return of “stale” cached answers before the next attempt to contact, if the name servers
for a given zone are not responding.
If the name servers for a given zone are not answering, this sets the time window for which named will promptly
return “stale” cached answers for that RRSet being requested before a new attempt in contacting the servers ismade. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601
duration formats.
The default stale-refresh-time is 30 seconds, as RFC 8767 recommends that attempts to refresh to bedone no more frequently than every 30 seconds. A value of zero disables the feature, meaning that normal resolution
will take place first, if that fails only then named will return “stale” cached answers.
nocookie-udp-sizeGrammar: nocookie-udp-size <integer>;
Blocks: options, viewTags: query

Sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE.
This sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE. A value
below 128 is silently raised to 128. The default value is 4096, but the max-udp-size option may further limit
the response size as the default for max-udp-size is 1232.
cookie-algorithm
Grammar: cookie-algorithm ( siphash24 );Blocks: options
Tags: server

Sets the algorithm to be used when generating a server cookie.
This sets the algorithm to be used when generating the server cookie. The default is “siphash24”, which is the only
supported option, as the previously supported “aes” option has been removed.
cookie-secret
Grammar: cookie-secret <string>; // may occur multiple times
Blocks: options
Tags: server

Specifies a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster.
If set, this is a shared secret used for generating and verifying EDNS COOKIE options within an anycast cluster.
If not set, the system generates a random secret at startup. The shared secret is encoded as a hex string and needs
to be 128 bits.
If there are multiple secrets specified, the first one listed in named.conf is used to generate new server cookies.
The others are only used to verify returned cookies.

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response-padding
Grammar: response-padding<integer>;{<address_match_element>;...

}

block-size

Blocks: options, viewTags: query

Adds an EDNS Padding option to encrypted messages, to reduce the chance of guessing the contents based on size.
The EDNS Padding option is intended to improve confidentiality when DNS queries are sent over an encryptedchannel, by reducing the variability in packet sizes. If a query:
1. contains an EDNS Padding option,
2. includes a valid server cookie or uses TCP,
3. is not signed using TSIG or SIG(0), and
4. is from a client whose address matches the specified ACL,
then the response is padded with an EDNS Padding option to a multiple of block-size bytes. If these conditions
are not met, the response is not padded.
If block-size is 0 or the ACL is none;, this feature is disabled and no padding occurs; this is the default. If
block-size is greater than 512, a warning is logged and the value is truncated to 512. Block sizes are ordinarily
expected to be powers of two (for instance, 128), but this is not mandatory.
trust-anchor-telemetry
Grammar: trust-anchor-telemetry <boolean>;
Blocks: options, viewTags: dnssec

Instructs named to send specially formed queries once per day to domains for which trust anchors have been
configured.
This causes named to send specially formed queries once per day to domains for which trust anchors have been
configured via, e.g., trust-anchors or dnssec-validation auto.
The query name used for these queries has the form _ta-xxxx(-xxxx)(...).<domain>, where each“xxxx” is a group of four hexadecimal digits representing the key ID of a trusted DNSSEC key. The key IDs
for each domain are sorted smallest to largest prior to encoding. The query type is NULL.
By monitoring these queries, zone operators are able to see which resolvers have been updated to trust a new key;
this may help them decide when it is safe to remove an old one.
The default is yes.
provide-ixfr
Grammar: provide-ixfr <boolean>;
Blocks: options, server, view, view.server
Tags: transfer

Controls whether a primary responds to an incremental zone request (IXFR) or only responds with a full zonetransfer (AXFR).

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The provide-ixfr clause determines whether the local server, acting as primary, responds with an incrementalzone transfer when the given remote server, a secondary, requests it. If set to yes, incremental transfer is provided
whenever possible. If set to no, all transfers to the remote server are non-incremental.
request-ixfr
Grammar: request-ixfr <boolean>;
Blocks: options, server, view, zone (mirror, secondary), view.server
Tags: transfer

Controls whether a secondary requests an incremental zone transfer (IXFR) or a full zone transfer (AXFR).
The request-ixfr statement determines whether the local server, acting as a secondary, requests incrementalzone transfers from the given remote server, a primary.
IXFR requests to servers that do not support IXFR automatically fall back to AXFR. Therefore, there is no needto manually list which servers support IXFR and which ones do not; the global default of yes should always work.
The purpose of the provide-ixfr and request-ixfr statements is to make it possible to disable the useof IXFR even when both primary and secondary claim to support it: for example, if one of the servers is buggy
and crashes or corrupts data when IXFR is used.
It may also be set in the zone block; if set there, it overrides the global or view setting for that zone. It may also be
set in the server block.
request-expire
Grammar: request-expire <boolean>;
Blocks: options, server, view, zone (mirror, secondary), view.server
Tags: query, transfer

Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.
The request-expire statement determines whether the local server, when acting as a secondary, requests the
EDNS EXPIRE value. The EDNS EXPIRE value indicates the remaining time before the zone data expires andneeds to be refreshed. This is used when a secondary server transfers a zone from another secondary server; whentransferring from the primary, the expiration timer is set from the EXPIRE field of the SOA record instead. The
default is yes.
match-mapped-addresses
Grammar: match-mapped-addresses <boolean>;
Blocks: options
Tags: server

Allows IPv4-mapped IPv6 addresses to match address-match list entries for corresponding IPv4 addresses.
If yes, then an IPv4-mapped IPv6 address matches any address-match list entries that match the corresponding
IPv4 address.
This option was introduced to work around a kernel quirk in some operating systems that causes IPv4 TCP connections, such as zone transfers, to be accepted on an IPv6 socket using mapped addresses. This caused address-matchlists designed for IPv4 to fail to match. However, named now solves this problem internally. The use of this option
is discouraged.

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ixfr-from-differences
Grammar zone (mirror, primary, secondary): ixfr-from-differences <boolean>;Grammar options, view: ixfr-from-differences ( primary | master | secondary |slave | <boolean> );Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Controls how IXFR transfers are calculated.
When yes and the server loads a new version of a primary zone from its zone file or receives a new version of asecondary file via zone transfer, it compares the new version to the previous one and calculates a set of differences.
The differences are then logged in the zone’s journal file so that the changes can be transmitted to downstream
secondaries as an incremental zone transfer.
By allowing incremental zone transfers to be used for non-dynamic zones, this option saves bandwidth at the expenseof increased CPU and memory consumption at the primary server. In particular, if the new version of a zone iscompletely different from the previous one, the set of differences is of a size comparable to the combined size of theold and new zone versions, and the server needs to temporarily allocate memory to hold this complete differenceset.
ixfr-from-differences also accepts primary and secondary at the view and options levels, whichcauses ixfr-from-differences to be enabled for all primary or secondary zones, respectively. It is off for
all zones by default.
Note: if inline signing is enabled for a zone, the user-provided ixfr-from-differences setting is ignored
for that zone.
multi-master
Grammar: multi-master <boolean>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Controls whether serial number mismatch errors are logged.
This should be set when there are multiple primary servers for a zone and the addresses refer to different machines.
If yes, named does not log when the serial number on the primary is less than what named currently has. The
default is no.
dnssec-validation
Grammar: dnssec-validation ( yes | no | auto );Blocks: options, viewTags: dnssec

Enables DNSSEC validation in named.
This option enables DNSSEC validation in named.
If set to auto, DNSSEC validation is enabled and a default trust anchor for the DNS root zone is used. This
trust anchor is provided as part of BIND and is kept up-to-date using Dynamic Trust Anchor Management key
management. Adding an explicit static key using the trust-anchors statement with a static-key anchor

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type (or using the deprecated trusted-keys statement) for the root zone is not supported with the auto setting,and is treated as a configuration error.
If set to yes, DNSSEC validation is enabled, but a trust anchor must be manually configured using atrust-anchors statement (or the managed-keys or trusted-keys statements, both deprecated). If
trust-anchors is not configured, it is a configuration error. If trust-anchors does not include a valid
root key, then validation does not take place for names which are not covered by any of the configured trust anchors.
If set to no, DNSSEC validation is disabled. (Note: the resolver will still set the DO bit in outgoing queries
indicating that it can accept DNSSEC responses, even if dnssec-validation is disabled.)
The default is auto, unless BIND is built with configure --disable-auto-validation, in whichcase the default is yes.
The default root trust anchor is compiled into named and is current as of the release date. If the root key changes,
a running BIND server will detect this and roll smoothly to the new key, but newly-installed servers will be unable
to start validation, so BIND must be upgraded to a newer version.
validate-except
Grammar: validate-except { <string>; ... };Blocks: options, viewTags: dnssec

Specifies a list of domain names at and beneath which DNSSEC validation should not be performed.
This specifies a list of domain names at and beneath which DNSSEC validation should not be performed, regardlessof the presence of a trust anchor at or above those names. This may be used, for example, when configuring a toplevel domain intended only for local use, so that the lack of a secure delegation for that domain in the root zone
does not cause validation failures. (This is similar to setting a negative trust anchor except that it is a permanent
configuration, whereas negative trust anchors expire and are removed after a set period of time.)
dnssec-accept-expired
Grammar: dnssec-accept-expired <boolean>;
Blocks: options, viewTags: dnssec

Instructs BIND 9 to accept expired DNSSEC signatures when validating.
This accepts expired signatures when verifying DNSSEC signatures. The default is no. Setting this option to yes
leaves named vulnerable to replay attacks.
querylog
Grammar: querylog <boolean>;
Blocks: options
Tags: server, logging

Specifies whether query logging should be active when named first starts.
Query logging provides a complete log of all incoming queries and all query errors. This provides more insight into
the server’s activity, but with a cost to performance which may be significant on heavily loaded servers.
The querylog option specifies whether query logging should be active when named first starts. If querylog
is not specified, then query logging is determined by the presence of the logging category queries. Query
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logging can also be activated at runtime using the command rndc querylog on, or deactivated with rndc
querylog off.
check-names
Grammar zone (hint, mirror, primary, secondary, stub): check-names ( fail | warn | ignore);
Grammar options, view: check-names ( primary | master | secondary | slave |response ) ( fail | warn | ignore ); // may occur multiple times
Blocks: options, view, zone (hint, mirror, primary, secondary, stub)Tags: query, server

Restricts the character set and syntax of certain domain names in primary files and/or DNS responses received fromthe network.
This option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS
responses received from the network. The default varies according to usage area. For type primary zones
the default is fail. For type secondary zones the default is warn. For answers received from the network(response), the default is ignore.
The rules for legal hostnames and mail domains are derived from RFC 952 and RFC 821 as modified by RFC
1123.
check-names applies to the owner names of A, AAAA, and MX records. It also applies to the domain names in
the RDATA of NS, SOA, MX, and SRV records. It further applies to the RDATA of PTR records where the ownername indicates that it is a reverse lookup of a hostname (the owner name ends in IN-ADDR.ARPA, IP6.ARPA,or IP6.INT).
check-dup-records
Grammar: check-dup-records ( fail | warn | ignore );Blocks: options, view, zone (primary)Tags: query, dnssec

Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain DNS.
This checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain
DNS. The default is to warn. Other possible values are fail and ignore.
check-mx
Grammar: check-mx ( fail | warn | ignore );Blocks: options, view, zone (primary)Tags: zone

Checks whether an MX record appears to refer to an IP address.
This checks whether the MX record appears to refer to an IP address. The default is to warn. Other possible
values are fail and ignore.
check-wildcard
Grammar: check-wildcard <boolean>;
Blocks: options, view, zone (primary)

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Tags: zone

Checks for non-terminal wildcards.
This option is used to check for non-terminal wildcards. The use of non-terminal wildcards is almost always asa result of a lack of understanding of the wildcard-matching algorithm (RFC 1034). This option affects primaryzones. The default (yes) is to check for non-terminal wildcards and issue a warning.
check-integrity
Grammar: check-integrity <boolean>;
Blocks: options, view, zone (primary)Tags: zone

Performs post-load zone integrity checks on primary zones.
This performs post-load zone integrity checks on primary zones. It checks that MX and SRV records refer to address(A or AAAA) records and that glue address records exist for delegated zones. For MX and SRV records, only inzone hostnames are checked (for out-of-zone hostnames, use named-checkzone). For NS records, only names
below top-of-zone are checked (for out-of-zone names and glue consistency checks, use named-checkzone).
DS records not at delegations are rejected. The default is yes.
The use of the SPF record to publish Sender Policy Framework is deprecated, as the migration from using TXT
records to SPF records was abandoned. Enabling this option also checks that a TXT Sender Policy Framework
record exists (starts with “v=spf1”) if there is an SPF record. Warnings are emitted if the TXT record does notexist; they can be suppressed with check-spf.
check-mx-cname
Grammar: check-mx-cname ( fail | warn | ignore );Blocks: options, view, zone (primary)Tags: zone

Sets the response to MX records that refer to CNAMEs.
If check-integrity is set, then fail, warn, or ignore MX records that refer to CNAMEs. The default is towarn.
check-srv-cname
Grammar: check-srv-cname ( fail | warn | ignore );Blocks: options, view, zone (primary)Tags: zone

Sets the response to SRV records that refer to CNAMEs.
If check-integrity is set, then fail, warn, or ignore SRV records that refer to CNAMEs. The default is towarn.
check-sibling
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Tags: zone

Specifies whether to check for sibling glue when performing integrity checks.
When performing integrity checks, also check that sibling glue exists. The default is yes.
check-spf
Grammar: check-spf ( warn | ignore );Blocks: options, view, zone (primary)Tags: zone

Specifies whether to check for a TXT Sender Policy Framework record, if an SPF record is present.
If check-integrity is set, check that there is a TXT Sender Policy Framework record present (starts with
“v=spf1”) if there is an SPF record present. The default is warn.
check-svcb
Grammar: check-svcb <boolean>;
Blocks: options, view, zone (primary)Tags: zone

Specifies whether to perform additional checks on SVCB records.
If yes, checks that SVCB records that start with a _dns label prefixed by an optional _<port> label (e.g.
_443._dns.ns1.example), have an alpn parameter and that the dohpath parameter exists when thealpn indicates that it should be present. The default is yes.
zero-no-soa-ttl
Grammar: zero-no-soa-ttl <boolean>;
Blocks: options, view, zone (mirror, primary, secondary)Tags: query, server, zone

Specifies whether to set the time to live (TTL) of the SOA record to zero, when returning authoritative negative
responses to SOA queries.
If yes, when returning authoritative negative responses to SOA queries, set the TTL of the SOA record returnedin the authority section to zero. The default is yes.
zero-no-soa-ttl-cache
Grammar: zero-no-soa-ttl-cache <boolean>;
Blocks: options, viewTags: query, server, zone

Sets the time to live (TTL) to zero when caching a negative response to an SOA query.
If yes, when caching a negative response to an SOA query set the TTL to zero. The default is no.

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update-check-ksk
Grammar: update-check-ksk <boolean>; // obsolete
Blocks: options, view, zone (primary, secondary)Tags: obsolete
This option no longer has any effect.
dnssec-dnskey-kskonly
Grammar: dnssec-dnskey-kskonly <boolean>; // obsolete
Blocks: options, view, zone (primary, secondary)Tags: obsolete
This option no longer has any effect.
try-tcp-refresh
Grammar: try-tcp-refresh <boolean>;
Blocks: options, view, zone (mirror, secondary)Tags: transfer

Specifies that BIND 9 should attempt to refresh a zone using TCP if UDP queries fail.
If yes, try to refresh the zone using TCP if UDP queries fail. The default is yes.
dnssec-secure-to-insecure
Grammar: dnssec-secure-to-insecure <boolean>; // obsolete
Blocks: options, view, zone (primary)Tags: obsolete
This option no longer has any effect.
synth-from-dnssec
Grammar: synth-from-dnssec <boolean>;
Blocks: options, viewTags: dnssec

Enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache.
This option enables support for RFC 8198, Aggressive Use of DNSSEC-Validated Cache. It allows the resolver
to send a smaller number of queries when resolving queries for DNSSEC-signed domains by synthesizing answers
from cached NSEC and other RRsets that have been proved to be correct using DNSSEC. The default is yes.
Note: DNSSEC validation must be enabled for this option to be effective. This initial implementation only
covers synthesis of answers from NSEC records; synthesis from NSEC3 is planned for the future. This will also becontrolled by synth-from-dnssec.

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Forwarding
The forwarding facility can be used to create a large site-wide cache on a few servers, reducing traffic over links to externalname servers. It can also be used to allow queries by servers that do not have direct access to the Internet, but wish tolook up exterior names anyway. Forwarding occurs only on those queries for which the server is not authoritative anddoes not have the answer in its cache.
forwardGrammar: forward ( first | only );Blocks: options, view, zone (forward, primary, secondary, static-stub, stub)Tags: query

Allows or disallows fallback to recursion if forwarding has failed; it is always used in conjunction with the forwarders statement.
This option is only meaningful if the forwarders list is not empty. A value of first is the default and causes theserver to query the forwarders first; if that does not answer the question, the server then looks for the answer itself.
If only is specified, the server only queries the forwarders.
forwarders
Grammar: forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };Blocks: options, view, zone (forward, primary, secondary, static-stub, stub)Tags: query

Defines one or more hosts to which queries are forwarded.
This specifies a list of IP addresses to which queries are forwarded. The default is the empty list (no forwarding).
Each address in the list can be associated with an optional port number and a TLS transport. A default port number
and a TLS transport can be set for the entire list.
If a TLS configuration is specified, named will use DNS-over-TLS (DoT) connections when connecting to thespecified IP address(es), using the TLS configuration referenced by the tls statement.
Forwarding can also be configured on a per-domain basis, allowing for the global forwarding options to be overridden in avariety of ways. Particular domains can be set to use different forwarders, or have a different forward only/first
behavior, or not forward at all; see zone.
Dual-stack Servers
Dual-stack servers are used as servers of last resort, to work around problems in reachability due to the lack of support
for either IPv4 or IPv6 on the host machine.
dual-stack-servers
Grammar: dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port
<integer> ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port
<integer> ] ); ... };Blocks: options, viewTags: server

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Specifies host names or addresses of machines with access to both IPv4 and IPv6 transports.
This specifies host names or addresses of machines with access to both IPv4 and IPv6 transports. If a hostname isused, the server must be able to resolve the name using only the transport it has. If the machine is dual-stacked, thedual-stack-servers parameter has no effect unless access to a transport has been disabled on the commandline (e.g., named -4).
Access Control
Access to the server can be restricted based on the IP address of the requesting system. See Address Match Lists for details
on how to specify IP address lists.
allow-notify
Grammar: allow-notify { <address_match_element>; ... };Blocks: options, view, zone (mirror, secondary)Tags: transfer

Defines an address_match_list that is allowed to send NOTIFY messages for the zone, in addition to addresses defined in the primaries option for the zone.
This ACL specifies which hosts may send NOTIFY messages to inform this server of changes to zones for which itis acting as a secondary server. This is only applicable for secondary zones (i.e., type secondary or slave).
If this option is set in view or options, it is globally applied to all secondary zones. If set in the zone statement,
the global value is overridden.
If not specified, the default is to process NOTIFY messages only from the configured primaries for the zone.
allow-notify can be used to expand the list of permitted hosts, not to reduce it.
allow-proxyWarning: This option is experimental and subject to change.
Grammar: allow-proxy { <address_match_element>; ... }; // experimental
Blocks: options, viewTags: server

Defines an address_match_list for the client addresses allowed to send PROXYv2 headers.
The default address_match_list is none, which means that no client is allowed to do that by default for
security reasons, as the PROXYv2 protocol provides an easy way to spoof both source and destination addresses.
This address_match_list is primarily meant to have addresses and subnets of the proxies that are allowed
to send PROXYv2 headers to BIND. In most cases, we do not recommend setting this address_match_list
to be very allowing, in particular, to set it to any, especially in the cases when PROXYv2 headers can be acceptedon publically available networking interfaces.
The specified option is the only option that matches against real peer addresses when PROXYv2 headers are used.
Most of the options that work with peer addresses, use the ones extracted from PROXYv2 headers.
Also, see: allow-proxy-on

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allow-proxy-on

Warning: This option is experimental and subject to change.
Grammar: allow-proxy-on { <address_match_element>; ... }; // experimental
Blocks: options, viewTags: server

Defines an address_match_list for the interface addresses allowed to accept PROXYv2 headers. The option
is mostly intended for multi-homed configurations.
The default address_match_list is any, which means that accepting PROXYv2 is allowed on any interface.
The option is useful in cases when you need to have precise control over which interfaces PROXYv2 is allowed,
as it is the only one that matches against real interface addresses when PROXYv2 headers are used. Most of theoptions that work with interface addresses will use the ones extracted from PROXYv2 headers.
You may want to set allow-proxy first.
allow-query
Grammar: allow-query { <address_match_element>; ... };Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)Tags: query

Specifies which hosts (an IP address list) are allowed to send queries to this resolver.
allow-query may also be specified in the zone statement, in which case it overrides the options
allow-query statement. If not specified, the default is to allow queries from all hosts.
Note: allow-query-cache is used to specify access to the cache.
allow-query-on
Grammar: allow-query-on { <address_match_element>; ... };Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)Tags: query

Specifies which local addresses (an IP address list) are allowed to send queries to this resolver. Used in multi-homed
configurations.
This makes it possible, for instance, to allow queries on internal-facing interfaces but disallow them on externalfacing ones, without necessarily knowing the internal network’s addresses.
Note that allow-query-on is only checked for queries that are permitted by allow-query. A query mustbe allowed by both ACLs, or it is refused.
allow-query-on may also be specified in the zone statement, in which case it overrides the options
allow-query-on statement.
If not specified, the default is to allow queries on all addresses.

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Note: allow-query-cache is used to specify access to the cache.
allow-query-cache
Grammar: allow-query-cache { <address_match_element>; ... };Blocks: options, viewTags: query

Specifies which hosts (an IP address list) can access this server’s cache and thus effectively controls recursion.
Defines an address_match_list of IP address(es) which are allowed to issue queries that access the local cache.
Without access to the local cache recursive queries are effectively useless so, in effect, this statement (or its default)
controls recursive behavior. This statement’s default setting depends on:
1. If recursion no; present, defaults to allow-query-cache {none;};. No local cache accesspermitted.
2. If recursion
yes; (default) then, if allow-recursion present, defaults to the valueof allow-recursion.
Local cache access permitted to the same address_match_list as
allow-recursion.
3. If recursion
yes; (default) then, if allow-recursion is not present, defaults toallow-query-cache {localnets; localhost;};. Local cache access permitted to address_match_list localnets and localhost IP addresses only.
allow-query-cache-on
Grammar: allow-query-cache-on { <address_match_element>; ... };Blocks: options, viewTags: query

Specifies which hosts (an IP address list) can access this server’s cache. Used on servers with multiple interfaces.
This specifies which local addresses can send answers from the cache. If allow-query-cache-on is not set,
then allow-recursion-on is used if set. Otherwise, the default is to allow cache responses to be sent fromany address. Note: both allow-query-cache and allow-query-cache-on must be satisfied before acache response can be sent; a client that is blocked by one cannot be allowed by the other.
allow-recursion
Grammar: allow-recursion { <address_match_element>; ... };Blocks: options, viewTags: query

Defines an address_match_list of clients that are allowed to perform recursive queries.
This specifies which hosts are allowed to make recursive queries through this server. BIND checks to see if the following parameters are set, in order: allow-query-cache and allow-query. If neither of those parameters
is set, the default (localnets; localhost;) is used.

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allow-recursion-on
Grammar: allow-recursion-on { <address_match_element>; ... };Blocks: options, viewTags: query, server

Specifies which local addresses can accept recursive queries.
This specifies which local addresses can accept recursive queries. If allow-recursion-on is not set, thenallow-query-cache-on is used if set; otherwise, the default is to allow recursive queries on all addresses.
Any client permitted to send recursive queries can send them to any address on which named is listening. Note:
both allow-recursion and allow-recursion-on must be satisfied before recursion is allowed; a clientthat is blocked by one cannot be allowed by the other.
allow-update
Grammar: allow-update { <address_match_element>; ... };Blocks: options, view, zone (primary)Tags: transfer

Defines an address_match_list of hosts that are allowed to submit dynamic updates for primary zones.
A simple access control list. When set in the zone statement for a primary zone, this specifies which hosts areallowed to submit dynamic DNS updates to that zone. The default is to deny updates from all hosts.
Note that allowing updates based on the requestor’s IP address is insecure; see Dynamic Update Security for details.
In general, this option should only be set at the zone level. While a default value can be set at the options orview level and inherited by zones, this could lead to some zones unintentionally allowing updates.
Updates are written to the zone’s filename that is set in file.
allow-update-forwarding
Grammar: allow-update-forwarding { <address_match_element>; ... };Blocks: options, view, zone (mirror, secondary)Tags: transfer

Defines an address_match_list of hosts that are allowed to submit dynamic updates to a secondary server
for transmission to a primary.
When set in the zone statement for a secondary zone, this specifies which hosts are allowed to submit dynamic
DNS updates and have them be forwarded to the primary. The default is { none; }, which means that no update
forwarding is performed.
To enable update forwarding, specify allow-update-forwarding { any; }; in the zone statement.
Specifying values other than { none; } or { any; } is usually counterproductive; the responsibility for update
access control should rest with the primary server, not the secondary.
Note that enabling the update forwarding feature on a secondary server may expose primary servers to attacks if
they rely on insecure IP-address-based access control; see Dynamic Update Security for more details.
In general this option should only be set at the zone level. While a default value can be set at the options orview level and inherited by zones, this can lead to some zones unintentionally forwarding updates.

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allow-transfer
Grammar: allow-transfer [ port
<address_match_element>; ... };<integer>][transport<string>]{

Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Defines an address_match_list of hosts that are allowed to transfer the zone information from this server.
This specifies which hosts are allowed to receive zone transfers from the server. allow-transfer may also be
specified in the zone statement, in which case it overrides the allow-transfer statement set in options
or view.
The transport level limitations can also be specified. In particular, zone transfers can be restricted to a specific port
and/or DNS transport protocol by using the options port and transport. Either option can be specified; if bothare used, both constraints must be satisfied in order for the transfer to be allowed. Zone transfers are currently only
possible via the TCP and TLS transports.
For example: allow-transfer port 853 transport tls { any; }; allows outgoing zone transfers
to any host using the TLS transport over port 853.
If allow-transfer is not specified, then the default is none; outgoing zone transfers are disabled.
Warning: Please note that incoming TLS connections are not authenticated at the TLS level by default. Please
use TSIG to authenticate requestors or consider implementing Mutual TLS authentication.
blackhole
Grammar: blackhole { <address_match_element>; ... };Blocks: options
Tags: query

Defines an address_match_list of hosts to ignore. The server will neither respond to queries from nor send
queries to these addresses.
This specifies a list of addresses which the server does not accept queries from or use to resolve a query. Queries
from these addresses are not responded to. The default is none.
no-case-compress
Grammar: no-case-compress { <address_match_element>; ... };Blocks: options, viewTags: server

Specifies a list of addresses that require case-insensitive compression in responses.
This specifies a list of addresses which require responses to use case-insensitive compression. This ACL can beused when named needs to work with clients that do not comply with the requirement in RFC 1034 to use caseinsensitive name comparisons when checking for matching domain names.
If left undefined, the ACL defaults to none: case-sensitive compression is used for all clients. If the ACL is definedand matches a client, case is ignored when compressing domain names in DNS responses sent to that client.

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This can result in slightly smaller responses; if a response contains the names “example.com” and “example.COM”,
case-insensitive compression treats the second one as a duplicate. It also ensures that the case of the query nameexactly matches the case of the owner names of returned records, rather than matches the case of the records
entered in the zone file. This allows responses to exactly match the query, which is required by some clients due toincorrect use of case-sensitive comparisons.
Case-insensitive compression is always used in AXFR and IXFR responses, regardless of whether the client matches
this ACL.
There are circumstances in which named does not preserve the case of owner names of records: if a zone
file defines records of different types with the same name, but the capitalization of the name is different (e.g.,“www.example.com/A” and “WWW.EXAMPLE.COM/AAAA”), then all responses for that name use the firstversion of the name that was used in the zone file. This limitation may be addressed in a future release. However,domain names specified in the rdata of resource records (i.e., records of type NS, MX, CNAME, etc.) always havetheir case preserved unless the client matches this ACL.
resolver-query-timeout
Grammar: resolver-query-timeout <integer>;
Blocks: options, viewTags: query

Specifies the length of time, in milliseconds, that a resolver attempts to resolve a recursive query before failing.
This is the amount of time in milliseconds that the resolver spends attempting to resolve a recursive query before
failing. The default and minimum is 10000 and the maximum is 30000. Setting it to 0 results in the default
being used.
This value was originally specified in seconds. Values less than or equal to 300 are treated as seconds and converted
to milliseconds before applying the above limits.
Interfaces
The interfaces, ports, and protocols that the server can use to answer queries may be specified using the listen-on
and listen-on-v6 options.
listen-on
Grammar: listen-on [ port <integer> ] [ proxy <string> ] [ tls <string> ][ http <string> ] { <address_match_element>; ... }; // may occur multiple
times
Blocks: options
Tags: server

Specifies the IPv4 addresses on which a server listens for DNS queries.
listen-on-v6
Grammar: listen-on-v6 [ port <integer> ] [ proxy <string> ] [ tls <string>] [ http <string> ] { <address_match_element>; ... }; // may occur multiple
times
Blocks: options
Tags: server

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Specifies the IPv6 addresses on which a server listens for DNS queries.
The listen-on and listen-on-v6 statements can each take an optional port, PROXYv2 support switch,
TLS configuration identifier, and/or HTTP configuration identifier, in addition to an address_match_list.
The address_match_list in listen-on specifies the IPv4 addresses on which the server will listen. (IPv6 addresses are ignored, with a logged warning.) The server listens on all interfaces allowed by the address match list.
If no listen-on is specified, the default is to listen for standard DNS queries on port 53 of all IPv4 interfaces.
listen-on-v6 takes an address_match_list of IPv6 addresses. The server listens on all interfaces allowed by
the address match list. If no listen-on-v6 is specified, the default is to listen for standard DNS queries on
port 53 of all IPv6 interfaces.
When specified, the PROXYv2 support switch proxy allows enabling the PROXYv2 protocol support. The
PROXYv2 protocol provides the means for passing connection information, such as a client’s source and destination
addresses and ports, across multiple layers of NAT or TCP/UDP proxies to back-end servers. The addresses passed
to by the PROXYv2 protocol are then used instead of the peer and interface addresses provided by the operating
system.
The proxy switch can have the following values:• plain - accept plain PROXYv2 headers. It is the only valid option for transports that do not employ encryption. In the case of transports that employ encryption, it instructs BIND that PROXYv2 headers are sent
without encryption before the TLS handshake. In that case, only PROXYv2 headers are not encrypted.
• encrypted - accept encrypted PROXYv2 headers. In the case of transports that employ encryption, it
instructs BIND that PROXYv2 headers are sent encrypted immediately after the TLS handshake. The option
is valid only for the transports that employ encryption.
You must consult your proxying front-end software documentation to decide which value you need to use. If in
doubt, use plain for encrypted transports, especially for DNS-over-HTTPS (DoH), but DNS-specific software is
likely to need encrypted.
It should be noted that when PROXYv2 is enabled on a listener, it loses the ability to accept regular DNS queries
without associated PROXYv2 headers.
In some cases, PROXYv2 headers might not contain usable source and destination addresses. In particular, that
happens when the headers use LOCAL command or the headers that use unspecified or unsupported by BIND
address types. If otherwise correct, such headers are accepted by BIND and the real endpoint addresses are usedin these cases.
The PROXYv2 protocol is designed to be extensible and can carry additional information in the form of typelength-values (TLVs). Many of the types are defined in the protocol specification, and for some of these, we do areasonable amount of validation in order to detect and reject ill-formed or hand-crafted headers. Apart from that,
this additional data, while accepted, is not currently used by BIND for anything else.
By default, no client is allowed to send queries that contain PROXYv2 protocol headers, even when support for the
protocol is enabled in a listen-on statement. If you are interested in enabling the PROXYv2 protocol support,
you may also want to take a look at allow-proxy and allow-proxy-on options to adjust the corresponding
ACLs.
If a TLS configuration is specified, named will listen for DNS-over-TLS (DoT) connections, using the key andcertificate specified in the referenced tls statement. If the name ephemeral is used, an ephemeral key andcertificate created for the currently running named process will be used.
If an HTTP configuration is specified, named will listen for DNS-over-HTTPS (DoH) connections using the HTTP
endpoint specified in the referenced http statement. If the name default is used, then named will listen forconnections at the default endpoint, /dns-query.

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Use of an http specification requires tls to be specified as well. If an unencrypted connection is desired (forexample, on load-sharing servers behind a reverse proxy), tls none may be used.
If a port number is not specified, the default is 53 for standard DNS, 853 for DNS over TLS, 443 for DNS
over HTTPS, and 80 for DNS over HTTP (unencrypted). These defaults may be overridden using the port,
tls-port, https-port, and http-port options.
Multiple listen-on statements are allowed. For example:
listen-on { 5.6.7.8; };listen-on port 1234 { !1.2.3.4; 1.2/16; };listen-on port 8853 tls ephemeral { 4.3.2.1; };listen-on port 8453 tls ephemeral http myserver { 8.7.6.5; };listen-on port 5300 proxy plain { !1.2.3.4; 1.2/16; };listen-on port 8953 proxy encrypted tls ephemeral { 4.3.2.1; };listen-on port 8553 proxy plain tls ephemeral http myserver { 8.7.6.5; };The first two lines instruct the name server to listen for standard DNS queries on port 53 of the IP address 5.6.7.8
and on port 1234 of an address on the machine in net 1.2 that is not 1.2.3.4. The third line instructs the server tolisten for DNS-over-TLS connections on port 8853 of the IP address 4.3.2.1 using the ephemeral key and certifcate.
The fourth line enables DNS-over-HTTPS connections on port 8453 of address 8.7.6.5, using the ephemeral key
and certificate, and the HTTP endpoint or endpoints configured in an http statement with the name myserver.
Multiple listen-on-v6 options can be used. For example:
listen-on-v6 { any; };listen-on-v6 port 1234 { !2001:db8::/32; any; };listen-on-v6 port 8853 tls example-tls { 2001:db8::100; };listen-on-v6 port 8453 tls example-tls http default { 2001:db8::100; };listen-on-v6 port 8000 tls none http myserver { 2001:db8::100; };listen-on-v6 port 53000 proxy plain { !2001:db8::/32; any; };listen-on-v6 port 8953 proxy encrypted tls example-tls { 2001:db8::100; };listen-on-v6 port 8553 proxy plain tls example-tls http default { 2001:db8::100; },→;The first two lines instruct the name server to listen for standard DNS queries on port 53 of any IPv6 addresses, andon port 1234 of IPv6 addresses that are not in the prefix 2001:db8::/32. The third line instructs the server to listen
for for DNS-over-TLS connections on port 8853 of the address 2001:db8::100, using a TLS key and certificate
specified in the a tls statement with the name example-tls. The fourth instructs the server to listen for DNSover-HTTPS connections, again using example-tls, on the default HTTP endpoint. The fifth line, in which
the tls parameter is set to none, instructs the server to listen for unencrypted DNS queries over HTTP at theendpoint specified in myserver..
To instruct the server not to listen on any IPv6 addresses, use:
listen-on-v6 { none; };Query Address
query-source
Grammar: query-source [ address ] ( <ipv4_address> | * );Blocks: options, server, view, view.server
Tags: query

Controls the IPv4 address from which queries are issued.
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query-source-v6
Grammar: query-source-v6 [ address ] ( <ipv6_address> | * );Blocks: options, server, view, view.server
Tags: query

Controls the IPv6 address from which queries are issued.
If the server does not know the answer to a question, it queries other name servers. query-source specifies
the address and port used for such queries. For queries sent over IPv6, there is a separate query-source-v6
option. If address is * (asterisk) or is omitted, a wildcard IP address (INADDR_ANY) is used.
The defaults of the query-source and query-source-v6 options are:query-source address * port *;query-source-v6 address * port *;Note: port configuration is deprecated. A warning will be logged when this parameter is used.

Note: The address specified in the query-source option is used for both UDP and TCP queries, but the port
applies only to UDP queries. TCP queries always use a random unprivileged port.
use-v4-udp-ports

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: use-v4-udp-ports { <portrange>; ... }; // deprecated
Blocks: options
Tags: deprecatedSpecifies a list of ports that are valid sources for UDP/IPv4 messages.
use-v6-udp-ports

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: use-v6-udp-ports { <portrange>; ... }; // deprecated
Blocks: options
Tags: deprecatedSpecifies a list of ports that are valid sources for UDP/IPv6 messages.
These statements, which are deprecated and will be removed in a future release, specify a list of IPv4 and IPv6
UDP ports that are used as source ports for UDP messages.

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If port is * or is omitted, a random port number from a pre-configured range is selected and used for each query.
The port range(s) are specified in the use-v4-udp-ports (for IPv4) and use-v6-udp-ports (for IPv6)
options.
If use-v4-udp-ports or use-v6-udp-ports is unspecified, named checks whether the operating systemprovides a programming interface to retrieve the system’s default range for ephemeral ports. If such an interface isavailable, named uses the corresponding system default range; otherwise, it uses its own defaults:
use-v4-udp-ports { range 1024 65535; };use-v6-udp-ports { range 1024 65535; };avoid-v4-udp-ports

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: avoid-v4-udp-ports { <portrange>; ... }; // deprecated
Blocks: options
Tags: deprecatedSpecifies the range(s) of ports to be excluded from use as sources for UDP/IPv4 messages.
avoid-v6-udp-ports

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: avoid-v6-udp-ports { <portrange>; ... }; // deprecated
Blocks: options
Tags: deprecatedSpecifies the range(s) of ports to be excluded from use as sources for UDP/IPv6 messages.
These statements, which are deprecated and will be removed in a future release, specific ranges of port numbers
to exclude from those specified in the avoid-v4-udp-ports and avoid-v6-udp-ports options, respectively.
The defaults of the avoid-v4-udp-ports and avoid-v6-udp-ports options are:avoid-v4-udp-ports {};avoid-v6-udp-ports {};For example, with the following configuration:use-v6-udp-ports { range 32768 65535; };avoid-v6-udp-ports { 40000; range 50000 60000; };UDP ports of IPv6 messages sent from named are in one of the following ranges: 32768 to 39999, 40001 to
49999, or 60001 to 65535.
avoid-v4-udp-ports and avoid-v6-udp-ports can be used to prevent named from choosing as its
random source port a port that is blocked by a firewall or that is used by other applications; if a query went out

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with a source port blocked by a firewall, the answer would not pass through the firewall and the name server
would have to query again. Note: the desired range can also be represented only with use-v4-udp-ports anduse-v6-udp-ports, and the avoid- options are redundant in that sense; they are provided for backward
compatibility and to possibly simplify the port specification.
Note: Make sure the ranges are sufficiently large for security. A desirable size depends on several parameters, but
we generally recommend it contain at least 16384 ports (14 bits of entropy). Note also that the system’s default range
when used may be too small for this purpose, and that the range may even be changed while named is running; thenew range is automatically applied when named is reloaded. Explicit configuration of use-v4-udp-ports
and use-v6-udp-ports is encouraged, so that the ranges are sufficiently large and are reasonably independent
from the ranges used by other applications.

Note: The operational configuration where named runs may prohibit the use of some ports. For example, Unix
systems do not allow named, if run without root privilege, to use ports less than 1024. If such ports are includedin the specified (or detected) set of query ports, the corresponding query attempts will fail, resulting in resolution
failures or delay. It is therefore important to configure the set of ports that can be safely used in the expected
operational environment.

Warning: Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

Warning: The configured port must not be the same as the listening port.

Note: See also transfer-source, notify-source and parental-source.

Zone Transfers
BIND has mechanisms in place to facilitate zone transfers and set limits on the amount of load that transfers place on thesystem. The following options apply to zone transfers.
also-notify
Grammar: also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [tls <string> ]; ... };Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Defines one or more hosts that are sent NOTIFY messages when zone changes occur.
This option defines a global list of IP addresses of name servers that are also sent NOTIFY messages whenevera fresh copy of the zone is loaded, in addition to the servers listed in the zone’s NS records. This helps to ensure that copies of the zones quickly converge on stealth servers. Optionally, a port may be specified with eachalso-notify address to send the notify messages to a port other than the default of 53. An optional TSIG key

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can also be specified with each address to cause the notify messages to be signed; this can be useful when sending
notifies to multiple views. In place of explicit addresses, one or more named primaries lists can be used.
If an also-notify list is given in a zone statement, it overrides the options also-notify statement.
When a zone notify statement is set to no, the IP addresses in the global also-notify list are not sent
NOTIFY messages for that zone. The default is the empty list (no global notification list).
max-transfer-time-in
Grammar: max-transfer-time-in <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Specifies the number of minutes after which inbound zone transfers are terminated.
Inbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2 hours).
The maximum value is 28 days (40320 minutes).
max-transfer-idle-inGrammar: max-transfer-idle-in <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Specifies the number of minutes after which inbound zone transfers making no progress are terminated.
Inbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1 hour).
The maximum value is 28 days (40320 minutes).
Note:
The inbound zone transfers are also affected by tcp-idle-timeout, themax-transfer-idle-in will close the inbound zone transfer if there was no complete AXFR or nocomplete IXFR chunk. The tcp-idle-timeout will close the connection if there’s no progress on the TCPlevel.
max-transfer-time-out
Grammar: max-transfer-time-out <integer>;
Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Specifies the number of minutes after which outbound zone transfers are terminated.
Outbound zone transfers running longer than this many minutes are terminated. The default is 120 minutes (2hours). The maximum value is 28 days (40320 minutes).
max-transfer-idle-out
Grammar: max-transfer-idle-out <integer>;
Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

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Specifies the number of minutes after which outbound zone transfers making no progress are terminated.
Outbound zone transfers making no progress in this many minutes are terminated. The default is 60 minutes (1hour). The maximum value is 28 days (40320 minutes).
notify-rate
Grammar: notify-rate <integer>;
Blocks: options
Tags: zone, transfer

Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.
This specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations. (NOTIFY
requests due to initial zone loading are subject to a separate rate limit; see below.) The default is 20 per second.
The lowest possible rate is one per second; when set to zero, it is silently raised to one.
startup-notify-rate
Grammar: startup-notify-rate <integer>;
Blocks: options
Tags: zone, transfer

Specifies the rate at which NOTIFY requests are sent when the name server is first starting, or when new zones
have been added.
This is the rate at which NOTIFY requests are sent when the name server is first starting up, or when zones havebeen newly added to the name server. The default is 20 per second. The lowest possible rate is one per second;
when set to zero, it is silently raised to one.
serial-query-rate
Grammar: serial-query-rate <integer>;
Blocks: options
Tags: transfer

Defines an upper limit on the number of queries per second issued by the server, when querying the SOA RRs usedfor zone transfers.
Secondary servers periodically query primary servers to find out if zone serial numbers have changed. Each such
query uses a minute amount of the secondary server’s network bandwidth. To limit the amount of bandwidth used,
BIND 9 limits the rate at which queries are sent. The value of the serial-query-rate option, an integer, isthe maximum number of queries sent per second. The default is 20 per second. The lowest possible rate is one persecond; when set to zero, it is silently raised to one.
transfer-format
Grammar: transfer-format ( many-answers | one-answer );Blocks: options, server, view, view.server
Tags: transfer

Controls whether multiple records can be packed into a message during zone transfers.

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Zone transfers can be sent using two different formats, one-answer and many-answers.
The
transfer-format option is used on the primary server to determine which format it sends. one-answer
uses one DNS message per resource record transferred. many-answers packs as many resource records as possible into one message. many-answers is more efficient; the default is many-answers. transfer-format
may be overridden on a per-server basis by using the server block.
transfer-message-sizeGrammar: transfer-message-size <integer>;
Blocks: options
Tags: transfer

Limits the uncompressed size of DNS messages used in zone transfers over TCP.
This is an upper bound on the uncompressed size of DNS messages used in zone transfers over TCP. If a message
grows larger than this size, additional messages are used to complete the zone transfer. (Note, however, that this isa hint, not a hard limit; if a message contains a single resource record whose RDATA does not fit within the size
limit, a larger message will be permitted so the record can be transferred.)
Valid values are between 512 and 65535 octets; any values outside that range are adjusted to the nearest value
within it. The default is 20480, which was selected to improve message compression; most DNS messages of thissize will compress to less than 16536 bytes. Larger messages cannot be compressed as effectively, because 16536
is the largest permissible compression offset pointer in a DNS message.
This option is mainly intended for server testing; there is rarely any benefit in setting a value other than the default.
transfers-in
Grammar: transfers-in <integer>;
Blocks: options
Tags: transfer

Limits the number of concurrent inbound zone transfers.
This is the maximum number of inbound zone transfers that can run concurrently. The default value is 10. Increasing transfers-in may speed up the convergence of secondary zones, but it also may increase the load on
the local system.
transfers-out
Grammar: transfers-out <integer>;
Blocks: options
Tags: transfer

Limits the number of concurrent outbound zone transfers.
This is the maximum number of outbound zone transfers that can run concurrently. Zone transfer requests in excessof the limit are refused. The default value is 10.
transfers-per-ns
Grammar: transfers-per-ns <integer>;
Blocks: options
Tags: transfer

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Limits the number of concurrent inbound zone transfers from a remote server.
This is the maximum number of inbound zone transfers that can concurrently transfer from a given remote nameserver. The default value is 2. Increasing transfers-per-ns may speed up the convergence of secondary
zones, but it also may increase the load on the remote name server. transfers-per-ns may be overridden ona per-server basis by using the transfers phrase of the server statement.
transfer-source
Grammar: transfer-source ( <ipv4_address> | * );Blocks: options, server, view, zone (mirror, secondary, stub), view.server
Tags: transfer

Defines which local IPv4 address(es) are bound to TCP connections used to fetch zones transferred inbound by theserver.
transfer-source determines which local address is bound to IPv4 TCP connections used to fetch zones
transferred inbound by the server. It also determines the source IPv4 address, and optionally the UDP port,
used for the refresh queries and forwarded dynamic updates. If not set, it defaults to a system-controlled value
which is usually the address of the interface “closest to” the remote end. This address must appear in the remote end’s allow-transfer option for the zone being transferred, if one is specified. This statement sets
the transfer-source for all zones, but can be overridden on a per-view or per-zone basis by including atransfer-source statement within the view or zone block in the configuration file.
Note: port configuration is deprecated. A warning will be logged when this parameter is used.

Warning: Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

Warning: The configured port must not be the same as the listening port.
transfer-source-v6
Grammar: transfer-source-v6 ( <ipv6_address> | * );Blocks: options, server, view, zone (mirror, secondary, stub), view.server
Tags: transfer

Defines which local IPv6 address(es) are bound to TCP connections used to fetch zones transferred inbound by theserver.
This option is the same as transfer-source, except zone transfers are performed using IPv6.
notify-source
Grammar: notify-source ( <ipv4_address> | * );Blocks: options, server, view, zone (mirror, primary, secondary), view.server
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Defines the IPv4 address (and optional port) to be used for outgoing NOTIFY messages.
notify-source determines which local source address, and optionally UDP port, is used to send NOTIFY
messages. This address must appear in the secondary server’s primaries zone clause or in an allow-notify
clause. This statement sets the notify-source for all zones, but can be overridden on a per-zone or per-viewbasis by including a notify-source statement within the zone or view block in the configuration file.
Note: port configuration is deprecated. A warning will be logged when this parameter is used.

Warning: Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

Warning: The configured port must not be the same as the listening port.
notify-source-v6
Grammar: notify-source-v6 ( <ipv6_address> | * );Blocks: options, server, view, zone (mirror, primary, secondary), view.server
Tags: transfer

Defines the IPv6 address (and optional port) to be used for outgoing NOTIFY messages.
This option acts like notify-source, but applies to NOTIFY messages sent to IPv6 addresses.
Server Resource Limits
The following options set limits on the server’s resource consumption that are enforced internally by the server rather thanby the operating system.
max-journal-sizeGrammar: max-journal-size ( default | unlimited | <sizeval> );Blocks: options, view, zone (mirror, primary, secondary)Tags: transfer

Controls the size of journal files.
This sets a maximum size for each journal file (see The Journal File), expressed in bytes or, if followed by anoptional unit suffix (‘k’, ‘m’, or ‘g’), in kilobytes, megabytes, or gigabytes. When the journal file approaches the
specified size, some of the oldest transactions in the journal are automatically removed. The largest permitted
value is 2 gigabytes. Very small values are rounded up to 4096 bytes. It is possible to specify unlimited, which
also means 2 gigabytes. If the limit is set to default or left unset, the journal is allowed to grow up to twice aslarge as the zone. (There is little benefit in storing larger journals.)This option may also be set on a per-zone basis.
max-records
Grammar: max-records <integer>;
Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)

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Tags: server, zone

Sets the maximum number of records permitted in a zone.
This sets the maximum number of records permitted in a zone. The default is zero, which means the maximum isunlimited.
max-records-per-type
Grammar: max-records-per-type <integer>;
Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)Tags: server

Sets the maximum number of records that can be stored in an RRset
This sets the maximum number of resource records that can be stored in an RRset in a database. When configured
in options or view, it controls the cache database; it also sets the default value for zone databases, which can
be overridden by setting it at the zone level.
If set to a positive value, any attempt to cache or to add to a zone an RRset with more than the specified numberof records will result in a failure. If set to 0, there is no cap on RRset size. The default is 100.
max-types-per-nameGrammar: max-types-per-name <integer>;
Blocks: options, view, zone (mirror, primary, redirect, secondary, static-stub, stub)Tags: server

Sets the maximum number of RR types that can be stored for an owner name
This sets the maximum number of resource record types that can be stored for a single owner name in a database.
When configured in options or view, it controls the cache database and sets the default value for zone databases,
which can be overridden by setting it at the zone level.
An RR type and its corresponding signature are counted as two types. So, for example, a signed node containing
A and AAAA records has four types: A, RRSIG(A), AAAA, and RRSIG(AAAA).
The behavior is slightly different for zone and cache databases:
In a zone, if max-types-per-name is set to a positive number, any attempt to add a new resource record set
to a name that already has the specified number of types will fail.
In a cache, if max-types-per-name is set to a positive number, an attempt to add a new resource record set toa name that already has the specified number of types will temporarily succeed so that the query can be answered.
However, the newly added RRset will immediately be purged.
Certain high-priority types, including SOA, CNAME, DNSKEY, and their corresponding signatures, are always
cached. If max-types-per-name is set to a very low value, then it may be ignored to allow high-priority types
to be cached.
When max-types-per-name is set to 0, there is no cap on the number of RR types. The default is 100.
recursive-clients
Grammar: recursive-clients <integer>;
Blocks: options
Tags: query
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Specifies the maximum number of concurrent recursive queries the server can perform.
This sets the maximum number (a “hard quota”) of simultaneous recursive lookups the server performs on behalf ofclients. The default is 1000. Because each recursing client uses a fair bit of memory (on the order of 20 kilobytes),
the value of the recursive-clients option may have to be decreased on hosts with limited memory.
recursive-clients defines a “hard quota” limit for pending recursive clients; when more clients than thisare pending, new incoming requests are not accepted, and for each incoming request a previous pending request is
dropped.
A “soft quota” is also set. When this lower quota is exceeded, incoming requests are accepted, but for eachone, a pending request is dropped. If recursive-clients is greater than 1000, the soft quota is set torecursive-clients minus 100; otherwise it is set to 90% of recursive-clients.
tcp-clients
Grammar: tcp-clients <integer>;
Blocks: options
Tags: server

Specifies the maximum number of simultaneous client TCP connections accepted by the server.
This is the maximum number of simultaneous client TCP connections that the server accepts. The default is 150.
clients-per-query
Grammar: clients-per-query <integer>;
Blocks: options, viewTags: server

Sets the initial minimum number of simultaneous recursive clients accepted by the server for any given query before
the server drops additional clients.
This sets the initial value (minimum) number of simultaneous recursive clients for any given query(<qname,qtype,qclass>) that the server accepts before dropping additional clents. named attempts to self-tune
this value and changes are logged. The default value is 10.
The chosen value should reflect how many queries come in for a given name in the time it takes to resolve thatname.
max-clients-per-query
Grammar: max-clients-per-query <integer>;
Blocks: options, viewTags: server

Sets the maximum number of simultaneous recursive clients accepted by the server for any given query before theserver drops additional clients.
This sets the maximum number of simultaneous recursive clients for any given query (<qname,qtype,qclass>) thatthe server accepts before dropping additional clients.

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If the number of queries exceeds clients-per-query, named assumes that it is dealing with a non-responsivezone and drops additional queries. If it gets a response after dropping queries, it raises the estimate, up to a limitof max-clients-per-query. The estimate is then lowered after 20 minutes if it has remained unchanged.
If max-clients-per-query is set to zero, there is no upper bound, other than that imposed byrecursive-clients. If clients-per-query is set to zero, max-clients-per-query no longer
applies and there is no upper bound, other than that imposed by recursive-clients.
max-validations-per-fetch

Warning: This option is experimental and subject to change.
Grammar: max-validations-per-fetch <integer>; // experimental
Blocks: options, viewTags: server

Set the maximum number of DNSSEC validations that can happen in single fetch
This is an experimental setting to set the maximum number of DNSSEC validations that can happen in a single
resolver fetch. The default is 16.
max-validation-failures-per-fetch

Warning: This option is experimental and subject to change.
Grammar: max-validation-failures-per-fetch <integer>; // experimental
Blocks: options, viewTags: server

Set the maximum number of DNSSEC validation failures that can happen in single fetch
This is an experimental setting to set the maximum number of DNSSEC validation failures that can happen in asingle resolver fetch. The default is 1.
fetches-per-zone
Grammar: fetches-per-zone <integer> [ ( drop | fail ) ];Blocks: options, viewTags: query, server

Sets the maximum number of simultaneous iterative queries allowed to any one domain before the server blocks
new queries for data in or beneath that zone.
This sets the maximum number of simultaneous iterative queries to any one domain that the server permits before
blocking new queries for data in or beneath that zone. This value should reflect how many fetches would normally besent to any one zone in the time it would take to resolve them. It should be smaller than recursive-clients.
When many clients simultaneously query for the same name and type, the clients are all attached to the same fetch,
up to the max-clients-per-query limit, and only one iterative query is sent. However, when clients are

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simultaneously querying for different names or types, multiple queries are sent and max-clients-per-queryis not effective as a limit.
Optionally, this value may be followed by the keyword drop or fail, indicating whether queries which exceed
the fetch quota for a zone are dropped with no response, or answered with SERVFAIL. The default is drop.
If fetches-per-zone is set to zero, there is no limit on the number of fetches per query and no queries are
dropped. The default is zero.
The current list of active fetches can be dumped by running rndc recursing. The list includes the numberof active fetches for each domain and the number of queries that have been passed (allowed) or dropped (spilled)
as a result of the fetches-per-zone limit. (Note: these counters are not cumulative over time; whenever thenumber of active fetches for a domain drops to zero, the counter for that domain is deleted, and the next time afetch is sent to that domain, it is recreated with the counters set to zero.)fetches-per-server
Grammar: fetches-per-server <integer> [ ( drop | fail ) ];Blocks: options, viewTags: query, server

Sets the maximum number of simultaneous iterative queries allowed to be sent by a server to an upstream nameserver before the server blocks additional queries.
This sets the maximum number of simultaneous iterative queries that the server allows to be sent to a single upstream
name server before blocking additional queries. This value should reflect how many fetches would normally be sent
to any one server in the time it would take to resolve them. It should be smaller than recursive-clients.
Optionally, this value may be followed by the keyword drop or fail, indicating whether queries are dropped
with no response or answered with SERVFAIL, when all of the servers authoritative for a zone are found to haveexceeded the per-server quota. The default is fail.
If fetches-per-server is set to zero, there is no limit on the number of fetches per query and no queries are
dropped. The default is zero.
The fetches-per-server quota is dynamically adjusted in response to detected congestion. As queries
are sent to a server and either are answered or time out, an exponentially weighted moving average is calculatedof the ratio of timeouts to responses. If the current average timeout ratio rises above a “high” threshold, thenfetches-per-server is reduced for that server. If the timeout ratio drops below a “low” threshold, thenfetches-per-server is increased. The fetch-quota-params options can be used to adjust the parameters for this calculation.
fetch-quota-params
Grammar:fetch-quota-params<fixedpoint>;<integer><fixedpoint><fixedpoint>

Blocks: options, viewTags: query, server

Sets the parameters for dynamic resizing of the fetches-per-server quota in response to detected congestion.
This sets the parameters to use for dynamic resizing of the fetches-per-server quota in response to detected
congestion.

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The first argument is an integer value indicating how frequently to recalculate the moving average of the ratio of
timeouts to responses for each server. The default is 100, meaning that BIND recalculates the average ratio after
every 100 queries have either been answered or timed out.
The remaining three arguments represent the “low” threshold (defaulting to a timeout ratio of 0.1), the “high”
threshold (defaulting to a timeout ratio of 0.3), and the discount rate for the moving average (defaulting to 0.7).
A higher discount rate causes recent events to weigh more heavily when calculating the moving average; a lower
discount rate causes past events to weigh more heavily, smoothing out short-term blips in the timeout ratio. Thesearguments are all fixed-point numbers with precision of 1/100; at most two places after the decimal point are
significant.
max-cache-sizeGrammar: max-cache-size ( default | unlimited | <sizeval> | <percentage> );Blocks: options, viewTags: server

Sets the maximum amount of memory to use for an individual cache database and its associated metadata.
This sets the maximum amount of memory to use for an individual cache database and its associated metadata, inbytes or percentage of total physical memory. By default, each view has its own separate cache, which means thetotal amount of memory required for cache data is the sum of the cache database sizes for all views (unless theattach-cache option is used).
When the amount of data in a cache database reaches the configured limit, named starts purging non-expired
records (following an LRU-based strategy).
The default size limit for each individual cache is:• 90% of physical memory for views with recursion set to yes (the default), or• 2 MB for views with recursion set to no.
Any positive value smaller than 2 MB is ignored and reset to 2 MB. The keyword unlimited, or the value 0,
places no limit on the cache size; records are then purged from the cache only when they expire (according to their
TTLs).
Note: For configurations which define multiple views with separate caches and recursion enabled, it is recommended to set max-cache-size appropriately for each view, as using the default value of that option (90% of
physical memory for each individual cache) may lead to memory exhaustion over time.

Note: max-cache-size does not work reliably for the maximum amount of memory of 100 MB or lower.
Upon startup and reconfiguration, caches with a limited size preallocate a small amount of memory (less than 1%of max-cache-size for a given view). This preallocation serves as an optimization to eliminate extra latency
introduced by resizing internal cache structures.
On systems where detection of the amount of physical memory is not supported, percentage-based values fall backto unlimited. Note that the amount of physical memory available is only detected on startup, so named does
not adjust the cache size limits if the amount of physical memory is changed at runtime.
tcp-listen-queue
Grammar: tcp-listen-queue <integer>;
Blocks: options

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Tags: server

Sets the listen-queue depth.
This sets the listen-queue depth. The default and minimum is 10. If the kernel supports the accept filter “dataready”,
this also controls how many TCP connections are queued in kernel space waiting for some data before being passed
to accept. Non-zero values less than 10 are silently raised. A value of 0 may also be used; on most platforms thissets the listen-queue length to a system-defined default value.
tcp-initial-timeout
Grammar: tcp-initial-timeout <integer>;
Blocks: options
Tags: query, server

Sets the amount of time (in milliseconds) that the server waits on a new TCP connection for the first message fromthe client.
This sets the amount of time (in units of 100 milliseconds) that the server waits on a new TCP connection for the
first message from the client. The default is 300 (30 seconds), the minimum is 25 (2.5 seconds), and the maximum
is 1200 (two minutes). Values above the maximum or below the minimum are adjusted with a logged warning.
(Note: this value must be greater than the expected round-trip delay time; otherwise, no client will ever have enoughtime to submit a message.) This value can be updated at runtime by using rndc tcp-timeouts.
tcp-idle-timeout
Grammar: tcp-idle-timeout <integer>;
Blocks: options
Tags: query

Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the
EDNS TCP keepalive option is not in use.
This sets the amount of time (in units of 100 milliseconds) that the server waits on an idle TCP connection before
closing it, when the client is not using the EDNS TCP keepalive option. The default is 300 (30 seconds), themaximum is 1200 (two minutes), and the minimum is 1 (one-tenth of a second). Values above the maximum or
below the minimum are adjusted with a logged warning. See tcp-keepalive-timeout for clients using the
EDNS TCP keepalive option. This value can be updated at runtime by using rndc tcp-timeouts.
tcp-keepalive-timeout
Grammar: tcp-keepalive-timeout <integer>;
Blocks: options
Tags: query

Sets the amount of time (in milliseconds) that the server waits on an idle TCP connection before closing it, if the
EDNS TCP keepalive option is in use.
This sets the amount of time (in units of 100 milliseconds) that the server waits on an idle TCP connection before
closing it, when the client is using the EDNS TCP keepalive option. The default is 300 (30 seconds), the maximum
is 65535 (about 1.8 hours), and the minimum is 1 (one-tenth of a second). Values above the maximum or below
the minimum are adjusted with a logged warning. This value may be greater than tcp-idle-timeout because

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clients using the EDNS TCP keepalive option are expected to use TCP connections for more than one message.
This value can be updated at runtime by using rndc tcp-timeouts.
tcp-advertised-timeout
Grammar: tcp-advertised-timeout <integer>;
Blocks: options
Tags: query

Sets the timeout value (in milliseconds) that the server sends in responses containing the EDNS TCP keepalive
option.
This sets the timeout value (in units of 100 milliseconds) that the server sends in responses containing the EDNS
TCP keepalive option, which informs a client of the amount of time it may keep the session open. The default is 300 (30 seconds), the maximum is 65535 (about 1.8 hours), and the minimum is 0, which signalsthat the clients must close TCP connections immediately. Ordinarily this should be set to the same value as
tcp-keepalive-timeout. This value can be updated at runtime by using rndc tcp-timeouts.
update-quota
Grammar: update-quota <integer>;
Blocks: options
Tags: server

Specifies the maximum number of concurrent DNS UPDATE messages that can be processed by the server.
This is the maximum number of simultaneous DNS UPDATE messages that the server will accept for updating
local authoritiative zones or forwarding to a primary server. The default is 100.
sig0checks-quota

Warning: This option is experimental and subject to change.
Grammar: sig0checks-quota <integer>; // experimental
Blocks: options
Tags: server

Specifies the maximum number of concurrent SIG(0) signature checks that can be processed by the server.
This is the maximum number of simultaneous SIG(0)-signed messages that the server accepts. If the quota isreached, then named answers with a status code of REFUSED. The value of 0 disables the quota. The default is1.
sig0checks-quota-exempt

Warning: This option is experimental and subject to change.
Grammar: sig0checks-quota-exempt { <address_match_element>; ... }; // experimental

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Blocks: options
Tags: server

Exempts specific clients or client groups from SIG(0) signature checking quota.
DNS clients can be exempted from SIG(0) signature checking quota with the sig0checks-quota-exempt
clause using their IP and/or Network addresses. The default value is an empty list.
Example:sig0checks-quota-exempt {10.0.0.0/8;
2001:db8::100;};

Periodic Task Intervals
heartbeat-interval

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: heartbeat-interval <integer>; // deprecated
Blocks: options
Tags: deprecatedSets the interval at which the server performs zone maintenance tasks for all zones marked as dialup.
The server performs zone maintenance tasks for all zones marked as dialup whenever this interval expires. The
default is 60 minutes. Reasonable values are up to 1 day (1440 minutes). The maximum value is 28 days (40320
minutes). If set to 0, no zone maintenance for these zones occurs.
This option is deprecated and will be removed in a future release.
interface-interval
Grammar: interface-interval <duration>;
Blocks: options
Tags: server

Sets the interval at which the server scans the network interface list.
The server scans the network interface list every interface-interval minutes. The default is 60 minutes;
the maximum value is 28 days (40320 minutes). If set to 0, interface scanning only occurs when the configuration
file is loaded, or when automatic-interface-scan is enabled and supported by the operating system. Afterthe scan, the server begins listening for queries on any newly discovered interfaces (provided they are allowed by
the listen-on configuration), and stops listening on interfaces that have gone away. For convenience, TTL-style
time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.

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The sortlist Statement
The response to a DNS query may consist of multiple resource records (RRs) forming a resource record set (RRset). The
name server normally returns the RRs within the RRset in an indeterminate order (but see the rrset-order statement
in RRset Ordering). The client resolver code should rearrange the RRs as appropriate: that is, using any addresses on thelocal net in preference to other addresses. However, not all resolvers can do this or are correctly configured. When aclient is using a local server, the sorting can be performed in the server, based on the client’s address. This only requires
configuring the name servers, not all the clients.
sortlist

Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: sortlist { <address_match_element>; ... }; // deprecated
Blocks: options, viewTags: query, deprecatedControls the ordering of RRs returned to the client, based on the client’s IP address.
This option is deprecated and will be removed in a future release.
The sortlist statement (see below) takes an address_match_list and interprets it in a special way. Each toplevel statement in the sortlist must itself be an explicit address_match_list with one or two elements. The
first element (which may be an IP address, an IP prefix, an ACL name, or a nested address_match_list) of each
top-level list is checked against the source address of the query until a match is found. When the addresses in thefirst element overlap, the first rule to match is selected.
Once the source address of the query has been matched, if the top-level statement contains only one element, theactual primitive element that matched the source address is used to select the address in the response to move tothe beginning of the response. If the statement is a list of two elements, then the second element is interpreted asa topology preference list. Each top-level element is assigned a distance, and the address in the response with theminimum distance is moved to the beginning of the response.
In the following example, any queries received from any of the addresses of the host itself get responses preferring
addresses on any of the locally connected networks. Next most preferred are addresses on the 192.168.1/24 network, and after that either the 192.168.2/24 or 192.168.3/24 network, with no preference shown between these two
networks. Queries received from a host on the 192.168.1/24 network prefer other addresses on that network to the192.168.2/24 and 192.168.3/24 networks. Queries received from a host on the 192.168.4/24 or the 192.168.5/24
network only prefer other addresses on their directly connected networks.
sortlist {// IF the local host// THEN first fit on the following nets
{ localhost;{ localnets;
192.168.1/24;{ 192.168.2/24; 192.168.3/24; }; }; };// IF on class C 192.168.1 THEN use .1, or .2 or .3{ 192.168.1/24;{ 192.168.1/24;{ 192.168.2/24; 192.168.3/24; }; }; };// IF on class C 192.168.2 THEN use .2, or .1 or .3{ 192.168.2/24;(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page){ 192.168.2/24;{ 192.168.1/24; 192.168.3/24; }; }; };// IF on class C 192.168.3 THEN use .3, or .1 or .2{ 192.168.3/24;{ 192.168.3/24;{ 192.168.1/24; 192.168.2/24; }; }; };// IF .4 or .5 THEN prefer that net{ { 192.168.4/24; 192.168.5/24; };};};The following example illlustrates reasonable behavior for the local host and hosts on directly connected networks. Responses sent to queries from the local host favor any of the directly connected networks. Responses sent to queries fromany other hosts on a directly connected network prefer addresses on that same network. Responses to other queries are
not sorted.
sortlist {{ localhost; localnets; };{ localnets; };};RRset Ordering

Note: While alternating the order of records in a DNS response between subsequent queries is a known load distribution
technique, certain caveats apply (mostly stemming from caching) which usually make it a suboptimal choice for loadbalancing purposes when used on its own.
rrset-order
Grammar: rrset-order { [ class <string> ]<quoted_string> ] <string> <string>; ... };

[

type

<string>

]

[

name

Blocks: options, viewTags: query

Defines the order in which equal RRs (RRsets) are returned.
The rrset-order statement permits configuration of the ordering of the records in a multiple-record response.
See also: sortlist.
Each rule in an rrset-order statement is defined as follows:[class <class_name>] [type <type_name>] [name "<domain_name>"] order <ordering>

The default qualifiers for each rule are:• If no class is specified, the default is ANY.
• If no type is specified, the default is ANY.
• If no name is specified, the default is * (asterisk).
<domain_name> only matches the name itself, not any of its subdomains. To make a rule match all subdomainsof a given name, a wildcard name (*.<domain_name>) must be used. Note that *.<domain_name> does

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not match <domain_name> itself; to specify RRset ordering for a name and all of its subdomains, two separate
rules must be defined: one for <domain_name> and one for *.<domain_name>.
The legal values for <ordering> are:fixed
Records are returned in the order they are defined in the zone file.
This value is deprecated and will be removed in a future release.
Note: The fixed option is only available if BIND is configured with --enable-fixed-rrset at compile
time.

randomRecords are returned in a random order.
cyclicRecords are returned in a cyclic round-robin order, rotating by one record per query.
none
Records are returned in the order they were retrieved from the database. This order is indeterminate, but
remains consistent as long as the database is not modified.
The default RRset order used depends on whether any rrset-order statements are present in the configuration
file used by named:• If no rrset-order statement is present in the configuration file, the implicit default is to return all records
in random order.
• If any rrset-order statements are present in the configuration file, but no ordering rule specified in thesestatements matches a given RRset, the default order for that RRset is none.
Note that if multiple rrset-order statements are present in the configuration file (at both the options andview levels), they are not combined; instead, the more-specific one (view) replaces the less-specific one (options).
If multiple rules within a single rrset-order statement match a given RRset, the first matching rule is applied.
Example:rrset-order {type A name "foo.isc.org" order random;
type AAAA name "foo.isc.org" order cyclic;
name "bar.isc.org" order fixed;
name "*.bar.isc.org" order random;name "*.baz.isc.org" order cyclic;};

With the above configuration, the following RRset ordering is used:

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QNAME

QTYPE

RRset Order

foo.isc.org
foo.isc.org
foo.isc.org
sub.foo.isc.org
bar.isc.org
sub.bar.isc.org
baz.isc.org
sub.baz.isc.org

A
AAAA
TXT
all
all
all
all
all

randomcyclic
none
none
fixed
randomnone
cyclicTuninglame-ttl
Grammar: lame-ttl <duration>;
Blocks: options, viewTags: server

Sets the resolver’s lame cache.
This is always set to 0. More information is available in the security advisory for CVE-2021-25219.
servfail-ttl
Grammar: servfail-ttl <duration>;
Blocks: options, viewTags: server

Sets the length of time (in seconds) that a SERVFAIL response is cached.
This sets the number of seconds to cache a SERVFAIL response due to DNSSEC validation failure or other generalserver failure. If set to 0, SERVFAIL caching is disabled. The SERVFAIL cache is not consulted if a query has
the CD (Checking Disabled) bit set; this allows a query that failed due to DNSSEC validation to be retried without
waiting for the SERVFAIL TTL to expire.
The maximum value is 30 seconds; any higher value is silently reduced. The default is 1 second.
min-ncache-ttl
Grammar: min-ncache-ttl <duration>;
Blocks: options, viewTags: server

Specifies the minimum retention time (in seconds) for storage of negative answers in the server’s cache.
To reduce network traffic and increase performance, the server stores negative answers. min-ncache-ttl isused to set a minimum retention time for these answers in the server, in seconds. For convenience, TTL-style
time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default min-ncache-ttl is 0 seconds. min-ncache-ttl cannot exceed 90 seconds and is truncatedto 90 seconds if set to a greater value.
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min-cache-ttl
Grammar: min-cache-ttl <duration>;
Blocks: options, viewTags: server

Specifies the minimum time (in seconds) that the server caches ordinary (positive) answers.
This sets the minimum time for which the server caches ordinary (positive) answers, in seconds. For convenience,
TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default min-cache-ttl is 0 seconds. min-cache-ttl cannot exceed 90 seconds and is truncated to
90 seconds if set to a greater value.
max-ncache-ttl
Grammar: max-ncache-ttl <duration>;
Blocks: options, viewTags: server

Specifies the maximum retention time (in seconds) for storage of negative answers in the server’s cache.
To reduce network traffic and increase performance, the server stores negative answers. max-ncache-ttl isused to set a maximum retention time for these answers in the server, in seconds. For convenience, TTL-style
time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default max-ncache-ttl is 10800 seconds (3 hours). max-ncache-ttl cannot exceed 7 days and issilently truncated to 7 days if set to a greater value.
max-cache-ttl
Grammar: max-cache-ttl <duration>;
Blocks: options, viewTags: server

Specifies the maximum time (in seconds) that the server caches ordinary (positive) answers.
This sets the maximum time for which the server caches ordinary (positive) answers, in seconds. For convenience,
TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
The default max-cache-ttl is 604800 (one week). A value of zero may cause all queries to return SERVFAIL,
because of lost caches of intermediate RRsets (such as NS and glue AAAA/A records) in the resolution process.
max-stale-ttl
Grammar: max-stale-ttl <duration>;
Blocks: options, viewTags: server

Specifies the maximum time that the server retains records past their normal expiry, to return them as stale records.
If retaining stale RRsets in cache is enabled, and returning of stale cached answers is also enabled,
max-stale-ttl sets the maximum time for which the server retains records past their normal expiry to return

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them as stale records, when the servers for those records are not reachable. The default is 1 day. The minimum
allowed is 1 second; a value of 0 is updated silently to 1 second.
For stale answers to be returned, the retaining of them in cache must be enabled via the configuration option
stale-cache-enable, and returning cached answers must be enabled, either in the configuration file using
the stale-answer-enable option or by calling rndc serve-stale on.
When stale-cache-enable is set to no, setting the max-stale-ttl has no effect, the value of
max-cache-ttl will be 0 in such case.
sig-validity-interval
Grammar: sig-validity-interval <integer> [ <integer> ]; // obsolete
Blocks: options, view, zone (primary, secondary)Tags: obsolete
This option no longer has any effect.
dnskey-sig-validity
Grammar: dnskey-sig-validity <integer>; // obsolete
Blocks: options, view, zone (primary, secondary)Tags: obsolete
This option no longer has any effect.
sig-signing-nodes
Grammar: sig-signing-nodes <integer>;
Blocks: options, view, zone (primary, secondary)Tags: dnssec

Specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new
DNSKEY.
This specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new
DNSKEY. The default is 100.
sig-signing-signatures
Grammar: sig-signing-signatures <integer>;
Blocks: options, view, zone (primary, secondary)Tags: dnssec

Specifies the threshold for the number of signatures that terminates processing a quantum, when signing a zone
with a new DNSKEY.
This specifies a threshold number of signatures that terminates processing a quantum, when signing a zone with a
new DNSKEY. The default is 10.
sig-signing-type
Grammar: sig-signing-type <integer>;
Blocks: options, view, zone (primary, secondary)Tags: dnssec

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Specifies a private RDATA type to use when generating signing-state records.
This specifies a private RDATA type to be used when generating signing-state records. The default is 65534.
This parameter may be removed in a future version, once there is a standard type.
Signing-state records are used internally by named to track the current state of a zone-signing process, i.e., whether
it is still active or has been completed. The records can be inspected using the command rndc signing -list
zone. Once named has finished signing a zone with a particular key, the signing-state record associated with thatkey can be removed from the zone by running rndc signing -clear keyid/algorithm zone. To
clear all of the completed signing-state records for a zone, use rndc signing -clear all zone.
min-refresh-time
Grammar: min-refresh-time <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Limits the zone refresh interval to no more often than the specified value, in seconds.
This option controls the server’s behavior on refreshing a zone (querying for SOA changes). Usually, the SOA
refresh values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.
This option allows the administrator to set a minimum refresh time in seconds per-zone, per-view, or globally. This
option is valid for secondary and stub zones, and clamps the SOA refresh time to the specified value.
The default is 300 seconds.
max-refresh-time
Grammar: max-refresh-time <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Limits the zone refresh interval to no less often than the specified value, in seconds.
This option controls the server’s behavior on refreshing a zone (querying for SOA changes). Usually, the SOA
refresh values for the zone are used; however, these values are set by the primary, giving secondary server administrators little control over their contents.
This option allows the administrator to set a maximum refresh time in seconds per-zone, per-view, or globally.
This option is valid for secondary and stub zones, and clamps the SOA refresh time to the specified value.
The default is 2419200 seconds (4 weeks).
min-retry-time
Grammar: min-retry-time <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Limits the zone refresh retry interval to no more often than the specified value, in seconds.
This option controls the server’s behavior on retrying failed zone transfers. Usually, the SOA retry values for thezone are used; however, these values are set by the primary, giving secondary server administrators little control
over their contents.
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This option allows the administrator to set a minimum retry time in seconds per-zone, per-view, or globally. This
option is valid for secondary and stub zones, and clamps the SOA retry time to the specified value.
The default is 500 seconds.
max-retry-time
Grammar: max-retry-time <integer>;
Blocks: options, view, zone (mirror, secondary, stub)Tags: transfer

Limits the zone refresh retry interval to no less often than the specified value, in seconds.
This option controls the server’s behavior on retrying failed zone transfers. Usually, the SOA retry values for thezone are used; however, these values are set by the primary, giving secondary server administrators little control
over their contents.
This option allows the administrator to set a maximum retry time in seconds per-zone, per-view, or globally. This
option is valid for secondary and stub zones, and clamps the SOA retry time to the specified value.
The default is 1209600 seconds (2 weeks).
edns-udp-sizeGrammar: edns-udp-size <integer>;
Blocks: options, server, view, view.server
Tags: query

Sets the maximum advertised EDNS UDP buffer size to control the size of packets received from authoritative
servers in response to recursive queries.
This sets the maximum advertised EDNS UDP buffer size, in bytes, to control the size of packets received from
authoritative servers in response to recursive queries. Valid values are 512 to 4096; values outside this range aresilently adjusted to the nearest value within it. The default value is 1232.
The usual reason for setting edns-udp-size to a non-default value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or block UDP DNS packets that are greater than 512 bytes.
When named first queries a remote server, it advertises a UDP buffer size of 1232.
Query timeouts observed for any given server affect the buffer size advertised in queries sent to that server. Depending on observed packet dropping patterns, the query is retried over TCP. Per-server EDNS statistics are only
retained in memory for the lifetime of a given server’s ADB entry.
According to the measurements done by multiple parties the default value should not be causing the fragmentation
as most of the Internet “core” is able to cope with IP message sizes between 1400-1500 bytes, the 1232 size waspicked as a conservative minimal number that could be changed by the DNS operator to a estimated path MTU
minus the estimated header space. In practice, the smallest MTU witnessed in the operational DNS community is1500 octets, the Ethernet maximum payload size, so a a useful default for maximum DNS/UDP payload size on
reliable networks would be 1432.
Any server-specific edns-udp-size setting has precedence over all the above rules, i.e. configures a static value
for a given server block.
max-udp-sizeGrammar: max-udp-size <integer>;
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Tags: query

Sets the maximum EDNS UDP message size sent by named.
This sets the maximum EDNS UDP message size that named sends, in bytes. Valid values are 512 to 4096; values
outside this range are silently adjusted to the nearest value within it. The default value is 1232.
This value applies to responses sent by a server; to set the advertised buffer size in queries, see edns-udp-size.
The usual reason for setting max-udp-size to a non-default value is to allow UDP answers to pass throughbroken firewalls that block fragmented packets and/or block UDP packets that are greater than 512 bytes. This isindependent of the advertised receive buffer (edns-udp-size).
Setting this to a low value encourages additional TCP traffic to the name server.
masterfile-format
Grammar: masterfile-format ( raw | text );Blocks: options, view, zone (mirror, primary, redirect, secondary, stub)Tags: server, zone

Specifies the file format of zone files.
This specifies the file format of zone files (see Additional File Formats for details). The default value is text,
which is the standard textual representation, except for secondary zones, in which the default value is raw. Files informats other than text are typically expected to be generated by the named-compilezone tool, or dumped
by named.
Note that when a zone file in a format other than text is loaded, named may omit some of the checks which
are performed for a file in text format. For example, check-names only applies when loading zones in text
format. Zone files in raw format should be generated with the same check level as that specified in the named
configuration file.
When configured in options, this statement sets the masterfile-format for all zones, but it can be overridden on a per-zone or per-view basis by including a masterfile-format statement within the zone orview block in the configuration file.
masterfile-style
Grammar: masterfile-style ( full | relative );Blocks: options, view, zone (mirror, primary, redirect, secondary, stub)Tags: server

Specifies the format of zone files during a dump, when the masterfile-format is text.
This specifies the formatting of zone files during dump, when the masterfile-format is text. This option
is ignored with any other masterfile-format.
When set to relative, records are printed in a multi-line format, with owner names expressed relative to a sharedorigin. When set to full, records are printed in a single-line format with absolute owner names. The full format
is most suitable when a zone file needs to be processed automatically by a script. The relative format is morehuman-readable, and is thus suitable when a zone is to be edited by hand. The default is relative.

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max-recursion-depthGrammar: max-recursion-depth <integer>;
Blocks: options, viewTags: server

Sets the maximum number of levels of recursion permitted at any one time while servicing a recursive query.
This sets the maximum number of levels of recursion that are permitted at any one time while servicing a recursive
query. Resolving a name may require looking up a name server address, which in turn requires resolving anothername, etc.; if the number of recursions exceeds this value, the recursive query is terminated and returns SERVFAIL.
The default is 7.
max-recursion-queries
Grammar: max-recursion-queries <integer>;
Blocks: options, viewTags: query, server

Sets the maximum number of iterative queries while servicing a recursive query.
This sets the maximum number of iterative queries that may be sent while servicing a recursive query. If morequeries are sent, the recursive query is terminated and returns SERVFAIL. The default is 100.
notify-delay
Grammar: notify-delay <integer>;
Blocks: options, view, zone (mirror, primary, secondary)Tags: zone, transfer

Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.
This sets the delay, in seconds, between sending sets of NOTIFY messages for a zone. Whenever a NOTIFY
message is sent for a zone, a timer will be set for this duration. If the zone is updated again before the timer
expires, the NOTIFY for that update will be postponed. The default is 5 seconds.
The overall rate at which NOTIFY messages are sent for all zones is controlled by notify-rate.
max-rsa-exponent-sizeGrammar: max-rsa-exponent-size <integer>;
Blocks: options
Tags: query, dnssec

Sets the maximum RSA exponent size (in bits) when validating.
This sets the maximum RSA exponent size, in bits, that is accepted when validating. Valid values are 35 to 4096
bits. The default, zero, is also accepted and is equivalent to 4096.
prefetch
Grammar: prefetch <integer> [ <integer> ];Blocks: options, view

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Tags: query

Specifies the “trigger” time-to-live (TTL) value at which prefetch of the current query takes place.
When a query is received for cached data which is to expire shortly, named can refresh the data from the authoritative server immediately, ensuring that the cache always has an answer available.
prefetch specifies the “trigger” TTL value at which prefetch of the current query takes place; when a cacherecord with a lower or equal TTL value is encountered during query processing, it is refreshed. Valid trigger TTL
values are 1 to 10 seconds. Values larger than 10 seconds are silently reduced to 10. Setting a trigger TTL to zero
causes prefetch to be disabled. The default trigger TTL is 2.
An optional second argument specifies the “eligibility” TTL: the smallest original TTL value that is accepted for arecord to be eligible for prefetching. The eligibility TTL must be at least six seconds longer than the trigger TTL;
if not, named silently adjusts it upward. The default eligibility TTL is 9.
v6-biasGrammar: v6-bias <integer>;
Blocks: options, viewTags: query, serverIndicates the number of milliseconds of preference to give to IPv6 name servers.
When determining the next name server to try, this indicates by how many milliseconds to prefer IPv6 name servers.
The default is 50 milliseconds.
tcp-receive-buffer
Grammar: tcp-receive-buffer <integer>;
Blocks: options
Tags: server

Sets the operating system’s receive buffer size for TCP sockets.
udp-receive-buffer
Grammar: udp-receive-buffer <integer>;
Blocks: options
Tags: server

Sets the operating system’s receive buffer size for UDP sockets.
These options control the operating system’s receive buffer sizes (SO_RCVBUF) for TCP and UDP sockets, respectively. Buffering at the operating system level can prevent packet drops during brief load spikes, but if the buffer
size is set too high, a running server could get clogged with outstanding queries that have already timed out. The
default is 0, which means the operating system’s default value should be used. The minimum configurable value is4096; any nonzero value lower than that is silently raised. The maximum value is determined by the kernel, andvalues exceeding the maximum are silently reduced.

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tcp-send-buffer
Grammar: tcp-send-buffer <integer>;
Blocks: options
Tags: server

Sets the operating system’s send buffer size for TCP sockets.
udp-send-buffer
Grammar: udp-send-buffer <integer>;
Blocks: options
Tags: server

Sets the operating system’s send buffer size for UDP sockets.
These options control the operating system’s send buffer sizes (SO_SNDBUF) for TCP and UDP sockets, respectively. Buffering at the operating system level can prevent packet drops during brief load spikes, but if the buffer
size is set too high, a running server could get clogged with outstanding queries that have already timed out. The
default is 0, which means the operating system’s default value should be used. The minimum configurable value is4096; any nonzero value lower than that is silently raised. The maximum value is determined by the kernel, andvalues exceeding the maximum are silently reduced.
Built-in Server Information Zones
The server provides some helpful diagnostic information through a number of built-in zones under the pseudo-top-leveldomain bind in the CHAOS class. These zones are part of a built-in view (see view) of class CHAOS, which is separate
from the default view of class IN. Most global configuration options (allow-query, etc.) apply to this view, but someare locally overridden: notify, recursion, and allow-new-zones are always set to no, and rate-limit is
set to allow three responses per second.
To disable these zones, use the options below or hide the built-in CHAOS view by defining an explicit view of class CHAOS
that matches all clients.
versionGrammar: version ( <quoted_string> | none );Blocks: options
Tags: server

Specifies the version number of the server to return in response to a version.bind query.
This is the version the server should report via a query of the name version.bind with type TXT and class
CHAOS. The default is the real version number of this server. Specifying version none disables processing of
the queries.
Setting version to any value (including none) also disables queries for authors.bind TXT CH.
hostname
Grammar: hostname ( <quoted_string> | none );Blocks: options
Tags: server
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Specifies the hostname of the server to return in response to a hostname.bind query.
This is the hostname the server should report via a query of the name hostname.bind with type TXT and class
CHAOS. This defaults to the hostname of the machine hosting the name server, as found by the gethostname()function. The primary purpose of such queries is to identify which of a group of anycast servers is actually answering
the queries. Specifying hostname none; disables processing of the queries.
server-id
Grammar: server-id ( <quoted_string> | none | hostname );Blocks: options
Tags: server

Specifies the ID of the server to return in response to a ID.SERVER query.
This is the ID the server should report when receiving a Name Server Identifier (NSID) query, or a query of
the name ID.SERVER with type TXT and class CHAOS. The primary purpose of such queries is to identify
which of a group of anycast servers is actually answering the queries. Specifying server-id none; disables
processing of the queries. Specifying server-id hostname; causes named to use the hostname as foundby the gethostname() function. The default server-id is none.
Built-in Empty Zones
The named server has some built-in empty zones, for SOA and NS records only. These are for zones that should normallybe answered locally and for which queries should not be sent to the Internet’s root servers. The official servers that coverthese namespaces return NXDOMAIN responses to these queries. In particular, these cover the reverse namespaces foraddresses from RFC 1918, RFC 4193, RFC 5737, and RFC 6598. They also include the reverse namespace for the IPv6
local address (locally assigned), IPv6 link local addresses, the IPv6 loopback address, and the IPv6 unknown address.
The server attempts to determine if a built-in zone already exists or is active (covered by a forward-only forwarding
declaration) and does not create an empty zone if either is true.
The current list of empty zones is:• 10.IN-ADDR.ARPA• 16.172.IN-ADDR.ARPA• 17.172.IN-ADDR.ARPA• 18.172.IN-ADDR.ARPA• 19.172.IN-ADDR.ARPA• 20.172.IN-ADDR.ARPA• 21.172.IN-ADDR.ARPA• 22.172.IN-ADDR.ARPA• 23.172.IN-ADDR.ARPA• 24.172.IN-ADDR.ARPA• 25.172.IN-ADDR.ARPA• 26.172.IN-ADDR.ARPA• 27.172.IN-ADDR.ARPA

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BIND 9 Administrator Reference Manual, Release 9.20.0• 95.100.IN-ADDR.ARPA• 96.100.IN-ADDR.ARPA• 97.100.IN-ADDR.ARPA• 98.100.IN-ADDR.ARPA• 99.100.IN-ADDR.ARPA• 100.100.IN-ADDR.ARPA• 101.100.IN-ADDR.ARPA• 102.100.IN-ADDR.ARPA• 103.100.IN-ADDR.ARPA• 104.100.IN-ADDR.ARPA• 105.100.IN-ADDR.ARPA• 106.100.IN-ADDR.ARPA• 107.100.IN-ADDR.ARPA• 108.100.IN-ADDR.ARPA• 109.100.IN-ADDR.ARPA• 110.100.IN-ADDR.ARPA• 111.100.IN-ADDR.ARPA• 112.100.IN-ADDR.ARPA• 113.100.IN-ADDR.ARPA• 114.100.IN-ADDR.ARPA• 115.100.IN-ADDR.ARPA• 116.100.IN-ADDR.ARPA• 117.100.IN-ADDR.ARPA• 118.100.IN-ADDR.ARPA• 119.100.IN-ADDR.ARPA• 120.100.IN-ADDR.ARPA• 121.100.IN-ADDR.ARPA• 122.100.IN-ADDR.ARPA• 123.100.IN-ADDR.ARPA• 124.100.IN-ADDR.ARPA• 125.100.IN-ADDR.ARPA• 126.100.IN-ADDR.ARPA• 127.100.IN-ADDR.ARPA• 0.IN-ADDR.ARPA• 127.IN-ADDR.ARPA• 254.169.IN-ADDR.ARPA

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BIND 9 Administrator Reference Manual, Release 9.20.0• 2.0.192.IN-ADDR.ARPA• 100.51.198.IN-ADDR.ARPA• 113.0.203.IN-ADDR.ARPA• 255.255.255.255.IN-ADDR.ARPA• 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA• 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA• 8.B.D.0.1.0.0.2.IP6.ARPA• D.F.IP6.ARPA• 8.E.F.IP6.ARPA• 9.E.F.IP6.ARPA• A.E.F.IP6.ARPA• B.E.F.IP6.ARPA• EMPTY.AS112.ARPA• HOME.ARPA• RESOLVER.ARPA
Empty zones can be set at the view level and only apply to views of class IN. Disabled empty zones are only inherited from
options if there are no disabled empty zones specified at the view level. To override the options list of disabled zones,
disable the root zone at the view level. For example:
disable-empty-zone ".";

If using the address ranges covered here, reverse zones covering the addresses should already be in place. In practicethis appears to not be the case, with many queries being made to the infrastructure servers for names in these spaces. So
many, in fact, that sacrificial servers had to be deployed to channel the query load away from the infrastructure servers.
Note: The real parent servers for these zones should disable all empty zones under the parent zone they serve. For thereal root servers, this is all built-in empty zones. This enables them to return referrals to deeper in the tree.
empty-server
Grammar: empty-server <string>;
Blocks: options, viewTags: server, zone

Specifies the server name in the returned SOA record for empty zones.
This specifies the server name that appears in the returned SOA record for empty zones. If none is specified, thezone’s name is used.
empty-contact
Grammar: empty-contact <string>;
Blocks: options, viewTags: server, zone

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Specifies the contact name in the returned SOA record for empty zones.
This specifies the contact name that appears in the returned SOA record for empty zones. If none is specified, “.”is used.
empty-zones-enable
Grammar: empty-zones-enable <boolean>;
Blocks: options, viewTags: server, zone

Enables or disables all empty zones.
This enables or disables all empty zones. By default, they are enabled.
disable-empty-zone
Grammar: disable-empty-zone <string>; // may occur multiple times
Blocks: options, viewTags: server, zone

Disables individual empty zones.
This disables individual empty zones. By default, none are disabled. This option can be specified multiple times.
Content Filteringdeny-answer-addresses
Grammar: deny-answer-addresses{
except-from { <string>; ... } ];<address_match_element>;

...

}

[

Blocks: options, viewTags: query

Rejects A or AAAA records if the corresponding IPv4 or IPv6 addresses match a given address_match_list.
BIND 9 provides the ability to filter out responses from external DNS servers containing certain types of data in
the answer section. Specifically, it can reject address (A or AAAA) records if the corresponding IPv4 or IPv6
addresses match the given address_match_list of the deny-answer-addresses option.
In the address_match_list of the deny-answer-addresses option, only ip_address and netprefix are meaningful; any server_key is silently ignored.
deny-answer-aliases
Grammar: deny-answer-aliases { <string>; ... } [ except-from { <string>; ...
} ];Blocks: options, viewTags: query

Rejects CNAME or DNAME records if the “alias” name matches a given list of domain_name elements.

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It can also reject CNAME or DNAME records if the “alias” name (i.e., the CNAME alias or the substituted queryname due to DNAME) matches the given list of domain_name elements of the deny-answer-aliases option,
where “match” means the alias name is a subdomain of one of the listed domain names. If the optional list is specified in the except-from argument, records whose query name matches the list are accepted regardless of the filter setting. Likewise, if the alias name is a subdomain of the corresponding zone, the deny-answer-aliases
filter does not apply; for example, even if “example.com” is specified for deny-answer-aliases,
www.example.com. CNAME xxx.example.com.

returned by an “example.com” server is accepted.
If a response message is rejected due to the filtering, the entire message is discarded without being cached, and a SERVFAIL error is returned to the client.
This filtering is intended to prevent “DNS rebinding attacks,” in which an attacker, in response to a query for a domainname the attacker controls, returns an IP address within the user’s own network or an alias name within the user’s own
domain. A naive web browser or script could then serve as an unintended proxy, allowing the attacker to get accessto an internal node of the local network that could not be externally accessed otherwise. See the paper available athttps://dl.acm.org/doi/10.1145/1315245.1315298 for more details about these attacks.
For example, with a domain named “example.net” and an internal network using an IPv4 prefix 192.0.2.0/24, an administrator might specify the following rules:
deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };deny-answer-aliases { "example.net"; };If an external attacker let a web browser in the local network look up an IPv4 address of “attacker.example.com”, theattacker’s DNS server would return a response like this:
attacker.example.com. A 192.0.2.1

in the answer section. Since the rdata of this record (the IPv4 address) matches the specified prefix 192.0.2.0/24, this
response would be ignored.
On the other hand, if the browser looked up a legitimate internal web server “www.example.net” and the following
response were returned to the BIND 9 server:
www.example.net. A 192.0.2.2

it would be accepted, since the owner name “www.example.net” matches the except-from element, “example.net”.
Note that this is not really an attack on the DNS per se. In fact, there is nothing wrong with having an “external” namemapped to an “internal” IP address or domain name from the DNS point of view; it might actually be provided fora legitimate purpose, such as for debugging. As long as the mapping is provided by the correct owner, it either is notpossible or does not make sense to detect whether the intent of the mapping is legitimate within the DNS. The “rebinding”
attack must primarily be protected at the application that uses the DNS. For a large site, however, it may be difficult toprotect all possible applications at once. This filtering feature is provided only to help such an operational environment;
turning it on is generally discouraged unless there is no other choice and the attack is a real threat to applications.
Care should be particularly taken if using this option for addresses within 127.0.0.0/8. These addresses are obviously“internal,” but many applications conventionally rely on a DNS mapping from some name to such an address. Filteringout DNS records containing this address spuriously can break such applications.

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Response Policy Zone (RPZ) Rewriting
BIND 9 includes a limited mechanism to modify DNS responses for requests analogous to email anti-spam DNS rejection
lists. Responses can be changed to deny the existence of domains (NXDOMAIN), deny the existence of IP addresses fordomains (NODATA), or contain other IP addresses or data.
response-policy
Grammar: response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean>] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname | disabled | drop | given | no-op | nodata | nxdomain |passthru | tcp-only <quoted_string> ) ] [ recursive-only <boolean> ] [nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [ ede <string> ];... } [ add-soa <boolean> ] [ break-dnssec <boolean> ] [ max-policy-ttl<duration> ] [ min-update-interval <duration> ] [ min-ns-dots <integer>] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable<boolean> ] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [dnsrps-options { <unspecified-text> } ];Blocks: options, viewTags: query, server, zone, security

Specifies response policy zones for the view or among global options.
Response policy zones are named in the response-policy option for the view, or among the global options if
there is no response-policy option for the view. Response policy zones are ordinary DNS zones containing
RRsets that can be queried normally if allowed. It is usually best to restrict those queries with something likeallow-query { localhost; };.
A response-policy option can support multiple policy zones. To maximize performance, a radix tree is used
to quickly identify response policy zones containing triggers that match the current query. This imposes an upper
limit of 64 on the number of policy zones in a single response-policy option; more than that is a configuration
error.
Rules encoded in response policy zones are processed after those defined in Access Control. All queries from clients which
are not permitted access to the resolver are answered with a status code of REFUSED, regardless of configured RPZ rules.
Five policy triggers can be encoded in RPZ records.
RPZ-CLIENT-IP
IP records are triggered by the IP address of the DNS client. Client IP address triggers are encoded in records
that have owner names that are subdomains of rpz-client-ip, relativized to the policy zone origin name, andthat encode an address or address block. IPv4 addresses are represented as prefixlength.B4.B3.B2.B1.
rpz-client-ip. The IPv4 prefix length must be between 1 and 32. All four bytes - B4, B3, B2, and B1 - must
be present. B4 is the decimal value of the least significant byte of the IPv4 address as in IN-ADDR.ARPA.
IPv6 addresses are encoded in a format similar to the standard IPv6 text representation, prefixlength.W8.
W7.W6.W5.W4.W3.W2.W1.rpz-client-ip. Each of W8,…,W1 is a one- to four-digit hexadecimal number representing 16 bits of the IPv6 address as in the standard text representation of IPv6 addresses, but reversed
as in IP6.ARPA. (Note that this representation of IPv6 addresses is different from IP6.ARPA, where each hex
digit occupies a label.) All 8 words must be present except when one set of consecutive zero words is replaced with.zz., analogous to double colons (::) in standard IPv6 text encodings. The IPv6 prefix length must be between 1
and 128.
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generate the response. The owner name of a QNAME policy record is the query name relativized to the policyzone.
RPZ-IP
IP triggers are IP addresses in an A or AAAA record in the ANSWER section of a response. They are encoded
like client-IP triggers, except as subdomains of rpz-ip.
RPZ-NSDNAMENSDNAME triggers match names of authoritative servers for the query name, a parent of the query name, a
CNAME for the query name, or a parent of a CNAME. They are encoded as subdomains of rpz-nsdname,relativized to the RPZ origin name. NSIP triggers match IP addresses in A and AAAA RRsets for domains thatcan be checked against NSDNAME policy records. The nsdname-enable phrase turns NSDNAME triggers
off or on for a single policy zone or for all zones.
If authoritative name servers for the query name are not yet known, named recursively looks up the authoritative
servers for the query name before applying an RPZ-NSDNAME rule, which can cause a processing delay. To speed
up processing at the cost of precision, the nsdname-wait-recurse option can be used; when set to no, RPZNSDNAME rules are only applied when authoritative servers for the query name have already been looked up andcached. If authoritative servers for the query name are not in the cache, the RPZ-NSDNAME rule is ignored, but
the authoritative servers for the query name are looked up in the background and the rule is applied to subsequentqueries. The default is yes, meaning RPZ-NSDNAME rules are always applied, even if authoritative servers forthe query name need to be looked up first.
RPZ-NSIP
NSIP triggers match the IP addresses of authoritative servers. They are encoded like IP triggers, except as subdomains of rpz-nsip. NSDNAME and NSIP triggers are checked only for names with at least min-ns-dots
dots. The default value of min-ns-dots is 1, to exclude top-level domains. The nsip-enable phrase turns
NSIP triggers off or on for a single policy zone or for all zones.
If a name server’s IP address is not yet known, named recursively looks up the IP address before applying
an RPZ-NSIP rule, which can cause a processing delay. To speed up processing at the cost of precision, thensip-wait-recurse option can be used; when set to no, RPZ-NSIP rules are only applied when a nameserver’s IP address has already been looked up and cached. If a server’s IP address is not in the cache, the RPZNSIP rule is ignored, but the address is looked up in the background and the rule is applied to subsequent queries.
The default is yes, meaning RPZ-NSIP rules are always applied, even if an address needs to be looked up first.
The query response is checked against all response policy zones, so two or more policy records can be triggered by a
response. Because DNS responses are rewritten according to at most one policy record, a single record encoding an action(other than DISABLED actions) must be chosen. Triggers, or the records that encode them, are chosen for rewriting in
the following order:
1. Choose the triggered record in the zone that appears first in the response-policy option.
2. Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP triggers in a single zone.
3. Among NSDNAME triggers, prefer the trigger that matches the smallest name under the DNSSEC ordering.
4. Among IP or NSIP triggers, prefer the trigger with the longest prefix.
5. Among triggers with the same prefix length, prefer the IP or NSIP trigger that matches the smallest IP address.
When the processing of a response is restarted to resolve DNAME or CNAME records and a policy record set has notbeen triggered, all response policy zones are again consulted for the DNAME or CNAME names and addresses.
RPZ record sets are any types of DNS record, except DNAME or DNSSEC, that encode actions or responses to individual
queries. Any of the policies can be used with any of the triggers. For example, while the TCP-only policy is commonlyused with client-IP triggers, it can be used with any type of trigger to force the use of TCP for responses with ownernames in a zone.
PASSTHRU
The auto-acceptance policy is specified by a CNAME whose target is rpz-passthru. It causes the response to
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not be rewritten and is most often used to “poke holes” in policies for CIDR blocks.
DROP
The auto-rejection policy is specified by a CNAME whose target is rpz-drop. It causes the response to bediscarded. Nothing is sent to the DNS client.
TCP-Only
The “slip” policy is specified by a CNAME whose target is rpz-tcp-only. It changes UDP responses to short,truncated DNS responses that require the DNS client to try again with TCP. It is used to mitigate distributed DNS
reflection attacks.
NXDOMAIN
The “domain undefined” response is encoded by a CNAME whose target is the root domain (.).
NODATAThe empty set of resource records is specified by a CNAME whose target is the wildcard top-level domain (*.).
It rewrites the response to NODATA or ANCOUNT=0.
Local Data
A set of ordinary DNS records can be used to answer queries. Queries for record types not in the set are answeredwith NODATA.
A special form of local data is a CNAME whose target is a wildcard such as *.example.com. It is used as if an
ordinary CNAME after the asterisk (*) has been replaced with the query name. This special form is useful for
query logging in the walled garden’s authoritative DNS server.
All of the actions specified in all of the individual records in a policy zone can be overridden with a policy clause in
the response-policy option. An organization using a policy zone provided by another organization might use thismechanism to redirect domains to its own walled garden.
GIVEN
The placeholder policy says “do not override but perform the action specified in the zone.”
DISABLED
The testing override policy causes policy zone records to do nothing but log what they would have done if thepolicy zone were not disabled. The response to the DNS query is written (or not) according to any triggered policy
records that are not disabled. Disabled policy zones should appear first, because they are often not logged if ahigher-precedence trigger is found first.
PASSTHRU; DROP; TCP-Only; NXDOMAIN; NODATA
These settings each override the corresponding per-record policy.
CNAME domain
This causes all RPZ policy records to act as if they were “cname domain” records.
By default, the actions encoded in a response policy zone are applied only to queries that ask for recursion (RD=1). That
default can be changed for a single policy zone, or for all response policy zones in a view, with a recursive-only
no clause. This feature is useful for serving the same zone files both inside and outside an RFC 1918 cloud and using
RPZ to delete answers that would otherwise contain RFC 1918 values on the externally visible name server or view.
Also by default, RPZ actions are applied only to DNS requests that either do not request DNSSEC metadata (DO=0) or
when no DNSSEC records are available for the requested name in the original zone (not the response policy zone). Thisdefault can be changed for all response policy zones in a view with a break-dnssec yes clause. In that case, RPZ
actions are applied regardless of DNSSEC. The name of the clause option reflects the fact that results rewritten by RPZ
actions cannot verify.
No DNS records are needed for a QNAME or Client-IP trigger; the name or IP address itself is sufficient, so in principle
the query name need not be recursively resolved. However, not resolving the requested name can leak the fact that
response policy rewriting is in use, and that the name is listed in a policy zone, to operators of servers for listed names.
To prevent that information leak, by default any recursion needed for a request is done before any policy triggers are
considered. Because listed domains often have slow authoritative servers, this behavior can cost significant time. The
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qname-wait-recurse no option overrides the default and enables that behavior when recursion cannot change
a non-error response. The option does not affect QNAME or client-IP triggers in policy zones listed after other zones
containing IP, NSIP, and NSDNAME triggers, because those may depend on the A, AAAA, and NS records that would
be found during recursive resolution. It also does not affect DNSSEC requests (DO=1) unless break-dnssec yes isin use, because the response would depend on whether RRSIG records were found during resolution. Using this option
can cause error responses such as SERVFAIL to appear to be rewritten, since no recursion is being done to discoverproblems at the authoritative server.
dnsrps-enable
Grammar: dnsrps-enable <boolean>;
Blocks: options, viewTags: server, security

Turns on the DNS Response Policy Service (DNSRPS) interface.
The dnsrps-enable yes option turns on the DNS Response Policy Service (DNSRPS) interface, if it has
been compiled in named using configure --enable-dnsrps.
dnsrps-library
Grammar: dnsrps-library <quoted_string>;
Blocks: options
Tags: server, security

Turns on the DNS Response Policy Service (DNSRPS) interface.
This option specifies the path to the DNSRPS provider library. Typically this library is detected when building
with configure --enable-dnsrps and does not need to be specified in named.conf; the option exists
to override the default library for testing purposes.
dnsrps-options
Grammar: dnsrps-options { <unspecified-text> };Blocks: options, viewTags: server, security

Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS)
provider library.
The block provides additional RPZ configuration settings, which are passed through to the DNSRPS provider
library. Multiple DNSRPS settings in an dnsrps-options string should be separated with semi-colons (;). The
DNSRPS provider library is passed a configuration string consisting of the dnsrps-options text, concatenatedwith settings derived from the response-policy statement.
Note: the dnsrps-options text should only include configuration settings that are specific to the DNSRPS
provider. For example, the DNSRPS provider from Farsight Security takes options such as dnsrpzd-conf,
dnsrpzd-sock, and dnzrpzd-args (for details of these options, see the librpz documentation). Other
RPZ configuration settings could be included in dnsrps-options as well, but if named were switched backto traditional RPZ by setting dnsrps-enable to “no”, those options would be ignored.
The TTL of a record modified by RPZ policies is set from the TTL of the relevant record in the policy zone. It is thenlimited to a maximum value. The max-policy-ttl clause changes the maximum number of seconds from its default

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of 5. For convenience, TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration
formats.
For example, an administrator might use this option statement:
response-policy { zone "badlist"; };and this zone statement:zone "badlist" {type primary; file "primary/badlist"; allow-query {none;}; };with this zone file:$TTL 1H@NS

SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
LOCALHOST.

; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com
CNAME.
; NXDOMAIN policy*.nxdomain.domain.com
CNAME.
; NXDOMAIN policy
nodata.domain.com
CNAME*.
; NODATA policy*.nodata.domain.com
CNAME*.
; NODATA policy
bad.domain.com
A
10.0.0.1; redirect to a walled garden
AAAA
2001:2::1
bzone.domain.com
CNAME
garden.example.com.
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com
CNAME
rpz-passthru.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com*.bzone.domain.com
CNAME*.garden.example.com.
; IP policy records that rewrite all responses containing A records in 127/8;
except 127.0.0.1
8.0.0.0.127.rpz-ip
CNAME.
32.1.0.0.127.rpz-ip
CNAME
rpz-passthru.
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname
CNAME
48.zz.2.2001.rpz-nsip
CNAME

.
.

; auto-reject and auto-accept some DNS clients
112.zz.2001.rpz-client-ip
CNAME
rpz-drop.
8.0.0.0.127.rpz-client-ip
CNAME
rpz-drop.
; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip
CNAME
rpz-tcp-only.
example.com
CNAME
rpz-tcp-only.
*.example.com
CNAME
rpz-tcp-only.

Response policy zones can be configured to set an Extended DNS Error (EDE) code on the responses which have been
modified by the response policy:
response-policy { zone "badlist" ede filtered; };The following settings are supported for the ede option:none
No Extended DNS Error code is set (default).
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forgedExtended DNS Error code 4 - Forged Answer.
blockedExtended DNS Error code 15 - Blocked.
censored
Extended DNS Error code 16 - Censored.
filtered
Extended DNS Error code 17 - Filtered.
prohibited
Extended DNS Error code 18 - Prohibited.
See RFC 8914 for more information about the Extended DNS Error codes.
RPZ can affect server performance. Each configured response policy zone requires the server to perform one to four
additional database lookups before a query can be answered. For example, a DNS server with four policy zones, eachwith all four kinds of response triggers (QNAME, IP, NSIP, and NSDNAME), requires a total of 17 times as many
database lookups as a similar DNS server with no response policy zones. A BIND 9 server with adequate memory and
one response policy zone with QNAME and IP triggers might achieve a maximum queries-per-second (QPS) rate about
20% lower. A server with four response policy zones with QNAME and IP triggers might have a maximum QPS rate
about 50% lower.
Responses rewritten by RPZ are counted in the RPZRewrites statistics.
The log clause can be used to optionally turn off rewrite logging for a particular response policy zone. By default, allrewrites are logged.
The add-soa option controls whether the RPZ’s SOA record is added to the section for traceback of changes from thiszone. This can be set at the individual policy zone level or at the response-policy level. The default is yes.
Updates to RPZ zones are processed asynchronously; if there is more than one update pending they are bundled together.
If an update to a RPZ zone (for example, via IXFR) happens less than min-update-interval seconds after the mostrecent update, the changes are not carried out until this interval has elapsed. The default is 60 seconds. For convenience,
TTL-style time-unit suffixes may be used to specify the value. It also accepts ISO 8601 duration formats.
Response Rate Limiting
rate-limit
Grammar:rate-limit {all-per-second <integer>;errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;log-only <boolean>;max-table-size <integer>;min-table-size <integer>;nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;referrals-per-second <integer>;
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window <integer>;};

Blocks: options, viewTags: query

Controls excessive UDP responses, to prevent BIND 9 from being used to amplify reflection denial-of-service(DoS) attacks.
Excessive, almost-identical UDP responses can be controlled by configuring a rate-limit clause in an options or view statement. This mechanism keeps authoritative BIND 9 from being used to amplify reflection
denial-of-service (DoS) attacks. Short BADCOOKIE errors or truncated (TC=1) responses can be sent to provide
rate-limited responses to legitimate clients within a range of forged, attacked IP addresses. Legitimate clients react to dropped responses by retrying, to BADCOOKIE errors by including a server cookie when retrying, and to
truncated responses by switching to TCP.
This mechanism is intended for authoritative DNS servers. It can be used on recursive servers, but can slow
applications such as SMTP servers (mail receivers) and HTTP clients (web browsers) that repeatedly request thesame domains. When possible, closing “open” recursive servers is better.
Response rate limiting uses a “credit” or “token bucket” scheme. Each combination of identical response and client
has a conceptual “account” that earns a specified number of credits every second. A prospective response debits its
account by one. Responses are dropped or truncated while the account is negative.
window
Grammar: window <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Specifies the length of time during which responses are tracked.
Responses are tracked within a rolling window of time which defaults to 15 seconds, but which can be configured with the window option to any value from 1 to 3600 seconds (1 hour). The account cannot become
more positive than the per-second limit or more negative than window times the per-second limit. Whenthe specified number of credits for a class of responses is set to 0, those responses are not rate-limited.
ipv4-prefix-length
Grammar: ipv4-prefix-length <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: server

Specifies the prefix lengths of IPv4 address blocks.
ipv6-prefix-length
Grammar: ipv6-prefix-length <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: server

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Specifies the prefix lengths of IPv6 address blocks.
The notions of “identical response” and “DNS client” for rate limiting are not simplistic. All responses toan address block are counted as if to a single client. The prefix lengths of address blocks are specified with
ipv4-prefix-length (default 24) and ipv6-prefix-length (default 56).
responses-per-second
Grammar: responses-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Limits the number of non-empty responses for a valid domain name and record type.
All non-empty responses for a valid domain name (qname) and record type (qtype) are identical and have alimit specified with responses-per-second (default 0 or no limit). All valid wildcard domain names
are interpreted as the zone’s origin name concatenated to the “*” name.
nodata-per-second
Grammar: nodata-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Limits the number of empty (NODATA) responses for a valid domain name.
All empty (NODATA) responses for a valid domain, regardless of query type, are identical. Responses in the
NODATA class are limited by nodata-per-second (default responses-per-second).
nxdomains-per-second
Grammar: nxdomains-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Limits the number of undefined subdomains for a valid domain name.
Requests for any and all undefined subdomains of a given valid domain result in NXDOMAIN errors,
and are identical regardless of query type. They are limited by nxdomains-per-second (default
responses-per-second). This controls some attacks using random names, but can be relaxed or turnedoff (set to 0) on servers that expect many legitimate NXDOMAIN responses, such as from anti-spam rejection
lists.
referrals-per-second
Grammar: referrals-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Limits the number of referrals or delegations to a server for a given domain.
Referrals or delegations to the server of a given domain are identical and are limited byreferrals-per-second (default responses-per-second).

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Responses generated from local wildcards are counted and limited as if they were for the parent domain name.
This controls flooding using random.wild.example.com.
All requests that result in DNS errors other than NXDOMAIN, such as SERVFAIL and FORMERR, are identicalregardless of requested name (qname) or record type (qtype). This controls attacks using invalid requests or distant,broken authoritative servers.
errors-per-second
Grammar: errors-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: server

Limits the number of errors for a valid domain name and record type.
By default the limit on errors is the same as the responses-per-second value, but it can be set separately with errors-per-second.
slip
Grammar: slip <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Sets the number of “slipped” responses to minimize the use of forged source addresses for an attack.
Many attacks using DNS involve UDP requests with forged source addresses. Rate limiting prevents the useof BIND 9 to flood a network with responses to requests with forged source addresses, but could let a third
party block responses to legitimate requests. There is a mechanism that can answer some legitimate requests
from a client whose address is being forged in a flood. Setting slip to 2 (its default) causes every other
UDP request without a valid server cookie to be answered with a small response. The small size and reduced
frequency, and resulting lack of amplification, of “slipped” responses make them unattractive for reflection
DoS attacks. slip must be between 0 and 10. A value of 0 does not “slip”; no small responses are sent due
to rate limiting. Rather, all responses are dropped. A value of 1 causes every response to slip; values between
2 and 10 cause every nth response to slip.
If the request included a client cookie, then a “slipped” response is a BADCOOKIE error with a server cookie,
which allows a legitimate client to include the server cookie to be exempted from the rate limiting when it
retries the request. If the request did not include a cookie, then a “slipped” response is a truncated (TC=1)
response, which prompts a legitimate client to switch to TCP and thus be exempted from the rate limiting.
Some error responses, including REFUSED and SERVFAIL, cannot be replaced with truncated responses
and are instead leaked at the slip rate.
(Note: dropped responses from an authoritative server may reduce the difficulty of a third party successfully
forging a response to a recursive resolver. The best security against forged responses is for authoritative
operators to sign their zones using DNSSEC and for resolver operators to validate the responses. When thisis not an option, operators who are more concerned with response integrity than with flood mitigation may
consider setting slip to 1, causing all rate-limited responses to be truncated rather than dropped. This
reduces the effectiveness of rate-limiting against reflection attacks.)
qps-scale
Grammar: qps-scale <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

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Tightens defenses during DNS attacks by scaling back the ratio of the current query-per-second rate.
When the approximate query-per-second rate exceeds the qps-scale value,theresponses-per-second,errors-per-second,
nxdomains-per-second,
and
all-per-second values are reduced by the ratio of the current rate to the qps-scalevalue. This feature can tighten defenses during attacks. For example, with qps-scale 250;
responses-per-second 20; and a total query rate of 1000 queries/second for all queries from all
DNS clients including via TCP, then the effective responses/second limit changes to (250/1000)*20, or 5.
Responses to requests that included a valid server cookie, and responses sent via TCP, are not limited but
are counted to compute the query-per-second rate.
exempt-clients
Grammar: exempt-clients { <address_match_element>; ... };Blocks: options.rate-limit, view.rate-limit
Tags: query

Exempts specific clients or client groups from rate limiting.
Communities of DNS clients can be given their own parameters or no rate limiting by putting rate-limit
statements in view statements instead of in the global option statement. A rate-limit statement in aview replaces, rather than supplements, a rate-limit statement among the main options.
DNS clients within a view can be exempted from rate limits with the exempt-clients clause.
all-per-second
Grammar: all-per-second <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Limits UDP responses of all kinds.
UDP responses of all kinds can be limited with the all-per-second phrase. This rate limiting is unlike the rate limiting provided by responses-per-second, errors-per-second, andnxdomains-per-second on a DNS server, which are often invisible to the victim of a DNS reflection
attack. Unless the forged requests of the attack are the same as the legitimate requests of the victim, thevictim’s requests are not affected. Responses affected by an all-per-second limit are always dropped;
the slip value has no effect. An all-per-second limit should be at least 4 times as large as the otherlimits, because single DNS clients often send bursts of legitimate requests. For example, the receipt of asingle mail message can prompt requests from an SMTP server for NS, PTR, A, and AAAA records as theincoming SMTP/TCP/IP connection is considered. The SMTP server can need additional NS, A, AAAA,
MX, TXT, and SPF records as it considers the SMTP Mail From command. Web browsers often repeatedly resolve the same names that are duplicated in HTML <IMG> tags in a page. all-per-second issimilar to the rate limiting offered by firewalls but is often inferior. Attacks that justify ignoring the contentsof DNS responses are likely to be attacks on the DNS server itself. They usually should be discarded before
the DNS server spends resources making TCP connections or parsing DNS requests, but that rate limiting
must be done before the DNS server sees the requests.
max-table-sizeGrammar: max-table-size <integer>;
Blocks: options.rate-limit, view.rate-limit

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Tags: server

Sets the maximum size of the table used to track requests and rate-limit responses.
min-table-sizeGrammar: min-table-size <integer>;
Blocks: options.rate-limit, view.rate-limit
Tags: query

Sets the minimum size of the table used to track requests and rate-limit responses.
The maximum size of the table used to track requests and rate-limit responses is set with
max-table-size. Each entry in the table is between 40 and 80 bytes. The table needs approximately as
many entries as the number of requests received per second. The default is 20,000. To reduce the cold start ofgrowing the table, min-table-size (default 500) can set the minimum table size. Enable rate-limit
category logging to monitor expansions of the table and inform choices for the initial and maximum tablesize.
log-only
Grammar: log-only <boolean>;
Blocks: options.rate-limit, view.rate-limit
Tags: query, logging

Tests rate-limiting parameters without actually dropping any requests.
Use log-only yes to test rate-limiting parameters without actually dropping any requests.
Responses dropped by rate limits are included in the RateDropped and QryDropped statistics. Responses
that are truncated by rate limits are included in RateSlipped and RespTruncated.
NXDOMAIN Redirection
named supports NXDOMAIN redirection via two methods:• Redirect zone
• Redirect namespaceWith either method, when named gets an NXDOMAIN response it examines a separate namespace to see if the NXDOMAIN response should be replaced with an alternative response.
With a redirect zone (zone "." { type redirect; };), the data used to replace the NXDOMAIN is held ina single zone which is not part of the normal namespace. All the redirect information is contained in the zone; there are
no delegations.
nxdomain-redirect
Grammar: nxdomain-redirect <string>;
Blocks: options, viewTags: query

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Appends the specified suffix to the original query name, when replacing an NXDOMAIN with a redirect namespace.
With a redirect namespace (option { nxdomain-redirect <suffix> };), the data used to replace
the NXDOMAIN is part of the normal namespace and is looked up by appending the specified suffix to the original
query name. This roughly doubles the cache required to process NXDOMAIN responses, as both the original
NXDOMAIN response and the replacement data (or an NXDOMAIN indicating that there is no replacement)
must be stored.
If both a redirect zone and a redirect namespace are configured, the redirect zone is tried first.

8.2.17 server Block Grammar
serverGrammar:server <netprefix> {bogus <boolean>;edns <boolean>;edns-udp-size <integer>;edns-version <integer>;keys <server_key>;
max-udp-size <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );padding <integer>;provide-ixfr <boolean>;query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-cookie <boolean>;send-cookie <boolean>;
tcp-keepalive <boolean>;
tcp-only <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers <integer>;}; // may occur multiple times

Blocks: topmost, viewTags: server

Defines characteristics to be associated with a remote name server.

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8.2.18 server Block Definition and Usage
The server statement defines characteristics to be associated with a remote name server. If a prefix length is specified,then a range of servers is covered. Only the most specific server clause applies, regardless of the order in named.conf.
The server statement can occur at the top level of the configuration file or inside a view statement. If a viewstatement contains one or more server statements, only those apply to the view and any top-level ones are ignored. If
a view contains no server statements, any top-level server statements are used as defaults.
bogusGrammar: bogus <boolean>;
Blocks: server, view.server
Tags: server

Allows a remote server to be ignored.
If a remote server is giving out bad data, marking it as bogus prevents further queries to it. The default value ofbogus is no.
edns
Grammar: edns <boolean>;
Blocks: server, view.server
Tags: server

Controls the use of the EDNS0 (RFC 2671) feature.
The edns clause determines whether the local server attempts to use EDNS when communicating with the remote
server. The default is yes.
edns-version
Grammar: edns-version <integer>;
Blocks: server, view.server
Tags: server

Sets the maximum EDNS VERSION that is sent to the server(s) by the resolver.
The edns-version option sets the maximum EDNS VERSION that is sent to the server(s) by the resolver. The
actual EDNS version sent is still subject to normal EDNS version-negotiation rules (see RFC 6891), the maximum
EDNS version supported by the server, and any other heuristics that indicate that a lower version should be sent.
This option is intended to be used when a remote server reacts badly to a given EDNS version or higher; it should
be set to the highest version the remote server is known to support. Valid values are 0 to 255; higher values are
silently adjusted. This option is not needed until higher EDNS versions than 0 are in use.
padding
Grammar: padding <integer>;
Blocks: server, view.server
Tags: server

Adds EDNS Padding options to outgoing messages to increase the packet size.
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The option adds EDNS Padding options to outgoing messages, increasing the packet size to a multiple of thespecified block size. Valid block sizes range from 0 (the default, which disables the use of EDNS Padding) to 512
bytes. Larger values are reduced to 512, with a logged warning. Note: this option is not currently compatible withno TSIG or SIG(0), as the EDNS OPT record containing the padding would have to be added to the packet after
it had already been signed.
tcp-only
Grammar: tcp-only <boolean>;
Blocks: server, view.server
Tags: server

Sets the transport protocol to TCP.
The option sets the transport protocol to TCP. The default is to use the UDP transport and to fallback on TCP only
when a truncated response is received.
tcp-keepalive
Grammar: tcp-keepalive <boolean>;
Blocks: server, view.server
Tags: server

Adds EDNS TCP keepalive to messages sent over TCP.
The option adds EDNS TCP keepalive to messages sent over TCP. Note that currently idle timeouts in responses
are ignored.
transfers
Grammar: transfers <integer>;
Blocks: server, view.server
Tags: server

Limits the number of concurrent inbound zone transfers from a server.
transfers is used to limit the number of concurrent inbound zone transfers from the specified server. If notransfers clause is specified, the limit is set according to the transfers-per-ns option.
keys
Blocks: dnssec-policy, server, view.server
Tags: server, security

Specifies one or more server_key s to be used with a remote server.
Warning: Not to be confused with keys in dnssec-policy specification. Although statements with thesame name exist in both contexts, they refer to fundamentally incompatible concepts.
In the context of a server block, the option identifies a server_key defined by the key statement, to be used fortransaction security (see TSIG) when talking to the remote server. When a request is sent to the remote server,

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a request signature is generated using the key specified here and appended to the message. A request originatingfrom the remote server is not required to be signed by this key.
Only a single key per server is currently supported.
It is possible to override the following values defined in view and options blocks:• edns-udp-size• max-udp-size• notify-source-v6• notify-source• provide-ixfr• query-source-v6• query-source• request-expire• request-ixfr• request-nsid• require-cookie• send-cookie• transfer-format• transfer-source-v6• transfer-source

8.2.19 statistics-channels Block Grammar
statistics-channels
Grammar:statistics-channels {inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] [␣,→allow { <address_match_element>; ... } ]; // may occur multiple times}; // may occur multiple times

Blocks: topmost
Tags: logging

Specifies the communication channels to be used by system administrators to access statistics information on thename server.

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8.2.20 statistics-channels Block Definition and Usage
The statistics-channels statement declares communication channels to be used by system administrators to get
access to statistics information on the name server.
This statement is intended to be flexible to support multiple communication protocols in the future, but currently only
HTTP access is supported. It requires that BIND 9 be compiled with libxml2 and/or json-c (also known as libjson0); thestatistics-channels statement is still accepted even if it is built without the library, but any HTTP access fails
with an error.
An inet control channel is a TCP socket listening at the specified port on the specified ip_address, which can be an IPv4
or IPv6 address. An ip_address of * (asterisk) is interpreted as the IPv4 wildcard address; connections are accepted on
any of the system’s IPv4 addresses. To listen on the IPv6 wildcard address, use an ip_address of ::.
If no port is specified, port 80 is used for HTTP channels. The asterisk (*) cannot be used for port.
Attempts to open a statistics channel are restricted by the optional allow clause. Connections to the statistics channel
are permitted based on the address_match_list. If no allow clause is present, named accepts connection attempts fromany address. Since the statistics may contain sensitive internal information, the source of connection requests must be
restricted appropriately so that only trusted parties can access the statistics channel.
Gathering data exposed by the statistics channel locks various subsystems in named, which could slow down query
processing if statistics data is requested too often.
An issue in the statistics channel would be considered a security issue only if it could be exploited by unprivileged users
circumventing the access control list. In other words, any issue in the statistics channel that could be used to accessinformation unavailable otherwise, or to crash named, is not considered a security issue if it can be avoided through theuse of a secure configuration.
If no statistics-channels statement is present, named does not open any communication channels.
The statistics are available in various formats and views, depending on the URI used to access them. For example, if
the statistics channel is configured to listen on 127.0.0.1 port 8888, then the statistics are accessible in XML format at
http://127.0.0.1:8888/ or http://127.0.0.1:8888/xml. A CSS file is included, which can format the XML statistics into
tables when viewed with a stylesheet-capable browser, and into charts and graphs using the Google Charts API whenusing a JavaScript-capable browser.
Broken-out subsets of the statistics can be viewed at http://127.0.0.1:8888/xml/v3/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/xml/v3/server (server and resolver statistics), http://127.0.0.1:8888/xml/v3/zones(zone statistics), http://127.0.0.1:8888/xml/v3/xfrins (incoming zone transfer statistics), http://127.0.0.1:8888/xml/v3/
net (network status and socket statistics), http://127.0.0.1:8888/xml/v3/mem (memory manager statistics), and http://127.0.0.1:8888/xml/v3/traffic (traffic sizes).
The full set of statistics can also be read in JSON format at http://127.0.0.1:8888/json, with the broken-out subsets at
http://127.0.0.1:8888/json/v1/status (server uptime and last reconfiguration time), http://127.0.0.1:8888/json/v1/server(server and resolver statistics), http://127.0.0.1:8888/json/v1/zones (zone statistics), http://127.0.0.1:8888/json/v1/xfrins(incoming zone transfer statistics), http://127.0.0.1:8888/json/v1/net (network status and socket statistics), http://127.0.
0.1:8888/json/v1/mem (memory manager statistics), and http://127.0.0.1:8888/json/v1/traffic (traffic sizes).

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8.2.21 tls Block Grammar
tls
Grammar:tls <string> {ca-file <quoted_string>;
cert-file <quoted_string>;
cipher-suites <string>;
ciphers <string>;
dhparam-file <quoted_string>;
key-file <quoted_string>;
prefer-server-ciphers <boolean>;
protocols { <string>; ... };remote-hostname <quoted_string>;
session-tickets <boolean>;}; // may occur multiple times

Blocks: topmost
Tags: security

Configures a TLS connection.

8.2.22 tls Block Definition and Usage
The tls statement is used to configure a TLS connection; this configuration can then be referenced by a listen-on orlisten-on-v6 statement to cause named to listen for incoming requests via TLS, or in the primaries statement
for a zone of type secondary to cause zone transfer requests to be sent via TLS.
tls can only be set at the top level of named.conf.
The following options can be specified in a tls statement:
key-file
Grammar: key-file <quoted_string>;
Blocks: tls
Tags: server, security

Specifies the path to a file containing the private TLS key for a connection.
Path to a file containing the private TLS key to be used for the connection.
cert-file
Grammar: cert-file <quoted_string>;
Blocks: tls
Tags: server, security

Specifies the path to a file containing the TLS certificate for a connection.

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Path to a file containing the TLS certificate to be used for the connection.
ca-fileGrammar: ca-file <quoted_string>;
Blocks: tls
Tags: server, security

Specifies the path to a file containing TLS certificates for trusted CA authorities, used to verify remote peer certificates.
Path to a file containing trusted CA authorities’ TLS certificates used to verify remote peer certificates.
Specifying this option enables remote peer certificates’ verification. For incoming connections, specifying this option makes BIND require a valid TLS certificate from a client. In the case of outgoingconnections, if remote-hostname is not specified, then the remote server IP address is used instead.
dhparam-fileGrammar: dhparam-file <quoted_string>;
Blocks: tls
Tags: server, security

Specifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.
Path to a file containing Diffie-Hellman parameters, which is needed to enable the cipher suites depending on the Diffie-Hellman ephemeral key exchange (DHE). Having these parameters specified isessential for enabling perfect forward secrecy capable ciphers in TLSv1.2.
remote-hostname
Grammar: remote-hostname <quoted_string>;
Blocks: tls
Tags: security

Specifies the expected hostname in the TLS certificate of the remote server.
The expected hostname in the TLS certificate of the remote server. This option enables a remote server
certificate verification. If ca-file is not specified, then the platform-specific certificates store is usedfor verification. This option is used when connecting to a remote peer only and, thus, is ignored whentls statements are referenced by listen-on or listen-on-v6 statements.
protocols
Grammar: protocols { <string>; ... };Blocks: tls
Tags: security

Specifies the allowed versions of the TLS protocol.
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Allowed versions of the TLS protocol. TLS version 1.2 and higher are supported, depending on thecryptographic library in use. Multiple versions might be specified (e.g. protocols { TLSv1.2;
TLSv1.3; };).
cipher-suites
Grammar: cipher-suites <string>;
Blocks: tls
Tags: security

Specifies a list of allowed cipher suites in the order of preference for TLSv1.3 only.
Ciphersuiteslist
whichdefines
allowedciphersuites,such
as
TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256.
The string must be formed according to the rules specified in the OpenSSL documentation (seehttps://www.openssl.org/docs/man1.1.1/man1/ciphers.html, section “TLS v1.3 cipher suites” fordetails).
ciphers
Grammar: ciphers <string>;
Blocks: tls
Tags: security

Specifies a list of allowed ciphers in the order of preference for TLSv1.2 only.
Cipher list which defines allowed ciphers, such as HIGH:!aNULL:!MD5:!SHA1:!SHA256:!
SHA384. The string must be formed according to the rules specified in the OpenSSL documentation(see https://www.openssl.org/docs/man1.1.1/man1/ciphers.html for details).
prefer-server-ciphers
Grammar: prefer-server-ciphers <boolean>;
Blocks: tls
Tags: server, security

Specifies that server ciphers should be preferred over client ones.
Specifies that server ciphers should be preferred over client ones.
session-tickets
Grammar: session-tickets <boolean>;
Blocks: tls
Tags: security

Enables or disables session resumption through TLS session tickets.

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Enables or disables session resumption through TLS session tickets, as defined in RFC 5077. Disabling
the stateless session tickets might be required in the cases when forward secrecy is needed, or the TLS
certificate and key pair is planned to be used across multiple BIND instances.

Warning: TLS configuration is subject to change and incompatible changes might be introduced in the future. Users
of TLS are encouraged to carefully read release notes when upgrading.
The options described above are used to control different aspects of TLS functioning. Thus, most of them have no welldefined default values, as these depend on the cryptographic library version in use and system-wide cryptographic policy.
On the other hand, by specifying the needed options one could have a uniform configuration deployable across a range ofplatforms.
An example of privacy-oriented, perfect forward secrecy enabled configuration can be found below. It can be used as astarting point.
tls local-tls {key-file "/path/to/key.pem";
cert-file "/path/to/fullchain_cert.pem";
dhparam-file "/path/to/dhparam.pem";
ciphers "HIGH:!kRSA:!aNULL:!eNULL:!RC4:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!SHA1:!
,→SHA256:!SHA384";
prefer-server-ciphers yes;session-tickets no;};

A Diffie-Hellman parameters file can be generated using e.g. OpenSSL, like follows:
openssl dhparam -out /path/to/dhparam.pem <3072_or_4096>

Ensure that it gets generated on a machine with enough entropy from external sources (e.g. the computer you work on
should be fine, the remote virtual machine or server might be not). These files do not contain any sensitive data and canbe shared if required.
There are two built-in TLS connection configurations: ephemeral, uses a temporary key and certificate created for thecurrent named session only, and none, which can be used when setting up an HTTP listener with no encryption.
The main motivation behind having the ephemeral configuration is to aid in testing, as trusted certificate authorities
do not issue the certificates associated with this configuration. Thus, these certificates will never be trusted by any clientsthat verify TLS certificates. They provide encryption of the traffic but no authentification of the transmission channel.
That might be enough in the case of deployment in a controlled environment.
It should be noted that on reconfiguration, the ephemeral TLS key and the certificate are recreated, and all TLS
certificates and keys, as well as associated data, are reloaded from the disk. In that case, listening sockets associated with
TLS remain intact.
Please keep in mind that doing reconfiguration can cause a short interruption in BIND’s ability to process inbound client
packets. The length of interruption is environment and configuration-specific. A good example of when reconfigurationis necessary is when TLS keys and certificates are updated on the disk.
BIND supports the following TLS authentication mechanisms described in the RFC 9103, Section 9.3: Opportunistic
TLS, Strict TLS, and Mutual TLS.
Opportunistic TLS provides encryption for data but does not provide any authentication for the channel. This mode is thedefault one and it is used whenever remote-hostname and ca-file options are not set in tls statements in use.
RFC 9103 allows optional fallback to clear-text DNS in the cases when TLS is not available. Still, BIND intentionally does
not support that in order to protect from unexpected data leaks due to misconfiguration. Both BIND and its complementary

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tools either successfully establish a secure channel via TLS when instructed to do so or fail to establish a connection
otherwise.
Strict TLS provides server authentication via a pre-configured hostname for outgoing connections. This mechanism offers
both channel confidentiality and channel authentication (of the server). In order to achieve Strict TLS, one needs to use
remote-hostname and, optionally, ca-file options in the tls statements used for establishing outgoing connections (e.g. the ones used to download zone from primaries via TLS). Providing any of the mentioned options will enable
server authentication. If remote-hostname is provided but ca-file is missing, then the platform-specific certificate authority certificates are used for authentication. The set roughly corresponds to the one used by WEB-browsers toauthenticate HTTPS hosts. On the other hand, if ca-file is provided but remote-hostname is missing, then the
remote side’s IP address is used instead.
Mutual TLS is an extension to Strict TLS that provides channel confidentiality and mutual channel authentication. It builds
up upon the clients offering client certificates when establishing connections and them doing the server authentication as
in the case of Strict TLS. The server verifies the provided client certificates and accepts the TLS connection in case of
successful verification or rejects it otherwise. In order to instruct the server to require and verify client TLS certificates,
one needs to specify the ca-file option in tls configurations used to configure server listeners. The provided file
must contain certificate authority certificates used to issue client certificates. In most cases, one should build one’s own
TLS certificate authority specifically to issue client certificates and include the certificate authority certificate into the file.
For authenticating zone transfers over TLS, Mutual TLS might be considered a standalone solution, while Strict TLS
paired with TSIG-based authentication and, optionally, IP-based access lists, might be considered acceptable for mostpractical purposes. Mutual TLS has the advantage of not requiring TSIG and thus, not having security issues related toshared cryptographic secrets.

8.2.23 http Block Grammar
httpGrammar:http <string> {endpoints { <quoted_string>; ... };listener-clients <integer>;streams-per-connection <integer>;}; // may occur multiple times

Blocks: topmost
Tags: query, server

Configures HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries.

8.2.24 http Block Definition and Usage
The http statement is used to configure HTTP endpoints on which to listen for DNS-over-HTTPS (DoH) queries. Thisconfiguration can then be referenced by a listen-on or listen-on-v6 statement to cause named to listen forincoming requests over HTTPS.
http can only be set at the top level of named.conf.
The following options can be specified in an http statement:

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endpoints
Grammar: endpoints { <quoted_string>; ... };Blocks: httpTags: query, server

Specifies a list of HTTP query paths on which to listen.
A list of HTTP query paths on which to listen. This is the portion of an RFC 3986-compliant URI
following the hostname; it must be an absolute path, beginning with “/”. The default value is "/dns-query", if omitted.
listener-clients
Grammar: listener-clients <integer>;
Blocks: httpTags: query, server

Specifies a per-listener quota for active connections.
The option specifies a per-listener quota for active connections.
streams-per-connection
Grammar: streams-per-connection <integer>;
Blocks: httpTags: query, server

Specifies the maximum number of concurrent HTTP/2 streams over an HTTP/2 connection.
The option specifies the hard limit on the number of concurrent HTTP/2 streams over an HTTP/2
connection.
Any of the options above could be omitted. In such a case, a global value specified in the options statement is used(see http-listener-clients, http-streams-per-connection.
For example, the following configuration enables DNS-over-HTTPS queries on all local addresses:
http local {endpoints { "/dns-query"; };};options {....
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8.2.25 trust-anchors Block Grammar
trust-anchors
Grammar: trust-anchors { <string> ( static-key | initial-key | static-ds |initial-ds ) <integer> <integer> <integer> <quoted_string>; ... }; // mayoccur multiple times
Blocks: topmost, viewTags: dnssec

Defines DNSSEC trust anchors.

8.2.26 trust-anchors Block Definition and Usage
The trust-anchors statement defines DNSSEC trust anchors. DNSSEC is described in DNSSEC.
A trust anchor is defined when the public key or public key digest for a non-authoritative zone is known but cannot be
securely obtained through DNS, either because it is the DNS root zone or because its parent zone is unsigned. Once a key
or digest has been configured as a trust anchor, it is treated as if it has been validated and proven secure.
The resolver attempts DNSSEC validation on all DNS data in subdomains of configured trust anchors. Validation below specified names can be temporarily disabled by using rndc nta, or permanently disabled with thevalidate-except option.
All keys listed in trust-anchors, and their corresponding zones, are deemed to exist regardless of what parent zones
say. Only keys configured as trust anchors are used to validate the DNSKEY RRset for the corresponding name. The
parent’s DS RRset is not used.
trust-anchors may be set at the top level of named.conf or within a view. If it is set in both places, the configurations are additive; keys defined at the top level are inherited by all views, but keys defined in a view are only used withinthat view.
The trust-anchors statement can contain multiple trust-anchor entries, each consisting of a domain name, followedby an “anchor type” keyword indicating the trust anchor’s format, followed by the key or digest data.
If the anchor type is static-key or initial-key, then it is followed with the key’s flags, protocol, and algorithm,
plus the Base64 representation of the public key data. This is identical to the text representation of a DNSKEY record.
Spaces, tabs, newlines, and carriage returns are ignored in the key data, so the configuration may be split into multiplelines.
If the anchor type is static-ds or initial-ds, it is followed with the key tag, algorithm, digest type, and thehexadecimal representation of the key digest. This is identical to the text representation of a DS record. Spaces, tabs,
newlines, and carriage returns are ignored.
Trust anchors configured with the static-key or static-ds anchor types are immutable, while keys configured
with initial-key or initial-ds can be kept up-to-date automatically, without intervention from the resolver
operator. (static-key keys are identical to keys configured using the deprecated trusted-keys statement.)
Suppose, for example, that a zone’s key-signing key was compromised, and the zone owner had to revoke and replace thekey. A resolver which had the original key configured using static-key or static-ds would be unable to validate
this zone any longer; it would reply with a SERVFAIL response code. This would continue until the resolver operator
had updated the trust-anchors statement with the new key.
If, however, the trust anchor had been configured using initial-key or initial-ds instead, the zone owner could
add a “stand-by” key to the zone in advance. named would store the stand-by key, and when the original key was revoked,
named would be able to transition smoothly to the new key. It would also recognize that the old key had been revoked214

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and cease using that key to validate answers, minimizing the damage that the compromised key could do. This is theprocess used to keep the ICANN root DNSSEC key up-to-date.
Whereas static-key and static-ds trust anchors continue to be trusted until they are removed from named.
conf, an initial-key or initial-ds is only trusted once: for as long as it takes to load the managed key databaseand start the RFC 5011 key maintenance process.
It is not possible to mix static with initial trust anchors for the same domain name.
The first time named runs with an initial-key or initial-ds configured in named.conf, it fetches the
DNSKEY RRset directly from the zone apex, and validates it using the trust anchor specified in trust-anchors.
If the DNSKEY RRset is validly signed by a key matching the trust anchor, then it is used as the basis for a new managedkeys database.
From that point on, whenever named runs, it sees the initial-key or initial-ds listed in trust-anchors,
checks to make sure RFC 5011 key maintenance has already been initialized for the specified domain, and if so, simply
moves on. The key specified in the trust-anchors statement is not used to validate answers; it is superseded by the
key or keys stored in the managed-keys database.
The next time named runs after an initial-key or initial-ds has been removed from the trust-anchorsstatement (or changed to a static-key or static-ds), the corresponding zone is removed from the managed-keys
database, and RFC 5011 key maintenance is no longer used for that domain.
In the current implementation, the managed-keys database is stored as a master-format zone file.
On servers which do not use views, this file is named managed-keys.bind. When views are in use, there is a separate
managed-keys database for each view; the filename is the view name (or, if a view name contains characters which would
make it illegal as a filename, a hash of the view name), followed by the suffix .mkeys.
When the key database is changed, the zone is updated. As with any other dynamic zone, changes are written into ajournal file, e.g., managed-keys.bind.jnl or internal.mkeys.jnl. Changes are committed to the primary
file as soon as possible afterward, usually within 30 seconds. Whenever named is using automatic key maintenance, thezone file and journal file can be expected to exist in the working directory. (For this reason, among others, the working
directory should be always be writable by named.)
If the dnssec-validation option is set to auto, named automatically sets up an initial-key for the rootzone. This initializing key is built in to named, and is current as of the release date. When the root zone key changes, arunning server will detect the change and roll to the new key, but newly-installed servers being run for the first time willneed to be from a recent enough version of BIND to have been built with the current key.

8.2.27 dnssec-policy Block Grammar
dnssec-policy
Grammar options, view, zone (primary, secondary): dnssec-policy <string>;
Grammar topmost:dnssec-policy <string> {cdnskey <boolean>;
cds-digest-types { <string>; ... };dnskey-ttl <duration>;
inline-signing <boolean>;keys { ( csk | ksk | zsk ) [ key-directory | key-store <string> ]␣
,→lifetime <duration_or_unlimited> algorithm <string> [ <integer> ]; ... };max-zone-ttl <duration>;
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parent-propagation-delay <duration>;publish-safety <duration>;purge-keys <duration>;retire-safety <duration>;signatures-jitter <duration>;signatures-refresh <duration>;signatures-validity <duration>;signatures-validity-dnskey <duration>;zone-propagation-delay <duration>;}; // may occur multiple times

Blocks: topmost, options, view, zone (primary, secondary)Tags: dnssec

Defines a key and signing policy (KASP) for zones.

8.2.28 dnssec-policy Block Definition and Usage
The dnssec-policy statement defines a key and signing policy (KASP) for zones.
A KASP determines how one or more zones are signed with DNSSEC. For example, it specifies how often keys shouldroll, which cryptographic algorithms to use, and how often RRSIG records need to be refreshed. Multiple key and signingpolicies can be configured with unique policy names.
A policy for a zone is selected using a dnssec-policy statement in the zone block, specifying the name of the policythat should be used.
There are three built-in policies:• default, which uses the default policy,• insecure, to be used when you want to gracefully unsign your zone,• none, which means no DNSSEC policy (the same as not selecting dnssec-policy at all; the zone is not
signed.)Keys are not shared among zones, which means that one set of keys per zone is generated even if they have the same
policy. If multiple views are configured with different versions of the same zone, each separate version uses the same setof signing keys.
The dnssec-policy statement requires dynamic DNS to be set up, or inline-signing to be enabled (which isthe default for DNSSEC zones).
If inline-signing is enabled, this means that a signed version of the zone is maintained separately and is writtenout to a different file on disk (the zone’s filename plus a .signed extension).
If inline-signing is disabled, the zone needs to be configured with an update-policy or allow-update.
In such case, the DNSSEC records are written to the filename set in the original zone’s file.
Key rollover timing is computed for each key according to the key lifetime defined in the KASP. The lifetime may be
modified by zone TTLs and propagation delays, to prevent validation failures. When a key reaches the end of its lifetime,
named generates and publishes a new key automatically, then deactivates the old key and activates the new one; finally,
the old key is retired according to a computed schedule.
Zone-signing key (ZSK) rollovers require no operator input. Key-signing key (KSK) and combined-signing key (CSK)
rollovers require action to be taken to submit a DS record to the parent. Rollover timing for KSKs and CSKs is adjusted
to take into account delays in processing and propagating DS updates.

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Policy default causes the zone to be signed with a single combined-signing key (CSK) using algorithm ECDSAP256SHA256; this key has an unlimited lifetime. (A verbose copy of this policy may be found in the source tree, inthe file doc/misc/dnssec-policy.default.conf.)
Note: The default signing policy may change in future releases. This could require changes to a signing policy whenupgrading to a new version of BIND. Check the release notes carefully when upgrading to be informed of such changes.
To prevent policy changes on upgrade, use an explicitly defined dnssec-policy, rather than default.
If a dnssec-policy statement is modified and the server restarted or reconfigured, named attempts to change thepolicy smoothly from the old one to the new. For example, if the key algorithm is changed, then a new key is generated
with the new algorithm, and the old algorithm is retired when the existing key’s lifetime ends.
Note: Rolling to a new policy while another key rollover is already in progress is not yet supported, and may result in
unexpected behavior.
The following options can be specified in a dnssec-policy statement:
cdnskey
Grammar: cdnskey <boolean>;
Blocks: dnssec-policy
Tags: dnssec

Specifies whether a CDNSKEY record should be published during KSK rollover.
When set to the default value of yes, a CDNSKEY record is published during KSK rollovers when the
DS of the successor key may be submitted to the parent.
cds-digest-types
Grammar: cds-digest-types { <string>; ... };Blocks: dnssec-policy
Tags: dnssec

Specifies the digest types to use for CDS resource records.
This indicates the digest types to use when generating CDS resource records. The default is SHA-256
only.
dnskey-ttl
Grammar: dnskey-ttl <duration>;
Blocks: dnssec-policy
Tags: dnssec

Specifies the time to live (TTL) for DNSKEY resource records.
This indicates the TTL to use when generating DNSKEY resource records. The default is 1 hour (3600
seconds).
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inline-signing
tags
dnssecshort
Specifies whether BIND 9 maintains a separate signed version of a zone.
If yes, BIND 9 maintains a separate signed version of the zone. An unsigned zone is transferred in or loaded fromdisk and the signed version of the zone is served with, possibly, a different serial number. The signed version of
the zone is stored in a file that is the zone’s filename (set in file) with a .signed extension.
This behavior is enabled by default.
Note: When changing the key-directory or the key-store, BIND will be unable to find existing key files. Make
sure you copy key files to the new directory before changing the path used in the configuration file. This is also true whenchanging to a built-in policy, for example to insecure. In this specific case you should move the existing key files tothe zone’s key-directory from the new configuration.
purge-keys
Grammar: purge-keys <duration>;
Blocks: dnssec-policy
Tags: dnssec

Specifies the amount of time after which DNSSEC keys that have been deleted from the zone can be removed from
disk.
This is the amount of time after which DNSSEC keys that have been deleted from the zone can beremoved from disk. If a key still determined to have presence (for example in some resolver cache),named will not remove the key files.
The default is P90D (90 days). Set this option to 0 to never purge deleted keys.
publish-safety
Grammar: publish-safety <duration>;
Blocks: dnssec-policy
Tags: dnssec

Increases the amount of time between when keys are published and when they become active, to allow for unforeseen
events.
This is a margin that is added to the pre-publication interval in rollover timing calculations, to give someextra time to cover unforeseen events. This increases the time between when keys are published andwhen they become active. The default is PT1H (1 hour).
retire-safety
Grammar: retire-safety <duration>;
Blocks: dnssec-policy
Tags: dnssec

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Increases the amount of time a key remains published after it is no longer active, to allow for unforeseen events.
This is a margin that is added to the post-publication interval in rollover timing calculations, to givesome extra time to cover unforeseen events. This increases the time a key remains published after it is
no longer active. The default is PT1H (1 hour).
signatures-jitter
Grammar: signatures-jitter <duration>;
Blocks: dnssec-policy
Tags: dnssec

Specifies a range for signatures expirations.
To prevent all signatures from expiring at the same moment, BIND 9 may vary the validity interval of individual signatures. The validity of a newly generated signatures is inrange between signatures-validity (maximum) and signatures-validity minus
signatures-jitter (minimum). The default jitter is 12 hours and the configured value must
be lower than signatures-validity and signatures-validity-dnskey.
signatures-refresh
Grammar: signatures-refresh <duration>;
Blocks: dnssec-policy
Tags: dnssec

Specifies how frequently an RRSIG record is refreshed.
This determines how frequently an RRSIG record needs to be refreshed. The signature is renewed
when the time until the expiration time is less than the specified interval. The default is P5D (5 days),meaning signatures that expire in 5 days or sooner are refreshed. The signatures-refresh
value must be less than 90% of the minimum value of signatures-validity andsignatures-validity-dnskey.
signatures-validity
Grammar: signatures-validity <duration>;
Blocks: dnssec-policy
Tags: dnssec

Indicates the validity period of an RRSIG record.
This indicates the validity period of an RRSIG record (subject to inception offset and jitter). The default
is P2W (2 weeks).

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signatures-validity-dnskey
Grammar: signatures-validity-dnskey <duration>;
Blocks: dnssec-policy
Tags: dnssec

Indicates the validity period of DNSKEY records.
This is similar to signatures-validity, but for DNSKEY records. The default is P2W (2 weeks).
max-zone-ttl
tags
zone, queryshort
Specifies a maximum permissible time-to-live (TTL) value, in seconds.
This specifies the maximum permissible TTL value for the zone. When a zone file is loaded, any record encounteredwith a TTL higher than max-zone-ttl causes the zone to be rejected.
This ensures that when rolling to a new DNSKEY, the old key will remain available until RRSIG records have
expired from caches. The max-zone-ttl option guarantees that the largest TTL in the zone is no higher than aknown and predictable value.
The default value PT24H (24 hours). A value of zero is treated as if the default value were in use.
nsec3param
Grammar: nsec3param [ iterations
salt-length <integer> ];<integer>][

optout<boolean>][

Blocks: dnssec-policy
Tags: dnssec

Specifies the use of NSEC3 instead of NSEC, and sets NSEC3 parameters.
Use NSEC3 instead of NSEC, and optionally set the NSEC3 parameters.
Here is an example of an nsec3 configuration:
nsec3param iterations 0 optout no salt-length 0;

The default is to use NSEC. The iterations, optout, and salt-length parts are optional, but
if not set, the values in the example above are the default NSEC3 parameters. Note that the specific salt
string is not specified by the user; named creates a salt of the indicated length.
Warning: Do not use extra iterations, salt, and opt-out unless their implications are fully understood. A higher number of iterations causes interoperability problems and opens servers to CPUexhausting DoS attacks. See RFC 9276.
zone-propagation-delay
Grammar: zone-propagation-delay <duration>;
Blocks: dnssec-policy

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Tags: zone, dnssec

Sets the propagation delay from the time a zone is first updated to when the new version of the zone is served by
all secondary servers.
This is the expected propagation delay from the time when a zone is first updated to the time when the
new version of the zone is served by all secondary servers. The default is PT5M (5 minutes).
parent-ds-ttl
Grammar: parent-ds-ttl <duration>;
Blocks: dnssec-policy
Tags: dnssec

Sets the time to live (TTL) of the DS RRset used by the parent zone.
This is the TTL of the DS RRset that the parent zone uses. The default is P1D (1 day).
parent-propagation-delay
Grammar: parent-propagation-delay <duration>;
Blocks: dnssec-policy
Tags: zone, dnssec

Sets the propagation delay from the time the parent zone is updated to when the new version is served by all of theparent zone’s name servers.
This is the expected propagation delay from the time when the parent zone is updated to the time when
the new version is served by all of the parent zone’s name servers. The default is PT1H (1 hour).
Automated KSK Rollovers
BIND has mechanisms in place to facilitate automated KSK rollovers. It publishes CDS and CDNSKEY records that canbe used by the parent zone to publish or withdraw the zone’s DS records. BIND will query the parental agents to see if
the new DS is actually published before withdrawing the old DNSSEC key.
Note: The DS response is not validated so it is recommended to set up a trust relationship with the parental
agent. For example, use TSIG to authenticate the parental agent, or point to a validating resolver.
The following options apply to DS queries sent to parental-agents:
checkds
Grammar: checkds ( explicit | <boolean> );Blocks: zone (primary, secondary)Tags: dnssec

Controls whether DS queries are sent to parental agents.
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If set to yes, DS queries are sent when a KSK rollover is in progress. The queries are sent to the servers listed in
the parent zone’s NS records. This is the default if there are no parental-agents configured for the zone.
If set to explicit, DS queries are sent only to servers explicitly listed using parental-agents. This is thedefault if there are parental agents configured.
If set to no, no DS queries are sent. Users should manually run rndc dnssec -checkds with the appropriate
parameters to signal that specific DS records are published and/or withdrawn.
parental-source
Grammar: parental-source ( <ipv4_address> | * );Blocks: options, view, zone (primary, secondary)Tags: dnssec

Specifies which local IPv4 source address is used to send parental DS queries.
parental-source determines which local source address, and optionally UDP port, is used to send parental
DS queries. This statement sets the parental-source for all zones, but can be overridden on a per-zone or
per-view basis by including a parental-source statement within the zone or view block in the configuration
file.
Note: port configuration is deprecated. A warning will be logged when this parameter is used.

Warning: Specifying a single port is discouraged, as it removes a layer of protection against spoofing errors.

Warning: The configured port must not be the same as the listening port.
parental-source-v6
Grammar: parental-source-v6 ( <ipv6_address> | * );Blocks: options, view, zone (primary, secondary)Tags: dnssec

Specifies which local IPv6 source address is used to send parental DS queries.
This option acts like parental-source, but applies to parental DS queries sent to IPv6 addresses.

8.2.29 managed-keys Block Grammar
managed-keys

Warning: This option is deprecated and will be removed in a future version of BIND.
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Blocks: topmost, viewTags: deprecated

8.2.30 managed-keys Block Definition and Usage
The managed-keys statement has been deprecated in favor of trust-anchors with the initial-key keyword.

8.2.31 trusted-keys Block Grammar
trusted-keys
Warning: This option is deprecated and will be removed in a future version of BIND.
Grammar: trusted-keys{<string><integer><integer><quoted_string>; ... }; // may occur multiple times, deprecated<integer>

Blocks: topmost, viewTags: deprecated

8.2.32 trusted-keys Block Definition and Usage
The trusted-keys statement has been deprecated in favor of trust-anchors with the static-key keyword.

8.2.33 view Block Grammar
view
Grammar:view <string> [ <class> ] {allow-new-zones <boolean>;allow-notify { <address_match_element>; ... };allow-proxy { <address_match_element>; ... }; // experimental
allow-proxy-on { <address_match_element>; ... }; // experimental
allow-query { <address_match_element>; ... };allow-query-cache { <address_match_element>; ... };allow-query-cache-on { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-recursion { <address_match_element>; ... };allow-recursion-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };attach-cache <string>;
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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)catalog-zones { zone <string> [ default-primaries [ port <integer> ] [␣,→source ( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { (,→<remote-servers> | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port,→<integer> ] ) [ key <string> ] [ tls <string> ]; ... } ] [ zone-directory,→<quoted_string> ] [ in-memory <boolean> ] [ min-update-interval <duration> ]; ..
,→. };
check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( primary | master | secondary | slave | response ) ( fail |␣,→warn | ignore ); // may occur multiple times
check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;clients-per-query <integer>;deny-answer-addresses { <address_match_element>; ... } [ except-from {,→<string>; ... } ];deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddisable-algorithms <string> { <string>; ... }; // may occur multiple times
disable-ds-digests <string> { <string>; ... }; // may occur multiple times
disable-empty-zone <string>; // may occur multiple times
dlz <string> {database <string>;
search <boolean>;}; // may occur multiple times
dns64 <netprefix> {break-dnssec <boolean>;clients { <address_match_element>; ... };exclude { <address_match_element>; ... };mapped { <address_match_element>; ... };recursive-only <boolean>;suffix <ipv6_address>;}; // may occur multiple times
dns64-contact <string>;
dns64-server <string>;
dnskey-sig-validity <integer>; // obsolete
dnsrps-enable <boolean>;
dnsrps-options { <unspecified-text> };dnssec-accept-expired <boolean>;dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-must-be-secure <string> <boolean>; // may occur multiple times,␣
,→deprecateddnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
dnssec-validation ( yes | no | auto );dnstap { ( all | auth | client | forwarder | resolver | update ) [ (␣,→query | response ) ]; ... };dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer>,→ ] | <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ..
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dyndb <string> <quoted_string> { <unspecified-text> }; // may occur␣,→multiple times
edns-udp-size <integer>;
empty-contact <string>;
empty-server <string>;
empty-zones-enable <boolean>;fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
fetches-per-server <integer> [ ( drop | fail ) ];fetches-per-zone <integer> [ ( drop | fail ) ];forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };ipv4only-contact <string>;
ipv4only-enable <boolean>;
ipv4only-server <string>;
ixfr-from-differences ( primary | master | secondary | slave | <boolean>␣
,→);key <string> {algorithm <string>;
secret <string>;}; // may occur multiple times
key-directory <quoted_string>;lame-ttl <duration>;
lmdb-mapsize <sizeval>;managed-keys { <string> ( static-key | initial-key | static-ds | initial,→ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur␣,→multiple times, deprecatedmasterfile-format ( raw | text );masterfile-style ( full | relative );match-clients { <address_match_element>; ... };match-destinations { <address_match_element>; ... };match-recursive-only <boolean>;max-cache-size ( default | unlimited | <sizeval> | <percentage> );max-cache-ttl <duration>;max-clients-per-query <integer>;max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-ncache-ttl <duration>;max-records <integer>;max-records-per-type <integer>;max-recursion-depth <integer>;max-recursion-queries <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-stale-ttl <duration>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-udp-size <integer>;max-validation-failures-per-fetch <integer>; // experimental
max-validations-per-fetch <integer>; // experimental
max-zone-ttl ( unlimited | <duration> ); // deprecatedmessage-compression <boolean>;min-cache-ttl <duration>;
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min-refresh-time <integer>;min-retry-time <integer>;minimal-any <boolean>;minimal-responses ( no-auth | no-auth-recursive | <boolean> );multi-master <boolean>;
new-zones-directory <quoted_string>;
no-case-compress { <address_match_element>; ... };nocookie-udp-size <integer>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
nta-lifetime <duration>;
nta-recheck <duration>;
nxdomain-redirect <string>;
parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur␣,→multiple times
preferred-glue <string>;
prefetch <integer> [ <integer> ];provide-ixfr <boolean>;qname-minimization ( strict | relaxed | disabled | off );query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );rate-limit {all-per-second <integer>;errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;log-only <boolean>;max-table-size <integer>;min-table-size <integer>;nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;referrals-per-second <integer>;
responses-per-second <integer>;slip <integer>;
window <integer>;};recursion <boolean>;request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-server-cookie <boolean>;resolver-query-timeout <integer>;
resolver-use-dns64 <boolean>;
response-padding { <address_match_element>; ... } block-size <integer>;
response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [␣,→max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname␣,→| disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only,→<quoted_string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [␣,→nsdname-enable <boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [␣(continues on next page)

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break-dnssec <boolean> ] [ max-policy-ttl <duration> ] [ min-update-interval,→<duration> ] [ min-ns-dots <integer> ] [ nsip-wait-recurse <boolean> ] [␣,→nsdname-wait-recurse <boolean> ] [ qname-wait-recurse <boolean> ] [ recursive,→only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable <boolean> ] [␣,→dnsrps-enable <boolean> ] [ dnsrps-options { <unspecified-text> } ];root-key-sentinel <boolean>;rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string>␣
,→] <string> <string>; ... };send-cookie <boolean>;serial-update-method ( date | increment | unixtime );server <netprefix> {bogus <boolean>;edns <boolean>;edns-udp-size <integer>;edns-version <integer>;keys <server_key>;
max-udp-size <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );padding <integer>;provide-ixfr <boolean>;query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-cookie <boolean>;send-cookie <boolean>;
tcp-keepalive <boolean>;
tcp-only <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers <integer>;}; // may occur multiple times
servfail-ttl <duration>;sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
sortlist { <address_match_element>; ... }; // deprecatedstale-answer-client-timeout ( disabled | off | <integer> );stale-answer-enable <boolean>;stale-answer-ttl <duration>;stale-cache-enable <boolean>;stale-refresh-time <duration>;synth-from-dnssec <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );trust-anchor-telemetry <boolean>;trust-anchors { <string> ( static-key | initial-key | static-ds | initial,→ds ) <integer> <integer> <integer> <quoted_string>; ... }; // may occur␣,→multiple times
trusted-keys { <string> <integer> <integer> <integer> <quoted_string>; ...
,→ }; // may occur multiple times, deprecatedtry-tcp-refresh <boolean>;,→(continues on next page)8.2. Blocks

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update-check-ksk <boolean>; // obsolete
v6-bias <integer>;validate-except { <string>; ... };zero-no-soa-ttl <boolean>;zero-no-soa-ttl-cache <boolean>;zone <string> [ <class> ] {in-view <string>;};zone <string> [ <class> ] {type forward;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>␣
,→| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };};zone <string> [ <class> ] {type hint;
check-names ( fail | warn | ignore );file <quoted_string>;};zone <string> [ <class> ] {type mirror;
allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] {,→<address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ]␣,→[ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [␣,→port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-names ( fail | warn | ignore );database <string>;
file <quoted_string>;
ixfr-from-differences <boolean>;journal <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type primary;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] {,→<address_match_element>; ... };allow-update { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ]␣,→[ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [␣,→port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( fail | warn | ignore );check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean>␣
,→); // deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete
dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>␣
,→| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;,→(continues on next page)8.2. Blocks

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)max-transfer-idle-out <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatednotify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
parental-agents [ port <integer> ] [ source ( <ipv4_address> | *␣,→) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address>␣
,→[ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );serial-update-method ( date | increment | unixtime );sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
update-check-ksk <boolean>; // obsolete
update-policy ( local | { ( deny | grant ) <string> ( 6to4-self |␣,→external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs␣
,→| ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self |␣,→selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ],→<rrtypelist>; ... } );zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type redirect;
allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };dlz <string>;
file <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatedprimaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type secondary;allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] {,→<address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ]␣(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)[ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [␣,→port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-names ( fail | warn | ignore );checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean>␣
,→); // deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete
dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>␣
,→| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
parental-agents [ port <integer> ] [ source ( <ipv4_address> | *␣,→) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address>␣
,→[ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;sig-signing-nodes <integer>;,→(continues on next page)8.2. Blocks

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sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsoletetransfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;
update-check-ksk <boolean>; // obsolete
zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type static-stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>␣
,→| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };server-names { <string>; ... };zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };check-names ( fail | warn | ignore );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean>␣
,→); // deprecatedfile <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address>␣
,→| <ipv6_address> ) [ port <integer> ] [ tls <string> ]; ... };masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-time-in <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );zone-statistics ( full | terse | none | <boolean> );};(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)zone-statistics ( full | terse | none | <boolean> );}; // may occur multiple times

Blocks: topmost
Tags: view

Allows a name server to answer a DNS query differently depending on who is asking.
view view_name [ class ] {match-clients { address_match_list } ;match-destinations { address_match_list } ;match-recursive-only <boolean> ;[ view_option ; ... ][ zone_statement ; ... ]} ;8.2.34 view Block Definition and Usage
The view statement is a powerful feature of BIND 9 that lets a name server answer a DNS query differently dependingon who is asking. It is particularly useful for implementing split DNS setups without having to run multiple servers.
match-clients
Grammar: match-clients { <address_match_element>; ... };Blocks: viewTags: view

Specifies a view of DNS namespace for a given subset of client IP addresses.
match-destinations
Grammar: match-destinations { <address_match_element>; ... };Blocks: viewTags: view

Specifies a view of DNS namespace for a given subset of destination IP addresses.
Each view statement defines a view of the DNS namespace that is seen by a subset of clients. A client matchesa view if its source IP address matches the address_match_list of the view’s match-clients clause, and its
destination IP address matches the address_match_list of the view’s match-destinations clause. If not
specified, both match-clients and match-destinations default to matching all addresses. In addition
to checking IP addresses, match-clients and match-destinations can also take the name of a TSIG
key, which provides a mechanism for the client to select the view.
match-recursive-onlyGrammar: match-recursive-only <boolean>;
Blocks: viewTags: view

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Specifies that only recursive requests can match this view of the DNS namespace.
A view can also be specified as match-recursive-only, which means that only recursive requests frommatching clients match that view. The order of the view statements is significant; a client request is resolved in
the context of the first view that it matches.
Zones defined within a view statement are only accessible to clients that match the view. By defining a zone of thesame name in multiple views, different zone data can be given to different clients: for example, “internal” and “external”
clients in a split DNS setup.
Many of the options given in the options statement can also be used within a view statement, and then apply only
when resolving queries with that view. When no view-specific value is given, the value in the options statement is used
as a default. Also, zone options can have default values specified in the view statement; these view-specific defaults takeprecedence over those in the options statement.
Views are class-specific. If no class is given, class IN is assumed. Note that all non-IN views must contain a hint zone,
since only the IN class has compiled-in default hints.
If there are no view statements in the config file, a default view that matches any client is automatically created in class
IN. Any zone statements specified on the top level of the configuration file are considered to be part of this default view,and the options statement applies to the default view. If any explicit view statements are present, all zone statements
must occur inside view statements.
Here is an example of a typical split DNS setup implemented using view statements:
view "internal" {// This should match our internal networks.
match-clients { 10.0.0.0/8; };// Provide recursive service to internal// clients only.
recursion yes;// Provide a complete view of the example.com// zone including addresses of internal hosts.
zone "example.com" {type primary;file "example-internal.db";};};
view "external" {// Match all clients not matched by the// previous view.
match-clients { any; };// Refuse recursive service to external clients.
recursion no;// Provide a restricted view of the example.com// zone containing only publicly accessible hosts.
zone "example.com" {type primary;file "example-external.db";
};
};

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8.2.35 zone Block Grammar
zone
Blocks: topmost, viewTags: zone

Specifies the zone in a BIND 9 configuration.

8.2.36 zone Block Definition and Usage
Zone Types
type
Blocks: zone (forward, hint, mirror, primary, redirect, secondary, static-stub, stub)Tags: zone

Specifies the kind of zone in a given configuration.
The type keyword is required for the zone configuration unless it is an in-view configuration. Its acceptable values are: primary (or master), secondary (or slave), mirror, hint, stub, static-stub,forward, or redirect.
type primary
Grammar:zone <string> [ <class> ] {type primary;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( fail | warn | ignore );check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete(continues on next page)8.2. Blocks

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-transfer-idle-out <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatednotify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );serial-update-method ( date | increment | unixtime );sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
update-check-ksk <boolean>; // obsolete
update-policy ( local | { ( deny | grant ) <string> ( 6to4-self |␣,→external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs␣
,→| ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self |␣,→selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string> ],→<rrtypelist>; ... } );zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains the main copy of the data for a zone.
A primary zone has a master copy of the data for the zone and is able to provide authoritative answers for it. Type
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master is a synonym for primary.
type secondary
Grammar:zone <string> [ <class> ] {type secondary;allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-names ( fail | warn | ignore );checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete
dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only(continues on next page)8.2. Blocks

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parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsoletetransfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;
update-check-ksk <boolean>; // obsolete
zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains a duplicate of the data for a zone that has been transferred from a primary server.
A secondary zone is a replica of a primary zone. Type slave is a synonym for secondary. The
primaries list specifies one or more IP addresses of primary servers that the secondary contacts
to update its copy of the zone. Primaries list elements can also be names of other primaries lists. By
default, transfers are made from port 53 on the servers; this can be changed for all servers by specifying aport number before the list of IP addresses, or on a per-server basis after the IP address. Authentication
to the primary can also be done with per-server TSIG keys. If a file is specified, then the replica iswritten to this file whenever the zone is changed, and reloaded from this file on a server restart. Use of afile is recommended, since it often speeds server startup and eliminates a needless waste of bandwidth.
Note that for large numbers (in the tens or hundreds of thousands) of zones per server, it is best to use a
two-level naming scheme for zone filenames. For example, a secondary server for the zone example.
com might place the zone contents into a file called ex/example.com, where ex/ is just the firsttwo letters of the zone name. (Most operating systems behave very slowly if there are 100,000 files ina single directory.)
type mirror
Grammar:zone <string> [ <class> ] {type mirror;
allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };(continues on next page)

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allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };check-names ( fail | warn | ignore );database <string>;
file <quoted_string>;
ixfr-from-differences <boolean>;journal <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains a DNSSEC-validated duplicate of the main data for a zone.
A mirror zone is similar to a zone of type secondary, except its data is subject to DNSSEC validation before
being used in answers. Validation is applied to the entire zone during the zone transfer process, and again when
the zone file is loaded from disk upon restarting named. If validation of a new version of a mirror zone fails, a
retransfer is scheduled; in the meantime, the most recent correctly validated version of that zone is used until iteither expires or a newer version validates correctly. If no usable zone data is available for a mirror zone, due toeither transfer failure or expiration, traditional DNS recursion is used to look up the answers instead. Mirror zones
cannot be used in a view that does not have recursion enabled.

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Answers coming from a mirror zone look almost exactly like answers from a zone of type secondary, with
the notable exceptions that the AA bit (“authoritative answer”) is not set, and the AD bit (“authenticated data”) is.
Mirror zones are intended to be used to set up a fast local copy of the root zone (see RFC 8806). A default list of
primary servers for the IANA root zone is built into named, so its mirroring can be enabled using the following
configuration:zone "." {type mirror;};

Mirror zone validation always happens for the entire zone contents. This ensures that each version of the zone usedby the resolver is fully self-consistent with respect to DNSSEC. For incoming mirror zone IXFRs, every revision of
the zone contained in the IXFR sequence is validated independently, in the order in which the zone revisions appear
on the wire. For this reason, it might be useful to force use of AXFR for mirror zones by setting request-ixfr
no; for the relevant zone (or view). Other, more efficient zone verification methods may be added in the future.
To make mirror zone contents persist between named restarts, use the file option.
Mirroring a zone other than root requires an explicit list of primary servers to be provided using the primaries
option (see primaries for details), and a key-signing key (KSK) for the specified zone to be explicitly configured
as a trust anchor (see trust-anchors).
When configuring NOTIFY for a mirror zone, only notify no; and notify explicit; can be used at thezone level; any other notify setting at the zone level is a configuration error. Using any other notify settingat the options or view level causes that setting to be overridden with notify explicit; for the mirrorzone. The global default for the notify option is yes, so mirror zones are by default configured with notify
explicit;.
Outgoing transfers of mirror zones are disabled by default but may be enabled using allow-transfer.
Note: Use of this zone type with any zone other than the root should be considered experimental and may cause
performance issues, especially for zones that are large and/or frequently updated.
type hint
Grammar:zone <string> [ <class> ] {type hint;
check-names ( fail | warn | ignore );file <quoted_string>;};

Blocks: zone, view.zone
Tags: zone

Contains the initial set of root name servers to be used at BIND 9 startup.
The initial set of root name servers is specified using a hint zone. When the server starts, it uses the root hints tofind a root name server and get the most recent list of root name servers. If no hint zone is specified for class IN,
the server uses a compiled-in default set of root servers hints. Classes other than IN have no built-in default hints.
type stubGrammar:

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zone <string> [ <class> ] {type stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };check-names ( fail | warn | ignore );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecatedfile <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-time-in <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains a duplicate of the NS records of a primary zone.
A stub zone is similar to a secondary zone, except that it replicates only the NS records of a primary zone instead of the entire zone. Stub zones are not a standard part of the DNS; they are a feature specific to the BIND
implementation.
Stub zones can be used to eliminate the need for a glue NS record in a parent zone, at the expense of maintaining
a stub zone entry and a set of name server addresses in named.conf. This usage is not recommended for new
configurations, and BIND 9 supports it only in a limited way. If a BIND 9 primary, serving a parent zone, has childstub zones configured, all the secondary servers for the parent zone also need to have the same child stub zones
configured.
Stub zones can also be used as a way to force the resolution of a given domain to use a particular set of authoritative
servers. For example, the caching name servers on a private network using RFC 1918 addressing may be configured
with stub zones for 10.in-addr.arpa to use a set of internal name servers as the authoritative servers for thatdomain.
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zone <string> [ <class> ] {type static-stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };server-names { <string>; ... };zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains a duplicate of the NS records of a primary zone, but statically configured rather than transferred from a
primary server.
A static-stub zone is similar to a stub zone, with the following exceptions: the zone data is statically configured,rather than transferred from a primary server; and when recursion is necessary for a query that matches a staticstub zone, the locally configured data (name server names and glue addresses) is always used, even if different
authoritative information is cached.
Zone data is configured via the server-addresses and server-names zone options.
The zone data is maintained in the form of NS and (if necessary) glue A or AAAA RRs internally, which can be seen
by dumping zone databases with rndc dumpdb -all. The configured RRs are considered local configuration
parameters rather than public data. Non-recursive queries (i.e., those with the RD bit off) to a static-stub zone are
therefore prohibited and are responded to with REFUSED.
Since the data is statically configured, no zone maintenance action takes place for a static-stub zone. For example,
there is no periodic refresh attempt, and an incoming notify message is rejected with an rcode of NOTAUTH.
Each static-stub zone is configured with internally generated NS and (if necessary) glue A or AAAA RRs.
type forward
Grammar:zone <string> [ <class> ] {type forward;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };};Blocks: zone, view.zone
Tags: zone

Contains forwarding statements that apply to queries within a given domain.
A forward zone is a way to configure forwarding on a per-domain basis. A zone statement of type forward
can contain a forward and/or forwarders statement, which applies to queries within the domain given by

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the zone name. If no forwarders statement is present, or an empty list for forwarders is given, then no
forwarding is done for the domain, canceling the effects of any forwarders in the options statement. Thus, to use
this type of zone to change the behavior of the global forward option (that is, “forward first” to, then “forward
only”, or vice versa), but use the same servers as set globally, re-specify the global forwarders.
type redirect
Grammar:zone <string> [ <class> ] {type redirect;
allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };dlz <string>;
file <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatedprimaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls,→<string> ]; ... };zone-statistics ( full | terse | none | <boolean> );};Blocks: zone, view.zone
Tags: zone

Contains information to answer queries when normal resolution would return NXDOMAIN.
Redirect zones are used to provide answers to queries when normal resolution would result in NXDOMAIN being
returned. Only one redirect zone is supported per view. allow-query can be used to restrict which clients see
these answers.
If the client has requested DNSSEC records (DO=1) and the NXDOMAIN response is signed, no substitution
occurs.
To redirect all NXDOMAIN responses to 100.100.100.2 and 2001:ffff:ffff::100.100.100.2, configure a typeredirect zone named “.”, with the zone file containing wildcard records that point to the desired addresses:*. IN A 100.100.100.2 and *. IN AAAA 2001:ffff:ffff::100.100.100.2.
As another example, to redirect all Spanish names (under .ES), use similar entries but with the names *.ES.
instead of *.. To redirect all commercial Spanish names (under COM.ES), use wildcard entries called *.COM.
ES..
Note that the redirect zone supports all possible types; it is not limited to A and AAAA records.
If a redirect zone is configured with a primaries option, then it is transferred in as if it were a secondary zone.
Otherwise, it is loaded from a file as if it were a primary zone.
Because redirect zones are not referenced directly by name, they are not kept in the zone lookup table with normal
primary and secondary zones. To reload a redirect zone, use rndc reload -redirect; to retransfer aredirect zone configured as a secondary, use rndc retransfer -redirect. When using rndc reload
without specifying a zone name, redirect zones are reloaded along with other zones.

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in-view
Grammar zone, view.zone:
zone <string> [ <class> ] {in-view <string>;};

Grammar zone (in-view): in-view <string>;
Blocks: zone, zone (in-view), view.zone
Tags: zone, view

Specifies the view in which a given zone is defined.
When using multiple views, a type primary or type secondary zone configured in one view can bereferenced in a subsequent view. This allows both views to use the same zone without the overhead of loading
it more than once. This is configured using a zone statement, with an in-view option specifying the view inwhich the zone is defined. A zone statement containing in-view does not need to specify a type, since that ispart of the zone definition in the other view.
See Multiple Views for more information.
Class
The zone’s name may optionally be followed by a class. If a class is not specified, class IN (for Internet) is assumed.
This is correct for the vast majority of cases.
The hesiod class is named for an information service from MIT’s Project Athena. It was used to share information
about various systems databases, such as users, groups, printers, and so on. The keyword HS is a synonym for hesiod.
Another MIT development is Chaosnet, a LAN protocol created in the mid-1970s. Zone data for it can be specified with
the CHAOS class.
Zone Options
allow-notify
See the description of allow-notify in Access Control.
allow-query
See the description of allow-query in Access Control.
allow-query-on
See the description of allow-query-on in Access Control.
allow-transfer
See the description of allow-transfer in Access Control.
allow-update
See the description of allow-update in Access Control.
update-policy
This specifies a “Simple Secure Update” policy. See Dynamic Update Policies.
allow-update-forwarding
See the description of allow-update-forwarding in Access Control.

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also-notify
This option is only meaningful if notify is active for this zone. The set of machines that receive a DNS NOTIFY
message for this zone is made up of all the listed name servers (other than the primary) for the zone, plus any IP
addresses specified with also-notify. A port may be specified with each also-notify address to send thenotify messages to a port other than the default of 53. A TSIG key may also be specified to cause the NOTIFY to
be signed by the given key. also-notify is not meaningful for stub zones. The default is the empty list.
check-names
This option is used to restrict the character set and syntax of certain domain names in primary files and/or DNS
responses received from the network. The default varies according to zone type. For primary zones the default
is fail; for secondary zones the default is warn. It is not implemented for hint zones.
check-mx
See the description of check-mx in Boolean Options.
check-spf
See the description of check-spf in Boolean Options.
check-wildcard
See the description of check-wildcard in Boolean Options.
check-integrity
See the description of check-integrity in Boolean Options.
check-sibling
See the description of check-sibling in Boolean Options.
zero-no-soa-ttl
See the description of zero-no-soa-ttl in Boolean Options.
update-check-ksk
See the description of update-check-ksk in Boolean Options.
dnssec-loadkeys-interval
See the description of dnssec-loadkeys-interval in options.
dnssec-update-mode
See the description of dnssec-update-mode in options.
dnssec-dnskey-kskonly
See the description of dnssec-dnskey-kskonly in Boolean Options.
try-tcp-refresh
See the description of try-tcp-refresh in Boolean Options.
database
Grammar: database <string>;
Blocks: dlz, zone (mirror, primary, secondary, stub), view.dlz
Tags: zone

Specifies the type of database to be used to store zone data.
This specifies the type of database to be used to store the zone data. The string following the database keyword isinterpreted as a list of whitespace-delimited words. The first word identifies the database type, and any subsequentwords are passed as arguments to the database to be interpreted in a way specific to the database type.
The default is rbt, BIND 9’s native in-memory red-black tree database. This database does not take arguments.
Other values are possible if additional database drivers have been linked into the server. Some sample drivers areincluded with the distribution but none are linked in by default.
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dialupSee the description of dialup in Boolean Options.
fileGrammar logging.channel: file <quoted_string> [ versions ( unlimited | <integer>) ] [ size <size> ] [ suffix ( increment | timestamp ) ];Grammar zone (hint, mirror, primary, redirect, secondary, stub): file <quoted_string>;
Blocks: zone (hint, mirror, primary, redirect, secondary, stub), logging.channel
Tags: zone

Specifies the zone’s filename.
This sets the zone’s filename. In primary, hint, and redirect zones which do not have primaries
defined, zone data is loaded from this file. In secondary, mirror, stub, and redirect zones which dohave primaries defined, zone data is retrieved from another server and saved in this file. This option is notapplicable to other zone types.
forwardThis option is only meaningful if the zone has a forwarders list. The only value causes the lookup to fail after
trying the forwarders and getting no answer, while first allows a normal lookup to be tried.
forwarders
This is used to override the list of global forwarders. If it is not specified in a zone of type forward, no forwarding
is done for the zone and the global options are not used.
journalGrammar: journal <quoted_string>;
Blocks: zone (mirror, primary, secondary)Tags: zone

Allows the default journal’s filename to be overridden.
This allows the default journal’s filename to be overridden. The default is the zone’s filename with “.jnl” appended. This is applicable to primary and secondary zones.
max-ixfr-ratio
See the description of max-ixfr-ratio in options.
max-journal-size
See the description of max-journal-size in Server Resource Limits.
max-records
See the description of max-records in Server Resource Limits.
max-transfer-time-in
See the description of max-transfer-time-in in Zone Transfers.
max-transfer-idle-in
See the description of max-transfer-idle-in in Zone Transfers.
max-transfer-time-out
See the description of max-transfer-time-out in Zone Transfers.
max-transfer-idle-out
See the description of max-transfer-idle-out in Zone Transfers.

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notifySee the description of notify in Boolean Options.
notify-delay
See the description of notify-delay in Tuning.
notify-to-soa
See the description of notify-to-soa in Boolean Options.
zone-statistics
See the description of zone-statistics in options.
server-addresses
Grammar: server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };Blocks: zone (static-stub)Tags: query, zone

Specifies a list of IP addresses to which queries should be sent in recursive resolution for a static-stub zone.
This option is only meaningful for static-stub zones. This is a list of IP addresses to which queries should be sentin recursive resolution for the zone. A non-empty list for this option internally configures the apex NS RR withassociated glue A or AAAA RRs.
For example, if “example.com” is configured as a static-stub zone with 192.0.2.1 and 2001:db8::1234 in aserver-addresses option, the following RRs are internally configured:
example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234

These records are used internally to resolve names under the static-stub zone. For instance, if the server receives
a query for “www.example.com” with the RD bit on, the server initiates recursive resolution and sends queries to
192.0.2.1 and/or 2001:db8::1234.
server-names
Grammar: server-names { <string>; ... };Blocks: zone (static-stub)Tags: zone

Specifies a list of domain names of name servers that act as authoritative servers of a static-stub zone.
This option is only meaningful for static-stub zones. This is a list of domain names of name servers that act asauthoritative servers of the static-stub zone. These names are resolved to IP addresses when named needs to send
queries to these servers. For this supplemental resolution to be successful, these names must not be a subdomain of
the origin name of the static-stub zone. That is, when “example.net” is the origin of a static-stub zone, “ns.example”
and “master.example.com” can be specified in the server-names option, but “ns.example.net” cannot; it isrejected by the configuration parser.
A non-empty list for this option internally configures the apex NS RR with the specified names. For example, if “example.com” is configured as a static-stub zone with “ns1.example.net” and “ns2.example.net” in aserver-names option, the following RRs are internally configured:
example.com. NS ns1.example.net.
example.com. NS ns2.example.net.

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These records are used internally to resolve names under the static-stub zone. For instance, if the server receives a query for “www.example.com” with the RD bit on, the server initiates recursive resolution, resolves“ns1.example.net” and/or “ns2.example.net” to IP addresses, and then sends queries to one or more of these addresses.
sig-validity-interval
See the description of sig-validity-interval in Tuning.
sig-signing-nodes
See the description of sig-signing-nodes in Tuning.
sig-signing-signatures
See the description of sig-signing-signatures in Tuning.
sig-signing-type
See the description of sig-signing-type in Tuning.
transfer-source
See the description of transfer-source in Zone Transfers.
transfer-source-v6
See the description of transfer-source-v6 in Zone Transfers.
notify-source
See the description of notify-source in Zone Transfers.
notify-source-v6
See the description of notify-source-v6 in Zone Transfers.
min-refresh-time; max-refresh-time; min-retry-time; max-retry-time
See the descriptions in Tuning.
ixfr-from-differences
See the description of ixfr-from-differences in Boolean Options.
(Note that theixfr-from-differences choices of primary and secondary are not available at the zone level.)
key-directory
See the description of key-directory in options.
serial-update-method
See the description of serial-update-method in options.
inline-signing
Grammar: inline-signing <boolean>;
Blocks: dnssec-policy, zone (primary, secondary)Tags: zone, dnssec

Specifies whether BIND 9 maintains a separate signed version of a zone.
The use of inline signing is determined by the dnssec-policy for the zone. If inline-signing is explicitly
set to yes or no in zone, then it overrides any value from dnssec-policy.
multi-masterSee the description of multi-master in Boolean Options.
masterfile-format
See the description of masterfile-format in Tuning.

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max-zone-ttl
See the description of max-zone-ttl in options. The use of this option in zone blocks is deprecated andwill be rendered nonoperational in a future release.
Dynamic Update Policies
BIND 9 supports two methods of granting clients the right to perform dynamic updates to a zone:• allow-update - a simple access control list
• update-policy - fine-grained access control
In both cases, BIND 9 writes the updates to the zone’s filename set in file.
In the case of a DNSSEC zone where inline-signing is disabled, DNSSEC records are also written to the zone’s
filename.
Note: The zone file can no longer be manually updated while named is running; it is now necessary to
perform rndc freeze, edit, and then perform rndc thaw. Comments and formatting in the zone file
are lost when dynamic updates occur.
update-policy
Grammar: update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external | krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs| ms-self | ms-selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self
| selfsub | selfwild | subdomain | tcp-self | wildcard | zonesub ) [ <string>] <rrtypelist>; ... } );Blocks: zone (primary)Tags: transfer

Sets fine-grained rules to allow or deny dynamic updates (DDNS), based on requester identity, updated content,
etc.
The update-policy clause allows more fine-grained control over which updates are allowed. It specifies a setof rules, in which each rule either grants or denies permission for one or more names in the zone to be updated
by one or more identities. Identity is determined by the key that signed the update request, using either TSIG or
SIG(0). In most cases, update-policy rules only apply to key-based identities. There is no way to specify
update permissions based on the client source address.
update-policy rules are only meaningful for zones of type primary, and are not allowed in any otherzone type. It is a configuration error to specify both allow-update and update-policy at the same time.
A pre-defined update-policy rule can be switched on with the command update-policy local;.
named automatically generates a TSIG session key when starting and stores it in a file; this key can then be
used by local clients to update the zone while named is running. By default, the session key is stored in thefile /run/session.key, the key name is “local-ddns”, and the key algorithm is HMAC-SHA256. These
values are configurable with the session-keyfile, session-keyname, and session-keyalg options,
respectively. A client running on the local system, if run with appropriate permissions, may read the session key
from the key file and use it to sign update requests. The zone’s update policy is set to allow that key to change any
record within the zone. Assuming the key name is “local-ddns”, this policy is equivalent to:
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with the additional restriction that only clients connecting from the local system are permitted to send updates.
Note that only one session key is generated by named; all zones configured to use update-policy local
accept the same key.
The command nsupdate -l implements this feature, sending requests to localhost and signing them using the
key retrieved from the session key file.
Other rule definitions look like this:( grant | deny ) identity ruletype

name

types

Each rule grants or denies privileges. Rules are checked in the order in which they are specified in the
update-policy statement. Once a message has successfully matched a rule, the operation is immediately
granted or denied, and no further rules are examined. There are 16 types of rules; the rule type is specified by theruletype field, and the interpretation of other fields varies depending on the rule type.
In general, a rule is matched when the key that signed an update request matches the identity field, the nameof the record to be updated matches the name field (in the manner specified by the ruletype field), and the typeof the record to be updated matches the types field. Details for each rule type are described below.
The identity field must be set to a fully qualified domain name. In most cases, this represents the name of
the TSIG or SIG(0) key that must be used to sign the update request. If the specified name is a wildcard, it issubject to DNS wildcard expansion, and the rule may apply to multiple identities. When a TKEY exchange has
been used to create a shared secret, the identity of the key used to authenticate the TKEY exchange is used as theidentity of the shared secret. Some rule types use identities matching the client’s Kerberos principal (e.g, "host/machine@REALM") or Windows realm (machine$@REALM).
The name field also specifies a fully qualified domain name. This often represents the name of the record to be
updated. Interpretation of this field is dependent on rule type.
If no types are explicitly specified, then a rule matches all types except RRSIG, NS, SOA, NSEC, and NSEC3.
Types may be specified by name, including ANY; ANY matches all types except NSEC and NSEC3, which cannever be updated. Note that when an attempt is made to delete all records associated with a name, the rules arechecked for each existing record type.
If the type is immediately followed by a number in parentheses, that number is the maximum number of recordsof that type permitted to exist in the RRset after an update has been applied. For example, PTR(1) indicates that
only one PTR record is allowed. If an attempt is made to add two PTR records in an update, the second one issilently discarded. If a PTR record already exists, both new records are silently discarded.
If type ANY is specified with a limit, then that limit applies to all types that are not otherwise specified. For
example, A PTR(1) ANY(2) indicates that an unlimited number of A records can exist, but only one PTR
record, and no more than two of any other type.
Typical use with a rule grant * tcp-self . PTR(1); in the zone 2.0.192.IN-ADDR.ARPA looks likethis:
nsupdate -v <<EOF
local 192.0.2.1
del 1.2.0.192.IN-ADDR.ARPA PTR
add 1.2.0.192.IN-ADDR.ARPA 0 PTR EXAMPLE.COM
send
EOF

The ruletype field has 18 values: name, subdomain, zonesub, wildcard, self, selfsub,
selfwild, ms-self, ms-selfsub, ms-subdomain, ms-subdomain-self-rhs, krb5-self,
krb5-selfsub, krb5-subdomain, krb5-subdomain-self-rhs, tcp-self, 6to4-self, andexternal.

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nameWith exact-match semantics, this rule matches when the name being updated is identical to the contents of
the name field.
subdomain
This rule matches when the name being updated is a subdomain of, or identical to, the contents of the namefield.
zonesub
This rule is similar to subdomain, except that it matches when the name being updated is a subdomain of
the zone in which the update-policy statement appears. This obviates the need to type the zone nametwice, and enables the use of a standard update-policy statement in multiple zones without modification.
When this rule is used, the name field is omitted.
wildcard
The name field is subject to DNS wildcard expansion, and this rule matches when the name being updated isa valid expansion of the wildcard.
selfThis rule matches when the name of the record being updated matches the contents of the identity field.
The name field is ignored. To avoid confusion, it is recommended that this field be set to the same value as
the identity field or to “.” The self rule type is most useful when allowing one key per name to update,where the key has the same name as the record to be updated. In this case, the identity field can be
specified as * (asterisk).
selfsub
This rule is similar to self, except that subdomains of self can also be updated.
selfwild
This rule is similar to self, except that only subdomains of self can be updated.
ms-self
When a client sends an UPDATE using a Windows machine principal (for example, machine$@REALM),
this rule allows records with the absolute name of machine.REALM to be updated.
The realm to be matched is specified in the identity field.
The name field has no effect on this rule; it should be set to “.” as a placeholder.
For example, grant EXAMPLE.COM ms-self . A AAAA allows any machine with a valid principal
in the realm EXAMPLE.COM to update its own address records.
ms-selfsub
This is similar to ms-self, except it also allows updates to any subdomain of the name specified in the
Windows machine principal, not just to the name itself.
ms-subdomain
When a client sends an UPDATE using a Windows machine principal (for example, machine$@REALM),
this rule allows any machine in the specified realm to update any record in the zone or in a specified subdomainof the zone.
The realm to be matched is specified in the identity field.
The name field specifies the subdomain that may be updated. If set to “.” or any other name at or above thezone apex, any name in the zone can be updated.
For example, if update-policy for the zone “example.com” includes grant EXAMPLE.COM
ms-subdomain hosts.example.com. AA AAAA, any machine with a valid principal in the realm
EXAMPLE.COM is able to update address records at or below hosts.example.com.

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ms-subdomain-self-rhs
This rule is similar to ms-subdomain, with an additional restriction that PTR and SRV target names mustmatch the name of the machine identified in the principal.
krb5-self
When a client sends an UPDATE using a Kerberos machine principal (for example, host/machine@REALM), this rule allows records with the absolute name of machine to be updated, provided
it has been authenticated by REALM. This is similar but not identical to ms-self, due to the machinepart of the Kerberos principal being an absolute name instead of an unqualified name.
The realm to be matched is specified in the identity field.
The name field has no effect on this rule; it should be set to “.” as a placeholder.
For example, grant EXAMPLE.COM krb5-self . A AAAA allows any machine with a valid principal
in the realm EXAMPLE.COM to update its own address records.
krb5-selfsub
This is similar to krb5-self, except it also allows updates to any subdomain of the name specified in themachine part of the Kerberos principal, not just to the name itself.
krb5-subdomain
This rule is identical to ms-subdomain, except that it works with Kerberos machine principals (i.e., host/machine@REALM) rather than Windows machine principals.
krb5-subdomain-self-rhs
This rule is similar to krb5-subdomain, with an additional restriction that PTR and SRV target names
must match the name of the machine identified in the principal.
tcp-self
This rule allows updates that have been sent via TCP and for which the standard mapping from the client’s
IP address into the in-addr.arpa and ip6.arpa namespaces matches the name to be updated. The
identity field must match that name. The name field should be set to “.”. Note that, since identity isbased on the client’s IP address, it is not necessary for update request messages to be signed.
Note: It is theoretically possible to spoof these TCP sessions.
6to4-self
This allows the name matching a 6to4 IPv6 prefix, as specified in RFC 3056, to be updated by any TCP
connection from either the 6to4 network or from the corresponding IPv4 address. This is intended to allow
NS or DNAME RRsets to be added to the ip6.arpa reverse tree.
The identity field must match the 6to4 prefix in ip6.arpa. The name field should be set to “.”. Note
that, since identity is based on the client’s IP address, it is not necessary for update request messages to besigned.
In addition, if specified for an ip6.arpa name outside of the 2.0.0.2.ip6.arpa namespace,
the corresponding /48 reverse name can be updated. For example, TCP/IPv6 connections from2001:DB8:ED0C::/48 can update records at C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa.
Note: It is theoretically possible to spoof these TCP sessions.
externalThis rule allows named to defer the decision of whether to allow a given update to an external daemon.
The method of communicating with the daemon is specified in the identity field, the format of whichis “local:path”, where “path” is the location of a Unix-domain socket. (Currently, “local” is the only

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supported mechanism.)
Requests to the external daemon are sent over the Unix-domain socket as datagrams with the following format:
Protocol version number (4 bytes, network byte order, currently 1)
Request length (4 bytes, network byte order)
Signer (null-terminated string)
Name (null-terminated string)
TCP source address (null-terminated string)
Rdata type (null-terminated string)
Key (null-terminated string)
TKEY token length (4 bytes, network byte order)
TKEY token (remainder of packet)

The daemon replies with a four-byte value in network byte order, containing either 0 or 1; 0 indicates that the
specified update is not permitted, and 1 indicates that it is.
Warning: The external daemon must not delay communication. This policy is evaluated synchronously;
any wait period negatively affects named performance.

Multiple Views
When multiple views are in use, a zone may be referenced by more than one of them. Often, the views contain different
zones with the same name, allowing different clients to receive different answers for the same queries. At times, however,
it is desirable for multiple views to contain identical zones. The in-view zone option provides an efficient way to do
this; it allows a view to reference a zone that was defined in a previously configured view. For example:
view internal {match-clients { 10/8; };zone example.com {type primary;file "example-external.db";};};
view external {match-clients { any; };zone example.com {in-view internal;};};

An in-view option cannot refer to a view that is configured later in the configuration file.
A zone statement which uses the in-view option may not use any other options, with the exception of forward andforwarders. (These options control the behavior of the containing view, rather than change the zone object itself.)
Zone-level ACLs (e.g., allow-query, allow-transfer), and other configuration details of the zone, are all set in the view thereferenced zone is defined in. Be careful to ensure that ACLs are wide enough for all views referencing the zone.
An in-view zone cannot be used as a response policy zone.
An in-view zone is not intended to reference a forward zone.

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8.3 Statements
BIND 9 supports many hundreds of statements; finding the right statement to control a specific behavior or solve a
particular problem can be a daunting task. To simplify the task for users, all statements have been assigned one ormore tags. Tags are designed to group together statements that have broadly similar functionality; thus, for example, allstatements that control the handling of queries or of zone transfers are respectively tagged under query and transfer.
DNSSEC Tag Statements are those that relate to or control DNSSEC.
Logging Tag Statements relate to or control logging, and typically only appear in a logging block.
Query Tag Statements relate to or control queries.
Security Tag Statements relate to or control security features.
Server Tag Statements relate to or control server behavior, and typically only appear in a server block.
Transfer Tag Statements relate to or control zone transfers.
View Tag Statements relate to or control view selection criteria, and typically only appear in a view block.
Zone Tag Statements relate to or control zone behavior, and typically only appear in a zone block.
Deprecated Tag Statements are those that are now deprecated, but are included here for historical reference.
The following table lists all statements permissible in named.conf, with their associated tags; the next section groups
the statements by tag. Please note that these sections are a work in progress.
Statement

Description

Tags

acl

serverAssigns a symbolic name to an address match list.

algorithm

security
Defines the algorithm to be used in a
key clause.

all-per-second

query
Limits UDP responses of all kinds.

allow-new-zones

server, zone
Controls the ability to add zones atruntime via rndc addzone.

allow-notify

transfer
Definesanaddress_match_list that isallowed to send NOTIFY messages
for the zone, in addition to addresses
defined in the primaries option
for the zone.
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Statement

Description

allow-proxy

Tags
serverDefinesanaddress_match_list for theclient addresses allowed to send
PROXYv2 headers.
allow-proxy-on

serverDefinesanaddress_match_list for theinterface addresses allowed to accept
PROXYv2 headers. The option ismostly intended for multi-homed
configurations.

allow-query

query
Specifies which hosts (an IP addresslist) are allowed to send queries to thisresolver.

allow-query-cache

query
Specifies which hosts (an IP addresslist) can access this server's cache andthus effectively controls recursion.

allow-query-cache-on

query
Specifies which hosts (an IP addresslist) can access this server's cache.
Used on servers with multiple interfaces.

allow-query-on

query
Specifies which local addresses (anIP address list) are allowed to send
queries to this resolver. Used in
multi-homed configurations.

allow-recursion

query
Definesanaddress_match_list of clientsthat are allowed to perform recursive
queries.

allow-recursion-on

query, server
Specifies which local addresses canaccept recursive queries.
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Statement

Description

Tags

allow-transfer

transfer
Definesanaddress_match_list of hoststhat are allowed to transfer the zone
information from this server.

allow-update

transfer
Definesanaddress_match_list of hoststhat are allowed to submit dynamic
updates for primary zones.

allow-update-forwardingtransfer
Definesanaddress_match_list of hoststhat are allowed to submit dynamic
updates to a secondary server fortransmission to a primary.

also-notify

transfer
Defines one or more hosts that aresent NOTIFY messages when zonechanges occur.

answer-cookie

query
Controls whether COOKIE EDNS
replies are sent in response to client
queries.

attach-cacheview
Allows multiple views to share a single cache database.

auth-nxdomain

query
Controls whether BIND, acting as a
resolver, provides authoritative NXDOMAIN (domain does not exist)
answers.

automatic-interface-scanserverControls the automatic rescanning of
network interfaces when addresses
are added or removed.

avoid-v4-udp-ports

deprecatedSpecifies the range(s) of ports to be
excluded from use as sources for
UDP/IPv4 messages.
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Statement

Description

avoid-v6-udp-ports

Tags
deprecatedSpecifies the range(s) of ports to be
excluded from use as sources for
UDP/IPv6 messages.
bindkeys-filednssecSpecifies the pathname of a file tooverride the built-in trusted keys provided by named.

blackholequery
Definesanaddress_match_list of hosts
to ignore. The server will neither
respond to queries from nor send
queries to these addresses.

bogus

serverAllows a remote server to be ignored.

break-dnssec

query
Enables dns64 synthesis even if
the validated result would cause a
DNSSEC validation failure.

bufferedlogging
Controls flushing of log messages.

ca-fileserver, security
Specifies the path to a file containing
TLS certificates for trusted CA authorities, used to verify remote peer
certificates.

catalog-zones

zone
Configures catalog zones in named.
conf.

category

loggingSpecifies the type of data logged to aparticular channel.

cdnskeydnssecSpecifies whether a CDNSKEY
record should be published during
KSK rollover.
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Statement

Description

Tags

cds-digest-types

dnssecSpecifies the digest types to use for
CDS resource records.

cert-fileserver, security
Specifies the path to a file containing
the TLS certificate for a connection.

channellogging
Defines a stream of data that can be
independently logged.

check-dup-records

query, dnssec
Checks primary zones for records
that are treated as different by
DNSSEC but are semantically equalin plain DNS.

check-integrity

zone
Performs post-load zone integrity
checks on primary zones.

check-mx

zone
Checks whether an MX record appears to refer to an IP address.

check-mx-cname

zone
Sets the response to MX records thatrefer to CNAMEs.

check-names

query, server
Restricts the character set and syntax
of certain domain names in primary
files and/or DNS responses received
from the network.

check-siblingzone
Specifies whether to check for sibling glue when performing integrity
checks.

check-spfzone
Specifies whether to check for a TXT
Sender Policy Framework record, if
an SPF record is present.

check-srv-cname

zone
Sets the response to SRV records thatrefer to CNAMEs.
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Statement

Description

check-svcb

Tags
zone

Specifies whether to perform additional checks on SVCB records.
check-wildcard

zone
Checks for non-terminal wildcards.

checkds

dnssecControls whether DS queries are sent
to parental agents.

cipher-suites

security
Specifies a list of allowed cipher
suites in the order of preference for
TLSv1.3 only.

ciphers

security
Specifies a list of allowed ciphers in
the order of preference for TLSv1.2
only.

clientsquery
Specifies an access control list (ACL)of clients that are affected by a given
dns64 directive.

clients-per-query

serverSets the initial minimum numberof simultaneous recursive clients accepted by the server for any given
query before the server drops additional clients.

controls

serverSpecifies control channels to be used
to manage the name server.

cookie-algorithm

serverSets the algorithm to be used whengenerating a server cookie.

cookie-secretserverSpecifies a shared secret used forgenerating and verifying EDNSCOOKIE options within an anycast
cluster.
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Statement

Description

Tags

databasezone
Specifies the type of database to be
used to store zone data.

deny-answer-addresses

query
Rejects A or AAAA records if
the corresponding IPv4 or IPv6
addresses match a given address_match_list.

deny-answer-aliases

query
Rejects CNAME or DNAME
records if the "alias" name matches
a given list of domain_nameelements.

dhparam-fileserver, security
Specifies the path to a file containing
Diffie-Hellman parameters, for enabling cipher suites.

dialupdeprecatedConcentrates zone maintenance sothat all transfers take place once every heartbeat-interval, ideally during a single call.

directory

serverSets the server's working directory.

disable-algorithms

dnssecDisables DNSSEC algorithms from a
specified zone.

disable-ds-digests

zone, dnssec
Disables DS digest types from a specified zone.

disable-empty-zone

server, zone
Disables individual empty zones.

dlz

zone
Configures a Dynamically Loadable
Zone (DLZ) database in named.
conf.
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Statement

Description

dns64

Tags
query

Instructs named to return mapped
IPv4 addresses to AAAA queries
when there are no AAAA records.
dns64-contact

serverSpecifies the name of the contact fordns64 zones.

dns64-server

serverSpecifies the name of the server fordns64 zones.

dnskey-sig-validity

obsoletednskey-ttl

dnssecSpecifies the time to live (TTL) for
DNSKEY resource records.

dnsrps-enable

server, security
Turns on the DNS Response Policy
Service (DNSRPS) interface.

dnsrps-libraryserver, security
Turns on the DNS Response Policy
Service (DNSRPS) interface.

dnsrps-options

server, security
Provides additional RPZ configuration settings, which are passed to
the DNS Response Policy Service(DNSRPS) provider library.

dnssec-accept-expired

dnssecInstructs BIND 9 to accept expired
DNSSEC signatures when validating.

dnssec-dnskey-kskonly

obsoletednssec-loadkeys-interval

dnssecSets the frequency of automatic
checks of the DNSSEC key repository.

dnssec-must-be-secure

deprecatedDefines hierarchies that must or may
not be secure (signed and validated).
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Statement

Description

Tags

dnssec-policy

dnssecDefines a key and signing policy(KASP) for zones.

dnssec-secure-to-insecure

obsoletednssec-update-mode

obsoletednssec-validation

dnssecEnables DNSSEC
named.

validationindnstaplogging
Enables logging of dnstap messages.

dnstap-identity

loggingSpecifies an identity string tosend in dnstap messages.

dnstap-output

logging
Configures the path to which the
dnstap frame stream is sent.

dnstap-version

loggingSpecifies a version string to sendin dnstap messages.

dual-stack-servers

serverSpecifies host names or addresses ofmachines with access to both IPv4
and IPv6 transports.

dump-file

logging
Indicates the pathname of the filewhere the server dumps the database
after rndc dumpdb.

dyndb

zone
Configures a DynDB database in
named.conf.

edns

serverControls the use of the EDNS0 (RFC2671) feature.
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Statement

Description

edns-udp-size

Tags
query

Sets the maximum advertised EDNS
UDP buffer size to control the sizeof packets received from authoritative servers in response to recursive
queries.
edns-version

serverSets the maximum EDNS VERSION
that is sent to the server(s) by the resolver.

empty-contact

server, zone
Specifies the contact name in the returned SOA record for empty zones.

empty-server

server, zone
Specifies the server name in the returned SOA record for empty zones.

empty-zones-enable

server, zone
Enables or disables all empty zones.

endpoints

query, server
Specifies a list of HTTP query paths
on which to listen.

errors-per-second

serverLimits the number of errors for avalid domain name and record type.

excludequery
Allows a list of IPv6 addresses to beignored if they appear in a domainname's AAAA records in dns64.

exempt-clients

query
Exempts specific clients or clientgroups from rate limiting.

fetch-quota-params

query, serverSetstheparametersfordynamic
resizingofthefetches-per-server quota in
response to detected congestion.
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Statement

Description

Tags

fetches-per-server

query, server
Sets the maximum number of simultaneous iterative queries allowed to
be sent by a server to an upstream
name server before the server blocks
additional queries.

fetches-per-zone

query, server
Sets the maximum number of simultaneous iterative queries allowed toany one domain before the server
blocks new queries for data in or beneath that zone.

file

zone
Specifies the zone's filename.

flush-zones-on-shutdown

zone
Controls whether pending zone
writes are flushed when the nameserver exits.

forwardquery
Allows or disallows fallback to recursion if forwarding has failed; it isalways used in conjunction with theforwarders statement.

forwarders

query
Defines one or more hosts to which
queries are forwarded.

fstrm-set-buffer-hint

logging
Sets the number of accumulated
bytes in the output buffer before forcing a buffer flush.

fstrm-set-flush-timeout

logging
Sets the number of seconds that unflushed data remains in the output
buffer.

fstrm-set-input-queue-size

logging
Sets the number of queue entries toallocate for each input queue.
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Statement

Description

fstrm-set-output-notify-threshold

Tags
logging

Sets the number of outstanding queue
entries allowed on an input queue before waking the I/O thread.
fstrm-set-output-queue-model

logging
Sets the queuing semantics to use forqueue objects.

fstrm-set-output-queue-size

logging
Sets the number of queue entries allocated for each output queue.

fstrm-set-reopen-interval

logging
Sets the number of seconds to wait
between attempts to reopen a closed
output stream.

geoip-directory

serverSpecifies the directory containing
GeoIP database files.

heartbeat-interval

deprecatedSets the interval at which the server
performs zone maintenance tasks forall zones marked as dialup.

hostnameserverSpecifies the hostname of theserver to return in response to ahostname.bind query.

httpquery, server
Configures HTTP endpoints on
which to listen for DNS-overHTTPS (DoH) queries.

http-listener-clients

serverLimits the number of active concurrent connections on a per-listener basis.

http-port

query, server
Specifies the TCP port number theserver uses to receive and send unencrypted DNS traffic via HTTP.
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Statement

Description

Tags

http-streams-per-connection

serverLimits the number of active concurrent HTTP/2 streams on a perconnection basis.

https-port

query, server
Specifies the TCP port number theserver uses to receive and send DNSover-HTTPS protocol traffic.

in-viewzone, view
Specifies the view in which a givenzone is defined.

inet

serverSpecifies a TCP socket as a control
channel.

inline-signingzone, dnssec
Specifies whether BIND 9 maintains
a separate signed version of a zone.

interface-interval

serverSets the interval at which the serverscans the network interface list.

ipv4-prefix-length

serverSpecifies the prefix lengths of IPv4
address blocks.

ipv4only-contact

serverSpecifies the contact for the
IPV4ONLY.ARPA zone created by
dns64.

ipv4only-enable

query
Enables automatic IPv4 zones if a
dns64 block is configured.

ipv4only-server

query, server
Specifies the name of the server for
the IPV4ONLY.ARPA zone createdby dns64.

ipv6-prefix-length

serverSpecifies the prefix lengths of IPv6
address blocks.
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Statement

Description

ixfr-from-differences

Tags
transfer

Controls how IXFR transfers are calculated.
journalzone
Allows the default journal's filename
to be overridden.

key

security
Defines a shared secret key for use
with TSIG or the command channel.

key-directorydnssecIndicates the directory where public
and private DNSSEC key files arefound.

key-file

server, security
Specifies the path to a file containing
the private TLS key for a connection.

key-store

dnssecConfigures a DNSSEC key store.

keys

server, security
Specifies one or more server_key
s to be used with a remote server.

lame-ttl

serverSets the resolver's lame cache.

listen-on

serverSpecifies the IPv4 addresses on which
a server listens for DNS queries.

listen-on-v6

serverSpecifies the IPv6 addresses on which
a server listens for DNS queries.

listener-clients

query, server
Specifies a per-listener quota for active connections.

lmdb-mapsize

serverSets a maximum size for the memory map of the new-zone database in
LMDB database format.
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Statement

Description

Tags

log-only

query, logging
Tests rate-limiting parameters without actually dropping any requests.

logging

logging
Configures logging options for thename server.

managed-keys

deprecatedmanaged-keys-directorydnssecSpecifies the directory in which tostore the files that track managed
DNSSEC keys.

mappedquery
Specifies an access control list (ACL)of IPv4 addresses that are to bemapped to the corresponding A
RRset in dns64.

masterfile-format

server, zone
Specifies the file format of zone files.

masterfile-style

serverSpecifies the format of zone
files during a dump, when themasterfile-format is text.

match-clientsview
Specifies a view of DNS namespace
for a given subset of client IP addresses.

match-destinationsview
Specifies a view of DNS namespace
for a given subset of destination IP
addresses.

match-mapped-addresses

serverAllows IPv4-mapped IPv6 addresses
to match address-match list entries
for corresponding IPv4 addresses.

match-recursive-onlyviewSpecifies that only recursive requests
can match this view of the DNS
namespace.
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Statement

Description

max-cache-size

Tags
serverSets the maximum amount of memory to use for an individual cache
database and its associated metadata.
max-cache-ttl

serverSpecifies the maximum time (in seconds) that the server caches ordinary(positive) answers.

max-clients-per-query

serverSets the maximum number of simultaneous recursive clients accepted by
the server for any given query before
the server drops additional clients.

max-ixfr-ratio

transfer
Sets the maximum size for IXFR responses to zone transfer requests.

max-journal-sizetransfer
Controls the size of journal files.

max-ncache-ttl

serverSpecifies the maximum retention
time (in seconds) for storage of negative answers in the server's cache.

max-records

server, zone
Sets the maximum number of records
permitted in a zone.

max-records-per-type

serverSets the maximum number of records
that can be stored in an RRset

max-recursion-depth

serverSets the maximum number of levels of recursion permitted at any
one time while servicing a recursive
query.

max-recursion-queries

query, server
Sets the maximum number of iterative queries while servicing a recursive query.
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Statement

Description

Tags

max-refresh-timetransfer
Limits the zone refresh interval to noless often than the specified value, inseconds.

max-retry-timetransfer
Limits the zone refresh retry interval to no less often than the specified
value, in seconds.

max-rsa-exponent-size

query, dnssec
Sets the maximum RSA exponent
size (in bits) when validating.

max-stale-ttl

serverSpecifies the maximum time that theserver retains records past their normal expiry, to return them as stale
records.

max-table-size

serverSets the maximum size of the tableused to track requests and rate-limit
responses.

max-transfer-idle-intransfer
Specifies the number of minutes after
which inbound zone transfers making
no progress are terminated.

max-transfer-idle-outtransfer
Specifies the number of minutes after
which outbound zone transfers making no progress are terminated.

max-transfer-time-intransfer
Specifies the number of minutes after which inbound zone transfers are
terminated.

max-transfer-time-outtransfer
Specifies the number of minutes after which outbound zone transfers are
terminated.

max-types-per-nameserverSets the maximum number of RR
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Statement

Description

max-udp-size

Tags
query

Sets the maximum EDNS UDP message size sent by named.
max-validation-failures-per-fetch

server
Set the maximum number of
DNSSEC validation failures that canhappen in single fetch

max-validations-per-fetch

server
Set the maximum number of
DNSSEC validations that canhappen in single fetch

max-zone-ttl

deprecatedSpecifies a maximum permissible
time-to-live (TTL) value, in seconds.

memstatistics

server, logging
Controls whether memory statistics
are written to the file specified by
memstatistics-file at exit.

memstatistics-file

logging
Sets the pathname of the file where
the server writes memory usage
statistics on exit.

message-compression

query
Controls whether DNS name compression is used in responses to regular queries.

min-cache-ttl

serverSpecifies the minimum time (in seconds) that the server caches ordinary(positive) answers.

min-ncache-ttl

serverSpecifies the minimum retention
time (in seconds) for storage ofnegative answers in the server's
cache.

min-refresh-timetransfer
Limits the zone refresh interval to no
more often than the specified value,
in seconds.
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Statement

Description

Tags

min-retry-timetransfer
Limits the zone refresh retry interval
to no more often than the specified
value, in seconds.

min-table-size

query
Sets the minimum size of the tableused to track requests and rate-limit
responses.

minimal-any

query
Controls whether the server replies
with only one of the RRsets for aquery name, when generating a positive response to a query of type ANY
over UDP.

minimal-responses

query
Controls whether the server only adds
records to the authority and additional data sections when they are required (e.g. delegations, negative responses). This improves server performance.

multi-mastertransfer
Controls whether serial number mismatch errors are logged.

new-zones-directoryzone
Specifies the directory where configuration parameters are stored forzones added by rndc addzone.

no-case-compress

serverSpecifies a list of addresses that require case-insensitive compression in
responses.

nocookie-udp-size

query
Sets the maximum size of UDP responses that are sent to queries without a valid server COOKIE.

nodata-per-second

query
Limits the number of empty (NODATA) responses for a valid domain
name.
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Statement

Description

notifyTagstransfer

Controls whether NOTIFY messages
are sent on zone changes.
notify-delay

zone, transfer
Sets the delay (in seconds) between
sending sets of NOTIFY messages
for a zone.

notify-ratezone, transfer
Specifies the rate at which NOTIFY
requests are sent during normal zone
maintenance operations.

notify-source

transfer
Defines the IPv4 address (and optional port) to be used for outgoing
NOTIFY messages.

notify-source-v6transfer
Defines the IPv6 address (and optional port) to be used for outgoing
NOTIFY messages.

notify-to-soatransfer
Controls whether the name servers in
the NS RRset are checked against the
SOA MNAME.

nsec3paramdnssecSpecifies the use of NSEC3 insteadof NSEC, and sets NSEC3 parameters.

nta-lifetime

dnssecSpecifies the lifetime, in seconds,
for negative trust anchors added via
rndc nta.

nta-recheck

dnssecSpecifies the time interval for checking whether negative trust anchors
added via rndc nta are still necessary.

null

logging
Causes all messages sent to the logging channel to be discarded.
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Statement

Description

Tags

nxdomain-redirect

query
Appends the specified suffix to theoriginal query name, when replacing an NXDOMAIN with a redirect
namespace.

nxdomains-per-second

query
Limits the number of undefined subdomains for a valid domain name.

options

serverDefines global options to be used by
BIND 9.

padding

serverAdds EDNS Padding options to outgoing messages to increase the packet
size.

parent-ds-ttl

dnssecSets the time to live (TTL) of the DS
RRset used by the parent zone.

parent-propagation-delay

zone, dnssec
Sets the propagation delay from thetime the parent zone is updated towhen the new version is served by allof the parent zone's name servers.

parental-agentszone
Defines a list of delegation agents to
be used by primary and secondary
zones.

parental-source

dnssecSpecifies which local IPv4 source address is used to send parental DS
queries.

parental-source-v6

dnssecSpecifies which local IPv6 source address is used to send parental DS
queries.

pid-file

serverSpecifies the pathname of the filewhere the server writes its process ID.

pkcs11-uri

pkcs11, dnssec
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Statement

Description

Tags

pluginserverConfiguresconf.

pluginsin

named.

port

query, server
Specifies the UDP/TCP port number
the server uses to receive and send
DNS protocol traffic.

prefer-server-ciphersserver, security
Specifies that server ciphers should
be preferred over client ones.

preferred-glue

queryControls the order of glue records inan A or AAAA response.

prefetch

query
Specifies the "trigger" time-to-live(TTL) value at which prefetch of thecurrent query takes place.

primaries

zone
Defines one or more primary servers
for a zone.

print-category

logging
Includes the category in log messages.

print-severity

logging
Includes the severity in log messages.

print-time

loggingSpecifies the time format for log messages.

protocols

security
Specifies the allowed versions of the
TLS protocol.

provide-ixfr

transfer
Controls whether a primary responds
to an incremental zone request(IXFR) or only responds with a fullzone transfer (AXFR).
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Statement

Description

Tags

publish-safety

dnssecIncreases the amount of time between when keys are published andwhen they become active, to allow for
unforeseen events.

purge-keys

dnssecSpecifies the amount of time after
which DNSSEC keys that have been
deleted from the zone can be removed from disk.

qname-minimization

query
Controls QNAME minimization behavior in the BIND 9 resolver.

qps-scalequery
Tightens defenses during DNS attacks by scaling back the ratio of thecurrent query-per-second rate.

query-source

query
Controls the IPv4 address from which
queries are issued.

query-source-v6

query
Controls the IPv6 address from which
queries are issued.

querylog

server, logging
Specifies whether query logging
should be active when named firststarts.

rate-limit

query
Controls excessive UDP responses,
to prevent BIND 9 from being used toamplify reflection denial-of-service(DoS) attacks.

recursing-fileserverSpecifies the pathname of the filewhere the server dumps queries thatare currently recursing via rndc
recursing.

recursion

query
Defines whether recursion
caching are allowed.

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Statement

Description

recursive-clients

Tags
query

Specifies the maximum numberof concurrent recursive queries theserver can perform.
recursive-only

query
Toggles whether dns64 synthesis
occurs only for recursive queries.

referrals-per-second

query
Limits the number of referrals or delegations to a server for a given domain.

remote-hostname

security
Specifies the expected hostname in
the TLS certificate of the remote
server.

request-expire

query, transfer
Specifies whether the local server
requests the EDNS EXPIRE value,
when acting as a secondary.

request-ixfr

transfer
Controls whether a secondary requests an incremental zone transfer (IXFR) or a full zone transfer(AXFR).

request-nsid

query
Controls whether an empty EDNS(0)NSID (Name Server Identifier) option is sent with all queries to authoritative name servers during iterative
resolution.

require-cookie

query
Controls whether responses without aserver cookie are accepted

require-server-cookie

query
Controls whether a valid server
cookie is required before sending afull response to a UDP request.
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Statement

Description

Tags

resolver-query-timeout

query
Specifies the length of time, in milliseconds, that a resolver attempts toresolve a recursive query before failing.

resolver-use-dns64

serverSpecifies whether to apply DNS64
mappings when sending queries.

response-padding

query
Adds an EDNS Padding option to
encrypted messages, to reduce thechance of guessing the contents
based on size.

response-policy

query, server, zone, security
Specifies response policy zones forthe view or among global options.

responses-per-second

query
Limits the number of non-empty responses for a valid domain name andrecord type.

retire-safety

dnssecIncreases the amount of time a key
remains published after it is no longer
active, to allow for unforeseen events.

reuseport

serverEnables kernel load-balancing ofsockets.

root-key-sentinel

serverControls whether BIND 9 responds toroot key sentinel probes.

rrset-order

query
Defines the order in which equal RRs(RRsets) are returned.

searchquery
Specifies whether a Dynamically
Loadable Zone (DLZ) module isqueried for an answer to a query
name.
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Statement

Description

secretTags
security

Defines a Base64-encoded string to
be used as the secret by the algorithm.
secroots-filednssecSpecifies the pathname of the filewhere the server dumps security
roots, when using rndc secroots.

send-cookie

query
Controls whether a COOKIE EDNS
option is sent along with a query.

serial-query-ratetransfer
Defines an upper limit on the numberof queries per second issued by theserver, when querying the SOA RRs
used for zone transfers.

serial-update-methodzone
Specifies the update method to be
used for the zone serial number in the
SOA record.

serverserverDefines characteristics to be associated with a remote name server.

server-addresses

query, zone
Specifies a list of IP addresses towhich queries should be sent in recursive resolution for a static-stub zone.

server-id

serverSpecifies the ID of the server to return in response to a ID.SERVER
query.

server-nameszone
Specifies a list of domain names ofname servers that act as authoritative
servers of a static-stub zone.

servfail-ttl

serverSets the length of time (in seconds)
that a SERVFAIL response is cached.
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Statement

Description

Tags

session-keyalg

security
Specifies the algorithm to use for the
TSIG session key.

session-keyfile

security
Specifies the pathname of the filewhere a TSIG session key is written,
when generated by named for use by
nsupdate -l.

session-keyname

security
Specifies the key name for the TSIG
session key.

session-tickets

security
Enables or disables session resumption through TLS session tickets.

severity

logging
Defines the priority level of log messages.

sig-signing-nodes

dnssecSpecifies the maximum number ofnodes to be examined in each quantum, when signing a zone with a new
DNSKEY.

sig-signing-signatures

dnssecSpecifies the threshold for the number of signatures that terminates processing a quantum, when signing azone with a new DNSKEY.

sig-signing-typednssecSpecifies a private RDATA typeto use when generating signing-state
records.

sig-validity-interval

obsolete

sig0checks-quota

serverSpecifies the maximum number ofconcurrent SIG(0) signature checks
that can be processed by the server.
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Statement

Description

sig0checks-quota-exempt

Tags
serverExempts specific clients or clientgroups from SIG(0) signature checking quota.
signatures-jitter

dnssecSpecifies a range for signatures expirations.

signatures-refresh

dnssecSpecifies how frequently an RRSIG
record is refreshed.

signatures-validity

dnssecIndicates the validity period of an
RRSIG record.

signatures-validity-dnskey

dnssecIndicates the validity period of
DNSKEY records.

slip

query
Sets the number of "slipped" responses to minimize the use of forgedsource addresses for an attack.

sortlistquery, deprecatedControls the ordering of RRs returned to the client, based on theclient's IP address.

stale-answer-client-timeout

query, server
Defines the amount of time (in milliseconds) that named waits before
attempting to answer a query with astale RRset from cache.

stale-answer-enable

query, server
Enables the returning of "stale"cached answers when the nameservers for a zone are not answering.

stale-answer-ttl

query
Specifies the time to live (TTL) to be
returned on stale answers, in seconds.

stale-cache-enable

query, server
Enables the retention of "stale"cached answers.
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Statement

Description

Tags

stale-refresh-timequery, server
Sets the time window for the returnof "stale" cached answers before thenext attempt to contact, if the nameservers for a given zone are not responding.

startup-notify-ratezone, transfer
Specifies the rate at which NOTIFY
requests are sent when the nameserver is first starting, or when newzones have been added.

statistics-channels

loggingSpecifies the communication channels to be used by system administrators to access statistics informationon the name server.

statistics-fileserver, logging
Specifies the pathname of the filewhere the server appends statistics,
when using rndc stats.

stderrlogging
Directs the logging channel output tothe server's standard error stream.

streams-per-connection

query, server
Specifies the maximum number ofconcurrent HTTP/2 streams over an
HTTP/2 connection.

suffixquery
Defines trailing bits for mapped IPv4
address bits in dns64.

synth-from-dnssec

dnssecEnables support for RFC 8198, Aggressive Use of DNSSEC-Validated
Cache.

sysloglogging
Directs the logging channel to the system log.
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Statement

Description

tcp-advertised-timeout

Tags
query

Sets the timeout value (in milliseconds) that the server sends in responses containing the EDNS TCP
keepalive option.
tcp-clients

serverSpecifies the maximum number of simultaneous client TCP connections
accepted by the server.

tcp-idle-timeout

query
Sets the amount of time (in milliseconds) that the server waits on an idle
TCP connection before closing it, if
the EDNS TCP keepalive option is
not in use.

tcp-initial-timeout

query, server
Sets the amount of time (in milliseconds) that the server waits on a new
TCP connection for the first message
from the client.

tcp-keepalive

serverAdds EDNS TCP keepalive to messages sent over TCP.

tcp-keepalive-timeout

query
Sets the amount of time (in milliseconds) that the server waits on an idle
TCP connection before closing it, if
the EDNS TCP keepalive option is inuse.

tcp-listen-queue

serverSets the listen-queue depth.

tcp-only

serverSets the transport protocol to TCP.

tcp-receive-buffer

serverSets the operating system's receive
buffer size for TCP sockets.

tcp-send-buffer

serverSets the operating system's sendbuffer size for TCP sockets.
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Statement

Description

Tagstkey-domain

security
Sets the domain appended to thenames of all shared keys generated
with TKEY.

tkey-gssapi-credential

security
Sets the security credential for authentication keys requested by the
GSS-TSIG protocol.

tkey-gssapi-keytab

security
Sets the KRB5 keytab file to use for
GSS-TSIG updates.

tls

security
Configures a TLS connection.

tls-port

query, server
Specifies the TCP port number theserver uses to receive and send DNSover-TLS protocol traffic.

transfer-format

transfer
Controls whether multiple records
can be packed into a message duringzone transfers.

transfer-message-sizetransfer
Limits the uncompressed size of
DNS messages used in zone transfers
over TCP.

transfer-source

transfer
Defines which local IPv4 address(es)are bound to TCP connections used
to fetch zones transferred inbound by
the server.

transfer-source-v6transfer
Defines which local IPv6 address(es)are bound to TCP connections used
to fetch zones transferred inbound by
the server.

transfers

serverLimits the number of concurrent inbound zone transfers from a server.
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Statement

Description

transfers-in

Tagstransfer

Limits the number of concurrent inbound zone transfers.
transfers-outtransfer
Limits the number of concurrent outbound zone transfers.

transfers-per-ns

transfer
Limits the number of concurrent inbound zone transfers from a remote
server.

trust-anchor-telemetry

dnssecInstructs named to send speciallyformed queries once per day to domains for which trust anchors havebeen configured.

trust-anchorsdnssecDefines DNSSEC trust anchors.

trusted-keys

deprecatedtry-tcp-refreshtransfer
Specifies that BIND 9 should attempt
to refresh a zone using TCP if UDP
queries fail.

type

zone
Specifies the kind of zone in a given
configuration.

type forward

zone
Contains forwarding statements that
apply to queries within a given domain.

type hint

zone
Contains the initial set of root nameservers to be used at BIND 9 startup.

type mirror

zone
Contains a DNSSEC-validated duplicate of the main data for a zone.

type primaryzone
Contains the main copy of the data
for a zone.
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Statement

Description

Tagstype redirectzone
Contains information to answer
queries when normal resolution
would return NXDOMAIN.

type secondary

zone
Contains a duplicate of the data for azone that has been transferred from a
primary server.

type static-stubzoneContains a duplicate of the NS
records of a primary zone, but statically configured rather than transferred from a primary server.

type stubzone
Contains a duplicate of the NS
records of a primary zone.

udp-receive-buffer

serverSets the operating system's receive
buffer size for UDP sockets.

udp-send-buffer

serverSets the operating system's sendbuffer size for UDP sockets.

unix

obsolete
Specifies a Unix domain socket as acontrol channel.

update-check-ksk

obsolete

update-policy

transfer
Sets fine-grained rules to allow ordeny dynamic updates (DDNS),
based on requester identity, updated
content, etc.

update-quota

serverSpecifies the maximum number ofconcurrent DNS UPDATE messages
that can be processed by the server.

use-v4-udp-ports

deprecatedSpecifies a list of ports that are valid
sources for UDP/IPv4 messages.
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Statement

Descriptionuse-v6-udp-ports

Tags
deprecatedSpecifies a list of ports that are valid
sources for UDP/IPv6 messages.
v6-biasquery, serverIndicates the number of milliseconds
of preference to give to IPv6 nameservers.

validate-except

dnssecSpecifies a list of domain names atand beneath which DNSSEC validation should not be performed.

versionserverSpecifies the version number of theserver to return in response to aversion.bind query.

view

view
Allows a name server to answer a
DNS query differently depending on
who is asking.

window

query
Specifies the length of time during
which responses are tracked.

zero-no-soa-ttl

query, server, zone
Specifies whether to set the time tolive (TTL) of the SOA record to zero,
when returning authoritative negative
responses to SOA queries.

zero-no-soa-ttl-cachequery, server, zone
Sets the time to live (TTL) to zero
when caching a negative response to
an SOA query.

zone

zone
Specifies the zone in a BIND 9 configuration.

zone-propagation-delay

zone, dnssec
Sets the propagation delay from thetime a zone is first updated to when
the new version of the zone is servedby all secondary servers.
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Statement

DescriptionTagszone-statistics

logging, zone
Controls the level of statistics gathered for all zones.

8.4 Statements by Tag
These tables group the various statements permissible in named.conf by their corresponding tag.

8.4.1 DNSSEC Tag Statements
Statement

Description

bindkeys-fileSpecifies the pathname of a file to override the built-in
trusted keys provided by named.
cdnskey
Specifies whether a CDNSKEY record should be published during KSK rollover.
cds-digest-types
Specifies the digest types to use for CDS resource records.
check-dup-records
Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain
DNS.
checkds
Controls whether DS queries are sent to parental agents.
disable-algorithms
Disables DNSSEC algorithms from a specified zone.
disable-ds-digests
Disables DS digest types from a specified zone.
dnskey-ttl
Specifies the time to live (TTL) for DNSKEY resource
records.
dnssec-accept-expired
Instructs BIND 9 to accept expired DNSSEC signatures
when validating.
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Statement

Description

dnssec-loadkeys-interval
Sets the frequency of automatic checks of the DNSSEC
key repository.
dnssec-policy
Defines a key and signing policy (KASP) for zones.
dnssec-validation
Enables DNSSEC validation in named.
inline-signing
Specifies whether BIND 9 maintains a separate signed
version of a zone.
key-directory
Indicates the directory where public and private DNSSEC
key files are found.
key-store
Configures a DNSSEC key store.
managed-keys-directorySpecifies the directory in which to store the files that track
managed DNSSEC keys.
max-rsa-exponent-size
Sets the maximum RSA exponent size (in bits) when validating.
nsec3paramSpecifies the use of NSEC3 instead of NSEC, and sets
NSEC3 parameters.
nta-lifetime
Specifies the lifetime, in seconds, for negative trust anchors added via rndc nta.
nta-recheck
Specifies the time interval for checking whether negative
trust anchors added via rndc nta are still necessary.
parent-ds-ttl
Sets the time to live (TTL) of the DS RRset used by theparent zone.
parent-propagation-delay
Sets the propagation delay from the time the parent zone
is updated to when the new version is served by all of theparent zone's name servers.
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Statement

Description

parental-source
Specifies which local IPv4 source address is used to sendparental DS queries.
parental-source-v6
Specifies which local IPv6 source address is used to sendparental DS queries.
pkcs11-uri
publish-safety
Increases the amount of time between when keys are published and when they become active, to allow for unforeseen events.
purge-keys
Specifies the amount of time after which DNSSEC keys
that have been deleted from the zone can be removed fromdisk.
retire-safety
Increases the amount of time a key remains published after it is no longer active, to allow for unforeseen events.
secroots-fileSpecifies the pathname of the file where the server dumps
security roots, when using rndc secroots.
sig-signing-nodes
Specifies the maximum number of nodes to be examined in each quantum, when signing a zone with a new
DNSKEY.
sig-signing-signatures
Specifies the threshold for the number of signatures thatterminates processing a quantum, when signing a zone
with a new DNSKEY.
sig-signing-typeSpecifies a private RDATA type to use when generating
signing-state records.
signatures-jitter
Specifies a range for signatures expirations.
signatures-refreshSpecifies how frequently an RRSIG record is refreshed.
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Statement

Description

signatures-validity
Indicates the validity period of an RRSIG record.
signatures-validity-dnskey
Indicates the validity period of DNSKEY records.
synth-from-dnssec
Enables support for RFC 8198, Aggressive Use of
DNSSEC-Validated Cache.
trust-anchor-telemetry
Instructs named to send specially formed queries once
per day to domains for which trust anchors have been configured.
trust-anchors
Defines DNSSEC trust anchors.
validate-except
Specifies a list of domain names at and beneath which
DNSSEC validation should not be performed.
zone-propagation-delay
Sets the propagation delay from the time a zone is first
updated to when the new version of the zone is served by
all secondary servers.

8.4.2 Logging Tag Statements
Statement

Description

bufferedControls flushing of log messages.
category
Specifies the type of data logged to a particular channel.
channelDefines a stream of data that can be independently logged.
dnstapEnables logging of dnstap messages.
dnstap-identity
Specifies an identity string to send in dnstap messages.
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Statement

Description

dnstap-output
Configures the path to which the dnstap frame stream
is sent.
dnstap-version
Specifies a version string to send in dnstap messages.
dump-file
Indicates the pathname of the file where the server dumps
the database after rndc dumpdb.
fstrm-set-buffer-hint
Sets the number of accumulated bytes in the output buffer
before forcing a buffer flush.
fstrm-set-flush-timeout
Sets the number of seconds that unflushed data remains in
the output buffer.
fstrm-set-input-queue-size
Sets the number of queue entries to allocate for each input
queue.
fstrm-set-output-notify-threshold
Sets the number of outstanding queue entries allowed on
an input queue before waking the I/O thread.
fstrm-set-output-queue-model
Sets the queuing semantics to use for queue objects.
fstrm-set-output-queue-size
Sets the number of queue entries allocated for each output
queue.
fstrm-set-reopen-interval
Sets the number of seconds to wait between attempts toreopen a closed output stream.
log-only
Tests rate-limiting parameters without actually dropping
any requests.
logging
Configures logging options for the name server.
memstatistics
Controls whether memory statistics are written to the filespecified by memstatistics-file at exit.
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Statement

Description

memstatistics-file
Sets the pathname of the file where the server writes memory usage statistics on exit.
null
Causes all messages sent to the logging channel to be discarded.
print-category
Includes the category in log messages.
print-severity
Includes the severity in log messages.
print-timeSpecifies the time format for log messages.
querylog
Specifies whether query logging should be active when
named first starts.
severity
Defines the priority level of log messages.
statistics-channels
Specifies the communication channels to be used by system administrators to access statistics information on thename server.
statistics-fileSpecifies the pathname of the file where the server appends statistics, when using rndc stats.
stderrDirects the logging channel output to the server's standard
error stream.
syslogDirects the logging channel to the system log.
zone-statistics
Controls the level of statistics gathered for all zones.

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8.4.3 Query Tag Statements
Statement

Description

all-per-second
Limits UDP responses of all kinds.
allow-query
Specifies which hosts (an IP address list) are allowed tosend queries to this resolver.
allow-query-cache
Specifies which hosts (an IP address list) can access thisserver's cache and thus effectively controls recursion.
allow-query-cache-on
Specifies which hosts (an IP address list) can access thisserver's cache. Used on servers with multiple interfaces.
allow-query-on
Specifies which local addresses (an IP address list) areallowed to send queries to this resolver. Used in multihomed configurations.
allow-recursion
Defines an address_match_list of clients that areallowed to perform recursive queries.
allow-recursion-on
Specifies which local addresses can accept recursive
queries.
answer-cookie
Controls whether COOKIE EDNS replies are sent in response to client queries.
auth-nxdomain
Controls whether BIND, acting as a resolver, provides
authoritative NXDOMAIN (domain does not exist) answers.
blackhole
Defines an address_match_list of hosts to ignore.
The server will neither respond to queries from nor send
queries to these addresses.
break-dnssec
Enables dns64 synthesis even if the validated result
would cause a DNSSEC validation failure.
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Statement

Description

check-dup-records
Checks primary zones for records that are treated as different by DNSSEC but are semantically equal in plain
DNS.
check-names
Restricts the character set and syntax of certain domainnames in primary files and/or DNS responses received
from the network.
clients
Specifies an access control list (ACL) of clients that are
affected by a given dns64 directive.
deny-answer-addresses
Rejects A or AAAA records if the corresponding IPv4 or IPv6 addresses match a given address_match_list.
deny-answer-aliases
Rejects CNAME or DNAME records if the "alias" namematches a given list of domain_name elements.
dns64
Instructs named to return mapped IPv4 addresses to
AAAA queries when there are no AAAA records.
edns-udp-size
Sets the maximum advertised EDNS UDP buffer size tocontrol the size of packets received from authoritative
servers in response to recursive queries.
endpoints
Specifies a list of HTTP query paths on which to listen.
excludeAllows a list of IPv6 addresses to be ignored if they appear
in a domain name's AAAA records in dns64.
exempt-clients
Exempts specific clients or client groups from rate limiting.
fetch-quota-params
Sets the parameters for dynamic resizing of thefetches-per-server quota in response to detected
congestion.
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Statement

Description

fetches-per-server
Sets the maximum number of simultaneous iterative
queries allowed to be sent by a server to an upstream nameserver before the server blocks additional queries.
fetches-per-zone
Sets the maximum number of simultaneous iterative
queries allowed to any one domain before the server
blocks new queries for data in or beneath that zone.
forwardAllows or disallows fallback to recursion if forwarding
has failed; it is always used in conjunction with the forwarders statement.
forwarders
Defines one or more hosts to which queries are forwarded.
httpConfigures HTTP endpoints on which to listen for DNSover-HTTPS (DoH) queries.
http-port
Specifies the TCP port number the server uses to receiveand send unencrypted DNS traffic via HTTP.
https-port
Specifies the TCP port number the server uses to receiveand send DNS-over-HTTPS protocol traffic.
ipv4only-enable
Enables automatic IPv4 zones if a dns64 block is configured.
ipv4only-server
Specifies the name of the server
IPV4ONLY.ARPA zone created by dns64.

for

the

listener-clients
Specifies a per-listener quota for active connections.
log-only
Tests rate-limiting parameters without actually dropping
any requests.
mappedSpecifies an access control list (ACL) of IPv4 addresses
that are to be mapped to the corresponding A RRset in
dns64.
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Statement

Description

max-recursion-queries
Sets the maximum number of iterative queries while servicing a recursive query.
max-rsa-exponent-size
Sets the maximum RSA exponent size (in bits) when validating.
max-udp-size
Sets the maximum EDNS UDP message size sent by
named.
message-compression
Controls whether DNS name compression is used in responses to regular queries.
min-table-size
Sets the minimum size of the table used to track requests
and rate-limit responses.
minimal-any
Controls whether the server replies with only one of the
RRsets for a query name, when generating a positive response to a query of type ANY over UDP.
minimal-responses
Controls whether the server only adds records to the authority and additional data sections when they are required(e.g. delegations, negative responses). This improves
server performance.
nocookie-udp-size
Sets the maximum size of UDP responses that are sent toqueries without a valid server COOKIE.
nodata-per-second
Limits the number of empty (NODATA) responses for avalid domain name.
nxdomain-redirect
Appends the specified suffix to the original query name,when replacing an NXDOMAIN with a redirect namespace.
nxdomains-per-second
Limits the number of undefined subdomains for a valid
domain name.
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Statement

Description

portSpecifies the UDP/TCP port number the server uses toreceive and send DNS protocol traffic.
preferred-glueControls the order of glue records in an A or AAAA response.
prefetch
Specifies the "trigger" time-to-live (TTL) value at which
prefetch of the current query takes place.
qname-minimization
Controls QNAME minimization behavior in the BIND 9
resolver.
qps-scaleTightens defenses during DNS attacks by scaling back theratio of the current query-per-second rate.
query-source
Controls the IPv4 address from which queries are issued.
query-source-v6
Controls the IPv6 address from which queries are issued.
rate-limit
Controls excessive UDP responses, to prevent BIND 9from being used to amplify reflection denial-of-service(DoS) attacks.
recursion
Defines whether recursion and caching are allowed.
recursive-clients
Specifies the maximum number of concurrent recursive
queries the server can perform.
recursive-only
Toggles whether dns64 synthesis occurs only for recursive queries.
referrals-per-second
Limits the number of referrals or delegations to a server
for a given domain.
request-expire
Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.
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Statement

Description

request-nsid
Controls whether an empty EDNS(0) NSID (NameServer Identifier) option is sent with all queries to authoritative name servers during iterative resolution.
require-cookie
Controls whether responses without a server cookie are
acceptedrequire-server-cookie
Controls whether a valid server cookie is required before
sending a full response to a UDP request.
resolver-query-timeout
Specifies the length of time, in milliseconds, that a resolver attempts to resolve a recursive query before failing.
response-padding
Adds an EDNS Padding option to encrypted messages, toreduce the chance of guessing the contents based on size.
response-policy
Specifies response policy zones for the view or among
global options.
responses-per-second
Limits the number of non-empty responses for a valid domain name and record type.
rrset-order
Defines the order in which equal RRs (RRsets) are returned.
searchSpecifies whether a Dynamically Loadable Zone (DLZ)
module is queried for an answer to a query name.
send-cookie
Controls whether a COOKIE EDNS option is sent alongwith a query.
server-addresses
Specifies a list of IP addresses to which queries should besent in recursive resolution for a static-stub zone.
slip
Sets the number of "slipped" responses to minimize theuse of forged source addresses for an attack.
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Statement

Description

sortlist
Controls the ordering of RRs returned to the client, basedon the client's IP address.
stale-answer-client-timeout
Defines the amount of time (in milliseconds) that named
waits before attempting to answer a query with a stale
RRset from cache.
stale-answer-enable
Enables the returning of "stale" cached answers when thename servers for a zone are not answering.
stale-answer-ttl
Specifies the time to live (TTL) to be returned on staleanswers, in seconds.
stale-cache-enable
Enables the retention of "stale" cached answers.
stale-refresh-time
Sets the time window for the return of "stale" cachedanswers before the next attempt to contact, if the nameservers for a given zone are not responding.
streams-per-connection
Specifies the maximum number of concurrent HTTP/2
streams over an HTTP/2 connection.
suffixDefines trailing bits for mapped IPv4 address bits in
dns64.
tcp-advertised-timeout
Sets the timeout value (in milliseconds) that the server
sends in responses containing the EDNS TCP keepalive
option.
tcp-idle-timeout
Sets the amount of time (in milliseconds) that the server
waits on an idle TCP connection before closing it, if the
EDNS TCP keepalive option is not in use.
tcp-initial-timeout
Sets the amount of time (in milliseconds) that the server
waits on a new TCP connection for the first message fromthe client.
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Statement

Description

tcp-keepalive-timeout
Sets the amount of time (in milliseconds) that the server
waits on an idle TCP connection before closing it, if the
EDNS TCP keepalive option is in use.
tls-port
Specifies the TCP port number the server uses to receiveand send DNS-over-TLS protocol traffic.
v6-biasIndicates the number of milliseconds of preference to giveto IPv6 name servers.
windowSpecifies the length of time during which responses aretracked.
zero-no-soa-ttl
Specifies whether to set the time to live (TTL) of the SOA
record to zero, when returning authoritative negative responses to SOA queries.
zero-no-soa-ttl-cache
Sets the time to live (TTL) to zero when caching a negative
response to an SOA query.

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8.4.4 Security Tag Statements
Statement

Description

algorithm
Defines the algorithm to be used in a key clause.
ca-fileSpecifies the path to a file containing TLS certificates for trusted CA authorities, used to verify
remote peer certificates.
cert-fileSpecifies the path to a file containing the TLS certificate for a connection.
cipher-suites
Specifies a list of allowed cipher suites in the order of preference for TLSv1.3 only.
ciphers
Specifies a list of allowed ciphers in the order of preference for TLSv1.2 only.
dhparam-fileSpecifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.
dnsrps-enable
Turns on the DNS Response Policy Service (DNSRPS) interface.
dnsrps-libraryTurns on the DNS Response Policy Service (DNSRPS) interface.
dnsrps-options
Provides additional RPZ configuration settings, which are passed to the DNS Response Policy Service (DNSRPS) provider library.
key
Defines a shared secret key for use with TSIG or the command channel.
key-file
Specifies the path to a file containing the private TLS key for a connection.
keys
Specifies one or more server_key s to be used with a remote server.
prefer-serverciphers

Specifies that server ciphers should be preferred over client ones.

protocolsSpecifies the allowed versions of the TLS protocol.
remotehostname

Specifies the expected hostname in the TLS certificate of the remote server.

response-policy
Specifies response policy zones for the view or among global options.
secretDefines
8.4. Statements by
Taga Base64-encoded string to be used as the secret by the algorithm.
session-keyalg
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8.4.5 Server Tag Statements
Statement

Description

acl
Assigns a symbolic name to an address match list.
allow-new-zones
Controls the ability to add zones at runtime via rndc
addzone.
allow-proxy
Defines an address_match_list for the client addresses allowed to send PROXYv2 headers.
allow-proxy-on
Defines an address_match_list for the interface
addresses allowed to accept PROXYv2 headers. The option is mostly intended for multi-homed configurations.
allow-recursion-on
Specifies which local addresses can accept recursive
queries.
automatic-interface-scan
Controls the automatic rescanning of network interfaces
when addresses are added or removed.
bogus
Allows a remote server to be ignored.
ca-fileSpecifies the path to a file containing TLS certificates fortrusted CA authorities, used to verify remote peer certificates.
cert-fileSpecifies the path to a file containing the TLS certificate
for a connection.
check-names
Restricts the character set and syntax of certain domainnames in primary files and/or DNS responses received
from the network.
clients-per-query
Sets the initial minimum number of simultaneous recursive clients accepted by the server for any given query before the server drops additional clients.
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Statement

Description

controls
Specifies control channels to be used to manage the nameserver.
cookie-algorithm
Sets the algorithm to be used when generating a server
cookie.
cookie-secretSpecifies a shared secret used for generating and verifying
EDNS COOKIE options within an anycast cluster.
dhparam-fileSpecifies the path to a file containing Diffie-Hellman parameters, for enabling cipher suites.
directory
Sets the server's working directory.
disable-empty-zone
Disables individual empty zones.
dns64-contact
Specifies the name of the contact for dns64 zones.
dns64-server
Specifies the name of the server for dns64 zones.
dnsrps-enable
Turns on the DNS Response Policy Service (DNSRPS)
interface.
dnsrps-libraryTurns on the DNS Response Policy Service (DNSRPS)
interface.
dnsrps-options
Provides additional RPZ configuration settings, which are
passed to the DNS Response Policy Service (DNSRPS)
provider library.
dual-stack-servers
Specifies host names or addresses of machines with accessto both IPv4 and IPv6 transports.
edns
Controls the use of the EDNS0 (RFC 2671) feature.
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Statement

Description

edns-version
Sets the maximum EDNS VERSION that is sent to theserver(s) by the resolver.
empty-contact
Specifies the contact name in the returned SOA record for
empty zones.
empty-server
Specifies the server name in the returned SOA record for
empty zones.
empty-zones-enable
Enables or disables all empty zones.
endpoints
Specifies a list of HTTP query paths on which to listen.
errors-per-second
Limits the number of errors for a valid domain name andrecord type.
fetch-quota-params
Sets the parameters for dynamic resizing of thefetches-per-server quota in response to detected
congestion.
fetches-per-server
Sets the maximum number of simultaneous iterative
queries allowed to be sent by a server to an upstream nameserver before the server blocks additional queries.
fetches-per-zone
Sets the maximum number of simultaneous iterative
queries allowed to any one domain before the server
blocks new queries for data in or beneath that zone.
geoip-directorySpecifies the directory containing GeoIP database files.
hostname
Specifies the hostname of the server to return in response
to a hostname.bind query.
httpConfigures HTTP endpoints on which to listen for DNSover-HTTPS (DoH) queries.
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Statement

Description

http-listener-clients
Limits the number of active concurrent connections on a
per-listener basis.
http-port
Specifies the TCP port number the server uses to receiveand send unencrypted DNS traffic via HTTP.
http-streams-per-connection
Limits the number of active concurrent HTTP/2 streams
on a per-connection basis.
https-port
Specifies the TCP port number the server uses to receiveand send DNS-over-HTTPS protocol traffic.
inetSpecifies a TCP socket as a control channel.
interface-interval
Sets the interval at which the server scans the network
interface list.
ipv4-prefix-length
Specifies the prefix lengths of IPv4 address blocks.
ipv4only-contact
Specifies the contact for the IPV4ONLY.ARPA zone created by dns64.
ipv4only-server
Specifies the name of the server
IPV4ONLY.ARPA zone created by dns64.

for

the

ipv6-prefix-length
Specifies the prefix lengths of IPv6 address blocks.
key-file
Specifies the path to a file containing the private TLS key
for a connection.
keys
Specifies one or more server_key s to be used with aremote server.
lame-ttl
Sets the resolver's lame cache.
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Statement

Description

listen-on
Specifies the IPv4 addresses on which a server listens for
DNS queries.
listen-on-v6
Specifies the IPv6 addresses on which a server listens for
DNS queries.
listener-clients
Specifies a per-listener quota for active connections.
lmdb-mapsize
Sets a maximum size for the memory map of the newzone database in LMDB database format.
masterfile-format
Specifies the file format of zone files.
masterfile-styleSpecifies the format of zone files during a dump, when themasterfile-format is text.
match-mapped-addresses
Allows IPv4-mapped IPv6 addresses to match addressmatch list entries for corresponding IPv4 addresses.
max-cache-size
Sets the maximum amount of memory to use for an individual cache database and its associated metadata.
max-cache-ttl
Specifies the maximum time (in seconds) that the server
caches ordinary (positive) answers.
max-clients-per-query
Sets the maximum number of simultaneous recursive
clients accepted by the server for any given query before
the server drops additional clients.
max-ncache-ttl
Specifies the maximum retention time (in seconds) for
storage of negative answers in the server's cache.
max-records
Sets the maximum number of records permitted in a zone.
max-records-per-type
Sets the maximum number of records that can be stored
in an RRset
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Statement

Description

max-recursion-depth
Sets the maximum number of levels of recursion permitted at any one time while servicing a recursive query.
max-recursion-queries
Sets the maximum number of iterative queries while servicing a recursive query.
max-stale-ttl
Specifies the maximum time that the server retains
records past their normal expiry, to return them as stale
records.
max-table-size
Sets the maximum size of the table used to track requests
and rate-limit responses.
max-types-per-nameSets the maximum number of RR types that can be stored
for an owner namemax-validation-failures-per-fetch
Set the maximum number of DNSSEC validation failuresthat can happen in single fetch
max-validations-per-fetch
Set the maximum number of DNSSEC validations that
can happen in single fetch
memstatistics
Controls whether memory statistics are written to the filespecified by memstatistics-file at exit.
min-cache-ttl
Specifies the minimum time (in seconds) that the server
caches ordinary (positive) answers.
min-ncache-ttl
Specifies the minimum retention time (in seconds) for
storage of negative answers in the server's cache.
no-case-compress
Specifies a list of addresses that require case-insensitive
compression in responses.
options
Defines global options to be used by BIND 9.
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Statement

Description

padding
Adds EDNS Padding options to outgoing messages to increase the packet size.
pid-file
Specifies the pathname of the file where the server writes
its process ID.
pluginConfigures plugins in named.conf.
port
Specifies the UDP/TCP port number the server uses toreceive and send DNS protocol traffic.
prefer-server-ciphers
Specifies that server ciphers should be preferred overclient ones.
querylog
Specifies whether query logging should be active when
named first starts.
recursing-fileSpecifies the pathname of the file where the server dumps
queries that are currently recursing via rndc recursing.
resolver-use-dns64
Specifies whether to apply DNS64 mappings when sending queries.
response-policy
Specifies response policy zones for the view or among
global options.
reuseport
Enables kernel load-balancing of sockets.
root-key-sentinel
Controls whether BIND 9 responds to root key sentinelprobes.
serverDefines characteristics to be associated with a remotename server.
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Statement

Description

server-id
Specifies the ID of the server to return in response to a
ID.SERVER query.
servfail-ttl
Sets the length of time (in seconds) that a SERVFAIL
response is cached.
sig0checks-quota
Specifies the maximum number of concurrent SIG(0) signature checks that can be processed by the server.
sig0checks-quota-exempt
Exempts specific clients or client groups from SIG(0) signature checking quota.
stale-answer-client-timeout
Defines the amount of time (in milliseconds) that named
waits before attempting to answer a query with a stale
RRset from cache.
stale-answer-enable
Enables the returning of "stale" cached answers when thename servers for a zone are not answering.
stale-cache-enable
Enables the retention of "stale" cached answers.
stale-refresh-time
Sets the time window for the return of "stale" cachedanswers before the next attempt to contact, if the nameservers for a given zone are not responding.
statistics-fileSpecifies the pathname of the file where the server appends statistics, when using rndc stats.
streams-per-connection
Specifies the maximum number of concurrent HTTP/2
streams over an HTTP/2 connection.
tcp-clients
Specifies the maximum number of simultaneous client
TCP connections accepted by the server.
tcp-initial-timeout
Sets the amount of time (in milliseconds) that the server
waits on a new TCP connection for the first message fromthe client.
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Statement

Description

tcp-keepalive
Adds EDNS TCP keepalive to messages sent over TCP.
tcp-listen-queue
Sets the listen-queue depth.
tcp-only
Sets the transport protocol to TCP.
tcp-receive-buffer
Sets the operating system's receive buffer size for TCP
sockets.
tcp-send-buffer
Sets the operating system's send buffer size for TCP sockets.
tls-port
Specifies the TCP port number the server uses to receiveand send DNS-over-TLS protocol traffic.
transfers
Limits the number of concurrent inbound zone transfersfrom a server.
udp-receive-buffer
Sets the operating system's receive buffer size for UDP
sockets.
udp-send-buffer
Sets the operating system's send buffer size for UDP sockets.
update-quota
Specifies the maximum number of concurrent DNS UPDATE messages that can be processed by the server.
v6-biasIndicates the number of milliseconds of preference to giveto IPv6 name servers.
versionSpecifies the version number of the server to return in response to a version.bind query.
zero-no-soa-ttl
Specifies whether to set the time to live (TTL) of the SOA
record to zero, when returning authoritative negative responses to SOA queries.
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Statement

Description

zero-no-soa-ttl-cache
Sets the time to live (TTL) to zero when caching a negative
response to an SOA query.

8.4.6 Transfer Tag Statements
Statement

Description

allow-notify
Defines an address_match_list that is allowed tosend NOTIFY messages for the zone, in addition to addresses defined in the primaries option for the zone.
allow-transfer
Defines an address_match_list of hosts that areallowed to transfer the zone information from this server.
allow-update
Defines an address_match_list of hosts that areallowed to submit dynamic updates for primary zones.
allow-update-forwarding
Defines an address_match_list of hosts that areallowed to submit dynamic updates to a secondary server
for transmission to a primary.
also-notify
Defines one or more hosts that are sent NOTIFY messages
when zone changes occur.
ixfr-from-differences
Controls how IXFR transfers are calculated.
max-ixfr-ratio
Sets the maximum size for IXFR responses to zone transfer requests.
max-journal-size
Controls the size of journal files.
max-refresh-time
Limits the zone refresh interval to no less often than thespecified value, in seconds.
max-retry-time
Limits the zone refresh retry interval to no less often than
the specified value, in seconds.
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Statement

Description

max-transfer-idle-inSpecifies the number of minutes after which inbound zonetransfers making no progress are terminated.
max-transfer-idle-out
Specifies the number of minutes after which outboundzone transfers making no progress are terminated.
max-transfer-time-in
Specifies the number of minutes after which inbound zonetransfers are terminated.
max-transfer-time-out
Specifies the number of minutes after which outboundzone transfers are terminated.
min-refresh-time
Limits the zone refresh interval to no more often than thespecified value, in seconds.
min-retry-time
Limits the zone refresh retry interval to no more often than
the specified value, in seconds.
multi-master
Controls whether serial number mismatch errors arelogged.
notifyControls whether NOTIFY messages are sent on zonechanges.
notify-delay
Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.
notify-rate
Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.
notify-source
Defines the IPv4 address (and optional port) to be used
for outgoing NOTIFY messages.
notify-source-v6
Defines the IPv6 address (and optional port) to be used
for outgoing NOTIFY messages.
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Statement

Description

notify-to-soa
Controls whether the name servers in the NS RRset arechecked against the SOA MNAME.
provide-ixfr
Controls whether a primary responds to an incrementalzone request (IXFR) or only responds with a full zonetransfer (AXFR).
request-expire
Specifies whether the local server requests the EDNS EXPIRE value, when acting as a secondary.
request-ixfr
Controls whether a secondary requests an incrementalzone transfer (IXFR) or a full zone transfer (AXFR).
serial-query-rate
Defines an upper limit on the number of queries per second issued by the server, when querying the SOA RRs
used for zone transfers.
startup-notify-rate
Specifies the rate at which NOTIFY requests are sent
when the name server is first starting, or when new zones
have been added.
transfer-format
Controls whether multiple records can be packed into amessage during zone transfers.
transfer-message-size
Limits the uncompressed size of DNS messages used inzone transfers over TCP.
transfer-source
Defines which local IPv4 address(es) are bound to TCP
connections used to fetch zones transferred inbound by
the server.
transfer-source-v6
Defines which local IPv6 address(es) are bound to TCP
connections used to fetch zones transferred inbound by
the server.
transfers-in
Limits the number of concurrent inbound zone transfers.
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Statement

Description

transfers-out
Limits the number of concurrent outbound zone transfers.
transfers-per-ns
Limits the number of concurrent inbound zone transfersfrom a remote server.
try-tcp-refreshSpecifies that BIND 9 should attempt to refresh a zone
using TCP if UDP queries fail.
update-policy
Sets fine-grained rules to allow or deny dynamic updates(DDNS), based on requester identity, updated content,
etc.

8.4.7 View Tag Statements
Statement

Description

attach-cache
Allows multiple views to share a single cache database.
in-view
Specifies the view in which a given zone is defined.
match-clients
Specifies a view of DNS namespace for a given subset of client IP addresses.
match-destinations
Specifies a view of DNS namespace for a given subset of destination IP addresses.
match-recursive-onlySpecifies that only recursive requests can match this view of the DNS namespace.
view
Allows a name server to answer a DNS query differently depending on who is asking.

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8.4.8 Zone Tag Statements
Statement

Description

allow-new-zones
Controls the ability to add zones at runtime via rndc
addzone.
catalog-zones
Configures catalog zones in named.conf.
check-integrity
Performs post-load zone integrity checks on primaryzones.
check-mx
Checks whether an MX record appears to refer to an IP
address.
check-mx-cname
Sets the response to MX records that refer to CNAMEs.
check-siblingSpecifies whether to check for sibling glue when performing integrity checks.
check-spf
Specifies whether to check for a TXT Sender Policy
Framework record, if an SPF record is present.
check-srv-cname
Sets the response to SRV records that refer to CNAMEs.
check-svcb
Specifies whether to perform additional checks on SVCB
records.
check-wildcard
Checks for non-terminal wildcards.
database
Specifies the type of database to be used to store zonedata.
disable-ds-digests
Disables DS digest types from a specified zone.
disable-empty-zone
Disables individual empty zones.
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Statement

Description

dlz
Configures a Dynamically Loadable Zone (DLZ) databasein named.conf.
dyndb
Configures a DynDB database in named.conf.
empty-contact
Specifies the contact name in the returned SOA record for
empty zones.
empty-server
Specifies the server name in the returned SOA record for
empty zones.
empty-zones-enable
Enables or disables all empty zones.
file
Specifies the zone's filename.
flush-zones-on-shutdown
Controls whether pending zone writes are flushed when
the name server exits.
in-view
Specifies the view in which a given zone is defined.
inline-signing
Specifies whether BIND 9 maintains a separate signed
version of a zone.
journalAllows the default journal's filename to be overridden.
masterfile-format
Specifies the file format of zone files.
max-records
Sets the maximum number of records permitted in a zone.
new-zones-directorySpecifies the directory where configuration parameters
are stored for zones added by rndc addzone.
notify-delay
Sets the delay (in seconds) between sending sets of NOTIFY messages for a zone.
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Statement

Description

notify-rate
Specifies the rate at which NOTIFY requests are sent during normal zone maintenance operations.
parent-propagation-delay
Sets the propagation delay from the time the parent zone
is updated to when the new version is served by all of theparent zone's name servers.
parental-agents
Defines a list of delegation agents to be used by primaryand secondary zones.
primaries
Defines one or more primary servers for a zone.
response-policy
Specifies response policy zones for the view or among
global options.
serial-update-method
Specifies the update method to be used for the zone serial
number in the SOA record.
server-addresses
Specifies a list of IP addresses to which queries should besent in recursive resolution for a static-stub zone.
server-names
Specifies a list of domain names of name servers that act
as authoritative servers of a static-stub zone.
startup-notify-rate
Specifies the rate at which NOTIFY requests are sent
when the name server is first starting, or when new zones
have been added.
type
Specifies the kind of zone in a given configuration.
type forward
Contains forwarding statements that apply to queries
within a given domain.
type hint
Contains the initial set of root name servers to be used at
BIND 9 startup.
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Statement

Description

type mirror
Contains a DNSSEC-validated duplicate of the main data
for a zone.
type primaryContains the main copy of the data for a zone.
type redirect
Contains information to answer queries when normal resolution would return NXDOMAIN.
type secondary
Contains a duplicate of the data for a zone that has beentransferred from a primary server.
type static-stubContains a duplicate of the NS records of a primary zone,
but statically configured rather than transferred from a primary server.
type stubContains a duplicate of the NS records of a primary zone.
zero-no-soa-ttl
Specifies whether to set the time to live (TTL) of the SOA
record to zero, when returning authoritative negative responses to SOA queries.
zero-no-soa-ttl-cache
Sets the time to live (TTL) to zero when caching a negative
response to an SOA query.
zone
Specifies the zone in a BIND 9 configuration.
zone-propagation-delay
Sets the propagation delay from the time a zone is first
updated to when the new version of the zone is served by
all secondary servers.
zone-statistics
Controls the level of statistics gathered for all zones.

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8.4.9 Deprecated Tag Statements
Statement

Description

avoid-v4-udpports

Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv4 messages.

avoid-v6-udpports

Specifies the range(s) of ports to be excluded from use as sources for UDP/IPv6 messages.

dialupConcentrates zone maintenance so that all transfers
heartbeat-interval, ideally during a single call.
dnssec-must-besecureheartbeatinterval

take

place

once

every

Defines hierarchies that must or may not be secure (signed and validated).

Sets the interval at which the server performs zone maintenance tasks for all zones marked as
dialup.

managed-keys
max-zone-ttl
Specifies a maximum permissible time-to-live (TTL) value, in seconds.
sortlist
Controls the ordering of RRs returned to the client, based on the client's IP address.
trusted-keys
use-v4-udpports

Specifies a list of ports that are valid sources for UDP/IPv4 messages.

use-v6-udpports

Specifies a list of ports that are valid sources for UDP/IPv6 messages.

8.5 BIND 9 Statistics
BIND 9 maintains lots of statistics information and provides several interfaces for users to access those statistics. The
available statistics include all statistics counters that are meaningful in BIND 9, and other information that is considered
useful.
The statistics information is categorized into the following sections:
Incoming Requests
The number of incoming DNS requests for each OPCODE.
Incoming Queries
The number of incoming queries for each RR type.

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Outgoing Queries
The number of outgoing queries for each RR type sent from the internal resolver, maintained per view.
Incoming Zone Transfers
Information about in-progress incoming zone transfers.
This section describes the information, which can be seen in the HTML table about in-progress incoming zonetransfers. It lists the meaning, units and possible range of values of each column, and the key/attribute/element
name (in parentheses) for the JSON and XML output formats.
Zone Name (name)
Text string. This is the name of the zone being transferred, as specified in the zone declaration on this server.
Zone Type (type)
Text string. This is the type of zone being transferred, as specified in the zone declaration on this server.
Possible values are: secondary, stub, redirect, mirror.
Local Serial (serial)
32 bit unsigned Integer. This is the current (old) serial number of the zone being transferred. It comes fromthe SOA record held on the current server.
Remote Serial (remoteserial)
32 bit unsigned Integer. This is the new serial number of the zone being transferred. It comes from the SOA
record held on the primary server from which the zone is being transferred.
IXFR (ixfr)
Boolean. This says whether the transfer is incremental (using IXFR) or full (using AXFR). Possible values
are: Yes, No.
State (state)
Text string. This is the current state of the transfer for this zone. Possible values and their meanings are:Needs Refresh
The zone needs a refresh, but the process hasn’t started yet, which can be due to different factors,
like the retry interval of the zone.
Pending
The zone is flagged for a refresh, but the process is currently in the queue and will start shortly,or is in a waiting state because of rate-limiting, see serial-query-rate. The Duration(s) timer starts before entering this state.
Refresh SOA
Sending a refresh SOA query to get the zone serial number, then initiate a zone transfer, if
necessary. If this step is successful, the SOA Query and Got SOA states will be skipped.
Otherwise, the zone transfer procedure can still be initiated, and the SOA request will be attempted using the same transport as the zone transfer. The Duration (s) timer restarts
before entering this state, and for each attempted connection (note that in UDP mode there canbe several retries during one “connection” attempt).
Deferred
The zone is going to be refreshed, but the process was deferred due to quota, seetransfers-in and transfers-per-ns. The Duration (s) timer restarts before
entering this state.
SOA Query
Sending SOA query to get the zone serial number, then follow with a zone transfer, if necessary.
The Duration (s) timer restarts before entering this state.
Got SOA
An answer for the SOA query from the previous step is received, initiating a transfer.

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Zone Transfer Request
Waiting for the zone transfer to start. The Duration (s) timer restarts before entering thisstate.
First Data
Waiting for the first data record of the transfer.
Receiving IXFR Data
Receiving data for an IXFR type incremental zone transfer.
Finalizing IXFRFinalizing an IXFR type incremental zone transfer.
Receiving AXFR Data
Receiving data for an AXFR type zone transfer.
Finalizing AXFR
Finalizing an AXFR type zone transfer.
Note: State names can change between BIND versions.
Additional Refresh Queued (refreshqueued)
Boolean. This shows that the zone is flagged for a refresh. This can be set to Yes either when the zonetransfer is still in one of the pending states (see the description of the State column), or when the transfer
is in a running state, but the zone was marked for another refresh again (e.g. because of “notify” request froma primary server). Possible values are: Yes, No.
Local Address (localaddr)
IP address - IPv4 or IPv6, as appropriate, and port number. This shows the source address used to establish
the connection for the transfer.
Remote Address (remoteaddr)
IP address - IPv4 or IPv6, as appropriate, and port number. This shows the destination address used toestablish the connection for the transfer.
SOA Transport (soatransport)
Text string. This is the transport protocol in use for the SOA query. Note, that this value can potentially change
during the process. For example, when the transfer is in the Refresh SOA state, the SOA Transportof the ongoing query can be shown as UDP. If that query fails or times out, it then can be retried using
another transport, or the transfer process can be initiated in “SOA before” mode, where the SOA query will
be attempted using the same transport as the zone transfer. See the description of the State field for more
information. Possible values are: UDP, TCP, TLS, None.
Transport (transport)
Text string. This is the transport protocol in use for the transfer. Possible values are: TCP, TLS.
TSIG Key Name (tsigkeyname)
Text string. This is the name of the TSIG key specified for use with this zone in the zone declaration (ifany).
Duration (s) (duration)
64 bit unsigned Integer. This is the time, in seconds, that the current major state of the transfer process has
been running so far. The timer starts after the refresh SOA request is queued (before the Pending state),then it restarts several times during the whole process to indicate the duration of the current major state. See
the descriptions of the different states to find out the states, before which this timer restarts.
Messages Received (nmsg)
64 bit unsigned Integer. This is the number of DNS messages received. It does not include transport overheads, such as TCP ACK.
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Records Received (nrecs)
64 bit unsigned Integer. This is the number of individual RRs received so far. If an address record has, forexample, five addresses associated with the same name, it counts as five RRs.
Bytes Received (nbytes)
64 bit unsigned Integer. This is the number of usable bytes of DNS data. It does not include transport
overhead.
Note: Depending on the current state of the transfer, some of the values may be empty or set to - (meaning “notavailable”). Also, in the case of the JSON output format, the corresponding keys can be missing or values can be
set to NULL. For example, it isn’t known whether a transfer is using AXFR or IXFR until the first data is received(see the description of the State column).
Name Server Statistics
Statistics counters for incoming request processing.
Zone Maintenance Statistics
Statistics counters regarding zone maintenance operations, such as zone transfers.
Resolver Statistics
Statistics counters for name resolutions performed in the internal resolver, maintained per view.
Cache DB RRsets
Statistics counters related to cache contents, maintained per view.
The “NXDOMAIN” counter is the number of names that have been cached as nonexistent. Counters named for
RR types indicate the number of active RRsets for each type in the cache database.
If an RR type name is preceded by an exclamation point (!), it represents the number of records in the cache whichindicate that the type does not exist for a particular name; this is also known as “NXRRSET”. If an RR type nameis preceded by a hash mark (#), it represents the number of RRsets for this type that are present in the cache but
whose TTLs have expired; these RRsets may only be used if stale answers are enabled. If an RR type name ispreceded by a tilde (~), it represents the number of RRsets for this type that are present in the cache database but
are marked for garbage collection; these RRsets cannot be used.
Socket I/O Statistics
Statistics counters for network-related events.
A subset of Name Server Statistics is collected and shown per zone for which the server has the authority, when zone-statistics is set to full (or yes), for backward compatibility. See the description ofzone-statistics in options for further details.
These statistics counters are shown with their zone and view names. The view name is omitted when the server is notconfigured with explicit views.
There are currently two user interfaces to get access to the statistics. One is in plain-text format, dumped to the filespecified by the statistics-file configuration option; the other is remotely accessible via a statistics channel when
the statistics-channels statement is specified in the configuration file.

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8.5.1 The Statistics File
The text format statistics dump begins with a line, like:+++ Statistics Dump +++ (973798949)
The number in parentheses is a standard Unix-style timestamp, measured in seconds since January 1, 1970. Followingthat line is a set of statistics information, which is categorized as described above. Each section begins with a line, like:++ Name Server Statistics ++Each section consists of lines, each containing the statistics counter value followed by its textual description; see below
for available counters. For brevity, counters that have a value of 0 are not shown in the statistics file.
The statistics dump ends with the line where the number is identical to the number in the beginning line; for example:--- Statistics Dump --- (973798949)

8.5.2 Statistics Counters
The following lists summarize the statistics counters that BIND 9 provides. For each counter, the abbreviated symbol nameis given; these symbols are shown in the statistics information accessed via an HTTP statistics channel. The descriptionof the counter is also shown in the statistics file but, in this document, may be slightly modified for better readability.
Name Server Statistics Counters
Requestv4
This indicates the number of IPv4 requests received. Note: this also counts non-query requests.
Requestv6
This indicates the number of IPv6 requests received. Note: this also counts non-query requests.
ReqEdns0
This indicates the number of requests received with EDNS(0).
ReqBadEDN SVerThis indicates the number of requests received with an unsupported EDNS version.
ReqTSIG
This indicates the number of requests received with TSIG.
ReqSIG0This indicates the number of requests received with SIG(0).
ReqBadSIG
This indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.
ReqTCP
This indicates the number of TCP requests received.
AuthQryRej
This indicates the number of rejected authoritative (non-recursive) queries.
RecQryRej
This indicates the number of rejected recursive queries.
XfrRejThis indicates the number of rejected zone transfer requests.
UpdateRej
This indicates the number of rejected dynamic update requests.
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Response
This indicates the number of responses sent.
RespTruncatedThis indicates the number of truncated responses sent.
RespEDNS0
This indicates the number of responses sent with EDNS(0).
RespTSIG
This indicates the number of responses sent with TSIG.
RespSIG0This indicates the number of responses sent with SIG(0).
QrySuccessThis indicates the number of queries that resulted in a successful answer, meaning queries which return a NOERROR response with at least one answer RR. This corresponds to the success counter of previous versions of
BIND 9.
QryAuthAns
This indicates the number of queries that resulted in an authoritative answer.
QryNoauthAns
This indicates the number of queries that resulted in a non-authoritative answer.
QryReferral
This indicates the number of queries that resulted in a referral answer. This corresponds to the referral counterof previous versions of BIND 9.
QryNxrrset
This indicates the number of queries that resulted in NOERROR responses with no data. This corresponds to thenxrrset counter of previous versions of BIND 9.
QrySERVFAIL
This indicates the number of queries that resulted in SERVFAIL.
QryFORMERRThis indicates the number of queries that resulted in FORMERR.
QryNXDOMAIN
This indicates the number of queries that resulted in NXDOMAIN. This corresponds to the nxdomain counterof previous versions of BIND 9.
QryRecursion
This indicates the number of queries that caused the server to perform recursion in order to find the final answer.
This corresponds to the recursion counter of previous versions of BIND 9.
QryDuplicate
This indicates the number of queries which the server attempted to recurse but for which it discovered an existing
query with the same IP address, port, query ID, name, type, and class already being processed. This corresponds
to the duplicate counter of previous versions of BIND 9.
QryDropped
This indicates the number of recursive queries dropped by the server as a result of configured limits. These limits
include the settings of the fetches-per-zone, fetches-per-server, clients-per-query, andmax-clients-per-query options, as well as the rate-limit option. This corresponds to the dropped
counter of previous versions of BIND 9.
QryFailureThis indicates the number of query failures. This corresponds to the failure counter of previous versions of
BIND 9. Note: this counter is provided mainly for backward compatibility with previous versions; normally, more
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fine-grained counters such as AuthQryRej and RecQryRej that would also fall into this counter are provided,so this counter is not of much interest in practice.
QryNXRedir
This indicates the number of queries that resulted in NXDOMAIN that were redirected.
QryNXRedirRLookup
This indicates the number of queries that resulted in NXDOMAIN that were redirected and resulted in a successful
remote lookup.
XfrReqDone
This indicates the number of requested and completed zone transfers.
UpdateReqFwd
This indicates the number of forwarded update requests.
UpdateRespFwd
This indicates the number of forwarded update responses.
UpdateFwdFailThis indicates the number of forwarded dynamic updates that failed.
UpdateDone
This indicates the number of completed dynamic updates.
UpdateFail
This indicates the number of failed dynamic updates.
UpdateBadPrereq
This indicates the number of dynamic updates rejected due to a prerequisite failure.
UpdateQuota
This indicates the number of times a dynamic update or update forwarding request was rejected because the numberof pending requests exceeded update-quota.
RateDropped
This indicates the number of responses dropped due to rate limits.
RateSlipped
This indicates the number of responses truncated by rate limits.
RPZRewrites
This indicates the number of response policy zone rewrites.
Zone Maintenance Statistics Counters
NotifyOutv4
This indicates the number of IPv4 notifies sent.
NotifyOutv6
This indicates the number of IPv6 notifies sent.
NotifyInv4
This indicates the number of IPv4 notifies received.
NotifyInv6
This indicates the number of IPv6 notifies received.
NotifyRej
This indicates the number of incoming notifies rejected.

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SOAOutv4
This indicates the number of IPv4 SOA queries sent.
SOAOutv6
This indicates the number of IPv6 SOA queries sent.
AXFRReqv4
This indicates the number of requested IPv4 AXFRs.
AXFRReqv6
This indicates the number of requested IPv6 AXFRs.
IXFRReqv4
This indicates the number of requested IPv4 IXFRs.
IXFRReqv6
This indicates the number of requested IPv6 IXFRs.
XfrSuccessThis indicates the number of successful zone transfer requests.
XfrFailThis indicates the number of failed zone transfer requests.
Resolver Statistics Counters
Queryv4
This indicates the number of IPv4 queries sent.
Queryv6
This indicates the number of IPv6 queries sent.
Responsev4
This indicates the number of IPv4 responses received.
Responsev6
This indicates the number of IPv6 responses received.
NXDOMAINThis indicates the number of NXDOMAINs received.
SERVFAILThis indicates the number of SERVFAILs received.
FORMERR
This indicates the number of FORMERRs received.
OtherError
This indicates the number of other errors received.
EDNS0Fail
This indicates the number of EDNS(0) query failures.
Mismatch
This indicates the number of mismatched responses received, meaning the DNS ID, response’s source address,
and/or the response’s source port does not match what was expected. (The port must be 53 or as defined by the
port option.) This may be an indication of a cache poisoning attempt.
Truncated
This indicates the number of truncated responses received.

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LameThis indicates the number of lame delegations received.
Retry
This indicates the number of query retries performed.
QueryAbort
This indicates the number of queries aborted due to quota control.
QuerySockFail
This indicates the number of failures in opening query sockets. One common reason for such failures is due to alimitation on file descriptors.
QueryCurUDP
This indicates the number of UDP queries in progress.
QueryCurTCP
This indicates the number of TCP queries in progress.
QueryTimeout
This indicates the number of query timeouts.
GlueFetchv4
This indicates the number of IPv4 NS address fetches invoked.
GlueFetchv6
This indicates the number of IPv6 NS address fetches invoked.
GlueFetchv4FailThis indicates the number of failed IPv4 NS address fetches.
GlueFetchv6FailThis indicates the number of failed IPv6 NS address fetches.
ValAttemptThis indicates the number of attempted DNSSEC validations.
ValOk
This indicates the number of successful DNSSEC validations.
ValNegOk
This indicates the number of successful DNSSEC validations on negative information.
ValFailThis indicates the number of failed DNSSEC validations.
QryRTTnn
This provides a frequency table on query round-trip times (RTTs). Each nn specifies the corresponding frequency.
In the sequence of nn_1, nn_2, …, nn_m, the value of nn_i is the number of queries whose RTTs are between
nn_(i-1) (inclusive) and nn_i (exclusive) milliseconds. For the sake of convenience, we define nn_0 to be 0.
The last entry should be represented as nn_m+, which means the number of queries whose RTTs are equal to or
greater than nn_m milliseconds.
NumFetch
This indicates the number of active fetches.
BucketSize
This indicates the number the resolver’s internal buckets (a static number).
REFUSED
This indicates the number of REFUSED responses received.

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ClientCookieOut
This indicates the number of COOKIE sent with client cookie only.
ServerCookieOut
This indicates the number of COOKIE sent with client and server cookie.
CookieInThis indicates the number of COOKIE replies received.
CookieClientOk
This indicates the number of COOKIE client ok.
BadEDNSVersion
This indicates the number of bad EDNS version replies received.
BadCookieRcode
This indicates the number of bad cookie rcode replies received.
ZoneQuota
This indicates the number of queries spilled due to zone quota.
ServerQuota
This indicates the number of queries spilled due to server quota.
ClientQuota
This indicates the number of queries spilled due to clients per query quota.
NextItemThis indicates the number of waits for next item, when an invalid response is received.
Priming
This indicates the number of priming fetches performed by the resolver.
Socket I/O Statistics Counters
Socket I/O statistics counters are defined per socket type, which are UDP4 (UDP/IPv4), UDP6 (UDP/IPv6), TCP4
(TCP/IPv4), and TCP6 (TCP/IPv6). In the following list, <TYPE> represents a socket type. Not all counters are available
for all socket types; exceptions are noted in the descriptions.
<TYPE>OpenThis indicates the number of sockets opened successfully.
<TYPE>OpenFailThis indicates the number of failures to open sockets.
<TYPE>Close
This indicates the number of closed sockets.
<TYPE>BindFailThis indicates the number of failures to bind sockets.
<TYPE>ConnFailThis indicates the number of failures to connect sockets.
<TYPE>Conn
This indicates the number of connections established successfully.
<TYPE>AcceptFail
This indicates the number of failures to accept incoming connection requests. This counter does not apply to the
UDP type.

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This indicates the number of incoming connections successfully accepted. This counter does not apply to the UDP
type.
<TYPE>SendErr
This indicates the number of errors in socket send operations.
<TYPE>RecvErr
This indicates the number of errors in socket receive operations, including errors of send operations on a connected
UDP socket, notified by an ICMP error message.

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TROUBLESHOOTING

9.1 Common Problems
9.1.1 It’s Not Working; How Can I Figure Out What’s Wrong?
The best solution to installation and configuration issues is to take preventive measures by setting up logging files beforehand. The log files provide hints and information that can be used to identify anything that went wrong and fix the
problem.

9.1.2 EDNS Compliance Issues
EDNS (Extended DNS) is a standard that was first specified in 1999. It is required for DNSSEC validation, DNS COOKIE
options, and other features. There are broken and outdated DNS servers and firewalls still in use which misbehave when
queried with EDNS; for example, they may drop EDNS queries rather than replying with FORMERR. BIND and otherrecursive name servers have traditionally employed workarounds in this situation, retrying queries in different ways andeventually falling back to plain DNS queries without EDNS.
Such workarounds cause unnecessary resolution delays, increase code complexity, and prevent deployment of new DNS
features. In February 2019, all major DNS software vendors removed these workarounds; see https://dnsflagday.net/2019
for further details. This change was implemented in BIND as of release 9.14.0.
As a result, some domains may be non-resolvable without manual intervention. In these cases, resolution can be restoredby adding server clauses for the offending servers, or by specifying edns no or send-cookie no, depending on
the specific noncompliance.
To determine which server clause to use, run the following commands to send queries to the authoritative servers forthe broken domain:
dig soa <zone> @<server> +dnssec
dig soa <zone> @<server> +dnssec +nocookie
dig soa <zone> @<server> +noedns

If the first command fails but the second succeeds, the server most likely needs send-cookie no. If the first two failbut the third succeeds, then the server needs EDNS to be fully disabled with edns no.
Please contact the administrators of noncompliant domains and encourage them to upgrade their broken DNS servers.

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9.1.3 Inspecting Encrypted DNS Traffic
Note: This feature requires support from the cryptographic library that BIND 9 is built against. For OpenSSL, version
1.1.1 or newer is required (use named -V to check).
By definition, TLS-encrypted traffic (e.g. DNS over TLS, DNS over HTTPS) is opaque to packet sniffers, which makes
debugging problems with encrypted DNS close to impossible. However, Wireshark offers a solution to this problem bybeing able to read key log files. In order to make named prepare such a file, set the SSLKEYLOGFILE environment
variable to either:• the string config (SSLKEYLOGFILE=config); this requires defining a logging channel which willhandle messages belonging to the sslkeylog category,• the path to the key file to write (SSLKEYLOGFILE=/path/to/file); this is equivalent to the following logging configuration:
channel default_sslkeylogfile {file "${SSLKEYLOGFILE}" versions 10 size 100m suffix timestamp;};
category sslkeylog {default_sslkeylogfile;};

Note: When using SSLKEYLOGFILE=config, augmenting the log channel output using options like print-timeor print-severity is strongly discouraged as it will likely make the key log file unusable.
When the SSLKEYLOGFILE environment variable is set, each TLS connection established by named (both incoming
and outgoing) causes about 1 kilobyte of data to be written to the key log file.
Warning: Due to the limitations of the current logging code in BIND 9, enabling TLS pre-master secret logging
adversely affects named performance.

9.2 Incrementing and Changing the Serial Number
Zone serial numbers are just numbers — they are not date-related. However, many people set them to a number that
represents a date, usually of the form YYYYMMDDRR. Occasionally they make a mistake and set the serial number toa date in the future, then try to correct it by setting it to the current date. This causes problems because serial numbers
are used to indicate that a zone has been updated. If the serial number on the secondary server is lower than the serial
number on the primary, the secondary server attempts to update its copy of the zone.
Setting the serial number to a lower number on the primary server than the one on the secondary server means that thesecondary will not perform updates to its copy of the zone.
The solution to this is to add 2147483647 (2^31-1) to the number, reload the zone and make sure all secondaries haveupdated to the new zone serial number, then reset it to the desired number and reload the zone again.

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9.3 Where Can I Get Help?
The BIND-users mailing list, at https://lists.isc.org/mailman/listinfo/bind-users, is an excellent resource for peer user
support. In addition, ISC maintains a Knowledgebase of helpful articles at https://kb.isc.org.
Internet Systems Consortium (ISC) offers annual support agreements for BIND 9, ISC DHCP, and Kea DHCP. All paid
support contracts include advance security notifications; some levels include service level agreements (SLAs), premium
software features, and increased priority on bug fixes and feature requests.
Please contact info@isc.org or visit https://www.isc.org/contact/ for more information.

9.3. Where Can I Get Help?

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CHAPTERTEN

BUILDING BIND 9

To build on a Unix or Linux system, use:
$ autoreconf -fi ### (only if building from the git repository)$ ./configure$ makeSeveral environment variables affect compilation, and they can be set before running configure. The most significant
ones are:Variable

Description

CC
The C compiler to use. configure tries to figure out the right one for supported systems.
CFLAGS The C compiler flags. Defaults to include -g and/or -O2 as supported by the compiler. Please include -g
if CFLAGS needs to be set.
LDThe linker flags. Defaults to an empty string.
FLAGS
Additional environment variables affecting the build are listed at the end of the configure help text, which can beobtained by running the command:$ ./configure --help

If using Emacs, the make tags command may be helpful.

10.1 Required Libraries
To build BIND 9, the following packages must be installed:• a C11-compliant compiler• libcrypto, libssl• liburcu• libuv• perl• pkg-config / pkgconfig / pkgconf
BIND 9.20 requires libuv 1.34.0 or higher, using libuv >= 1.40.0 is recommended. Compiling or running withlibuv 1.35.0 or 1.36.0 is not supported, as this could lead to an assertion failure in the UDP receive code. On older
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systems, an updated libuv package needs to be installed from sources such as EPEL, PPA, or other native sources. The
other option is to build and install libuv from source.
OpenSSL 1.0.2e or newer is required. If the OpenSSL library is installed in a nonstandard location, specify the prefix using--with-openssl=<PREFIX> on the configure command line. To use a PKCS#11 hardware service module forcryptographic operations, engine_pkcs11 from the OpenSC project must be compiled and used.
The Userspace RCU library liburcu (https://liburcu.org/) is used for lock-free data structures and concurrent safe
memory reclamation.
On Linux, process capabilities are managed in user space using the libcap library (https://git.kernel.org/pub/scm/libs/
libcap/libcap.git/), which can be installed on most Linux systems via the libcap-dev or libcap-devel package.
To build BIND from the git repository, the following tools must also be installed:• autoconf (includes autoreconf)• automake• libtool

10.2 Optional Features
To see a full list of configuration options, run configure --help.
To improve performance, use of the jemalloc library (https://jemalloc.net/) is strongly recommended. Version 4.0.0
or newer is required when in use.
To support DNS over HTTPS (DoH), the server must be linked with libnghttp2 (https://nghttp2.org/). If the libraryis unavailable, --disable-doh can be used to disable DoH support.
To support the HTTP statistics channel, the server must be linked with at least one of the following libraries: libxml2(http://xmlsoft.org) or json-c (https://github.com/json-c/json-c). If these are installed at a nonstandard location, then:• for libxml2, specify the prefix using --with-libxml2=/prefix,• for json-c, adjust PKG_CONFIG_PATH.
To support compression on the HTTP statistics channel, the server must be linked against zlib (https://zlib.net/). If thisis installed in a nonstandard location, specify the prefix using --with-zlib=/prefix.
To support storing configuration data for runtime-added zones in an LMDB database, the server must be linked withliblmdb (https://github.com/LMDB/lmdb). If this is installed in a nonstandard location, specify the prefix using--with-lmdb=/prefix.
To support MaxMind GeoIP2 location-based ACLs, the server must be linked with libmaxminddb (https://maxmind.
github.io/libmaxminddb/). This is turned on by default if the library is found; if the library is installed in a nonstandard location, specify the prefix using --with-maxminddb=/prefix. GeoIP2 support can be switched off with--disable-geoip.
For DNSTAP packet logging, libfstrm (https://github.com/farsightsec/fstrm) and libprotobuf-c (https://developers.google.com/protocol-buffers) must be installed, and BIND must be configured with --enable-dnstap.
To support internationalized domain names in dig, libidn2 (https://www.gnu.org/software/libidn/#libidn2) must be
installed. If the library is installed in a nonstandard location, specify the prefix using --with-libidn2=/prefix
or adjust PKG_CONFIG_PATH.
For line editing in nsupdate and nslookup, either the readline (https://tiswww.case.edu/php/chet/readline/rltop.
html) or the libedit library (https://www.thrysoee.dk/editline/) must be installed. If these are installed at a nonstandard location, adjust PKG_CONFIG_PATH. readline is used by default, and libedit can be explicitly requested
using --with-readline=libedit.

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On some platforms it is necessary to explicitly request large file support to handle files bigger than 2GB. This can be doneby using --enable-largefile on the configure command line.
Support for the “fixed” RRset-order option can be enabled or disabled by specifying --enable-fixed-rrset or--disable-fixed-rrset on the configure command line. By default, fixed RRset-order is disabled to reduce
memory footprint.
The --enable-querytrace option causes named to log every step while processing every query. The--enable-singletrace option turns on the same verbose tracing, but allows an individual query to be separately
traced by setting its query ID to 0. These options should only be enabled when debugging, because they have a significant
negative impact on query performance.
make install installs named and the various BIND 9 libraries. By default, installation is into /usr/local, but this canbe changed with the --prefix option when running configure.
The option --sysconfdir can be specified to set the directory where configuration files such as named.conf go bydefault; --localstatedir can be used to set the default parent directory of run/named.pid. --sysconfdir
defaults to $prefix/etc and --localstatedir defaults to $prefix/var.

10.3 macOS
Building on macOS assumes that the “Command Tools for Xcode” are installed. These can be downloaded from https://developer.apple.com/download/more/ or, if Xcode is already installed, simply run xcode-select --install.
(Note that an Apple ID may be required to access the download page.)

10.3. macOS

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Chapter 10. Building BIND 9CHAPTERELEVENRELEASE NOTES

Contents• Release Notes– Introduction– Supported Platforms– Download– Known Issues– Notes for BIND 9.20.0∗ New Features∗ Removed Features∗ Deprecated Features∗ Feature Changes∗ Bug Fixes∗ Known Issues– License– End of Life
– Thank You

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11.1 Introduction
BIND 9.20 is a stable branch, suitable for production use. This document summarizes significant changes since the lastproduction release on the 9.18 branch.

11.2 Supported Platforms
See the Supported Platforms section in the Resource Requirements chapter.

11.3 Download
The latest versions of BIND 9 software can always be found at https://www.isc.org/download/. There you will findadditional information about each release, and source code.

11.4 Known Issues• On some platforms, including FreeBSD, named must be run as root to use the rndc control channel on a privileged
port (i.e., with a port number less than 1024; this includes the default rndc port, 953). Currently, using thenamed -u option to switch to an unprivileged user makes rndc unusable. This will be fixed in a future release; inthe meantime, mac_portacl can be used as a workaround, as documented in https://kb.isc.org/docs/aa-00621.
[GL #4793]

11.5 Notes for BIND 9.20.0
Note: This section only lists changes since BIND 9.18.28, the most recent release on the previous stable branch of BIND
at the time of the publication of BIND 9.20.0.

11.5.1 New Features• The forwarders statement now supports the tls argument, to be used to forward queries to DoT-enabledservers. [GL #3726]• named now supports forwarding Dynamic DNS updates through DNS-over-TLS (DoT). [GL #3512]• The nsupdate tool now supports DNS-over-TLS (DoT). [GL !6752]• The tls block was extended with a new cipher-suites option that allows permitted cipher suites for TLSv1.3
to be set. Please consult the documentation for additional details. [GL #3504]• Initial support for the PROXYv2 protocol was added. named can now accept PROXYv2 headers over all currently
implemented DNS transports and dig can insert these headers into the queries it sends. Please consult the related
documentation (allow-proxy, allow-proxy-on, listen-on, and listen-on-v6 for named, dig+proxy and dig +proxy-plain for dig) for additional details. [GL #4388]

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BIND 9 Administrator Reference Manual, Release 9.20.0• The client-side support of the EDNS EXPIRE option has been expanded to include IXFR and AXFR query types.
This enhancement enables named to perform AXFR and IXFR queries while incorporating the EDNS EXPIRE
option. [GL #4170]• A new configuration option require-cookie has been introduced. It specifies whether there should be a DNSCOOKIE in the response for a given prefix; if not, named falls back to TCP. This is useful if it is known that agiven server supports DNS COOKIE. It can also be used to force all non-DNS COOKIE responses to fall back to
TCP. [GL #2295]• The check-svcb option has been added to control the checking of additional constraints on SVCB records. Thischange affects named, named-checkconf, named-checkzone, named-compilezone, and nsupdate. [GL #3576]• The new resolver-use-dns64 option enables named to apply dns64 rules to IPv4 server addresses whensending recursive queries, so that resolution can be performed over a NAT64 connection. [GL #608]• A new option to dnssec-policy has been added, cdnskey, that allows users to enable or disable the publication of CDNSKEY records. [GL #4050]• When using dnssec-policy, it is now possible to configure the digest type to use when CDS records need tobe published with cds-digest-types. Also, publication of specific CDNSKEY/CDS records can now be set
with dnssec-signzone -G. [GL #3837]• Support for multi-signer model 2 (RFC 8901) when using inline-signing was added. [GL #2710]• HSM support was added to dnssec-policy. Keys can now be configured with a key-store that allows users
to set the directory where key files are stored and to set a PKCS#11 URI string. The latter requires OpenSSL 3
and a valid PKCS#11 provider to be configured for OpenSSL. [GL #1129]• A new DNSSEC tool dnssec-ksr has been added to create Key Signing Request (KSR) and Signed Key Response (SKR) files. [GL #1128]• dnssec-verify and dnssec-signzone now accept a -J option to specify a journal file to read whenloading the zone to be verified or signed. [GL #2486]• dnssec-keygen now allows the options -k and -f to be used together. This allows the creation of keys for agiven dnssec-policy that match only the KSK (-fK) or ZSK (-fZ) roles. [GL #1128]• The response-policy statement was extended with a new argument ede. It enables an RFC 8914 Extended
DNS Error (EDE) code of choice to be set for responses which have been modified by a given RPZ. [GL #3410]• A new way of configuring the preferred source address when talking to remote servers, such as primaries andparental-agents, has been added: setting the source and/or source-v6 arguments for a given statement
is now possible. This new approach is intended to eventually replace statements such as parental-source,
parental-source-v6, transfer-source, etc. [GL #3762]• The new command-line delv +ns option activates name server mode, to more accurately reproduce the behaviorof named when resolving a query. In this mode, delv uses an internal recursive resolver rather than an external
server. All messages sent and received during the resolution and validation process are logged. This can be usedin place of dig +trace. [GL #3842]• The read timeout in rndc can now be specified on the command line using the -t option, allowing commands
that take a long time to complete sufficient time to do so. [GL #4046]• The statistics channel now includes information about incoming zone transfers that are currently in progress. [GL#3883]• Information on incoming zone transfers in the statistics channel now also shows the zones’ “first refresh” flag, whichindicates that a zone is not fully ready and that its first ever refresh is pending or is in progress. The number of suchzones is now also exposed by the rndc status command. [GL #4241]

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BIND 9 Administrator Reference Manual, Release 9.20.0• Added a new statistics variable recursive high-water that reports the maximum number of simultaneousrecursive clients BIND has handled while running. [GL #4668]• A new command, rndc fetchlimit, prints a list of name server addresses that are currently rate-limited due
to fetches-per-server and domain names that are rate-limited due to fetches-per-zone. [GL #665]• Queries and responses now emit distinct dnstap entries for DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH),
and dnstap-read understands these entries. [GL #4523]• dnstap-read can now print long timestamps with millisecond precision. [GL #2360]• Support for libsystemd’s sd_notify() function was added, enabling named to report its status to the init system.
This allows systemd to wait until named is fully ready before starting other services that depend on name resolution.
[GL #1176]• Support for User Statically Defined Tracing (USDT) probes has been added. These probes enable fine-grained
application tracing and introduce no overhead when they are not enabled. [GL #4041]

11.5.2 Removed Features• Support for Red Hat Enterprise Linux version 7 (and clones) has been dropped. A C11-compliant compiler is now
required to compile BIND 9. [GL #3729]• Compiling with jemalloc versions older than 4.0.0 is no longer supported; those versions do not provide the features
required by current BIND 9 releases. [GL #4296]• The auto-dnssec configuration statement has been removed. Please use dnssec-policy or manual signinginstead. See article how to migrate from auto-dnssec to dnssec-policy.
The following statements have become obsolete: dnskey-sig-validity, dnssec-dnskey-kskonly,
dnssec-update-mode, sig-validity-interval, and update-check-ksk. [GL #3672]• Dynamic updates that add and remove DNSKEY and NSEC3PARAM records no longer trigger key rollovers anddenial-of-existence operations. This also means that the dnssec-secure-to-insecure option has been
obsoleted. [GL #3686]• The glue-cache option has been removed. The glue cache feature still works and is now permanently enabled.
[GL #2147]• Configuring the control channel to use a Unix domain socket has been a fatal error since BIND 9.18. The feature
has now been completely removed and named-checkconf now reports it as a configuration error. [GL #4311]• The statements setting alternate local addresses for inbound zone transfers (alt-transfer-source,
alt-transfer-source-v6, and use-alt-transfer-source) have been removed. [GL #3714]• The resolver-nonbackoff-tries and resolver-retry-interval statements have been removed.
Using them is now a fatal error. [GL #4405]• BIND 9 no longer supports non-zero stale-answer-client-timeout values, when the feature is turned
on. When using a non-zero value, named now generates a warning log message, and treats the value as 0. [GL#4447]• The Differentiated Services Code Point (DSCP) feature has been removed: configuring DSCP values in named.
conf is now a configuration error. [GL #3789]• The keep-response-order option has been declared obsolete and the functionality has been removed.
named expects DNS clients to be fully compliant with RFC 7766. [GL #3140]• Zone type delegation-only, and the delegation-only and root-delegation-only statements,
have been removed. Using them is a configuration error.

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These statements were created to address the SiteFinder controversy, in which certain top-level domains redirected
misspelled queries to other sites instead of returning NXDOMAIN responses. Since top-level domains are now
DNSSEC-signed, and DNSSEC validation is active by default, the statements are no longer needed. [GL #3953]• The coresize, datasize, files, and stacksize options have been removed. The limits these options
set should be enforced externally, either by manual configuration (e.g. using ulimit) or via the process supervisor(e.g. systemd). [GL #3676]• Support for using AES as the DNS COOKIE algorithm (cookie-algorithm aes;) has been removed. The
only supported DNS COOKIE algorithm is now the current default, SipHash-2-4. [GL #4421]• The TKEY Mode 2 (Diffie-Hellman Exchanged Keying Mode) has been removed and using TKEY Mode 2 is now
a fatal error. Users are advised to switch to TKEY Mode 3 (GSS-API). [GL #3905]• Special-case code that was originally added to allow GSS-TSIG to work around bugs in the Windows 2000 versionof Active Directory has now been removed, since Windows 2000 is long past end-of-life. The -o option andthe oldgsstsig command to nsupdate have been deprecated, and are now treated as synonyms for -g andgsstsig respectively. [GL #4012]• Support for the lock-file statement and the named -X command-line option has been removed. An external
process supervisor should be used instead. [GL #4391]
Alternatively, the flock utility (part of util-linux) can be used on Linux systems to achieve the same effect as
lock-file or named -X:
flock -n -x <directory>/named.lock <path>/named <arguments>• The named command-line option -U, which specified the number of UDP dispatches, has been removed. Using
it now returns a warning. [GL #1879]• The --with-tuning option for configure has been removed. Each of the compile-time settings
that required different values based on the “workload” (which were previously affected by the value of the--with-tuning option) has either been removed or changed to a sensible default. [GL #3664]• The functions that were in the libbind9 shared library have been moved to the libisc and libisccfg
libraries. The now-empty libbind9 has been removed and is no longer installed. [GL #3903]• The irs_resconf module has been moved to the libdns shared library. The now-empty libirs libraryhas been removed and is no longer installed. [GL #3904]

11.5.3 Deprecated Features
Features listed in this section still work but are scheduled for eventual removal.
• The use of the max-zone-ttl option in options and zone blocks has been deprecated; it should now be
configured as part of dnssec-policy. A warning is logged if this option is used in options or zone blocks.
In a future release, it will become nonoperational. [GL #2918]• The sortlist option has been deprecated and will be removed in a future BIND 9.21.x release. Users should
not rely on a specific order of resource records in DNS messages. [GL #4593]• The fixed value for the rrset-order option and the corresponding configure script option have been
deprecated and will be removed in a future BIND 9.21.x release. Users should not rely on a specific order ofresource records in DNS messages. [GL #4446]

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11.5.4 Feature Changes• BIND now depends on liburcu, Userspace RCU, for lock-free data structures. [GL #3934]• On Linux, libcap is now a required dependency to help named keep needed privileges. [GL #3583]• Compiling BIND 9 now requires at least libuv version 1.34.0 or higher. libuv should be available on all supported
platforms either as a native package or as a backport. [GL #3567]• Outgoing zone transfers are no longer enabled by default. An explicit allow-transfer ACL must now be set
at the zone, view, or options level to enable outgoing transfers. [GL #4728]• DNS zones signed using dnssec-policy now automatically detect their parent servers, and BIND queries themto check the content of the DS RRset. This allows DNSSEC key rollovers to safely and automatically proceed when
the parent zone is updated with new DNSSEC keys, i.e. using the CDS/CDNSKEY mechanism. This behavior
is facilitated by the new checkds feature, which automatically populates parental-agents by resolving theparent NS records. These parent name servers are queried to check the DS RRset during a KSK rollover initiatedby dnssec-policy. [GL #3901]• The responsiveness of named was improved, when serving as an authoritative DNS server for a delegation-heavyzone(s) shortly after loading such zone(s). [GL #4045]• To improve query-processing latency under load, the uninterrupted time spent on resolving long chains of cacheddomain names has been reduced. [GL #4185]• QNAME minimization is now used when looking up the addresses of name servers during the recursive resolution
process. [GL #4209]• BIND now returns BADCOOKIE for out-of-date or otherwise bad but well-formed DNS server cookies. [GL#4194]• The DNS name compression algorithm used in BIND 9 has been revised: it now compresses more thoroughly than
before, so responses containing names with many labels might have a smaller encoding than before. [GL #3661]• Processing large incremental transfers (IXFR) has been offloaded to a separate work thread so that it does notprevent networking threads from processing regular traffic in the meantime. [GL #4367]• Querying the statistics channel no longer blocks DNS communication on the networking event loop level. [GL#4680]• The inline-signing zone option is now ignored if there is no dnssec-policy configured for the zone.
This means that unsigned zones no longer create redundant signed versions of the zone. [GL #4349]• The inline-signing statement can now also be set inside dnssec-policy. The built-in policies default and insecure enable the use of inline-signing. If inline-signing is set at the zone level,it overrides the value set in dnssec-policy. [GL #3677]• Following RFC 9276 recommendations, dnssec-policy now only allows an NSEC3 iteration count of 0 for
the DNSSEC-signed zones using NSEC3 that the policy manages. [GL #4363]• The maximum number of NSEC3 iterations allowed for validation purposes has been lowered from 150 to 50.
DNSSEC responses containing NSEC3 records with iteration counts greater than 50 are now treated as insecure.
[GL #4363]• The dnssec-validation yes option now requires an explicitly configured trust-anchors statement.
If using manual trust anchors is not operationally required, then please consider using dnssec-validation
auto instead. [GL #4373]• named-compilezone no longer performs zone integrity checks by default; this allows faster conversion of azone file from one format to another. [GL #4364]
Zone checks can be performed by running named-checkzone separately, or the previous default behavior canbe restored by using:
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named-compilezone -i full -k fail -n fail -r warn -m warn -M warn -S warn -T warn␣
,→-W warn -C check-svcb:fail• The red-black tree data structure used in the RBTDB (the default database implementation for cache and zone
databases), has been replaced with QP-tries. This is expected to improve performance and scalability, though
in the current implementation large zones require roughly 15% more memory than the old red-black tree data
structure.
A side effect of this change is that zone files that are created with masterfile-style relative - for example, the output of dnssec-signzone - will no longer have multiple different $ORIGIN statements. There
should be no other changes to server behavior.
The old RBT-based database still exists for now, and can be used by specifying database rbt
in a zone statement in named.conf, or by compiling with configure --with-zonedb=rbt--with-cachedb=rbt. [GL #4411] [GL #4614]• Multiple RNDC messages are now processed when sent in a single TCP message.
ISC would like to thank Dominik Thalhammer for reporting the issue and preparing the initial patch. [GL #4416]• The DNSSEC signing data included in zone statistics identified keys only by the key ID; this caused confusion when
two keys using different algorithms had the same ID. Zone statistics now identify keys using the algorithm number,
followed by “+”, followed by the key ID: for example, 8+54274. [GL #3525]• The TTL of the NSEC3PARAM record for every NSEC3-signed zone was previously set to 0. It is now changed
to match the SOA MINIMUM value for the given zone. [GL #3570]• On startup, named now sets the limit on the number of open files to the maximum allowed by the operating system,
instead of trying to set it to “unlimited”. [GL #3676]• When an international domain name is not valid according to IDNA2008, dig now tries to convert it according to
IDNA2003 rules, or pass it through unchanged, instead of stopping with an error message. The idna2 utility canbe used to check IDNA syntax. [GL #3527]• The memory statistics have been reduced to a single counter, InUse; Malloced is an alias that holds the samevalue. The other counters were usable with the old BIND 9 internal memory allocator, but they are unnecessary
now that the latter has been removed. [GL #3718]• The log message resolver priming query complete has been moved from the INFO log level to
the DEBUG(1) log level, to prevent delv from emitting that message when setting up its internal resolver. [GL#3842]• Worker threads’ event loops are now managed by a new “loop manager” API, significantly changing the architectureof the task, timer, and networking subsystems for improved performance and code flow. [GL #3508]• The code for DNS over TCP and DNS over TLS transports has been replaced with a new, unified transport implementation. [GL #3374]

11.5.5 Bug Fixes• When the same notify-source address and port number was configured for multiple destinations and zones, anunresponsive server could tie up the relevant network socket until it timed out; in the meantime, NOTIFY messages
for other servers silently failed. named will now retry sending such NOTIFY messages over TCP. Furthermore,
NOTIFY failures are now logged at the INFO level. [GL #4001] [GL #4002]• DNS compression is no longer applied to the root name (.) if it is repeatedly used in the same RRset. [GL #3423]• named could incorrectly return non-truncated, glueless referrals for responses whose size was close to the UDP
packet size limit. This has been fixed. [GL #1967]

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11.5.6 Known Issues• On some platforms, including FreeBSD, named must be run as root to use the rndc control channel on a privileged
port (i.e., with a port number less than 1024; this includes the default rndc port, 953). Currently, using thenamed -u option to switch to an unprivileged user makes rndc unusable. This will be fixed in a future release; inthe meantime, mac_portacl can be used as a workaround, as documented in https://kb.isc.org/docs/aa-00621.
[GL #4793]• See above for a list of all known issues affecting this BIND 9 branch.

11.6 License
BIND 9 is open source software licensed under the terms of the Mozilla Public License, version 2.0 (see the COPYING
file for the full text).
Those wishing to discuss license compliance may contact ISC at https://www.isc.org/contact/.

11.7 End of Life
BIND 9.20 is a stable branch, suitable for production use. After it has been in production use for a while it will be
designated as an Extended Support Version (ESV). Until then, the current ESV is BIND 9.18, which will be supported
until at least December 2025. See https://kb.isc.org/docs/aa-00896 for details of ISC’s software support policy.

11.8 Thank You
Thank you to everyone who assisted us in making this release possible.

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CHAPTERTWELVEDNSSEC GUIDE

12.1 Preface
12.1.1 Organization
This document provides introductory information on how DNSSEC works, how to configure BIND 9 to support somecommon DNSSEC features, and some basic troubleshooting tips. The chapters are organized as follows:
Introduction covers the intended audience for this document, assumed background knowledge, and a basic introduction
to the topic of DNSSEC.
Getting Started covers various requirements before implementing DNSSEC, such as software versions, hardware capacity,
network requirements, and security changes.
Validation walks through setting up a validating resolver, and gives both more information on the validation process andsome examples of tools to verify that the resolver is properly validating answers.
Signing explains how to set up a basic signed authoritative zone, details the relationship between a child and a parent zone,
and discusses ongoing maintenance tasks.
Basic DNSSEC Troubleshooting provides some tips on how to analyze and diagnose DNSSEC-related problems.
Advanced Discussions covers several topics, including key generation, key storage, key management, NSEC and NSEC3,and some disadvantages of DNSSEC.
Recipes provides several working examples of common DNSSEC solutions, with step-by-step details.
Commonly Asked Questions lists some commonly asked questions and answers about DNSSEC.

12.1.2 Acknowledgements
This document was originally authored by Josh Kuo of DeepDive Networking. He can be reached at josh.kuo@gmail.com.
Thanks to the following individuals (in no particular order) who have helped in completing this document: Jeremy C. Reed,
Heidi Schempf, Stephen Morris, Jeff Osborn, Vicky Risk, Jim Martin, Evan Hunt, Mark Andrews, Michael McNally,
Kelli Blucher, Chuck Aurora, Francis Dupont, Rob Nagy, Ray Bellis, Matthijs Mekking, and Suzanne Goldlust.
Special thanks goes to Cricket Liu and Matt Larson for their selflessness in knowledge sharing.
Thanks to all the reviewers and contributors, including John Allen, Jim Young, Tony Finch, Timothe Litt, and Dr. Jeffry
A. Spain.
The sections on key rollover and key timing metadata borrowed heavily from the Internet Engineering Task Force draft
titled “DNSSEC Key Timing Considerations” by S. Morris, J. Ihren, J. Dickinson, and W. Mekking, subsequently published as RFC 7583.

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Icons made by Freepik and SimpleIcon from Flaticon, licensed under Creative Commons BY 3.0.

12.2 Introduction
12.2.1 Who Should Read this Guide?
This guide is intended as an introduction to DNSSEC for the DNS administrator who is already comfortable working
with the existing BIND and DNS infrastructure. He or she might be curious about DNSSEC, but may not have had thetime to investigate DNSSEC, to learn whether DNSSEC should be a part of his or her environment, and understand what
it means to deploy it in the field.
This guide provides basic information on how to configure DNSSEC using BIND 9.16.0 or later. Most of the informationand examples in this guide also apply to versions of BIND later than 9.9.0, but some of the key features described here
were only introduced in version 9.16.0. Readers are assumed to have basic working knowledge of the Domain Name
System (DNS) and related network infrastructure, such as concepts of TCP/IP. In-depth knowledge of DNS and TCP/IP
is not required. The guide assumes no prior knowledge of DNSSEC or related technology such as public key cryptography.

12.2.2 Who May Not Want to Read this Guide?
If you are already operating a DNSSEC-signed zone, you may not learn much from the first half of this document, andyou may want to start with Advanced Discussions. If you want to learn about details of the protocol extension, such as data
fields and flags, or the new record types, this document can help you get started but it does not include all the technicaldetails.
If you are experienced in DNSSEC, you may find some of the concepts in this document to be overly simplified for yourtaste, and some details are intentionally omitted at times for ease of illustration.
If you administer a large or complex BIND environment, this guide may not provide enough information for you, as it isintended to provide only basic, generic working examples.
If you are a top-level domain (TLD) operator, or administer zones under signed TLDs, this guide can help you get started,but it does not provide enough details to serve all of your needs.
If your DNS environment uses DNS products other than (or in addition to) BIND, this document may provide somebackground or overlapping information, but you should check each product’s vendor documentation for specifics.
Finally, deploying DNSSEC on internal or private networks is not covered in this document, with the exception of a brief
discussion in DNSSEC on Private Networks.

12.2.3 What is DNSSEC?
The Domain Name System (DNS) was designed in a day and age when the Internet was a friendly and trusting place.
The protocol itself provides little protection against malicious or forged answers. DNS Security Extensions (DNSSEC)
addresses this need, by adding digital signatures into DNS data so that each DNS response can be verified for integrity(the answer did not change during transit) and authenticity (the data came from the true source, not an impostor). In theideal world, when DNSSEC is fully deployed, every single DNS answer can be validated and trusted.
DNSSEC does not provide a secure tunnel; it does not encrypt or hide DNS data. It operates independently of an existing
Public Key Infrastructure (PKI). It does not need SSL certificates or shared secrets. It was designed with backwards
compatibility in mind, and can be deployed without impacting “old” unsecured domain names.
DNSSEC is deployed on the three major components of the DNS infrastructure:

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Chapter 12. DNSSEC GuideBIND 9 Administrator Reference Manual, Release 9.20.0• Recursive Servers: People use recursive servers to lookup external domain names such as www.example.com.
Operators of recursive servers need to enable DNSSEC validation. With validation enabled, recursive servers carryout additional tasks on each DNS response they receive to ensure its authenticity.
• Authoritative Servers: People who publish DNS data on their name servers need to sign that data. This entails
creating additional resource records, and publishing them to parent domains where necessary. With DNSSEC
enabled, authoritative servers respond to queries with additional DNS data, such as digital signatures and keys, inaddition to the standard answers.
• Applications: This component lives on every client machine, from web servers to smart phones. This includes
resolver libraries on different operating systems, and applications such as web browsers.
In this guide, we focus on the first two components, Recursive Servers and Authoritative Servers, and only lightly touchon the third component. We look at how DNSSEC works, how to configure a validating resolver, how to sign DNS zone
data, and other operational tasks and considerations.

12.2.4 What Does DNSSEC Add to DNS?
Note: Public Key Cryptography works on the concept of a pair of keys: one made available to the world publicly, andone kept in secrecy privately. Not surprisingly, they are known as a public key and a private key. If you are not familiar
with the concept, think of it as a cleverly designed lock, where one key locks and one key unlocks. In DNSSEC, we giveout the unlocking public key to the rest of the world, while keeping the locking key private. To learn how this is used tosecure DNS messages, see How Are Answers Verified?.
DNSSEC introduces eight new resource record types:• RRSIG (digital resource record signature)• DNSKEY (public key)
• DS (parent-child)• NSEC (proof of nonexistence)• NSEC3 (proof of nonexistence)• NSEC3PARAM (proof of nonexistence)• CDS (child-parent signaling)• CDNSKEY (child-parent signaling)
This guide does not go deep into the anatomy of each resource record type; the details are left for the reader to researchand explore. Below is a short introduction on each of the new record types:• RRSIG: With DNSSEC enabled, just about every DNS answer (A, PTR, MX, SOA, DNSKEY, etc.) comes withat least one resource record signature, or RRSIG. These signatures are used by recursive name servers, also known
as validating resolvers, to verify the answers received. To learn how digital signatures are generated and used, see
How Are Answers Verified?.
• DNSKEY: DNSSEC relies on public-key cryptography for data authenticity and integrity. There are several keys
used in DNSSEC, some private, some public. The public keys are published to the world as part of the zone data,
and they are stored in the DNSKEY record type.
In general, keys in DNSSEC are used for one or both of the following roles: as a Zone Signing Key (ZSK), used toprotect all zone data; or as a Key Signing Key (KSK), used to protect the zone’s keys. A key that is used for bothroles is referred to as a Combined Signing Key (CSK). We talk about keys in more detail in DNSSEC Keys.

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BIND 9 Administrator Reference Manual, Release 9.20.0• DS: One of the critical components of DNSSEC is that the parent zone can “vouch” for its child zone. The DS
record is verifiable information (generated from one of the child’s public keys) that a parent zone publishes about
its child as part of the chain of trust. To learn more about the Chain of Trust, see Chain of Trust.
• NSEC, NSEC3, NSEC3PARAM: These resource records all deal with a very interesting problem: proving that something does not exist. We look at these record types in more detail in Proof of Non-Existence (NSEC and NSEC3).
• CDS, CDNSKEY: The CDS and CDNSKEY resource records apply to operational matters and are a way to signal
to the parent zone that the DS records it holds for the child zone should be updated. This is covered in more detailin The CDS and CDNSKEY Resource Records.

12.2.5 How Does DNSSEC Change DNS Lookup?
Traditional (insecure) DNS lookup is simple: a recursive name server receives a query from a client to lookup a name likewww.isc.org. The recursive name server tracks down the authoritative name server(s) responsible, sends the query to
one of the authoritative name servers, and waits for it to respond with the answer.
With DNSSEC validation enabled, a validating recursive name server (a.k.a. a validating resolver) asks for additional
resource records in its query, hoping the remote authoritative name servers respond with more than just the answer to thequery, but some proof to go along with the answer as well. If DNSSEC responses are received, the validating resolver
performs cryptographic computation to verify the authenticity (the origin of the data) and integrity (that the data was notaltered during transit) of the answers, and even asks the parent zone as part of the verification. It repeats this process ofget-key, validate, ask-parent, and its parent, and its parent, all the way until the validating resolver reaches a key that ittrusts. In the ideal, fully deployed world of DNSSEC, all validating resolvers only need to trust one key: the root key.

12.2.6 The 12-Step DNSSEC Validation Process (Simplified)
The following example shows the 12 steps of the DNSSEC validating process at a very high level, looking up the namewww.isc.org :1. Upon receiving a DNS query from a client to resolve www.isc.org, the validating resolver follows standard
DNS protocol to track down the name server for isc.org, and sends it a DNS query to ask for the A record of
www.isc.org. But since this is a DNSSEC-enabled resolver, the outgoing query has a bit set indicating it wants
DNSSEC answers, hoping the name server that receives it is DNSSEC-enabled and can honor this secure request.
2. The isc.org name server is DNSSEC-enabled, so it responds with both the answer (in this case, an A record)
and a digital signature for verification purposes.
3. The validating resolver requires cryptographic keys to be able to verify the digital signature, so it asks the isc.org
name server for those keys.
4. The isc.org name server responds with the cryptographic keys (and digital signatures of the keys) used togenerate the digital signature that was sent in #2. At this point, the validating resolver can use this information to
verify the answers received in #2.
Let’s take a quick break here and look at what we’ve got so far… how can our server trust this answer? If a cleverattacker had taken over the isc.org name server(s), of course she would send matching keys and signatures. We
need to ask someone else to have confidence that we are really talking to the real isc.org name server. Thisis a critical part of DNSSEC: at some point, the DNS administrators at isc.org uploaded some cryptographic
information to its parent, .org, maybe through a secure web form, maybe through an email exchange, or perhaps
in person. In any event, at some point some verifiable information about the child (isc.org) was sent to theparent (.org) for safekeeping.
5. The validating resolver asks the parent (.org) for the verifiable information it keeps on its child, isc.org.
6. Verifiable information is sent from the .org server. At this point, the validating resolver compares this to theanswer it received in #4; if the two of them match, it proves the authenticity of isc.org.

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Let’s examine this process. You might be thinking to yourself, what if the clever attacker that took over isc.org
also compromised the .org servers? Of course all this information would match! That’s why we turn our attention
now to the .org server, interrogate it for its cryptographic keys, and move one level up to .org’s parent, root.
7. The validating resolver asks the .org authoritative name server for its cryptographic keys, to verify the answers
received in #6.
8. The .org name server responds with the answer (in this case, keys and signatures). At this point, the validating
resolver can verify the answers received in #6.
9. The validating resolver asks root (.org’s parent) for the verifiable information it keeps on its child, .org.
10. The root name server sends back the verifiable information it keeps on .org. The validating resolver uses thisinformation to verify the answers received in #8.
So at this point, both isc.org and .org check out. But what about root? What if this attacker is really cleverand somehow tricked us into thinking she’s the root name server? Of course she would send us all matching
information! So we repeat the interrogation process and ask for the keys from the root name server.
11. The validating resolver asks the root name server for its cryptographic keys to verify the answer(s) received in #10.
12. The root name server sends its keys; at this point, the validating resolver can verify the answer(s) received in #10.

12.2.7 Chain of Trust
But what about the root server itself? Who do we go to verify root’s keys? There’s no parent zone for root. In security,
you have to trust someone, and in the perfectly protected world of DNSSEC (we talk later about the current imperfectstate and ways to work around it), each validating resolver would only have to trust one entity, that is, the root nameserver. The validating resolver already has the root key on file (we discuss later how we got the root key file). So after theanswer in #12 is received, the validating resolver compares it to the key it already has on file. Providing one of the keys
in the answer matches the one on file, we can trust the answer from root. Thus we can trust .org, and thus we can trust
isc.org. This is known as the “chain of trust” in DNSSEC.
We revisit this 12-step process again later in How Does DNSSEC Change DNS Lookup (Revisited)? with more technicaldetails.

12.2.8 Why is DNSSEC Important? (Why Should I Care?)
You might be thinking to yourself: all this DNSSEC stuff sounds wonderful, but why should I care? Below are somereasons why you may want to consider deploying DNSSEC:
1. Being a good netizen: By enabling DNSSEC validation (as described in Validation) on your DNS servers, you’re
protecting your users and yourself a little more by checking answers returned to you; by signing your zones (asdescribed in Signing), you are making it possible for other people to verify your zone data. As more people adopt
DNSSEC, the Internet as a whole becomes more secure for everyone.
2. Compliance: You may not even get a say in implementing DNSSEC, if your organization is subject to compliancestandards that mandate it. For example, the US government set a deadline in 2008 to have all .gov subdomains
signed by December 20091 . So if you operate a subdomain in .gov, you must implement DNSSEC to be compliant. ICANN also requires that all new top-level domains support DNSSEC.
3. Enhanced Security: Okay, so the big lofty goal of “let’s be good” doesn’t appeal to you, and you don’t have any
compliance standards to worry about. Here is a more practical reason why you should consider DNSSEC: in theevent of a DNS-based security breach, such as cache poisoning or domain hijacking, after all the financial and brand
1 The Office of Management and Budget (OMB) for the US government published a memo in 2008, requesting all .gov subdomains to be DNSSECsigned by December 2009. This explains why .gov is the most-deployed DNSSEC domain currently, with around 90% of subdomains signed.

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damage done to your domain name, you might be placed under scrutiny for any preventive measure that could havebeen put in place. Think of this like having your website only available via HTTP but not HTTPS.
4. New Features: DNSSEC brings not only enhanced security, but also a whole new suite of features. Once DNS
can be trusted completely, it becomes possible to publish SSL certificates in DNS, or PGP keys for fully automaticcross-platform email encryption, or SSH fingerprints…. New features are still being developed, but they all rely on
a trustworthy DNS infrastructure. To take a peek at these next-generation DNS features, check out Introduction to
DANE.

12.2.9 How Does DNSSEC Change My Job as a DNS Administrator?
With this protocol extension, some of the things you were used to in DNS have changed. As the DNS administrator,
you have new maintenance tasks to perform on a regular basis (as described in Maintenance Tasks); when there is a
DNS resolution problem, you have new troubleshooting techniques and tools to use (as described in Basic DNSSEC Troubleshooting). BIND 9 tries its best to make these things as transparent and seamless as possible. In this guide, we try touse configuration examples that result in the least amount of work for BIND 9 DNS administrators.

12.3 Getting Started
12.3.1 Software Requirements
This guide assumes BIND 9.18.0 or newer, although the more elaborate manual procedures do work with all versions of
BIND later than 9.9.
We recommend running the latest stable version to get the most complete DNSSEC configuration, as well as the latest
security fixes.

12.3.2 Hardware Requirements
Recursive Server Hardware
Enabling DNSSEC validation on a recursive server makes it a validating resolver. The job of a validating resolver is tofetch additional information that can be used to computationally verify the answer set. Contrary to popular belief, theincrease in resource consumption is very modest:
1. CPU: a validating resolver executes cryptographic functions on cache-miss answers, which leads to increased CPU
usage. Thanks to standard DNS caching and contemporary CPUs, the increase in CPU-time consumption in a
steady state is negligible - typically on the order of 5%. For a brief period (a few minutes) after the resolver starts,
the increase might be as much as 20%, but it quickly decreases as the DNS cache fills in.
2. System memory: DNSSEC leads to larger answer sets and occupies more memory space. With typical ISP traffic
and the state of the Internet as of mid-2022, memory consumption for the cache increases by roughly 20%.
3. Network interfaces: although DNSSEC does increase the amount of DNS traffic overall, in practice this increase isoften within measurement error.

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Authoritative Server Hardware
On the authoritative server side, DNSSEC is enabled on a zone-by-zone basis. When a zone is DNSSEC-enabled, it isalso known as “signed.” Below are the expected changes to resource consumption caused by serving DNSSEC-signed
zones:
1. CPU: a DNSSEC-signed zone requires periodic re-signing, which is a cryptographic function that is CPU-intensive.
If your DNS zone is dynamic or changes frequently, that also adds to higher CPU loads.
2. System storage: A signed zone is definitely larger than an unsigned zone. How much larger? See Your Zone, Before
and After DNSSEC for a comparison example. The final size depends on the structure of the zone, the signingalgorithm, the number of keys, the choice of NSEC or NSEC3, the ratio of signed delegations, the zone file format,
etc. Usually, the size of a signed zone ranges from a negligible increase to as much as three times the size of theunsigned zone.
3. System memory: Larger DNS zone files take up not only more storage space on the file system, but also more spacewhen they are loaded into system memory. The final memory consumption also depends on all the variables listed
above: in the typical case the increase is around half of the unsigned zone memory consumption, but it can be as
high as three times for some corner cases.
4. Network interfaces: While your authoritative name servers will begin sending back larger responses, it is unlikelythat you need to upgrade your network interface card (NIC) on the name server unless you have some truly outdated
hardware.
One factor to consider, but over which you really have no control, is the number of users who query your domain name
who themselves have DNSSEC enabled. As of mid-2022, measurements by APNIC show 41% of Internet users send
DNSSEC-aware queries. This means that more DNS queries for your domain will take advantage of the additional security
features, which will result in increased system load and possibly network traffic.

12.3.3 Network Requirements
From a network perspective, DNS and DNSSEC packets are very similar; DNSSEC packets are just bigger, which means
DNS is more likely to use TCP. You should test for the following two items to make sure your network is ready for
DNSSEC:
1. DNS over TCP: Verify network connectivity over TCP port 53, which may mean updating firewall policies or AccessControl Lists (ACL) on routers. See Wait… DNS Uses TCP? for more details.
2. Large UDP packets: Some network equipment, such as firewalls, may make assumptions about the size of DNS
UDP packets and incorrectly reject DNS traffic that appears “too big.” Verify that the responses your name server
generates are being seen by the rest of the world: see What’s EDNS All About (And Why Should I Care)? for moredetails.

12.3.4 Operational Requirements
Parent Zone
Before starting your DNSSEC deployment, check with your parent zone administrators to make sure they support
DNSSEC. This may or may not be the same entity as your registrar. As you will see later in Working With the Parent Zone, a crucial step in DNSSEC deployment is establishing the parent-child trust relationship. If your parent zone
does not yet support DNSSEC, contact that administrator to voice your concerns.

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Security Requirements
Some organizations may be subject to stricter security requirements than others. Check to see if your organization requires
stronger cryptographic keys be generated and stored, and how often keys need to be rotated. The examples presented
in this document are not intended for high-value zones. We cover some of these security considerations in Advanced
Discussions.

12.4 Validation
12.4.1 Easy-Start Guide for Recursive Servers
This section provides the basic information needed to set up a working DNSSEC-aware recursive server, also known as
a validating resolver. A validating resolver performs validation for each remote response received, following the chain oftrust to verify that the answers it receives are legitimate, through the use of public key cryptography and hashing functions.
Enabling DNSSEC Validation
So how do we turn on DNSSEC validation? It turns out that you may not need to reconfigure your name server at all, since
the most recent versions of BIND 9 - including packages and distributions - have shipped with DNSSEC validation enabled
by default. Before making any configuration changes, check whether you already have DNSSEC validation enabled byfollowing the steps described in So You Think You Are Validating (How To Test A Recursive Server).
In earlier versions of BIND, including 9.11-ESV, DNSSEC validation must be explicitly enabled. To do this, you only
need to add one line to the options section of your configuration file:
options {...
dnssec-validation auto;...
};

Restart named or run rndc reconfig, and your recursive server is now happily validating each DNS response. If
this does not work for you, you may have some other network-related configurations that need to be adjusted. Take a lookat Network Requirements to make sure your network is ready for DNSSEC.
Effects of Enabling DNSSEC Validation
Once DNSSEC validation is enabled, any DNS response that does not pass the validation checks results in a failure to
resolve the domain name (often a SERVFAIL status seen by the client). If everything has been configured properly, thisis the correct result; it means that an end user has been protected against a malicious attack.
However, if there is a DNSSEC configuration issue (sometimes outside of the administrator’s control), a specific name orsometimes entire domains may “disappear” from the DNS, and become unreachable through that resolver. For the end
user, the issue may manifest itself as name resolution being slow or failing altogether; some parts of a URL not loading;or the web browser returning an error message indicating that the page cannot be displayed. For example, if root nameservers were misconfigured with the wrong information about .org, it could cause all validation for .org domains to
fail. To end users, it would appear that all .org web sites were out of service2 . Should you encounter DNSSEC-related
problems, don’t be tempted to disable validation; there is almost certainly a solution that leaves validation enabled. A
basic troubleshooting guide can be found in Basic DNSSEC Troubleshooting.
2 Of course, something like this could happen for reasons other than DNSSEC: for example, the root publishing the wrong addresses for the .org
nameservers.

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12.4.2 So You Think You Are Validating (How To Test A Recursive Server)
Now that you have reconfigured your recursive server and restarted it, how do you know that your recursive name serveris actually verifying each DNS query? There are several ways to check, and we’ve listed a few of them below.
Using Web-Based Tools to Verify
For most people, the simplest way to check if a recursive name server is indeed validating DNS queries is to use one of
the many web-based tools available.
Configure your client computer to use the newly reconfigured recursive server for DNS resolution; then use one of these
web-based tests to confirm that it is in fact validating DNS responses.
• Internet.nl• DNSSEC or Not (VeriSign)
Using dig to Verify
Web-based DNSSEC-verification tools often employ JavaScript. If you don’t trust the JavaScript magic that the webbased tools rely on, you can take matters into your own hands and use a command-line DNS tool to check your validating
resolver yourself.
While nslookup is popular, partly because it comes pre-installed on most systems, it is not DNSSEC-aware. dig,on the other hand, fully supports the DNSSEC standard and comes as a part of BIND. If you do not have dig alreadyinstalled on your system, install it by downloading it from ISC’s website.
dig is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are
returned from the name servers that were queried. Most seasoned DNS administrators use dig to troubleshoot DNS
problems because of its flexibility, ease of use, and clarity of output.
The example below shows how to use dig to query the name server 10.53.0.1 for the A record for ftp.isc.org when
DNSSEC validation is enabled (i.e. the default). The address 10.53.0.1 is only used as an example; replace it with theactual address or host name of your recursive name server.
$ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good);; QUESTION SECTION:;ftp.isc.org.
IN A;; ANSWER SECTION:
ftp.isc.org.
300 IN A 149.20.1.49
ftp.isc.org.
300 IN RRSIG A 13 3 300 (20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== )(continues on next page)

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The important detail in this output is the presence of the ad flag in the header. This signifies that BIND has retrieved
all related DNSSEC information related to the target of the query (ftp.isc.org) and that the answer received has
passed the validation process described in How Are Answers Verified?. We can have confidence in the authenticity andintegrity of the answer, that ftp.isc.org really points to the IP address 149.20.1.49, and that it was not a spoofed
answer from a clever attacker.
Unlike earlier versions of BIND, the current versions of BIND always request DNSSEC records (by setting the do bit
in the query they make to upstream servers), regardless of DNSSEC settings. However, with validation disabled, thereturned signature is not checked. This can be seen by explicitly disabling DNSSEC validation. To do this, add the line
dnssec-validation no; to the “options” section of the configuration file, i.e.:
options {...
dnssec-validation no;...
};If the server is restarted (to ensure a clean cache) and the same dig command executed, the result is very similar:$ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39050;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: a8dc9d1b9ec45e75010000005e67a8a69399741fdbe126f2 (good);; QUESTION SECTION:;ftp.isc.org.
IN A;; ANSWER SECTION:
ftp.isc.org.
300 IN A 149.20.1.49
ftp.isc.org.
300 IN RRSIG A 13 3 300 (20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== );; Query time: 261 msec;; SERVER: 10.53.0.1#53(10.53.0.1);; WHEN: Tue Mar 10 14:48:06 GMT 2020;; MSG SIZE rcvd: 187

However, this time there is no ad flag in the header. Although dig is still returning the DNSSEC-related resource
records, it is not checking them, and thus cannot vouch for the authenticity of the answer. If you do carry out this test,
remember to re-enable DNSSEC validation (by removing the dnssec-validation no; line from the configurationfile) before continuing.

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12.4.3 Verifying Protection From Bad Domain Names
It is also important to make sure that DNSSEC is protecting your network from domain names that fail to validate; such
failures could be caused by attacks on your system, attempting to get it to accept false DNS information. Validation could
fail for a number of reasons: maybe the answer doesn’t verify because it’s a spoofed response; maybe the signature wasa replayed network attack that has expired; or maybe the child zone has been compromised along with its keys, and theparent zone’s information tells us that things don’t add up. There is a domain name specifically set up to fail DNSSEC
validation, www.dnssec-failed.org.
With DNSSEC validation enabled (the default), an attempt to look up that name fails:$ dig @10.53.0.1 www.dnssec-failed.org. A; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 22667;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 69c3083144854587010000005e67bb57f5f90ff2688e455d (good);; QUESTION SECTION:;www.dnssec-failed.org.
IN A;; Query time: 2763 msec;; SERVER: 10.53.0.1#53(10.53.0.1);; WHEN: Tue Mar 10 16:07:51 GMT 2020;; MSG SIZE rcvd: 78

On the other hand, if DNSSEC validation is disabled (by adding the statement dnssec-validation no; to theoptions clause in the configuration file), the lookup succeeds:$ dig @10.53.0.1 www.dnssec-failed.org. A; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54704;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 251eee58208917f9010000005e67bb6829f6dabc5ae6b7b9 (good);; QUESTION SECTION:;www.dnssec-failed.org.
IN A;; ANSWER SECTION:
www.dnssec-failed.org.
www.dnssec-failed.org.

7200
7200

IN
IN

A
A

68.87.109.242
69.252.193.191;; Query time: 439 msec;; SERVER: 10.53.0.1#53(10.53.0.1);; WHEN: Tue Mar 10 16:08:08 GMT 2020;; MSG SIZE rcvd: 110

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Do not be tempted to disable DNSSEC validation just because some names are failing to resolve. Remember, DNSSEC
protects your DNS lookup from hacking. The next section describes how to quickly check whether the failure to successfully look up a name is due to a validation failure.
How Do I Know I Have a Validation Problem?
Since all DNSSEC validation failures result in a general SERVFAIL message, how do we know if it was really a validation
error? Fortunately, there is a flag in dig, (“CD” for “checking disabled”) which tells the server to disable DNSSEC
validation. If you receive a SERVFAIL message, re-run the query a second time and set the dig +cd flag. If the query
succeeds with dig +cd, but ends in SERVFAIL without it, you know you are dealing with a validation problem. So
using the previous example of www.dnssec-failed.org and with DNSSEC validation enabled in the resolver:$ dig @10.53.0.1 www.dnssec-failed.org A +cd; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A +cd; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62313;; flags: qr rd ra cd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 73ca1be3a74dd2cf010000005e67c8c8e6df64b519cd87fd (good);; QUESTION SECTION:;www.dnssec-failed.org.
IN A;; ANSWER SECTION:
www.dnssec-failed.org.
www.dnssec-failed.org.

7197
7197

IN
IN

A
A

68.87.109.242
69.252.193.191;; Query time: 0 msec;; SERVER: 10.53.0.1#53(10.53.0.1);; WHEN: Tue Mar 10 17:05:12 GMT 2020;; MSG SIZE rcvd: 110

For more information on troubleshooting, please see Basic DNSSEC Troubleshooting.

12.4.4 Validation Easy Start Explained
In Easy-Start Guide for Recursive Servers, we used one line of configuration to turn on DNSSEC validation: the actof chasing down signatures and keys, making sure they are authentic. Now we are going to take a closer look at what
DNSSEC validation actually does, and some other options.

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dnssec-validation
options {dnssec-validation auto;};

This “auto” line enables automatic DNSSEC trust anchor configuration using the managed-keys feature. In this case,no manual key configuration is needed. There are three possible choices for the dnssec-validation option:• yes: DNSSEC validation is enabled, but a trust anchor must be manually configured. No validation actually takes
place until at least one trusted key has been manually configured.
• no: DNSSEC validation is disabled, and the recursive server behaves in the “old-fashioned” way of performing
insecure DNS lookups.
• auto: DNSSEC validation is enabled, and a default trust anchor (included as part of BIND 9) for the DNS rootzone is used. This is the default; BIND automatically does this if there is no dnssec-validation line in theconfiguration file.
Let’s discuss the difference between yes and auto. If set to yes, the trust anchor must be manually defined and maintainedusing the trust-anchors statement (with either the static-key or static-ds modifier) in the configuration
file; if set to auto (the default, and as shown in the example), then no further action should be required as BIND includes
a copy3 of the root key. When set to auto, BIND automatically keeps the keys (also known as trust anchors, discussed in
Trust Anchors) up-to-date without intervention from the DNS administrator.
When using yes, please note that if trust-anchors does not include a valid root key, then validation does not takeplace for names which are not covered by any of the configured trust anchors.
We recommend using the default auto unless there is a good reason to require a manual trust anchor. To learn more about
trust anchors, please refer to Trusted Keys and Managed Keys.
How Does DNSSEC Change DNS Lookup (Revisited)?
Now you’ve enabled validation on your recursive name server and verified that it works. What exactly changed? In How
Does DNSSEC Change DNS Lookup? we looked at a very high-level, simplified version of the 12 steps of the DNSSEC
validation process. Let’s revisit that process now and see what your validating resolver is doing in more detail. Again, as
an example we are looking up the A record for the domain name www.isc.org (see The 12-Step DNSSEC Validation
Process (Simplified)):1. The validating resolver queries the isc.org name servers for the A record of www.isc.org. This query has
the DNSSEC OK (do) bit set to 1, notifying the remote authoritative server that DNSSEC answers are desired.
2. Since the zone isc.org is signed, and its name servers are DNSSEC-aware, it responds with the answer to the
A record query plus the RRSIG for the A record.
3. The validating resolver queries for the DNSKEY for isc.org.
4. The isc.org name server responds with the DNSKEY and RRSIG records. The DNSKEY is used to verify theanswers received in #2.
5. The validating resolver queries the parent (.org) for the DS record for isc.org.
6. The .org name server is also DNSSEC-aware, so it responds with the DS and RRSIG records. The DS record isused to verify the answers received in #4.
7. The validating resolver queries for the DNSKEY for .org.
3 The root zone was signed in July 2010 and, as at the time of this writing (mid-2020), the key has been changed once, in October 2018.

The

intention going forward is to roll the key once every five years.

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8. The .org name server responds with its DNSKEY and RRSIG. The DNSKEY is used to verify the answers
received in #6.
9. The validating resolver queries the parent (root) for the DS record for .org.
10. The root name server, being DNSSEC-aware, responds with DS and RRSIG records. The DS record is used toverify the answers received in #8.
11. The validating resolver queries for the DNSKEY for root.
12. The root name server responds with its DNSKEY and RRSIG. The DNSKEY is used to verify the answers received
in #10.
After step #12, the validating resolver takes the DNSKEY received and compares it to the key or keys it has configured,
to decide whether the received key can be trusted. We talk about these locally configured keys, or trust anchors, in Trust
Anchors.
With DNSSEC, every response includes not just the answer, but a digital signature (RRSIG) as well, so the validating
resolver can verify the answer received. That is what we look at in the next section, How Are Answers Verified?.
How Are Answers Verified?

Note: Keep in mind, as you read this section, that although words like “encryption” and “decryption” are used here fromtime to time, DNSSEC does not provide privacy. Public key cryptography is used to verify data authenticity (who sentit) and data integrity (it did not change during transit), but any eavesdropper can still see DNS requests and responses inclear text, even when DNSSEC is enabled.
So how exactly are DNSSEC answers verified? Let’s first see how verifiable information is generated. On the authoritative
server, each DNS record (or message) is run through a hash function, and this hashed value is then encrypted by a private
key. This encrypted hash value is the digital signature.

Fig. 1: Signature Generation
When the validating resolver queries for the resource record, it receives both the plain-text message and the digital signature(s). The validating resolver knows the hash function used (it is listed in the digital signature record itself), so it cantake the plain-text message and run it through the same hash function to produce a hashed value, which we’ll call hashvalue X. The validating resolver can also obtain the public key (published as DNSKEY records), decrypt the digital signature, and get back the original hashed value produced by the authoritative server, which we’ll call hash value Y. If hashvalues X and Y are identical, and the time is correct (more on what this means below), the answer is verified, meaning
this answer came from the authoritative server (authenticity), and the content remained intact during transit (integrity).
Take the A record ftp.isc.org, for example. The plain text is:
ftp.isc.org.

4 IN A

149.20.1.49

The digital signature portion is:
ftp.isc.org.

300 IN RRSIG A 13 3 300 (20200401191851 20200302184340 27566 isc.org.
(continues on next page)

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Fig. 2: Signature Verification(continued from previous page)e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== )When a validating resolver queries for the A record ftp.isc.org, it receives both the A record and the RRSIG
record. It runs the A record through a hash function (in this example, SHA256 as indicated by the number 13, signifying
ECDSAP256SHA256) and produces hash value X. The resolver also fetches the appropriate DNSKEY record to decrypt
the signature, and the result of the decryption is hash value Y.
But wait, there’s more! Just because X equals Y doesn’t mean everything is good. We still have to look at the time.
Remember we mentioned a little earlier that we need to check if the time is correct? Look at the two timestamps in our
example above:• Signature Expiration: 20200401191851• Signature Inception: 20200302184340
This tells us that this signature was generated UTC March 2nd, 2020, at 6:43:40 PM (20200302184340), and it is good
until UTC April 1st, 2020, 7:18:51 PM (20200401191851). The validating resolver’s current system time needs to fall
between these two timestamps. If it does not, the validation fails, because it could be an attacker replaying an old captured
answer set from the past, or feeding us a crafted one with incorrect future timestamps.
If the answer passes both the hash value check and the timestamp check, it is validated and the authenticated data (ad)bit is set, and the response is sent to the client; if it does not verify, a SERVFAIL is returned to the client.

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12.4.5 Trust Anchors
A trust anchor is a key that is placed into a validating resolver, so that the validator can verify the results of a given request
with a known or trusted public key (the trust anchor). A validating resolver must have at least one trust anchor installed
to perform DNSSEC validation.

12.4.6 How Trust Anchors are Used
In the section How Does DNSSEC Change DNS Lookup (Revisited)?, we walked through the 12 steps of the DNSSEC
lookup process. At the end of the 12 steps, a critical comparison happens: the key received from the remote server andthe key we have on file are compared to see if we trust it. The key we have on file is called a trust anchor, sometimes also
known as a trust key, trust point, or secure entry point.
The 12-step lookup process describes the DNSSEC lookup in the ideal world, where every single domain name is signed
and properly delegated, and where each validating resolver only needs to have one trust anchor - that is, the root’s public
key. But there is no restriction that the validating resolver must only have one trust anchor. In fact, in the early stages of
DNSSEC adoption, it was not unusual for a validating resolver to have more than one trust anchor.
For instance, before the root zone was signed (in July 2010), some validating resolvers that wished to validate domainnames in the .gov zone needed to obtain and install the key for .gov. A sample lookup process for www.fbi.gov
at that time would have been eight steps rather than 12:

1. The validating resolver queried fbi.gov name server for the A record of www.fbi.gov.
2. The FBI’s name server responded with the answer and its RRSIG.
3. The validating resolver queried the FBI’s name server for its DNSKEY.
4. The FBI’s name server responded with the DNSKEY and its RRSIG.
5. The validating resolver queried a .gov name server for the DS record of fbi.gov.

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6. The .gov name server responded with the DS record and the associated RRSIG for fbi.gov.
7. The validating resolver queried the .gov name server for its DNSKEY.
8. The .gov name server responded with its DNSKEY and the associated RRSIG.
This all looks very similar, except it’s shorter than the 12 steps that we saw earlier. Once the validating resolver receives
the DNSKEY file in #8, it recognizes that this is the manually configured trusted key (trust anchor), and never goes to theroot name servers to ask for the DS record for .gov, or ask the root name servers for their DNSKEY.
In fact, whenever the validating resolver receives a DNSKEY, it checks to see if this is a configured trusted key to decide
whether it needs to continue chasing down the validation chain.
Trusted Keys and Managed Keys
Since the resolver is validating, we must have at least one key (trust anchor) configured. How did it get here, and how do
we maintain it?
If you followed the recommendation in Easy-Start Guide for Recursive Servers, by setting dnssec-validation toauto, there is nothing left to do. BIND already includes a copy of the root key, and automatically updates it when the root
key changes.4 It looks something like this:trust-anchors {# This key (20326) was published in the root zone in 2017.
. initial-key 257 3 8 "AwEAAaz/,→tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kv
ArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF
0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfd
RUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwN
R1AkUTV74bU=";};

You can, of course, decide to manage this key manually yourself.
dnssec-validation is set to yes rather than auto:

First, you need to make sure that

options {dnssec-validation yes;};

Then, download the root key manually from a trustworthy source, and put it into a trust-anchors statement as shown
below:
trust-anchors {# This key (20326) was published in the root zone in 2017.
. static-key 257 3 8 "AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kv
ArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF
0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfd
RUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwN
R1AkUTV74bU=";};
4 Well, almost every record: NS records and glue records for delegations do not have RRSIG records. If there are no delegations, then every recordin your zone is signed and comes with its own RRSIG.

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While this trust-anchors statement looks similar to the built-in version above, the built-in key has theinitial-key modifier, whereas in the statement in the configuration file, that is replaced by static-key. Thereis an important difference between the two: a key defined with static-key is always trusted until it is deleted fromthe configuration file. With the initial-key modifier, keys are only trusted once: for as long as it takes to load
the managed key database and start the key maintenance process. Thereafter, BIND uses the managed keys database(managed-keys.bind.jnl) as the source of key information.
Warning: Remember, if you choose to manage the keys on your own, whenever the key changes (which, for mostzones, happens on a periodic basis), the configuration needs to be updated manually. Failure to do so will result inbreaking nearly all DNS queries for the subdomain of the key. So if you are manually managing .gov, all domainnames in the .gov space may become unresolvable; if you are manually managing the root key, you could break all
DNS requests made to your recursive name server.
Explicit management of keys was common in the early days of DNSSEC, when neither the root zone nor many top-leveldomains were signed. Since then, over 90% of the top-level domains have been signed, including all the largest ones.
Unless you have a particular need to manage keys yourself, it is best to use the BIND defaults and let the software manage
the root key.

12.4.7 What’s EDNS All About (And Why Should I Care)?
EDNS Overview
Traditional DNS responses are typically small in size (less than 512 bytes) and fit nicely into a small UDP packet. The
Extension mechanism for DNS (EDNS, or EDNS(0)) offers a mechanism to send DNS data in larger packets over UDP.
To support EDNS, both the DNS server and the network need to be properly prepared to support the larger packet sizes
and multiple fragments.
This is important for DNSSEC, since the dig +do bit that signals DNSSEC-awareness is carried within EDNS, and
DNSSEC responses are larger than traditional DNS ones. If DNS servers and the network environment cannot support
large UDP packets, it will cause retransmission over TCP, or the larger UDP responses will be discarded. Users will likely
experience slow DNS resolution or be unable to resolve certain names at all.
Note that EDNS applies regardless of whether you are validating DNSSEC, because BIND has DNSSEC enabled bydefault.
Please see Network Requirements for more information on what DNSSEC expects from the network environment.
EDNS on DNS Servers
For many years, BIND has had EDNS enabled by default, and the UDP packet size is set to a maximum of 4096 bytes.
The DNS administrator should not need to perform any reconfiguration. You can use dig to verify that your server
supports EDNS and see the UDP packet size it allows with this dig command:$ dig @10.53.0.1 www.isc.org. A +dnssec +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page);; OPT PSEUDOSECTION:; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good);; QUESTION SECTION:;ftp.isc.org.
IN A;; ANSWER SECTION:
ftp.isc.org.
300 IN A 149.20.1.49
ftp.isc.org.
300 IN RRSIG A 13 3 300 (20200401191851 20200302184340 27566 isc.org.
e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4
L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== );; Query time: 452 msec;; SERVER: 10.53.0.1#53(10.53.0.1);; WHEN: Tue Mar 10 14:30:57 GMT 2020;; MSG SIZE rcvd: 187

There is a helpful testing tool available (provided by DNS-OARC) that you can use to verify resolver behavior regarding
EDNS support: https://www.dns-oarc.net/oarc/services/replysizetest/ .
Once you’ve verified that your name servers have EDNS enabled, that should be the end of the story, right? Unfortunately,
EDNS is a hop-by-hop extension to DNS. This means the use of EDNS is negotiated between each pair of hosts in a DNS
resolution process, which in turn means if one of your upstream name servers (for instance, your ISP’s recursive nameserver that your name server forwards to) does not support EDNS, you may experience DNS lookup failures or be unable
to perform DNSSEC validation.
Support for Large Packets on Network Equipment
If both your recursive name server and your ISP’s name servers support EDNS, we are all good here, right? Not so fast.
Since these large packets have to traverse the network, the network infrastructure itself must allow them to pass.
When data is physically transmitted over a network, it has to be broken down into chunks. The size of the data chunk is
known as the Maximum Transmission Unit (MTU), and it can differ from network to network. IP fragmentation occurs
when a large data packet needs to be broken down into chunks smaller than the MTU; these smaller chunks then need tobe reassembled back into the large data packet at their destination. IP fragmentation is not necessarily a bad thing, and it
most likely occurs on your network today.
Some network equipment, such as a firewall, may make assumptions about DNS traffic. One of these assumptions may
be how large each DNS packet is. When a firewall sees a larger DNS packet than it expects, it may either reject the large
packet or drop its fragments because the firewall thinks it’s an attack. This configuration probably didn’t cause problems
in the past, since traditional DNS packets are usually pretty small in size. However, with DNSSEC, these configurations
need to be updated, since DNSSEC traffic regularly exceeds 1500 bytes (a common MTU value). If the configuration is
not updated to support a larger DNS packet size, it often results in the larger packets being rejected, and to the end user itlooks like the queries go unanswered. Or in the case of fragmentation, only a part of the answer makes it to the validating
resolver, and your validating resolver may need to re-ask the question again and again, creating the appearance for end
users that the DNS/network is slow.
While you are updating the configuration on your network equipment, make sure TCP port 53 is also allowed for DNS
traffic.

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Wait… DNS Uses TCP?
Yes. DNS uses TCP port 53 as a fallback mechanism, when it cannot use UDP to transmit data. This has always been
the case, even long before the arrival of DNSSEC. Traditional DNS relies on TCP port 53 for operations such as zonetransfer. The use of DNSSEC, or DNS with IPv6 records such as AAAA, increases the chance that DNS data will betransmitted via TCP.
Due to the increased packet size, DNSSEC may fall back to TCP more often than traditional (insecure) DNS. If yournetwork blocks or filters TCP port 53 today, you may already experience instability with DNS resolution, before even
deploying DNSSEC.

12.5 Signing
12.5.1 Easy-Start Guide for Signing Authoritative Zones
This section provides the basic information needed to set up a DNSSEC-enabled authoritative name server. A DNSSECenabled (or “signed”) zone contains additional resource records that are used to verify the authenticity of its zone information.
To convert a traditional (insecure) DNS zone to a secure one, we need to create some additional records (DNSKEY,RRSIG, and NSEC or NSEC3), and upload verifiable information (such as a DS record) to the parent zone to complete
the chain of trust. For more information about DNSSEC resource records, please see What Does DNSSEC Add to DNS?.
Note: In this chapter, we assume all configuration files, key files, and zone files are stored in /etc/bind, and mostexamples show commands run as the root user. This may not be ideal, but the point is not to distract from what is important
here: learning how to sign a zone. There are many best practices for deploying a more secure BIND installation, withtechniques such as jailed process and restricted user privileges, but those are not covered in this document. We trust you,a responsible DNS administrator, to take the necessary precautions to secure your system.
For the examples below, we work with the assumption that there is an existing insecure zone example.com that we areconverting to a secure zone.
Enabling Automated DNSSEC Zone Maintenance and Key Generation
To sign a zone, add the following statement to its zone clause in the BIND 9 configuration file:
options {directory "/etc/bind";recursion no;...
};zone "example.com" in {...
dnssec-policy default;...
};

The dnssec-policy statement causes the zone to be signed and turns on automatic maintenance for the zone. This
includes re-signing the zone as signatures expire and replacing keys on a periodic basis. The value default selects thedefault policy, which contains values suitable for most situations. We cover the creation of a custom policy in Creating a
Custom DNSSEC Policy, but for the moment we are accepting the default values.

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Using dnssec-policy requires dynamic DNS or inline-signing to be enabled.
When the configuration file is updated, tell named to reload the configuration file by running rndc reconfig:# rndc reconfig

And that’s it - BIND signs your zone.
At this point, before you go away and merrily add dnssec-policy statements to all your zones, we should mention
that, like a number of other BIND configuration options, its scope depends on where it is placed. In the example above,
we placed it in a zone clause, so it applied only to the zone in question. If we had placed it in a view clause, it would
have applied to all zones in the view; and if we had placed it in the options clause, it would have applied to all zones
served by this instance of BIND.
Verification
The BIND 9 reconfiguration starts the process of signing the zone. First, it generates a key for the zone and includes it in
the published zone. The log file shows messages such as these:
07-Apr-2020 16:02:55.045 zone example.com/IN (signed): reconfiguring zone keys
07-Apr-2020 16:02:55.045 reloading configuration succeeded
07-Apr-2020 16:02:55.046 keymgr: DNSKEY example.com/ECDSAP256SHA256/10376 (CSK)␣
,→created for policy default
07-Apr-2020 16:02:55.046 Fetching example.com/ECDSAP256SHA256/10376 (CSK) from key␣,→repository.
07-Apr-2020 16:02:55.046 DNSKEY example.com/ECDSAP256SHA256/10376 (CSK) is now␣,→published07-Apr-2020 16:02:55.046 DNSKEY example.com/ECDSAP256SHA256/10376 (CSK) is now active
07-Apr-2020 16:02:55.048 zone example.com/IN (signed): next key event: 07-Apr-2020␣
,→18:07:55.045

It then starts signing the zone. How long this process takes depends on the size of the zone, the speed of the server, andhow much activity is taking place. We can check what is happening by using rndc, entering the command:# rndc signing -list example.com

While the signing is in progress, the output is something like:
Signing with key 10376/ECDSAP256SHA256

and when it is finished:
Done signing with key 10376/ECDSAP256SHA256

When the second message appears, the zone is signed.
Before moving on to the next step of coordinating with the parent zone, let’s make sure everything looks good usingdelv. We want to simulate what a validating resolver will check, by telling delv to use a specific trust anchor.
First, we need to make a copy of the key created by BIND. This is in the directory you set with the directory statement
in your configuration file’s options clause, and is named something like Kexample.com.+013.10376.key:# cp /etc/bind/Kexample.com.+013+10376.key /tmp/example.key

The original key file looks like this (with the actual key shortened for ease of display, and comments omitted):

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Chapter 12. DNSSEC GuideBIND 9 Administrator Reference Manual, Release 9.20.0# cat /etc/bind/Kexample.com.+013+10376.key...
example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw==

We want to edit the copy to be in the trust-anchors format, so that it looks like this:# cat /tmp/example.key
trust-anchors {example.com. static-key 257 3 13 "6saiq99qDB...dqp+o0dw==";};

Now we can run the delv command and instruct it to use this trusted-key file to validate the answer it receives from theauthoritative name server 192.168.1.13:$ delv @192.168.1.13 -a /tmp/example.key +root=example.com example.com. SOA +multiline; fully validated
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020040703 ; serial1800; refresh (30 minutes)
900; retry (15 minutes)
2419200; expire (4 weeks)300; minimum (5 minutes))
example.com.
600 IN RRSIG SOA 13 2 600 (
20200421150255 20200407140255 10376 example.com.
jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF
oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== )Uploading Information to the Parent Zone
Once everything is complete on our name server, we need to generate some information to be uploaded to the parent
zone to complete the chain of trust. The format and the upload methods are actually dictated by your parent zone’s
administrator, so contact your registrar or parent zone administrator to find out what the actual format should be and how
to deliver or upload the information to the parent zone.
What about your zone between the time you signed it and the time your parent zone accepts the upload? To the rest of theworld, your zone still appears to be insecure, because if a validating resolver attempts to validate your domain name via
your parent zone, your parent zone will indicate that you are not yet signed (as far as it knows). The validating resolver
will then give up attempting to validate your domain name, and will fall back to the insecure DNS. Until you complete
this final step with your parent zone, your zone remains insecure.
Note: Before uploading to your parent zone, verify that your newly signed zone has propagated to all of your nameservers (usually via zone transfers). If some of your name servers still have unsigned zone data while the parent tells theworld it should be signed, validating resolvers around the world cannot resolve your domain name.
Here are some examples of what you may upload to your parent zone, with the DNSKEY/DS data shortened for display.
Note that no matter what format may be required, the end result is the parent zone publishing DS record(s) based on theinformation you upload. Again, contact your parent zone administrator(s) to find out the correct format for their system.
1. DS record format:
example.com. 3600 IN DS 10376 13 2 B92E22CAE0...33B8312EF0

2. DNSKEY format:
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example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw==

The DS record format may be generated from the DNSKEY using the dnssec-dsfromkey tool, which is covered in
DS Record Format. For more details and examples on how to work with your parent zone, please see Working With the
Parent Zone.
So… What Now?
Congratulations! Your zone is signed, your secondary servers have received the new zone data, and the parent zone has
accepted your upload and published your DS record. Your zone is now officially DNSSEC-enabled. What happens next?
That is basically it - BIND takes care of everything else. As for updating your zone file, you can continue to update it
the same way as prior to signing your zone; the normal work flow of editing a zone file and using the rndc command toreload the zone still works as usual, and although you are editing the unsigned version of the zone, BIND generates thesigned version automatically.
Curious as to what all these commands did to your zone file? Read on to Your Zone, Before and After DNSSEC and findout. If you are interested in how to roll this out to your existing primary and secondary name servers, check out DNSSEC
Signing in the Recipes chapter.

12.5.2 Your Zone, Before and After DNSSECWhen we assigned the default DNSSEC policy to the zone, we provided the minimal amount of information to convert a
traditional DNS zone into a DNSSEC-enabled zone. This is what the zone looked like before we started:$ dig @192.168.1.13 example.com. AXFR +multiline +onesoa; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com AXFR +multiline +onesoa; (1 server found);; global options: +cmd
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020040700 ; serial1800; refresh (30 minutes)
900; retry (15 minutes)
2419200; expire (4 weeks)300; minimum (5 minutes))
example.com.
600 IN NS ns1.example.com.
ftp.example.com.
600 IN A 192.168.1.200
ns1.example.com.
600 IN A 192.168.1.1
web.example.com.
600 IN CNAME www.example.com.
www.example.com.
600 IN A 192.168.1.100

Below shows the test zone example.com after reloading the server configuration. Clearly, the zone grew in size, andthe number of records multiplied:# dig @192.168.1.13 example.com. AXFR +multiline +onesoa; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com AXFR +multiline +onesoa; (1 server found);; global options: +cmd
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020040703 ; serial1800; refresh (30 minutes)
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example.com.
300 IN RRSIG NSEC 13 2 300 (20200413050536 20200407140255 10376 example.com.
drtV1rJbo5OMi65OJtu7Jmg/thgpdTWrzr6O3Pzt12+B
oCxMAv3orWWYjfP2n9w5wj0rx2Mt2ev7MOOG8IOUCA== )example.com.
300 IN NSEC ftp.example.com. NS SOA RRSIG NSEC DNSKEY TYPE65534
example.com.
600 IN RRSIG NS 13 2 600 (
20200413130638 20200407140255 10376 example.com.
2ipmzm1Ei6vfE9OLowPMsxLBCbjrCpWPgWJ0ekwZBbux
MLffZOXn8clt0Ql2U9iCPdyoQryuJCiojHSE2d6nrw== )example.com.
600 IN RRSIG SOA 13 2 600 (
20200421150255 20200407140255 10376 example.com.
jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF
oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== )example.com.
0 IN RRSIG TYPE65534 13 2 0 (20200413050536 20200407140255 10376 example.com.
Xjkom24N6qeCJjg9BMUfuWf+euLeZB169DHvLYZPZNlm
GgM2czUDPio6VpQbUw6JE5DSNjuGjgpgXC5SipC42g== )example.com.
3600 IN RRSIG DNSKEY 13 2 3600 (
20200421150255 20200407140255 10376 example.com.
maK75+28oUyDtci3V7wjTsuhgkLUZW+Q++q46Lea6bKn
Xj77kXcLNogNdUOr5am/6O6cnPeJKJWsnmTLISm62g== )0 IN TYPE65534 \# 5 ( 0D28880001 )example.com.
example.com.
3600 IN DNSKEY 257 3 13 (6saiq99qDBb5b4G4cx13cPjFTrIvUs3NW44SvbbHorHb
kXwOzeGAWyPORN+pwEV/LP9+FHAF/JzAJYdqp+o0dw==) ; KSK; alg = ECDSAP256SHA256 ; key id = 10376
example.com.
600 IN NS ns1.example.com.
ftp.example.com.
600 IN RRSIG A 13 3 600 (
20200413130638 20200407140255 10376 example.com.
UYo1njeUA49VhKnPSS3JO4G+/Xd2PD4m3Vaacnd191yz
BIoouEBAGPcrEM2BNrgR0op1EWSus9tG86SM1ZHGuQ== )ftp.example.com.
300 IN RRSIG NSEC 13 3 300 (20200413130638 20200407140255 10376 example.com.
rPADrAMAPIPSF3S45OSY8kXBTYMS3nrZg4Awj7qRL+/bsOKy6044MbIbjg+YWL69dBjKoTSeEGSCSt73uIxrYA== )300 IN NSEC ns1.example.com. A RRSIG NSEC
ftp.example.com.
ftp.example.com.
600 IN A 192.168.1.200
ns1.example.com.
600 IN RRSIG A 13 3 600 (
20200413130638 20200407140255 10376 example.com.
Yeojg7qrJmxL6uLTnALwKU5byNldZ9Ggj5XjcbpPvujQ
ocG/ovGBg6pdugXC9UxE39bCDl8dua1frjDcRCCZAA== )ns1.example.com.
300 IN RRSIG NSEC 13 3 300 (20200413130638 20200407140255 10376 example.com.
vukgQme6k7JwCf/mJOOzHXbE3fKtSro+Kc10T6dHMdscoM1/oXioZvgBZ9cKrQhIAUt7r1KUnrUwM6Je36wWFA== )ns1.example.com.
300 IN NSEC web.example.com. A RRSIG NSEC
ns1.example.com.
600 IN A 192.168.1.1
web.example.com.
600 IN RRSIG CNAME 13 3 600 (
20200413130638 20200407140255 10376 example.com.
JXi4WYypofD5geUowVqlqJyHzvcRnsvU/ONhTBaUCw5Y
XtifKAXRHWrUL1HIwt37JYPLf5uYu90RfkWLj0GqTQ== )web.example.com.
300 IN RRSIG NSEC 13 3 300 (20200413130638 20200407140255 10376 example.com.
XF4Hsd58dalL+s6Qu99bG80PQyMf7ZrHEzDiEflRuykP(continues on next page)

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DfBRuf34z27vj70LO1lp2ZiX4BB1ahcEK2ae9ASAmA== )web.example.com.
300 IN NSEC www.example.com. CNAME RRSIG NSEC
web.example.com.
600 IN CNAME www.example.com.
www.example.com.
600 IN RRSIG A 13 3 600 (
20200413050536 20200407140255 10376 example.com.
mACKXrDOF5JMWqncSiQ3pYWA6abyGDJ4wgGCumjLXhPy
0cMzJmKv2s7G6+tW3TsA6BK3UoMfv30oblY2Mnl4/A== )www.example.com.
300 IN RRSIG NSEC 13 3 300 (20200413050536 20200407140255 10376 example.com.
1YQ22odVt0TeP5gbNJwkvS684ipDmx6sEOsF0eCizhCvx8osuOATdlPjIEztt+rveaErZ2nsoLor5k1nQAHsbQ== )www.example.com.
300 IN NSEC example.com. A RRSIG NSEC
www.example.com.
600 IN A 192.168.1.100

But this is a really messy way to tell if the zone is set up properly with DNSSEC. Fortunately, there are tools to help us
with that. Read on to How To Test Authoritative Zones to learn more.

12.5.3 How To Test Authoritative Zones
So we’ve activated DNSSEC and uploaded some data to our parent zone. How do we know our zone is signed correctly?
Here are a few ways to check.
Look for Key Data in Your Zone
One way to see if your zone is signed is to check for the presence of DNSKEY record types. In our example, we createda single key, and we expect to see it returned when we query for it.
$ dig @192.168.1.13 example.com. DNSKEY +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com DNSKEY +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18637;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; WARNING: recursion requested but not available;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: efe186423313fb66010000005e8c997e99864f7d69ed7c11 (good);; QUESTION SECTION:;example.com.
IN DNSKEY;; ANSWER SECTION:
example.com.
3600 IN DNSKEY 257 3 13 (6saiq99qDBb5b4G4cx13cPjFTrIvUs3NW44SvbbHorHb
kXwOzeGAWyPORN+pwEV/LP9+FHAF/JzAJYdqp+o0dw==) ; KSK; alg = ECDSAP256SHA256 ; key id = 10376

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Look for Signatures in Your Zone
Another way to see if your zone data is signed is to check for the presence of a signature. With DNSSEC, every record5
now comes with at least one corresponding signature, known as an RRSIG.
$ dig @192.168.1.13 example.com. SOA +dnssec +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com SOA +dnssec +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45219;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; WARNING: recursion requested but not available;; OPT PSEUDOSECTION:; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: 75adff4f4ce916b2010000005e8c99c0de47eabb7951b2f5 (good);; QUESTION SECTION:;example.com.
IN SOA;; ANSWER SECTION:
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020040703 ; serial1800; refresh (30 minutes)
900; retry (15 minutes)
2419200; expire (4 weeks)300; minimum (5 minutes))
example.com.
600 IN RRSIG SOA 13 2 600 (
20200421150255 20200407140255 10376 example.com.
jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF
oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== )The serial number was automatically incremented from the old, unsigned version. named keeps track of the serial numberof the signed version of the zone independently of the unsigned version. If the unsigned zone is updated with a new serial
number that is higher than the one in the signed copy, then the signed copy is increased to match it; otherwise, the two
are kept separate.
Examine the Zone File
Our original zone file example.com.db remains untouched, and named has generated three additional files automatically for us (shown below). The signed DNS data is stored in example.com.db.signed and in the associatedjournal file.
# cd /etc/bind# lsexample.com.db

example.com.db.jbk

example.com.db.signed

example.com.db.signed.jnl

A quick description of each of the files:• .jbk: a transient file used by named• .signed: the signed version of the zone in raw format
5 For security reasons, a parent zone that supports CDS/CDNSKEY may require the DS record to be manually uploaded when we first sign the zone.
Until our zone is signed, the parent cannot be sure that a CDS or CDNSKEY record it finds by querying our zone really comes from our zone; thus, itneeds to use some other form of secure transfer to obtain the information.

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BIND 9 Administrator Reference Manual, Release 9.20.0• .signed.jnl: a journal file for the signed version of the zone
These files are stored in raw (binary) format for faster loading. To reveal the human-readable version, use
named-compilezone as shown below. In the example below, we run the command on the raw format zone
example.com.db.signed to produce a text version of the zone example.com.text:# named-compilezone -f raw -F text -o example.com.text example.com example.com.db.
,→signedzone example.com/IN: loaded serial 2014112008 (DNSSEC signed)
dump zone to example.com.text...done
OK

Check the Parent
Although this is not strictly related to whether the zone is signed, a critical part of DNSSEC is the trust relationshipbetween the parent and the child. Just because we, the child, have all the correctly signed records in our zone does notmean it can be fully validated by a validating resolver, unless our parent’s data agrees with ours. To check if our uploadto the parent was successful, ask the parent name server for the DS record of our child zone; we should get back the DS
record(s) containing the information we uploaded in Uploading Information to the Parent Zone:$ dig example.com. DS; <<>> DiG 9.16.0 <<>> example.com DS; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16954;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: db280d5b52576780010000005e8c9bf5b0d8de103d934e5d (good);; QUESTION SECTION:;example.com.
IN DS;; ANSWER SECTION:
example.com. 61179 IN DS 10376 13 2␣
,→B92E22CAE0B41430EC38D3F7EDF1183C3A94F4D4748569250C15EE33B8312EF0

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External Testing Tools
We recommend two tools, below: Verisign DNSSEC Debugger and DNSViz. Others can be found via a simple online
search. These excellent online tools are an easy way to verify that your domain name is fully secured.
Verisign DNSSEC Debugger
URL: https://dnssec-debugger.verisignlabs.com/
This tool shows a nice summary of checks performed on your domain name. You can expand it to view more details foreach of the items checked, to get a detailed report.
DNSViz
URL: https://dnsviz.net/
DNSViz provides a visual analysis of the DNSSEC authentication chain for a domain name and its resolution path in the
DNS namespace.

12.5.4 Signing Easy Start Explained
Enable Automatic DNSSEC Maintenance Explained
Signing a zone requires a number of separate steps:• Generation of the keys to sign the zone.
• Inclusion of the keys into the zone.
• Signing of the records in the file (including the generation of the NSEC or NSEC3 records).
Maintaining a signed zone comprises a set of ongoing tasks:• Re-signing the zone as signatures approach expiration.
• Generation of new keys as the time approaches for a key roll.
• Inclusion of new keys into the zone when the rollover starts.
• Transition from signing the zone with the old set of keys to signing the zone with the new set of keys.
• Waiting the appropriate interval before removing the old keys from the zone.
• Deleting the old keys.
That is quite complex, and it is all handled in BIND 9 with the single dnssec-policy default statement. We
will see later on (in the Creating a Custom DNSSEC Policy section) how these actions can be tuned, by setting up our own
DNSSEC policy with customized parameters. However, in many cases the defaults are adequate.
dnssec-policy is the preferred way to run DNSSEC in a zone, but sometimes a more “hands-on” approach to signingand key maintenance is needed. For this reason, we cover manual signing techniques in Manual Signing.

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Fig. 3: Verisign DNSSEC Debugger

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Fig. 4: DNSViz

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12.5.5 Working With the Parent Zone
As mentioned in Uploading Information to the Parent Zone, the format of the information uploaded to your parent zone
is dictated by your parent zone administrator. The two main formats are:
1. DS record format
2. DNSKEY format
Check with your parent zone to see which format they require.
But how can you get each of the formats from your existing data?
When named turned on automatic DNSSEC maintenance, essentially the first thing it did was to create the DNSSEC keys
and put them in the directory you specified in the configuration file. If you look in that directory, you will see three files withnames like Kexample.com.+013+10376.key, Kexample.com.+013+10376.private, and Kexample.
com.+013+10376.state. The one we are interested in is the one with the .key suffix, which contains the zone’s
public key. (The other files contain the zone’s private key and the DNSSEC state associated with the key.) This public
key is used to generate the information we need to pass to the parent.
DS Record Format
Below is an example of a DS record format generated from the KSK we created earlier (Kexample.com.
+013+10376.key):# cd /etc/binddnssec-dsfromkey Kexample.com.+013+10376.key
example.com. IN DS 10376 13 2␣
,→B92E22CAE0B41430EC38D3F7EDF1183C3A94F4D4748569250C15EE33B8312EF0

Some registrars ask their customers to manually specify the types of algorithm and digest used. In this example, 13
represents the algorithm used, and 2 represents the digest type (SHA-256). The key tag or key ID is 10376.
DNSKEY Format
Below is an example of the same key ID (10376) using DNSKEY format (with the actual key shortened for ease ofdisplay):
example.com. 3600 IN DNSKEY 257 3 13 (6saiq99qDB...dqp+o0dw==) ; key id = 10376

The key itself is easy to find (it’s difficult to miss that long base64 string) in the file.
# cd /etc/bind# cat Kexample.com.+013+10376.key; This is a key-signing key, keyid 10376, for example.com.
; Created: 20200407150255 (Tue Apr 7 16:02:55 2020); Publish: 20200407150255 (Tue Apr 7 16:02:55 2020); Activate: 20200407150255 (Tue Apr 7 16:02:55 2020)
example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw==

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12.5.6 Creating a Custom DNSSEC Policy
The remainder of this section describes the contents of a custom DNSSEC policy. Advanced Discussions describes theconcepts involved here and the pros and cons of choosing particular values. If you are not already familiar with DNSSEC,
it may be worth reading that chapter first.
Setting up your own DNSSEC policy means that you must include a dnssec-policy clause in the zone file. This setsvalues for the various parameters that affect the signing of zones and the rolling of keys. The following is an example ofsuch a clause:dnssec-policy standard {dnskey-ttl 600;
keys {
ksk lifetime 365d algorithm ecdsap256sha256;
zsk lifetime 60d algorithm ecdsap256sha256;};
max-zone-ttl 600;
parent-ds-ttl 600;
parent-propagation-delay 2h;
publish-safety 7d;
retire-safety 7d;
signatures-refresh 5d;
signatures-validity 15d;
signatures-validity-dnskey 15d;zone-propagation-delay 2h;};

The policy has multiple parts:• The name must be specified. As each zone can use a different policy, named needs to be able to distinguishbetween policies. This is done by giving each policy a name, such as standard in the above example.
• The keys clause lists all keys that should be in the zone, along with their associated parameters. In this example, we are using the conventional KSK/ZSK split, with the KSK changed every year and the ZSK changed
every two months (the default DNSSEC policy sets a CSK that is never changed). Keys are created using
the ECDSAPS256SHA256 algorithm; each KSK/ZSK pair must have the same algorithm. A CSK combines thefunctionality of a ZSK and a KSK.
• The parameters ending in -ttl are, as expected, the TTLs of the associated records. Remember that during a key
rollover, we have to wait for records to expire from caches? The values here tell BIND 9 the maximum amount oftime it has to wait for this to happen. Values can be set for the DNSKEY records in your zone, the non-DNSKEY
records in your zone, and the DS records in the parent zone.
• Another set of time-related parameters are those ending in -propagation-delay. These tell BIND how longit takes for a change in zone contents to become available on all secondary servers. (This may be non-negligible:
for example, if a large zone is transferred over a slow link.)• The policy also sets values for the various signature parameters: how long the signatures on the DNSKEY andnon-DNSKEY records are valid, and how often BIND should re-sign the zone.
• The parameters ending in -safety are there to give you a bit of leeway in case a key roll doesn’t go to plan.
When introduced into the zone, the publish-safety time is the amount of additional time, over and abovethat calculated from the other parameters, during which the new key is in the zone but before BIND starts to sign
records with it. Similarly, the retire-safety is the amount of additional time, over and above that calculated
from the other parameters, during which the old key is retained in the zone before being removed.
• Finally, the purge-keys option allows you to clean up key files automatically after a period of time. If a key has
been removed from the zone, this option will determine how long its key files will be retained on disk.

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BIND 9 Administrator Reference Manual, Release 9.20.0(You do not have to specify all the items listed above in your policy definition. Any that are not set simply take the default
value.)
Usually, the exact timing of a key roll, or how long a signature remains valid, is not critical. For this reason, err on theside of caution when setting values for the parameters. It is better to have an operation like a key roll take a few days
longer than absolutely required, than it is to have a quick key roll but have users get validation failures during the process.
Having defined a new policy called “standard”, we now need to tell named to use it. We do this by adding a
dnssec-policy standard; statement to the configuration file. Like many other configuration statements, it canbe placed in the options statement (thus applying to all zones on the server), a view statement (applying to all zones
in the view), or a zone statement (applying only to that zone). In this example, we’ll add it to the zone statement:zone "example.net" in {...
dnssec-policy standard;...
};

Finally, tell named to use the new policy:# rndc reconfig… and that’s it. named now applies the “standard” policy to your zone.

12.5.7 Maintenance Tasks
Zone data is signed and the parent zone has published your DS records: at this point your zone is officially secure. Whenother validating resolvers look up information in your zone, they are able to follow the 12-step process as described in
How Does DNSSEC Change DNS Lookup (Revisited)? and verify the authenticity and integrity of the answers.
There is not that much left for you, as the DNS administrator, to do on an ongoing basis. Whenever you update yourzone, BIND automatically re-signs your zone with new RRSIG and NSEC/NSEC3 records, and even increments the serial
number for you. If you choose to split your keys into a KSK and ZSK, the rolling of the ZSK is completely automatic.
Rolling of a KSK or CSK may require some manual intervention, though, so let’s examine two more DNSSEC-relatedresource records, CDS and CDNSKEY.
The CDS and CDNSKEY Resource Records
Passing the DS record to the organization running the parent zone has always been recognized as a bottleneck in the key
rollover process. To automate the process, the CDS and CDNSKEY resource records were introduced.
The CDS and CDNSKEY records are identical to the DS and DNSKEY records, except in the type code and the name.
When such a record appears in the child zone, it is a signal to the parent that it should update the DS it has for that zone.
In essence, when the parent notices the presence of the CDS and/or CDNSKEY record(s) in the child zone, it checks
these records to verify that they are signed by a valid key for the zone. If the record(s) successfully validate, the parent
zone’s DS RRset for the child zone is changed to correspond to the CDS (or CDNSKEY) records. (For more information
on how the signaling works and the issues surrounding it, please refer to RFC 7344 and RFC 8078.)

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Working with the Parent Zone (2)Once the zone is signed, the only required manual tasks are to monitor KSK or CSK key rolls and pass the new DS record
to the parent zone. However, if the parent can process CDS or CDNSKEY records, you may not even have to do that6 .
When the time approaches for the roll of a KSK or CSK, BIND adds a CDS and a CDNSKEY record for the key inquestion to the apex of the zone. If your parent zone supports polling for CDS/CDNSKEY records, they are uploaded
and the DS record published in the parent - at least ideally.
If BIND is configured with parental-agents, it will check for the DS presence. Let’s look at the following configuration excerpt:
parental-agents "net" {10.53.0.11; 10.53.0.12;};
zone "example.net" in {...
dnssec-policy standard;parental-agents { "net"; };checkds explicit;...
};

BIND will check for the presence of the DS record in the parent zone by querying its parental agents (defined in RFC
7344 to be the entities that the child zone has a relationship with to change its delegation information). In the example
above, The zone example.net is configured with two parental agents, at the addresses 10.53.0.11 and 10.53.0.12. These
addresses are used as an example only. Both addresses will have to respond with a DS RRset that includes the DS record
identifying the key that is being rolled. If one or both don’t have the DS included yet the rollover is paused, and the checkfor DS presence is retried after an hour. The same applies for DS withdrawal.
The example also has checkds set to explicit. This means that only the addresses defined in parental-agents arebeing queried. If set to yes, the parental agents are being looked up by querying for the parent NS records.
Alternatively, you can use the rndc tool to tell named that the DS record has been published or withdrawn. For example:# rndc dnssec -checkds published example.net

This command should also be used when checkds is set to no.
If your parent zone doesn’t support CDS/CDNSKEY, you will have to supply the DNSKEY or DS record to the parent
zone manually when a new KSK appears in your zone, presumably using the same mechanism you used to upload therecords for the first time. Again, you need to use the rndc tool to tell named that the DS record has been published.

12.5.8 Manual Signing
Manual signing of a zone was the first method of signing introduced into BIND and offers, as the name suggests, noautomation. The user must handle everything: create the keys, sign the zone file with them, load the signed zone, periodically re-sign the zone, and manage key rolls, including interaction with the parent. A user certainly can do all this, but
why not use one of the automated methods?
Although use of the automatic dnssec-policy is the preferred way to sign zones in BIND, there are occasions wherea manual approach may be needed. dnssec-policy does not currently support the use of external hardware, so if
your security policy requires it, you need to use manual signing.
6 The dates can also be modified using an editor, but that is likely to be more error-prone than using dnssec-settime.

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BIND 9 ships with several tools that are used in this process, which are explained in more detail below. In all cases,
the -h option prints a full list of parameters. Note that the DNSSEC tools require the keyset files to be in the working
directory or the directory specified by the -d option.
To convert a traditional (insecure) DNS zone to a secure one, we need to create various additional records (DNSKEY,RRSIG, NSEC/NSEC3) and, as with fully automatic signing, to upload verifiable information (such as a DS record) tothe parent zone to complete the chain of trust.
The first step is to create the keys as described in Generate Keys, then using the BIND-provided tools dnssec-keygento create the keys and dnssec-signzone to sign the zone. The signed zone is stored in another file and is the one
you tell BIND to load. To update the zone (for example, to add a resource record), you update the unsigned zone, re-sign
it, and tell named to load the updated signed copy. The same goes for refreshing signatures or rolling keys; the user is
responsible for providing the signed zone served by named. (In the case of rolling keys, you are also responsible for
ensuring that the keys are added and removed at the correct times.)
Why would you want to sign your zone this way? You probably wouldn’t in the normal course of events, but as there may
be circumstances in which it is required, the scripts have been left in the BIND distribution.
Note: Again, we assume all configuration files, key files, and zone files are stored in /etc/bind, and most examples
show commands run as the root user. This may not be ideal, but the point is not to distract from what is important
here: learning how to sign a zone. There are many best practices for deploying a more secure BIND installation, withtechniques such as jailed process and restricted user privileges, but those are not covered in this document. We trust you,a responsible DNS administrator, to take the necessary precautions to secure your system.
For our examples below, we work with the assumption that there is an existing insecure zone example.com that weare converting to a secure version. The secure version uses both a KSK and a ZSK.

Generate Keys
Everything in DNSSEC centers around keys, so we begin by generating our own keys.
# cd /etc/bind/keys# dnssec-keygen -a ECDSAP256SHA256 example.com
Generating key pair...........................+++++ ......................+++++
Kexample.com.+013+34371# dnssec-keygen -a ECDSAP256SHA256 -f KSK example.com
Generating key pair........................+++ ..................................+++
Kexample.com.+013+00472

This command generates four key files in /etc/bind/keys:• Kexample.com.+013+34371.key• Kexample.com.+013+34371.private• Kexample.com.+013+00472.key• Kexample.com.+013+00472.private
The two files ending in .key are the public keys. These contain the DNSKEY resource records that appear in the zone.
The two files ending in .private are the private keys, and contain the information that named actually uses to sign
the zone.
Of the two pairs, one is the zone-signing key (ZSK), and one is the key-signing key (KSK). We can tell which is which
by looking at the file contents (the actual keys are shortened here for ease of display):384

Chapter 12. DNSSEC GuideBIND 9 Administrator Reference Manual, Release 9.20.0# cat Kexample.com.+013+34371.key; This is a zone-signing key, keyid 34371, for example.com.
; Created: 20200616104249 (Tue Jun 16 11:42:49 2020); Publish: 20200616104249 (Tue Jun 16 11:42:49 2020); Activate: 20200616104249 (Tue Jun 16 11:42:49 2020)
example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8=# cat Kexample.com.+013+00472.key; This is a key-signing key, keyid 472, for example.com.
; Created: 20200616104254 (Tue Jun 16 11:42:54 2020); Publish: 20200616104254 (Tue Jun 16 11:42:54 2020); Activate: 20200616104254 (Tue Jun 16 11:42:54 2020)
example.com. IN DNSKEY 257 3 13 AwEAAbCR6U...l8xPjokVU=

The first line of each file tells us what type of key it is. Also, by looking at the actual DNSKEY record, we can tell themapart: 256 is ZSK, and 257 is KSK.
The name of the file also tells us something about the contents. See chapter Zone keys for more details.
Make sure that these files are readable by named and that the .private files are not readable by anyone else.
Alternativelly, the dnssec-keyfromlabel program is used to get a key pair from a crypto hardware device and build
the key files. Its usage is similar to dnssec-keygen.
Setting Key Timing Information
Key files contain time information related to rolling keys. This is placed there by dnssec-keygen when the file iscreated, and it can be modified using dnssec-settime. By default, only a limited amount of timing information is
included in the file, as illustrated in the examples in the previous section.
Note that dnssec-policy does set key timing information, but it uses its own state machine to determine what actions
to perform.
But when performing manual signing the key parameters and the timing information in the key files, you can implement
any DNSSEC policy you want for your zones.
All the dates are the same, and are the date and time that dnssec-keygen created the key. We can use
dnssec-settime to modify the dates7 . For example, to publish this key in the zone on 1 July 2020, use it to sign
records for a year starting on 15 July 2020, and remove it from the zone at the end of July 2021, we can use the following
command:# dnssec-settime -P 20200701 -A 20200715 -I 20210715 -D 20210731 Kexample.com.
,→+013+34371.key./Kexample.com.+013+34371.key./Kexample.com.+013+34371.private

which would set the contents of the key file to:; This is a zone-signing key, keyid 34371, for example.com.
; Created: 20200616104249 (Tue Jun 16 11:42:49 2020); Publish: 20200701000000 (Wed Jul 1 01:00:00 2020); Activate: 20200715000000 (Wed Jul 15 01:00:00 2020); Inactive: 20210715000000 (Thu Jul 15 01:00:00 2021); Delete: 20210731000000 (Sat Jul 31 01:00:00 2021)
example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8=(The actual key is truncated here to improve readability.)
7 Only one key file - for either a KSK or ZSK - is needed to signal the presence of the zone. dnssec-keygen creates files of both types as needed.

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Below is a complete list of each of the metadata fields, and how each one affects the signing of your zone:
1. Created: This records the date on which the key was created. It is not used in calculations; it is useful simply for
documentation purposes.
2. Publish: This sets the date on which a key is to be published to the zone. After that date, the key is included in thezone but is not used to sign it. This allows validating resolvers to get a copy of the new key in their cache before
there are any resource records signed with it. By default, if not specified at creation time, this is set to the current
time, meaning the key is published as soon as named picks it up.
3. Activate: This sets the date on which the key is to be activated. After that date, resource records are signed withthe key. By default, if not specified during creation time, this is set to the current time, meaning the key is used tosign data as soon as named picks it up.
4. Revoke: This sets the date on which the key is to be revoked. After that date, the key is flagged as revoked, although
it is still included in the zone and used to sign it. This is used to notify validating resolvers that this key is about tobe removed or retired from the zone. (This state is not used in normal day-to-day operations. See RFC 5011 tounderstand the circumstances where it may be used.)
5. Inactive: This sets the date on which the key is to become inactive. After that date, the key is still included in thezone, but it is no longer used to sign it. This sets the “expiration” or “retire” date for a key.
6. Delete: This sets the date on which the key is to be deleted. After that date, the key is no longer included in thezone, but it continues to exist on the file system or key repository.
This can be summarized as follows:
Table 1: Key Metadata Comparison
Metadata

Included in Zone File?

Used to Sign Data?

PurposeCreatedPublishActivate
RevokeInactive
Delete

No
Yes
Yes
Yes
Yes
No

No
No
Yes
Yes
No
No

Recording of key creation
Introduction of a key soon to be active
Activation date for new key
Notification of a key soon to be retired
Inactivation or retirement of a key
Deletion or removal of a key from a zone

The publication date is the date the key should be introduced into the zone. The activation date can be used to determine
when to sign resource records. With “Inactive” you signal when the signer should stop generating new signatures with thegiven key, and the “Delete” metadata specifies when the key should be removed from the zone.
Finally, we should note that the dnssec-keygen command supports the same set of switches so we could have set thedates when we created the key.
Signing the Zone
Now, edit the zone file to make sure the proper DNSKEY entries are included. The public keys should be inserted into
the zone file by including the .key files using $INCLUDE statements.
Use the command dnssec-signzone. Any keyset files corresponding to secure sub-zones should be present. Thezone signer generates NSEC, NSEC3, and RRSIG records for the zone, as well as DS for the child zones if -g is specified.
If -g is not specified, then DS RRsets for the secure child zones need to be added manually.
The following command signs the zone, assuming it is in a file called zone.child.example, using manually specified
keys:

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Chapter 12. DNSSEC GuideBIND 9 Administrator Reference Manual, Release 9.20.0# cd /etc/bind/keys/example.com/# dnssec-signzone -t -N INCREMENT -o example.com -f /etc/bind/db/example.com.signed.
,→db \/etc/bind/db/example.com.db Kexample.com.+013+17694.key Kexample.com.+013+06817.
,→key
Verifying the zone using the following algorithms: ECDSAP256SHA256.
Zone fully signed:
Algorithm: ECDSAP256SHA256: KSKs: 1 active, 0 stand-by, 0 revoked
ZSKs: 1 active, 0 stand-by, 0 revoked/etc/bind/db/example.com.signed.db
Signatures generated:
17
Signatures retained:
0
Signatures dropped:0Signatures successfully verified:0
Signatures unsuccessfully verified:0
Signing time in seconds:
0.046
Signatures per second:364.634
Runtime in seconds:
0.055

The -o switch explicitly defines the domain name (example.com in this case), while the -f switch specifies the output
file name. The second line has three parameters: the unsigned zone name (/etc/bind/db/example.com.db),
the ZSK file name, and the KSK file name. This also generates a plain-text file /etc/bind/db/example.com.
signed.db, which can be manually verified for correctness.
dnssec-signzone also produces keyset and dsset files. These are used to provide the parent zone administrators with
the DNSKEY records (or their corresponding DS records) that are the secure entry point to the zone.
By default, all zone keys which have an available private key are used to generate signatures. You can use the -S to only
include keys that have the “Activate” timing metadata in the past and the “Inactive” timing metadata in the future (or notpresent).
Reloading the Zone
Now it is time to inform BIND that a new signed zonefile is available. We can do this with the rndc reload
example.com command.
Verifying That the Zone Is Signed Correctly
You should now check that the zone is signed. Follow the steps in Verification.
Uploading the DS Record to the Parent
As described in Uploading Information to the Parent Zone, we must now upload the new information to the parent zone.
The format of the information and how to generate it is described in Working With the Parent Zone, although it is importantto remember that you must use the contents of the KSK file that you generated above as part of the process.
The file dsset-example.com (created by dnssec-signzone when it signed the example.com zone) contains
the DS record for the zone’s KSK.
If not yet done so, you will need to pass that to the administrator of the parent zone, to be placed in the zone. When the
DS record is published in the parent zone, your zone is fully signed.

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Checking That Your Zone Can Be Validated
Finally, follow the steps in How To Test Authoritative Zones to confirm that a query recognizes the zone as properly signed
and vouched for by the parent zone.
Re-signing the Zone
Since this is a manual process, you will need to re-sign periodically, as well as every time the zone data changes. You
will also need to manually roll the keys by adding and removing DNSKEY records (and interacting with the parent) at
the appropriate times.
So… What Now?
Once the zone is signed, it must be monitored as described in Maintenance Tasks. However, as the time approaches for a
key roll, you must create the new key. Of course, it is possible to create keys for the next fifty years all at once and set thekey times appropriately. Whether the increased risk in having the private key files for future keys available on disk offsets
the overhead of having to remember to create a new key before a rollover depends on your organization’s security policy.

12.6 Basic DNSSEC Troubleshooting
In this chapter, we cover some basic troubleshooting techniques, some common DNSSEC symptoms, and their causes
and solutions. This is not a comprehensive “how to troubleshoot any DNS or DNSSEC problem” guide, because that
could easily be an entire book by itself.

12.6.1 Query Path
The first step in troubleshooting DNS or DNSSEC should be to determine the query path. Whenever you are working
with a DNS-related issue, it is always a good idea to determine the exact query path to identify the origin of the problem.
End clients, such as laptop computers or mobile phones, are configured to talk to a recursive name server, and the recursive
name server may in turn forward requests on to other recursive name servers before arriving at the authoritative nameserver. The giveaway is the presence of the Authoritative Answer (aa) flag in a query response: when present, we know
we are talking to the authoritative server; when missing, we are talking to a recursive server. The example below showsan answer to a query for www.example.com without the Authoritative Answer flag:$ dig @10.53.0.3 www.example.com A; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.com a; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62714;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: c823fe302625db5b010000005e722b504d81bb01c2227259 (good);; QUESTION SECTION:;www.example.com.
IN A;; ANSWER SECTION:(continues on next page)

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Chapter 12. DNSSEC GuideBIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)www.example.com.

60

IN

A

10.1.0.1;; Query time: 3 msec;; SERVER: 10.53.0.3#53(10.53.0.3);; WHEN: Wed Mar 18 14:08:16 GMT 2020;; MSG SIZE rcvd: 88

Not only do we not see the aa flag, we see an ra flag, which indicates Recursion Available. This indicates that the server
we are talking to (10.53.0.3 in this example) is a recursive name server: although we were able to get an answer for
www.example.com, we know that the answer came from somewhere else.
If we query the authoritative server directly, we get:$ dig @10.53.0.2 www.example.com A; <<>> DiG 9.16.0 <<>> @10.53.0.2 www.example.com a; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39542;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; WARNING: recursion requested but not available...

The aa flag tells us that we are now talking to the authoritative name server for www.example.com, and that this is nota cached answer it obtained from some other name server; it served this answer to us right from its own database. In fact,
the Recursion Available (ra) flag is not present, which means this name server is not configured to perform recursion (atleast not for this client), so it could not have queried another name server to get cached results.

12.6.2 Visible DNSSEC Validation Symptoms
After determining the query path, it is necessary to determine whether the problem is actually related to DNSSEC validation. You can use the dig +cd flag to disable validation, as described in How Do I Know I Have a Validation
Problem?.
When there is indeed a DNSSEC validation problem, the visible symptoms, unfortunately, are very limited. WithDNSSEC validation enabled, if a DNS response is not fully validated, it results in a generic SERVFAIL message, as
shown below when querying against a recursive name server at 192.168.1.7:$ dig @10.53.0.3 www.example.org. A; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.org A; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 28947;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: d1301968aca086ad010000005e723a7113603c01916d136b (good);; QUESTION SECTION:;www.example.org.
IN A;; Query time: 3 msec
(continues on next page)

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With delv, a “resolution failed” message is output instead:$ delv @10.53.0.3 www.example.org. A +rtrace;; fetch: www.example.org/A;; resolution failed: SERVFAIL

BIND 9 logging features may be useful when trying to identify DNSSEC errors.

12.6.3 Basic Logging
DNSSEC validation error messages show up in syslog as a query error by default. Here is an example of what it may
look like:validating www.example.org/A: no valid signature found
RRSIG failed to verify resolving 'www.example.org/A/IN': 10.53.0.2#53

Usually, this level of error logging is sufficient. Debug logging, described in BIND DNSSEC Debug Logging, gives information on how to get more details about why DNSSEC validation may have failed.

12.6.4 BIND DNSSEC Debug Logging
A word of caution: before you enable debug logging, be aware that this may dramatically increase the load on your nameservers. Enabling debug logging is thus not recommended for production servers.
With that said, sometimes it may become necessary to temporarily enable BIND debug logging to see more details of how
and whether DNSSEC is validating. DNSSEC-related messages are not recorded in syslog by default, even if query
log is enabled; only DNSSEC errors show up in syslog.
The example below shows how to enable debug level 3 (to see full DNSSEC validation messages) in BIND 9 and have it
sent to syslog:
logging {channel dnssec_log {syslog daemon;
severity debug 3;
print-category yes;};
category dnssec { dnssec_log; };};The example below shows how to log DNSSEC messages to their own file (here, /var/log/dnssec.log):
logging {channel dnssec_log {file "/var/log/dnssec.log";
severity debug 3;};
category dnssec { dnssec_log; };};390

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After turning on debug logging and restarting BIND, a large number of log messages appear in syslog. The example
below shows the log messages as a result of successfully looking up and validating the domain name ftp.isc.org.
validating ./NS: starting
validating ./NS: attempting positive response validation
validating ./DNSKEY: starting
validating ./DNSKEY: attempting positive response validation
validating ./DNSKEY: verify rdataset (keyid=20326): successvalidating ./DNSKEY: marking as secure (DS)validating ./NS: in validator_callback_dnskey
validating ./NS: keyset with trust secure
validating ./NS: resuming validate
validating ./NS: verify rdataset (keyid=33853): successvalidating ./NS: marking as secure, noqname proof not neededvalidating ftp.isc.org/A: starting
validating ftp.isc.org/A: attempting positive response validation
validating isc.org/DNSKEY: starting
validating isc.org/DNSKEY: attempting positive response validation
validating isc.org/DS: starting
validating isc.org/DS: attempting positive response validation
validating org/DNSKEY: starting
validating org/DNSKEY: attempting positive response validation
validating org/DS: starting
validating org/DS: attempting positive response validation
validating org/DS: keyset with trust secure
validating org/DS: verify rdataset (keyid=33853): successvalidating org/DS: marking as secure, noqname proof not neededvalidating org/DNSKEY: in validator_callback_ds
validating org/DNSKEY: dsset with trust secure
validating org/DNSKEY: verify rdataset (keyid=9795): successvalidating org/DNSKEY: marking as secure (DS)validating isc.org/DS: in fetch_callback_dnskey
validating isc.org/DS: keyset with trust secure
validating isc.org/DS: resuming validate
validating isc.org/DS: verify rdataset (keyid=33209): successvalidating isc.org/DS: marking as secure, noqname proof not neededvalidating isc.org/DNSKEY: in validator_callback_ds
validating isc.org/DNSKEY: dsset with trust secure
validating isc.org/DNSKEY: verify rdataset (keyid=7250): successvalidating isc.org/DNSKEY: marking as secure (DS)validating ftp.isc.org/A: in fetch_callback_dnskey
validating ftp.isc.org/A: keyset with trust secure
validating ftp.isc.org/A: resuming validate
validating ftp.isc.org/A: verify rdataset (keyid=27566): successvalidating ftp.isc.org/A: marking as secure, noqname proof not needed

Note that these log messages indicate that the chain of trust has been established and ftp.isc.org has been successfully validated.
If validation had failed, you would see log messages indicating errors. We cover some of the most validation problems in
the next section.

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12.6.5 Common Problems
Security Lameness
Similar to lame delegation in traditional DNS, security lameness refers to the condition when the parent zone holds a
set of DS records that point to something that does not exist in the child zone. As a result, the entire child zone may“disappear,” having been marked as bogus by validating resolvers.
Below is an example attempting to resolve the A record for a test domain name www.example.net. From the user’s
perspective, as described in How Do I Know I Have a Validation Problem?, only a SERVFAIL message is returned. On
the validating resolver, we see the following messages in syslog:
named[126063]: validating example.net/DNSKEY: no valid signature found (DS)
named[126063]: no valid RRSIG resolving 'example.net/DNSKEY/IN': 10.53.0.2#53
named[126063]: broken trust chain resolving 'www.example.net/A/IN': 10.53.0.2#53

This gives us a hint that it is a broken trust chain issue. Let’s take a look at the DS records that are published for the zone
(with the keys shortened for ease of display):$ dig @10.53.0.3 example.net. DS; <<>> DiG 9.16.0 <<>> @10.53.0.3 example.net DS; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59602;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 7026d8f7c6e77e2a010000005e735d7c9d038d061b2d24da (good);; QUESTION SECTION:;example.net.
IN DS;; ANSWER SECTION:
example.net.

256 IN

DS

14956 8 2 9F3CACD...D3E3A396;; Query time: 0 msec;; SERVER: 10.53.0.3#53(10.53.0.3);; WHEN: Thu Mar 19 11:54:36 GMT 2020;; MSG SIZE rcvd: 116

Next, we query for the DNSKEY and RRSIG of example.net to see if there’s anything wrong. Since we are having
trouble validating, we can use the dig +cd option to temporarily disable checking and return results, even though they
do not pass the validation tests. The dig +multiline option causes dig to print the type, algorithm type, and key
id for DNSKEY records. Again, some long strings are shortened for ease of display:$ dig @10.53.0.3 example.net. DNSKEY +dnssec +cd +multiline; <<>> DiG 9.16.0 <<>> @10.53.0.3 example.net DNSKEY +cd +multiline +dnssec; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42980;; flags: qr rd ra cd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:(continues on next page)392

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; COOKIE: 4b5e7c88b3680c35010000005e73722057551f9f8be1990e (good);; QUESTION SECTION:;example.net.
IN DNSKEY;; ANSWER SECTION:
example.net.
287 IN DNSKEY 256 3 8 (AwEAAbu3NX...ADU/D7xjFFDu+8WRIn) ; ZSK; alg = RSASHA256 ; key id = 35328
example.net.
287 IN DNSKEY 257 3 8 (AwEAAbKtU1...PPP4aQZTybk75ZW+uL
6OJMAF63NO0s1nAZM2EWAVasbnn/X+J4N2rLuhk=) ; KSK; alg = RSASHA256 ; key id = 27247
example.net.
287 IN RRSIG DNSKEY 8 2 300 (
20811123173143 20180101000000 27247 example.net.
Fz1sjClIoF...YEjzpAWuAj9peQ== )example.net.
287 IN RRSIG DNSKEY 8 2 300 (
20811123173143 20180101000000 35328 example.net.
seKtUeJ4/l...YtDc1rcXTVlWIOw= );; Query time: 0 msec;; SERVER: 10.53.0.3#53(10.53.0.3);; WHEN: Thu Mar 19 13:22:40 GMT 2020;; MSG SIZE rcvd: 962

Here is the problem: the parent zone is telling the world that example.net is using the key 14956, but the authoritative
server indicates that it is using keys 27247 and 35328. There are several potential causes for this mismatch: one possibility
is that a malicious attacker has compromised one side and changed the data. A more likely scenario is that the DNS
administrator for the child zone did not upload the correct key information to the parent zone.
Incorrect TimeIn DNSSEC, every record comes with at least one RRSIG, and each RRSIG contains two timestamps: one indicatingwhen it becomes valid, and one when it expires. If the validating resolver’s current system time does not fall within the
two RRSIG timestamps, error messages appear in the BIND debug log.
The example below shows a log message when the RRSIG appears to have expired. This could mean the validating resolver
system time is incorrectly set too far in the future, or the zone administrator has not kept up with RRSIG maintenance.
validating example.com/DNSKEY: verify failed due to bad signature (keyid=19036):␣
,→RRSIG has expired

The log below shows that the RRSIG validity period has not yet begun. This could mean the validation resolver’s systemtime is incorrectly set too far in the past, or the zone administrator has incorrectly generated signatures for this domain
name.
validating example.com/DNSKEY: verify failed due to bad signature (keyid=4521): RRSIG␣,→validity period has not begun

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Unable to Load Keys
This is a simple yet common issue. If the key files are present but unreadable by named for some reason, the syslog
returns clear error messages, as shown below:
named[32447]: zone example.com/IN (signed): reconfiguring zone keys
named[32447]: dns_dnssec_findmatchingkeys: error reading key file Kexample.com.
,→+008+06817.private: permission denied
named[32447]: dns_dnssec_findmatchingkeys: error reading key file Kexample.com.
,→+008+17694.private: permission denied
named[32447]: zone example.com/IN (signed): next key event: 27-Nov-2014 20:04:36.521

However, if no keys are found, the error is not as obvious. Below shows the syslog messages after executing rndc
reload with the key files missing from the key directory:
named[32516]: received control channel command 'reload'
named[32516]: loading configuration from '/etc/bind/named.conf'
named[32516]: using default UDP/IPv4 port range: [1024, 65535]
named[32516]: using default UDP/IPv6 port range: [1024, 65535]
named[32516]: sizing zone task pool based on 6 zones
named[32516]: the working directory is not writable
named[32516]: reloading configuration succeeded
named[32516]: reloading zones succeeded
named[32516]: all zones loaded
named[32516]: running
named[32516]: zone example.com/IN (signed): reconfiguring zone keys
named[32516]: zone example.com/IN (signed): next key event: 27-Nov-2014 20:07:09.292

This happens to look exactly the same as if the keys were present and readable, and appears to indicate that named loaded
the keys and signed the zone. It even generates the internal (raw) files:# cd /etc/bind/db# ls
example.com.db example.com.db.jbk

example.com.db.signed

If named really loaded the keys and signed the zone, you should see the following files:# cd /etc/bind/db# ls
example.com.db example.com.db.jbk

example.com.db.signed

example.com.db.signed.jnl

So, unless you see the *.signed.jnl file, your zone has not been signed.
Invalid Trust Anchors
In most cases, you never need to explicitly configure trust anchors. named supplies the current root trust anchor and,with the default setting of dnssec-validation, updates it on the infrequent occasions when it is changed.
However, in some circumstances you may need to explicitly configure your own trust anchor. As we saw in the Trust
Anchors section, whenever a DNSKEY is received by the validating resolver, it is compared to the list of keys the resolver
explicitly trusts to see if further action is needed. If the two keys match, the validating resolver stops performing further
verification and returns the answer(s) as validated.
But what if the key file on the validating resolver is misconfigured or missing? Below we show some examples of log
messages when things are not working properly.
First of all, if the key you copied is malformed, BIND does not even start and you will likely find this error message insyslog:394

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named[18235]: /etc/bind/named.conf.options:29: bad base64 encoding
named[18235]: loading configuration: failure

If the key is a valid base64 string but the key algorithm is incorrect, or if the wrong key is installed, the first thing you
will notice is that virtually all of your DNS lookups result in SERVFAIL, even when you are looking up domain namesthat have not been DNSSEC-enabled. Below shows an example of querying a recursive server 10.53.0.3:$ dig @10.53.0.3 www.example.com. A; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.org A +dnssec; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 29586;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:; EDNS: version: 0, flags: do; udp: 4096
; COOKIE: ee078fc321fa1367010000005e73a58bf5f205ca47e04bed (good);; QUESTION SECTION:;www.example.org.
IN A

delv shows a similar result:$ delv @192.168.1.7 www.example.com. +rtrace;; fetch: www.example.com/A;; resolution failed: SERVFAIL

The next symptom you see is in the DNSSEC log messages:
managed-keys-zone: DNSKEY set for zone '.' could not be verified with current keys
validating ./DNSKEY: starting
validating ./DNSKEY: attempting positive response validation
validating ./DNSKEY: no DNSKEY matching DS
validating ./DNSKEY: no DNSKEY matching DS
validating ./DNSKEY: no valid signature found (DS)

These errors are indications that there are problems with the trust anchor.

12.6.6 Negative Trust Anchors
BIND 9.11 introduced Negative Trust Anchors (NTAs) as a means to temporarily disable DNSSEC validation for a zone
when you know that the zone’s DNSSEC is misconfigured.
NTAs are added using the rndc command, e.g.:$ rndc nta example.com
Negative trust anchor added: example.com/_default, expires 19-Mar-2020 19:57:42.000

The list of currently configured NTAs can also be examined using rndc, e.g.:$ rndc nta -dump
example.com/_default: expiry 19-Mar-2020 19:57:42.000

The default lifetime of an NTA is one hour, although by default, BIND polls the zone every five minutes to see if thezone correctly validates, at which point the NTA automatically expires. Both the default lifetime and the polling interval

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may be configured via named.conf, and the lifetime can be overridden on a per-zone basis using the -lifetime
duration parameter to rndc nta. Both timer values have a permitted maximum value of one week.

12.6.7 NSEC3 Troubleshooting
BIND includes a tool called nsec3hash that runs through the same steps as a validating resolver, to generate thecorrect hashed name based on NSEC3PARAM parameters. The command takes the following parameters in order: salt,
algorithm, iterations, and domain. For example, if the salt is 1234567890ABCDEF, hash algorithm is 1, and iteration is10, to get the NSEC3-hashed name for www.example.com we would execute a command like this:$ nsec3hash 1234567890ABCEDF 1 10 www.example.com
RN7I9ME6E1I6BDKIP91B9TCE4FHJ7LKF (salt=1234567890ABCEDF, hash=1, iterations=10)

Zero-length salt can be specified as -.
While it is unlikely you would construct a rainbow table of your own zone data, this tool may be useful when troubleshooting NSEC3 problems.

12.7 Advanced Discussions
12.7.1 Signature Validity Periods and Zone Re-Signing Intervals
In How Are Answers Verified?, we saw that record signatures have a validity period outside of which they are not valid.
This means that at some point, a signature will no longer be valid and a query for the associated record will fail DNSSEC
validation. But how long should a signature be valid for?
The maximum value for the validity period should be determined by the impact of a replay attack: if this is low, theperiod can be long; if high, the period should be shorter. There is no “right” value, but periods of between a few days toa month are common.
Deciding a minimum value is probably an easier task. Should something fail (e.g., a hidden primary distributing tosecondary servers that actually answer queries), how long will it take before the failure is noticed, and how long before it
is fixed? If you are a large 24x7 operation with operators always on-site, the answer might be less than an hour. In smaller
companies, if the failure occurs just after everyone has gone home for a long weekend, the answer might be several days.
Again, there are no “right” values - they depend on your circumstances. The signature validity period you decide to use
should be a value between the two bounds. At the time of this writing (mid-2020), the default policy used by BIND sets
a value of 14 days.
To keep the zone valid, the signatures must be periodically refreshed since they expire - i.e., the zone must be periodicallyre-signed. The frequency of the re-signing depends on your network’s individual needs. For example, signing puts a loadon your server, so if the server is very highly loaded, a lower re-signing frequency is better. Another consideration is thesignature lifetime: obviously the intervals between signings must not be longer than the signature validity period. But
if you have set a signature lifetime close to the minimum (see above), the signing interval must be much shorter. Whatwould happen if the system failed just before the zone was re-signed?
Again, there is no single “right” answer; it depends on your circumstances. The BIND 9 default policy sets the signature
refresh interval to 5 days.

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12.7.2 Proof of Non-Existence (NSEC and NSEC3)
How do you prove that something does not exist? This zen-like question is an interesting one, and in this section we
provide an overview of how DNSSEC solves the problem.
Why is it even important to have authenticated denial of existence in DNS? Couldn’t we just send back “hey, what you
asked for does not exist,” and somehow generate a digital signature to go with it, proving it really is from the correct
authoritative source? Aside from the technical challenge of signing something that doesn’t exist, this solution has flaws,
one of which is it gives an attacker a way to create the appearance of denial of service by replaying this message on the
network.
Let’s use a little story, told three different ways, to illustrate how proof of nonexistence works. In our story, we run asmall company with three employees: Alice, Edward, and Susan. For reasons that are far too complicated to go into, they
don’t have email accounts; instead, email for them is sent to a single account and a nameless intern passes the message tothem. The intern has access to our private DNSSEC key to create signatures for their responses.
If we followed the approach of giving back the same answer no matter what was asked, when people emailed and asked
for the message to be passed to “Bob,” our intern would simply answer “Sorry, that person doesn’t work here” and sign
this message. This answer could be validated because our intern signed the response with our private DNSSEC key.
However, since the signature doesn’t change, an attacker could record this message. If the attacker were able to intercept
our email, when the next person emailed asking for the message to be passed to Susan, the attacker could return the exact
same message: “Sorry, that person doesn’t work here,” with the same signature. Now the attacker has successfully fooled
the sender into thinking that Susan doesn’t work at our company, and might even be able to convince all senders that noone works at this company.
To solve this problem, two different solutions were created. We will look at the first one, NSEC, next.
NSEC
The NSEC record is used to prove that something does not exist, by providing the name before it and the name after it.
Using our tiny company example, this would be analogous to someone sending an email for Bob and our nameless intern
responding with with: “I’m sorry, that person doesn’t work here. The name before the location where ‘Bob’ would be is
Alice, and the name after that is Edward.” Let’s say another email was received for a non-existent person, this time Oliver;
our intern would respond “I’m sorry, that person doesn’t work here. The name before the location where ‘Oliver’ would
be is Edward, and the name after that is Susan.” If another sender asked for Todd, the answer would be: “I’m sorry, that
person doesn’t work here. The name before the location where ‘Todd’ would be is Susan, and there are no other names
after that.”
So we end up with four NSEC records:
example.com.
300 IN
alice.example.com. 300 IN
edward.example.com. 300 IN
susan.example.com. 300 IN

NSEC
NSEC
NSEC
NSEC

alice.example.com. A RRSIG NSEC
edward.example.com. A RRSIG NSEC
susan.example.com. A RRSIG NSEC
example.com.
A RRSIG NSEC

What if the attacker tried to use the same replay method described earlier? If someone sent an email for Edward, noneof the four answers would fit. If attacker replied with message #2, “I’m sorry, that person doesn’t work here. The namebefore it is Alice, and the name after it is Edward,” it is obviously false, since “Edward” is in the response; and the samegoes for #3, Edward and Susan. As for #1 and #4, Edward does not fall in the alphabetical range before Alice or after
Susan, so the sender can logically deduce that it was an incorrect answer.
When BIND signs your zone, the zone data is automatically sorted on the fly before generating NSEC records, much likehow a phone directory is sorted.
The NSEC record allows for a proof of non-existence for record types. If you ask a signed zone for a name that exists but
for a record type that doesn’t (for that name), the signed NSEC record returned lists all of the record types that do exist
for the requested domain name.

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NSEC records can also be used to show whether a record was generated as the result of a wildcard expansion. The detailsof this are not within the scope of this document, but are described well in RFC 7129.
Unfortunately, the NSEC solution has a few drawbacks, one of which is trivial “zone walking.” In our story, a curious
person can keep sending emails, and our nameless, gullible intern keeps divulging information about our employees.
Imagine if the sender first asked: “Is Bob there?” and received back the names Alice and Edward. Our sender could thenemail again: “Is Edwarda there?”, and will get back Edward and Susan. (No, “Edwarda” is not a real name. However,
it is the first name alphabetically after “Edward” and that is enough to get the intern to reply with a message telling us
the next valid name after Edward.) Repeat the process enough times and the person sending the emails eventually learns
every name in our company phone directory. For many of you, this may not be a problem, since the very idea of DNS issimilar to a public phone book: if you don’t want a name to be known publicly, don’t put it in DNS! Consider using DNS
views (split DNS) and only display your sensitive names to a select audience.
The second potential drawback of NSEC is a bigger zone file and memory consumption; there is no opt-out mechanism
for insecure child zones, so each name in the zone will get an additional NSEC record and a RRSIG record to go with it.
In practice this is a problem only for parent-zone operators dealing with mostly insecure child zones, such as com.. To
learn more about opt-out, please see NSEC3 Opt-Out.
NSEC3
NSEC3 adds two additional features that NSEC does not have:
1. It offers no easy zone enumeration.
2. It provides a mechanism for the parent zone to exclude insecure delegations (i.e., delegations to zones that are notsigned) from the proof of non-existence.
Recall that in NSEC we provided a range of names to prove that something does not exist. But as it turns out, even
disclosing these ranges of names becomes a problem: this made it very easy for the curious-minded to look at our entire
zone. Not only that, unlike a zone transfer, this “zone walking” is more resource-intensive. So how do we disclose
something without actually disclosing it?
The answer is actually quite simple: hashing functions, or one-way hashes. Without going into many details, think of it
like a magical meat grinder. A juicy piece of ribeye steak goes in one end, and out comes a predictable shape and size ofground meat (hash) with a somewhat unique pattern. No matter how hard you try, you cannot turn the ground meat backinto the ribeye steak: that’s what we call a one-way hash.
NSEC3 basically runs the names through a one-way hash before giving them out, so the recipients can verify the nonexistence without any knowledge of the other names in the zone.
So let’s tell our little story for the third time, this time with NSEC3. In this version, our intern is not given a list of actualnames; he is given a list of “hashed” names. So instead of Alice, Edward, and Susan, the list he is given reads like this(hashes shortened for easier reading):
FSK5.... (produced from Edward)
JKMA.... (produced from Susan)
NTQ0.... (produced from Alice)

Then, an email is received for Bob again. Our intern takes the name Bob through a hash function, and the result is L8J2…,
so he replies: “I’m sorry, that person doesn’t work here. The name before that is JKMA…, and the name after that is
NTQ0…”. There, we proved Bob doesn’t exist, without giving away any names! To put that into proper NSEC3 resource
records, they would look like this (again, hashes shortened for ease of display):
FSK5....example.com. 300 IN NSEC3 1 0 0 JKMA....example.com. 300 IN NSEC3 1 0 0 NTQ0....example.com. 300 IN NSEC3 1 0 0 -398

JKMA... A RRSIG
NTQ0... A RRSIG
FSK5... A RRSIG

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Note: Just because we employed one-way hash functions does not mean there is no way for a determined individual tofigure out our zone data.
Most names published in the DNS are rarely secret or unpredictable. They are published to be memorable, used andconsumed by humans. They are often recorded in many other network logs such as email logs, certificate transparency
logs, web page links, intrusion detection systems, malware scanners, email archives, etc. Many times a simple dictionaryof commonly used domain-name prefixes (www, mail, imap, login, database, etc.) can be used to quickly reveal a large
number of labels within a zone. Additionally, if an adversary really wants to expend significant CPU resources to mount
an offline dictionary attack on a zone’s NSEC3 chain, they will likely be able to find most of the “guessable” names despite
any level of hashing.
Also, it is still possible to gather all of our NSEC3 records and hashed names and perform an offline brute-force attackby trying all possible combinations to figure out what the original name is. In our meat-grinder analogy, this would be
like someone buying all available cuts of meat and grinding them up at home using the same model of meat grinder, andcomparing the output with the meat you gave him. It is expensive and time-consuming (especially with real meat), butlike everything else in cryptography, if someone has enough resources and time, nothing is truly private forever. If you areconcerned about someone performing this type of attack on your zone data, use some of the special techniques describedin RFC 4470.
NSEC3PARAM

Warning: Before we dive into the details of NSEC3 parametrization, please note: the defaults should not be changed
without a strong justification and a full understanding of the potential impact. See RFC 9276.
The above NSEC3 examples used four parameters: 1, 0, 0, and zero-length salt. 1 represents the algorithm, 0 represents
the opt-out flag, 0 represents the number of additional iterations, and - is the salt. Let’s look at how each one can be
configured:
Algorithm
NSEC3 Hashing Algorithm
The only currently defined value is 1 for SHA-1, so there is no configuration field for it.
Opt-out
Setting this bit to 1 enables NSEC3 opt-out, which is discussed in NSEC3 Opt-Out.
Iterations
Iterations defines the number of _additional_ times to apply the algorithm when generating an NSEC3 hash. Moreiterations consume more resources for both authoritative servers and validating resolvers. The considerations here
are similar to those seen in Key Sizes, of security versus resources.
Warning: Do not use values higher than zero. A value of zero provides one round of SHA-1 hashing andprotects from non-determined attackers.
A greater number of additional iterations causes interoperability problems and opens servers to CPU-exhausting
DoS attacks, while providing only doubtful security benefits.
Salt
A salt value, which can be combined with an FQDN to influence the resulting hash. Salt is discussed in more detailin NSEC3 Salt.

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NSEC3 Opt-Out
First things first: For most DNS administrators who do not manage a huge number of insecure delegations, the NSEC3
opt-out featuere is not relevant. See RFC 9276.
Opt-out allows for blocks of unsigned delegations to be covered by a single NSEC3 record. In other words, use of the
opt-out allows large registries to only sign as many NSEC3 records as there are signed DS or other RRsets in the zone;
with opt-out, unsigned delegations do not require additional NSEC3 records. This sacrifices the tamper-resistance proof
of non-existence offered by NSEC3 in order to reduce memory and CPU overheads, and decreases the effectiveness ofthe cache (RFC 8198).
Why would that ever be desirable? If a significant number of delegations are not yet securely delegated, meaning theylack DS records and are still insecure or unsigned, generating DNSSEC records for all their NS records might consume
lots of memory and is not strictly required by the child zones.
This resource-saving typically makes a difference only for huge zones like com.. Imagine that you are the operator ofbusy top-level domains such as com., with millions of insecure delegated domain names. As of mid-2022, around 3% of
all com. zones are signed. Basically, without opt-out, with 1,000,000 delegations, only 30,000 of which are secure, you
still have to generate NSEC RRsets for the other 970,000 delegations; with NSEC3 opt-out, you will have saved yourself
970,000 sets of records.
In contrast, for a small zone the difference is operationally negligible and the drawbacks outweigh the benefits.
If NSEC3 opt-out is truly essential for a zone, the following configuration can be added to dnssec-policy; forexample, to create an NSEC3 chain using the SHA-1 hash algorithm, with the opt-out flag, no additional iterations, andno extra salt, use:
dnssec-policy "nsec3" {...
nsec3param iterations 0 optout yes salt-length 0;};

To learn more about how to configure NSEC3 opt-out, please see NSEC3 Opt-Out.
NSEC3 Salt

Warning: Contrary to popular belief, adding salt provides little value. Each DNS zone is always uniquely saltedusing the zone name. Operators should use a zero-length salt value.
The properties of this extra salt are complicated and beyond scope of this document. For detailed description why thesalt in the context of DNSSEC provides little value please see RFC 9276.
NSEC or NSEC3?
So which is better: NSEC or NSEC3? There is no single right answer here that fits everyone; it comes down to a given
network’s needs or requirements.
In most cases, NSEC is a good choice for zone administrators. It relieves the authoritative servers and resolver of theadditional cryptographic operations that NSEC3 requires, and NSEC is comparatively easier to troubleshoot than NSEC3.
NSEC3 comes with many drawbacks and should be implemented only if zone enumeration prevention is really needed,or when opt-out provides a significant reduction in memory and CPU overheads (in other words, with a huge zone withmostly insecure delegations).

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12.7.3 DNSSEC Keys
Types of Keys
Although DNSSEC documentation talks about three types of keys, they are all the same thing - but they have different
roles. The roles are:Zone-Signing Key (ZSK)This is the key used to sign the zone. It signs all records in the zone apart from the DNSSEC key-related RRsets:
DNSKEY, CDS, and CDNSKEY.
Key-Signing Key (KSK)This is the key used to sign the DNSSEC key-related RRsets and is the key used to link the parent and child zones.
The parent zone stores a digest of the KSK. When a resolver verifies the chain of trust it checks to see that the
DS record in the parent (which holds the digest of a key) matches a key in the DNSKEY RRset, and that it is able
to use that key to verify the DNSKEY RRset. If it can do that, the resolver knows that it can trust the DNSKEY
resource records, and so can use one of them to validate the other records in the zone.
Combined Signing Key (CSK)A CSK combines the functionality of a ZSK and a KSK. Instead of having one key for signing the zone and one
for linking the parent and child zones, a CSK is a single key that serves both roles.
It is important to realize the terms ZSK, KSK, and CSK describe how the keys are used - all these keys are represented
by DNSKEY records. The following examples are the DNSKEY records from a zone signed with a KSK and ZSK:
$ dig @192.168.1.12 example.com DNSKEY; <<>> DiG 9.16.0 <<>> @192.168.1.12 example.com dnskey +multiline; (1 server found);; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54989;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1;; WARNING: recursion requested but not available;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 5258d7ed09db0d76010000005ea1cc8c672d8db27a464e37 (good);; QUESTION SECTION:;example.com.
IN DNSKEY;; ANSWER SECTION:
example.com.
60 IN DNSKEY 256 3 13 (tAeXLtIQ3aVDqqS/1UVRt9AE6/nzfoAuaT1Vy4dYl2CK
pLNcUJxME1Z//pnGXY+HqDU7Gr5HkJY8V0W3r5fzlw==) ; ZSK; alg = ECDSAP256SHA256 ; key id = 63722
example.com.
60 IN DNSKEY 257 3 13 (cxkNegsgubBPXSra5ug2P8rWy63B8jTnS4n0IYSsD9eW
VhiyQDmdgevKUhfG3SE1wbLChjJc2FAbvSZ1qk03Nw==) ; KSK; alg = ECDSAP256SHA256 ; key id = 42933… and a zone signed with just a CSK:
$ dig @192.168.1.13 example.com DNSKEY; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com dnskey +multiline; (1 server found);; global options: +cmd
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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page);; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22628;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; WARNING: recursion requested but not available;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 4096
; COOKIE: bf19ee914b5df46e010000005ea1cd02b66c06885d274647 (good);; QUESTION SECTION:;example.com.
IN DNSKEY;; ANSWER SECTION:
example.com.
60 IN DNSKEY 257 3 13 (p0XM6AJ68qid2vtOdyGaeH1jnrdk2GhZeVvGzXfP/PNa
71wGtzR6jdUrTbXo5Z1W5QeeJF4dls4lh4z7DByF5Q==) ; KSK; alg = ECDSAP256SHA256 ; key id = 1231

The only visible difference between the records (apart from the key data itself) is the value of the flags fields; this is 256
for a ZSK and 257 for a KSK or CSK. Even then, the flags field is only a hint to the software using it as to the role of thekey: zones can be signed by any key. The fact that a CSK and KSK both have the same flags emphasizes this. A KSK
usually only signs the DNSSEC key-related RRsets in a zone, whereas a CSK is used to sign all records in the zone.
The original idea of separating the function of the key into a KSK and ZSK was operational. With a single key, changing
it for any reason is “expensive,” as it requires interaction with the parent zone (e.g., uploading the key to the parent may
require manual interaction with the organization running that zone). By splitting it, interaction with the parent is required
only if the KSK is changed; the ZSK can be changed as often as required without involving the parent.
The split also allows the keys to be of different lengths. So the ZSK, which is used to sign the record in the zone, canbe of a (relatively) short length, lowering the load on the server. The KSK, which is used only infrequently, can be of amuch longer length. The relatively infrequent use also allows the private part of the key to be stored in a way that is moresecure but that may require more overhead to access, e.g., on an HSM (see Hardware Security Modules (HSMs)).
In the early days of DNSSEC, the idea of splitting the key went more or less unchallenged. However, with the advent of
more powerful computers and the introduction of signaling methods between the parent and child zones (see The CDS
and CDNSKEY Resource Records), the advantages of a ZSK/KSK split are less clear and, for many zones, a single key is
all that is required.
As with many questions related to the choice of DNSSEC policy, the decision on which is “best” is not clear and depends
on your circumstances.
Which Algorithm?
There are three algorithm choices for DNSSEC as of this writing (mid-2020):• RSA• Elliptic Curve DSA (ECDSA)• Edwards Curve Digital Security Algorithm (EdDSA)
All are supported in BIND 9, but only RSA and ECDSA (specifically RSASHA256 and ECDSAP256SHA256) aremandatory to implement in DNSSEC. However, RSA is a little long in the tooth, and ECDSA/EdDSA are emerging as
the next new cryptographic standards. In fact, the US federal government recommended discontinuing RSA use altogether
by September 2015 and migrating to using ECDSA or similar algorithms.
For now, use ECDSAP256SHA256 but keep abreast of developments in this area. For details about rolling over
DNSKEYs to a new algorithm, see Algorithm Rollovers.

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Key Sizes
If using RSA keys, the choice of key sizes is a classic issue of finding the balance between performance and security.
The larger the key size, the longer it takes for an attacker to crack the key; but larger keys also mean more resources areneeded both when generating signatures (authoritative servers) and verifying signatures (recursive servers).
Of the two sets of keys, ZSK is used much more frequently. ZSK is used whenever zone data changes or when signatures
expire, so performance certainly is of a bigger concern. As for KSK, it is used less frequently, so performance is less ofa factor, but its impact is bigger because of its role in signing other keys.
In earlier versions of this guide, the following key lengths were chosen for each set, with the recommendation that they
be rotated more frequently for better security:• ZSK: RSA 1024 bits, rollover every year
• KSK: RSA 2048 bits, rollover every five years
These should be considered minimum RSA key sizes. At the time of this writing (mid-2020), the root zone and many
TLDs are already using 2048 bit ZSKs. If you choose to implement larger key sizes, keep in mind that larger key sizes
result in larger DNS responses, which this may mean more load on network resources. Depending on your network
configuration, end users may even experience resolution failures due to the increased response sizes, as discussed in
What’s EDNS All About (And Why Should I Care)?.
ECDSA key sizes can be much smaller for the same level of security, e.g., an ECDSA key length of 224 bits provides thesame level of security as a 2048-bit RSA key. Currently BIND 9 sets a key size of 256 for all ECDSA keys.
Key Storage
Public Key Storage
The beauty of a public key cryptography system is that the public key portion can and should be distributed to as many
people as possible. As the administrator, you may want to keep the public keys on an easily accessible file system for
operational ease, but there is no need to securely store them, since both ZSK and KSK public keys are published in thezone data as DNSKEY resource records.
Additionally, a hash of the KSK public key is also uploaded to the parent zone (see Working With the Parent Zone formore details), and is published by the parent zone as DS records.
Private Key Storage
Ideally, private keys should be stored offline, in secure devices such as a smart card. Operationally, however, this creates
certain challenges, since the private key is needed to create RRSIG resource records, and it is a hassle to bring the private
key out of storage every time the zone file changes or signatures expire.
A common approach to strike the balance between security and practicality is to have two sets of keys: a ZSK set anda KSK set. A ZSK private key is used to sign zone data, and can be kept online for ease of use, while a KSK private
key is used to sign just the DNSKEY (the ZSK); it is used less frequently, and can be stored in a much more secure andrestricted fashion.
For example, a KSK private key stored on a USB flash drive that is kept in a fireproof safe, only brought online once a
year to sign a new pair of ZSKs, combined with a ZSK private key stored on the network file system and available forroutine use, may be a good balance between operational flexibility and security.
For more information on changing keys, please see Key Rollovers.

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Hardware Security Modules (HSMs)
A Hardware Security Module (HSM) may come in different shapes and sizes, but as the name indicates, it is a physicaldevice or devices, usually with some or all of the following features:• Tamper-resistant key storage• Strong random-number generation• Hardware for faster cryptographic operations
Most organizations do not incorporate HSMs into their security practices due to cost and the added operational complexity.
BIND supports Public Key Cryptography Standard #11 (PKCS #11) for communication with HSMs and other cryptographic support devices. For more information on how to configure BIND to work with an HSM, please refer to the
BIND 9 Administrator Reference Manual.

12.7.4 Rollovers
Key Rollovers
A key rollover is where one key in a zone is replaced by a new one. There are arguments for and against regularly rollingkeys. In essence these are:Pros:
1. Regularly changing the key hinders attempts at determination of the private part of the key by cryptanalysis of
signatures.
2. It gives administrators practice at changing a key; should a key ever need to be changed in an emergency, theywould not be doing it for the first time.
Cons:
1. A lot of effort is required to hack a key, and there are probably easier ways of obtaining it, e.g., by breaking into
the systems on which it is stored.
2. Rolling the key adds complexity to the system and introduces the possibility of error. We are more likely to havean interruption to our service than if we had not rolled it.
Whether and when to roll the key is up to you. How serious would the damage be if a key were compromised without
you knowing about it? How serious would a key roll failure be?
Before going any further, it is worth noting that if you sign your zone with dnssec-policy, you don’t really need toconcern yourself with the details of a key rollover: BIND 9 takes care of it all for you. If you are doing a manual key roll,
you do need to familiarize yourself with the various steps involved and the timing details.
Rolling a key is not as simple as replacing the DNSKEY statement in the zone. That is an essential part of it, but timing iseverything. For example, suppose that we run the example.com zone and that a friend queries for the AAAA record ofwww.example.com. As part of the resolution process (described in How Does DNSSEC Change DNS Lookup?), theirrecursive server looks up the keys for the example.com zone and uses them to verify the signature associated with the
AAAA record. We’ll assume that the records validated successfully, so they can use the address to visit example.com’s
website.
Let’s also assume that immediately after the lookup, we want to roll the ZSK for example.com. Our first attempt at
this is to remove the old DNSKEY record and signatures, add a new DNSKEY record, and re-sign the zone with it. So
one minute our server is serving the old DNSKEY and records signed with the old key, and the next minute it is serving
the new key and records signed with it. We’ve achieved our goal - we are serving a zone signed with the new keys; tocheck this is really the case, we booted up our laptop and looked up the AAAA record ftp.example.com. The

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lookup succeeded so all must be well. Or is it? Just to be sure, we called our friend and asked them to check. They tried
to lookup ftp.example.com but got a SERVFAIL response from their recursive server. What’s going on?
The answer, in a word, is “caching.” When our friend looked up www.example.com, their recursive server retrieved
and cached not only the AAAA record, but also a lot of other records. It cached the NS records for com and example.
com, as well as the AAAA (and A) records for those name servers (and this action may, in turn, have caused the lookup
and caching of other NS and AAAA/A records). Most importantly for this example, it also looked up and cached the
DNSKEY records for the root, com, and example.com zones. When a query was made for ftp.example.com, therecursive server believed it already had most of the information we needed. It knew what nameservers served example.
com and their addresses, so it went directly to one of those to get the AAAA record for ftp.example.com and its
associated signature. But when it tried to validate the signature, it used the cached copy of the DNSKEY, and that is when
our friend had the problem. Their recursive server had a copy of the old DNSKEY in its cache, but the AAAA record
for ftp.example.com was signed with the new key. So, not surprisingly, the signature could not validate.
How should we roll the keys for example.com? A clue to the answer is to note that the problem came about because the
DNSKEY records were cached by the recursive server. What would have happened had our friend flushed the DNSKEY
records from the recursive server’s cache before making the query? That would have worked; those records would havebeen retrieved from example.com’s nameservers at the same time that we retrieved the AAAA record for ftp.
example.com. Our friend’s server would have obtained the new key along with the AAAA record and associatedsignature created with the new key, and all would have been well.
As it is obviously impossible for us to notify all recursive server operators to flush our DNSKEY records every time weroll a key, we must use another solution. That solution is to wait for the recursive servers to remove old records fromcaches when they reach their TTL. How exactly we do this depends on whether we are trying to roll a ZSK, a KSK, or aCSK.
ZSK Rollover Methods
The ZSK can be rolled in one of the following two ways:
1. Pre-Publication: Publish the new ZSK into zone data before it is actually used. Wait at least one TTL interval, so
the world’s recursive servers know about both keys, then stop using the old key and generate a new RRSIG using
the new key. Wait at least another TTL, so the cached old key data is expunged from the world’s recursive servers,
and then remove the old key.
The benefit of the pre-publication approach is it does not dramatically increase the zone size; however, the durationof the rollover is longer. If insufficient time has passed after the new ZSK is published, some resolvers may only
have the old ZSK cached when the new RRSIG records are published, and validation may fail. This is the method
described in ZSK Rollover.
2. Double-Signature: Publish the new ZSK and new RRSIG, essentially doubling the size of the zone. Wait at least
one TTL interval, and then remove the old ZSK and old RRSIG.
The benefit of the double-signature approach is that it is easier to understand and execute, but it causes a significantly
increased zone size during a rollover event.

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KSK Rollover Methods
Rolling the KSK requires interaction with the parent zone, so operationally this may be more complex than rolling ZSKs.
There are three methods of rolling the KSK:
1. Double-KSK: Add the new KSK to the DNSKEY RRset, which is then signed with both the old and new keys. After
waiting for the old RRset to expire from caches, change the DS record in the parent zone. After waiting a further
TTL interval for this change to be reflected in caches, remove the old key from the RRset.
Basically, the new KSK is added first at the child zone and used to sign the DNSKEY; then the DS record is changed,
followed by the removal of the old KSK. Double-KSK keeps the interaction with the parent zone to a minimum,
but for the duration of the rollover, the size of the DNSKEY RRset is increased.
2. Double-DS: Publish the new DS record. After waiting for this change to propagate into caches, change the KSK.
After a further TTL interval during which the old DNSKEY RRset expires from caches, remove the old DS record.
Double-DS is the reverse of Double-KSK: the new DS is published at the parent first, then the KSK at the child is
updated, then the old DS at the parent is removed. The benefit is that the size of the DNSKEY RRset is kept to aminimum, but interactions with the parent zone are increased to two events. This is the method described in KSK
Rollover.
3. Double-RRset: Add the new KSK to the DNSKEY RRset, which is then signed with both the old and new key, andadd the new DS record to the parent zone. After waiting a suitable interval for the old DS and DNSKEY RRsets
to expire from caches, remove the old DNSKEY and old DS record.
Double-RRset is the fastest way to roll the KSK (i.e., it has the shortest rollover time), but has the drawbacks ofboth of the other methods: a larger DNSKEY RRset and two interactions with the parent.
CSK Rollover Methods
Rolling the CSK is more complex than rolling either the ZSK or KSK, as the timing constraints relating to both theparent zone and the caching of records by downstream recursive servers must be taken into account. There are numerous
possible methods that are a combination of ZSK rollover and KSK rollover methods. BIND 9 automatic signing uses a
combination of ZSK Pre-Publication and Double-KSK rollover.
Emergency Key Rollovers
Keys are generally rolled on a regular schedule - if you choose to roll them at all. But sometimes, you may have to rollover
keys out-of-schedule due to a security incident. The aim of an emergency rollover is to re-sign the zone with a new key
as soon as possible, because when a key is suspected of being compromised, a malicious attacker (or anyone who hasaccess to the key) could impersonate your server and trick other validating resolvers into believing that they are receiving
authentic, validated answers.
During an emergency rollover, follow the same operational procedures described in Rollovers, with the added task of reducing the TTL of the current active (potentially compromised) DNSKEY RRset, in an attempt to phase out the compromised key faster before the new key takes effect. The time frame should be significantly reduced from the 30-days-apartexample, since you probably do not want to wait up to 60 days for the compromised key to be removed from your zone.
Another method is to carry a spare key with you at all times. If you have a second key pre-published and that one is notcompromised at the same time as the first key, you could save yourself some time by immediately activating the spare key
if the active key is compromised. With pre-publication, all validating resolvers should already have this spare key cached,thus saving you some time.
With a KSK emergency rollover, you also need to consider factors related to your parent zone, such as how quickly they
can remove the old DS records and publish the new ones.

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As with many other facets of DNSSEC, there are multiple aspects to take into account when it comes to emergency key
rollovers. For more in-depth considerations, please check out RFC 7583.
Algorithm Rollovers
From time to time, new digital signature algorithms with improved security are introduced, and it may be desirable foradministrators to roll over DNSKEYs to a new algorithm, e.g., from RSASHA1 (algorithm 5 or 7) to RSASHA256(algorithm 8). The algorithm rollover steps must be followed with care to avoid breaking DNSSEC validation.
If you are managing DNSSEC by using the dnssec-policy configuration, named handles these steps for you. Simply
change the algorithm for the relevant keys, and named uses the new algorithm when the key is next rolled. It performs asmooth transition to the new algorithm, ensuring that the zone remains valid throughout rollover.

12.7.5 Other Topics
DNSSEC and Dynamic Updates
Dynamic DNS (DDNS) is actually independent of DNSSEC. DDNS provides a mechanism, separate from editing thezone file or zone database, to edit DNS data. Most DNS clients and servers are able to handle dynamic updates, and
DDNS can also be integrated as part of your DHCP environment.
When you have both DNSSEC and dynamic updates in your environment, updating zone data works the same way aswith traditional (insecure) DNS: you can use rndc freeze before editing the zone file, and rndc thaw when you
have finished editing, or you can use the command nsupdate to add, edit, or remove records like this:$ nsupdate> server 192.168.1.13> update add xyz.example.com. 300 IN A 1.1.1.1> send> quit

The examples provided in this guide make named automatically re-sign the zone whenever its content has changed. If
you decide to sign your own zone file manually, you need to remember to execute the dnssec-signzone command
whenever your zone file has been updated.
As far as system resources and performance are concerned, be mindful that with a DNSSEC zone that changes frequently,
every time the zone changes your system is executing a series of cryptographic operations to (re)generate signatures and
NSEC or NSEC3 records.
DNSSEC on Private Networks
Let’s clarify what we mean: in this section, “private networks” really refers to a private or internal DNS view. Most DNS
products offer the ability to have different versions of DNS answers, depending on the origin of the query. This feature isoften called “DNS views” or “split DNS,” and is most commonly implemented as an “internal” versus an “external” setup.
For instance, your organization may have a version of example.com that is offered to the world, and its names most
likely resolve to publicly reachable IP addresses. You may also have an internal version of example.com that is only
accessible when you are on the company’s private networks or via a VPN connection. These private networks typicallyfall under 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 for IPv4.
So what if you want to offer DNSSEC for your internal version of example.com? This can be done: the golden rule
is to use the same key for both the internal and external versions of the zones. This avoids problems that can occur whenmachines (e.g., laptops) move between accessing the internal and external zones, when it is possible that they may havecached records from the wrong zone.

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Introduction to DANE
With your DNS infrastructure secured with DNSSEC, information can now be stored in DNS and its integrity and authenticity can be proved. One of the new features that takes advantage of this is the DNS-Based Authentication of Named
Entities, or DANE. This improves security in a number of ways, including:• The ability to store self-signed X.509 certificates and bypass having to pay a third party (such as a Certificate
Authority) to sign the certificates (RFC 6698).
• Improved security for clients connecting to mail servers (RFC 7672).
• A secure way of getting public PGP keys (RFC 7929).

12.7.6 Disadvantages of DNSSECDNSSEC, like many things in this world, is not without its problems. Below are a few challenges and disadvantages that
DNSSEC faces.
1. Increased, well, everything: With DNSSEC, signed zones are larger, thus taking up more disk space; for DNSSECaware servers, the additional cryptographic computation usually results in increased system load; and the network
packets are bigger, possibly putting more strains on the network infrastructure.
2. Different security considerations: DNSSEC addresses many security concerns, most notably cache poisoning. But
at the same time, it may introduce a set of different security considerations, such as amplification attack and zone
enumeration through NSEC. These concerns are still being identified and addressed by the Internet community.
3. More complexity: If you have read this far, you have probably already concluded this yourself. With additional
resource records, keys, signatures, and rotations, DNSSEC adds many more moving pieces on top of the existing
DNS machine. The job of the DNS administrator changes, as DNS becomes the new secure repository of everythingfrom spam avoidance to encryption keys, and the amount of work involved to troubleshoot a DNS-related issue
becomes more challenging.
4. Increased fragility: The increased complexity means more opportunities for things to go wrong. Before DNSSEC,
DNS was essentially “add something to the zone and forget it.” With DNSSEC, each new component - re-signing,
key rollover, interaction with parent zone, key management - adds more opportunity for error. It is entirely possiblethat a failure to validate a name may come down to errors on the part of one or more zone operators rather than
the result of a deliberate attack on the DNS.
5. New maintenance tasks: Even if your new secure DNS infrastructure runs without any hiccups or security breaches,it still requires regular attention, from re-signing to key rollovers. While most of these can be automated, some of
the tasks, such as KSK rollover, remain manual for the time being.
6. Not enough people are using it today: While it’s estimated (as of mid-2020) that roughly 30% of the global Internet
DNS traffic is validating8 , that doesn’t mean that many of the DNS zones are actually signed. What this means is,even if your company’s zone is signed today, fewer than 30% of the Internet’s servers are taking advantage of thisextra security. It gets worse: with less than 1.5% of the com. domains signed, even if your DNSSEC validation isenabled today, it’s not likely to buy you or your users a whole lot more protection until these popular domain names
decide to sign their zones.
The last point may have more impact than you realize. Consider this: HTTP and HTTPS make up the majority of
traffic on the Internet. While you may have secured your DNS infrastructure through DNSSEC, if your web hosting is
outsourced to a third party that does not yet support DNSSEC in its own domain, or if your web page loads contents
and components from insecure domains, end users may experience validation problems when trying to access your web
page. For example, although you may have signed the zone company.com, the web address www.company.com
may actually be a CNAME to foo.random-cloud-provider.com. As long as random-cloud-provider.
com remains an insecure DNS zone, users cannot fully validate everything when they visit your web page and could be
redirected elsewhere by a cache poisoning attack.
8 Based on APNIC statistics at https://stats.labs.apnic.net/dnssec/XA

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12.8 Recipes
This chapter provides step-by-step “recipes” for some common DNSSEC configurations.

12.8.1 DNSSEC Signing
There are two recipes here: the first shows an example using DNSSEC signing on the primary server, which has been
covered in this guide; the second shows how to setup a “bump in the wire” between a hidden primary and the secondary
servers to seamlessly sign the zone “on the fly.”Primary Server DNSSEC Signing
In this recipe, our servers are illustrated as shown in DNSSEC Signing Recipe #1: we have a primary server (192.168.1.1)
and three secondary servers (192.168.1.2, 192.168.1.3, and 192.168.1.4) that receive zone transfers. To get the zone
signed, we need to reconfigure the primary server. Once reconfigured, a signed version of the zone is generated on thefly; zone transfers take care of synchronizing the signed zone data to all secondary name servers, without configuration orsoftware changes on them.

Fig. 5: DNSSEC Signing Recipe #1
Using the method described in Easy-Start Guide for Signing Authoritative Zones, we just need to add a dnssec-policy
statement to the relevant zone clause. This is what the named.conf zone statement looks like on the primary server,
192.168.1.1:
zone "example.com" IN {type primary;file "db/example.com.db";
key-directory "keys/example.com";dnssec-policy default;
allow-transfer { 192.168.1.2; 192.168.1.3; 192.168.1.4; };};We have chosen to use the default policy, storing the keys generated for the zone in the directory keys/example.
com. To use a custom policy, define the policy in the configuration file and select it in the zone statement (as describedin Creating a Custom DNSSEC Policy).
On the secondary servers, named.conf does not need to be updated, and it looks like this:zone "example.com" IN {type secondary;file "db/example.com.db";(continues on next page)

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primaries { 192.168.1.1; };};In fact, the secondary servers do not even need to be running BIND; they can run any DNS product that supports DNSSEC.
“Bump in the Wire” Signing
In this recipe, we take advantage of the power of automated signing by placing an additional name server (192.168.1.5)
between the hidden primary (192.168.1.1) and the DNS secondaries (192.168.1.2, 192.168.1.3, and 192.168.1.4). The
additional name server, 192.168.1.5, acts as a “bump in the wire,” taking an unsigned zone from the hidden primary, andsending out signed data on the other end to the secondary name servers. The steps described in this recipe may be used aspart of a DNSSEC deployment strategy, since it requires only minimal changes made to the existing hidden DNS primaryand DNS secondaries.

Fig. 6: DNSSEC Signing Recipe #2
It is important to remember that 192.168.1.1 in this case is a hidden primary not exposed to the world, and it must not
be listed in the NS RRset. Otherwise the world will get conflicting answers: unsigned answers from the hidden primaryand signed answers from the other name servers.
The only configuration change needed on the hidden primary, 192.168.1.1, is to make sure it allows our middle box toperform a zone transfer:zone "example.com" IN {...
allow-transfer { 192.168.1.5; };...
};On the middle box, 192.168.1.5, all the tasks described in Easy-Start Guide for Signing Authoritative Zones still need tobe performed, such as generating key pairs and uploading information to the parent zone. This server is configured as
secondary to the hidden primary 192.168.1.1 to receive the unsigned data; then, using keys accessible to this middle box,
to sign data on the fly; and finally, to send out the signed data via zone transfer to the other three DNS secondaries. Its
named.conf zone statement looks like this:zone example.com {type secondary;primaries { 192.168.1.1; };file "db/example.com.db";
key-directory "keys/example.com";dnssec-policy default;(continues on next page)

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allow-transfer { 192.168.1.2; 192.168.1.3; 192.168.1.4; };};(As before, the default policy has been selected here. See Creating a Custom DNSSEC Policy for instructions on how todefine and use a custom policy.)
Finally, on the three secondary servers, the configuration should be updated to receive a zone transfer from 192.168.1.5(the middle box) instead of from 192.168.1.1 (the hidden primary). If using BIND, the named.conf file looks likethis:zone "example.com" IN {type secondary;file "db/example.com.db";
primaries { 192.168.1.5; };};# this was 192.168.1.1 before!

12.8.2 Rollovers
If you are signing your zone using a dnssec-policy statement, this section is not really relevant to you. In the policy
statement, you set how long you want your keys to be valid for, the time taken for information to propagate throughyour zone, the time it takes for your parent zone to register a new DS record, etc., and that’s more or less it. named
implements everything for you automatically, apart from uploading the new DS records to your parent zone - which iscovered in Uploading Information to the Parent Zone. (Some screenshots from a session where a KSK is uploaded tothe parent zone are presented here for convenience.) However, these recipes may be useful in describing what happens
through the rollover process and what you should be monitoring.
ZSK Rollover
This recipe covers how to perform a ZSK rollover using what is known as the Pre-Publication method. For other ZSK
rolling methods, please see ZSK Rollover Methods in Advanced Discussions.
Below is a sample timeline for a ZSK rollover to occur on January 1, 2021:
1. December 1, 2020 (one month before rollover)• Generate new ZSK• Add DNSKEY for new ZSK to zone
2. January 1, 2021 (day of rollover)• New ZSK used to replace RRSIGs for the bulk of the zone
3. February 1, 2021 (one month after rollover)• Remove old ZSK DNSKEY RRset from zone
• DNSKEY signatures made with KSK are changed
The current active ZSK has the ID 17694 in the example below. For more information on key management and rollovers,
please see Rollovers.

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One Month Before ZSK Rollover
On December 1, 2020, a month before the example rollover, you (as administrator) should change the parameters on thecurrent key (17694). Set it to become inactive on January 1, 2021 and be deleted from the zone on February 1, 2021;
also, generate a successor key (51623):# cd /etc/bind/keys/example.com/# dnssec-settime -I 20210101 -D 20210201 Kexample.com.+008+17694./Kexample.com.+008+17694.key/GoDaddy./Kexample.com.+008+17694.private# dnssec-keygen -S Kexample.com.+008+17694
Generating key pair..++++++ ...........++++++
Kexample.com.+008+51623

The first command gets us into the key directory /etc/bind/keys/example.com/, where keys for example.
com are stored.
The second, dnssec-settime, sets an inactive (-I) date of January 1, 2021, and a deletion (-D) date of February 1,
2021, for the current ZSK (Kexample.com.+008+17694).
The third command, dnssec-keygen, creates a successor key, using the exact same parameters (algorithms, key sizes,etc.) as the current ZSK. The new ZSK created in our example is Kexample.com.+008+51623.
Make sure the successor keys are readable by named.
named’s logging messages indicate when the next key checking event is scheduled to occur, the frequency of which canbe controlled by dnssec-loadkeys-interval. The log message looks like this:zone example.com/IN (signed): next key event: 01-Dec-2020 00:13:05.385

And you can check the publish date of the key by looking at the key file:# cd /etc/bind/keys/example.com# cat Kexample.com.+008+51623.key; This is a zone-signing key, keyid 11623, for example.com.
; Created: 20201130160024 (Mon Dec 1 00:00:24 2020); Publish: 20201202000000 (Fri Dec 2 08:00:00 2020); Activate: 20210101000000 (Sun Jan 1 08:00:00 2021)...

Since the publish date is set to the morning of December 2, and our example scenario takes place on December 1, thenext morning you will notice that your zone has gained a new DNSKEY record, but the new ZSK is not yet being used
to generate signatures. Below is the abbreviated output - with shortened DNSKEY and RRSIG - when querying theauthoritative name server, 192.168.1.13:$ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline...
;; ANSWER SECTION:
example.com.
600 IN DNSKEY 257 3 8 (AwEAAcWDps...lM3NRn/G/R) ; KSK; alg = RSASHA256; key id = 6817
example.com.
600 IN DNSKEY 256 3 8 (AwEAAbi6Vo...qBW5+iAqNz) ; ZSK; alg = RSASHA256; key id = 51623
example.com.
600 IN DNSKEY 256 3 8 (AwEAAcjGaU...0rzuu55If5(continues on next page)

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example.com.

example.com.

) ; ZSK; alg = RSASHA256; key id = 17694
600 IN RRSIG DNSKEY 8 2 600 (
20210101000000 20201201230000 6817 example.com.
LAiaJM26T7...FU9syh/TQ= )600 IN RRSIG DNSKEY 8 2 600 (
20210101000000 20201201230000 17694 example.com.
HK4EBbbOpj...n5V6nvAkI= )...

For good measure, let’s take a look at the SOA record and its signature for this zone. Notice the RRSIG is signed by thecurrent ZSK, 17694. This will come in handy later when you want to verify whether the new ZSK is in effect:$ dig @192.168.1.13 example.com. SOA +dnssec +multiline...
;; ANSWER SECTION:
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020120102 ; serial1800; refresh (30 minutes)
900; retry (15 minutes)
2419200; expire (4 weeks)300; minimum (5 minutes))
example.com.
600 IN RRSIG SOA 8 2 600 (
20201230160109 20201130150109 17694 example.com.
YUTC8rFULaWbW+nAHzbfGwNqzARHevpryzRIJMvZBYPo
NAeejNk9saNAoCYKWxGJ0YBc2k+r5fYq1Mg4ll2JkBF5
buAsAYLw8vEOIxVpXwlArY+oSp9T1w2wfTZ0vhVIxaYX
6dkcz4I3wbDx2xmG0yngtA6A8lAchERx2EGy0RM= )These are all the manual tasks you need to perform for a ZSK rollover. If you have followed the configuration examples
in this guide of using inline-signing and dnssec-policy, everything else is automated for you by BIND.
Day of ZSK Rollover
On the actual day of the rollover, although there is technically nothing for you to do, you should still keep an eye on thezone to make sure new signatures are being generated by the new ZSK (51623 in this example). The easiest way is toquery the authoritative name server 192.168.1.13 for the SOA record as you did a month ago:
$ dig @192.168.1.13 example.com. SOA +dnssec +multiline...
;; ANSWER SECTION:
example.com.
600 IN SOA ns1.example.com. admin.example.com. (2020112011 ; serial1800; refresh (30 minutes)
900; retry (15 minutes)
2419200; expire (4 weeks)300; minimum (5 minutes))
example.com.
600 IN RRSIG SOA 8 2 600 (
20210131000000 20201231230000 51623 example.com.
J4RMNpJPOmMidElyBugJp0RLqXoNqfvo/2AT6yAAvx9X
zZRL1cuhkRcyCSLZ9Z+zZ2y4u2lvQGrNiondaKdQCor7
uTqH5WCPoqalOCBjqU7c7vlAM27O9RD11nzPNpVQ7xPs(continues on next page)

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As you can see, the signature generated by the old ZSK (17694) has disappeared, replaced by a new signature generated
from the new ZSK (51623).
Note: Not all signatures will disappear magically on the same day; it depends on when each one was generated. In theworst-case scenario, a new signature could have been signed by the old ZSK (17694) moments before it was deactivated,meaning that the signature could live for almost 30 more days, until just before February 1.
This is why it is important to keep the old ZSK in the zone and not delete it right away.

One Month After ZSK Rollover
Again, technically there is nothing you need to do on this day, but it doesn’t hurt to verify that the old ZSK (17694)
is now completely gone from your zone. named will not touch Kexample.com.+008+17694.private andKexample.com.+008+17694.key on your file system. Running the same dig command for DNSKEY should
suffice:$ dig @192.168.1.13 example.com. DNSKEY +multiline +dnssec...
;; ANSWER SECTION:
example.com.
600 IN DNSKEY 257 3 8 (AwEAAcWDps...lM3NRn/G/R) ; KSK; alg = RSASHA256; key id = 6817
example.com.
600 IN DNSKEY 256 3 8 (AwEAAdeCGr...1DnEfX+Xzn) ; ZSK; alg = RSASHA256; key id = 51623
example.com.
600 IN RRSIG DNSKEY 8 2 600 (
20170203000000 20170102230000 6817 example.com.
KHY8P0zE21...Y3szrmjAM= )example.com.
600 IN RRSIG DNSKEY 8 2 600 (
20170203000000 20170102230000 51623 example.com.
G2g3crN17h...Oe4gw6gH8= )...

Congratulations, the ZSK rollover is complete! As for the actual key files (the files ending in .key and .private),
they may be deleted at this point, but they do not have to be.
KSK Rollover
This recipe describes how to perform KSK rollover using the Double-DS method. For other KSK rolling methods, please
see KSK Rollover Methods in Advanced Discussions. The registrar used in this recipe is GoDaddy. Also for this recipe,
we are keeping the number of DS records down to just one per active set using just SHA-1, for the sake of better clarity,
although in practice most zone operators choose to upload two DS records as shown in Working With the Parent Zone.
For more information on key management and rollovers, please see Rollovers.
Below is a sample timeline for a KSK rollover to occur on January 1, 2021:
1. December 1, 2020 (one month before rollover)• Change timer on the current KSK

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• Upload new DS records to parent zone
2. January 1, 2021 (day of rollover)• Use the new KSK to sign all DNSKEY RRsets, which generates new RRSIGs• Add new RRSIGs to the zone
• Remove RRSIG for the old ZSK from zone
• Start using the new KSK to sign DNSKEY
3. February 1, 2021 (one month after rollover)• Remove the old KSK DNSKEY from zone
• Remove old DS records from parent zone
The current active KSK has the ID 24828, and this is the DS record that has already been published by the parent zone:# dnssec-dsfromkey -a SHA-1 Kexample.com.+007+24828.key
example.com. IN DS 24828 7 1 D4A33E8DD550A9567B4C4971A34AD6C4B80A6AD3

One Month Before KSK Rollover
On December 1, 2020, a month before the planned rollover, you (as administrator) should change the parameters on thecurrent key. Set it to become inactive on January 1, 2021, and be deleted from the zone on February 1st, 2021; also
generate a successor key (23550). Finally, generate a new DS record based on the new key, 23550:# cd /etc/bind/keys/example.com/# dnssec-settime -I 20210101 -D 20210201 Kexample.com.+007+24828./Kexample.com.+007+24848.key./Kexample.com.+007+24848.private# dnssec-keygen -S Kexample.com.+007+24848
Generating key pair...................................................................
,→....................++ ...................................++
Kexample.com.+007+23550# dnssec-dsfromkey -a SHA-1 Kexample.com.+007+23550.key
example.com. IN DS 23550 7 1 54FCF030AA1C79C0088FDEC1BD1C37DAA2E70DFB

The first command gets us into the key directory /etc/bind/keys/example.com/, where keys for example.
com are stored.
The second, dnssec-settime, sets an inactive (-I) date of January 1, 2021, and a deletion (-D) date of February 1,
2021 for the current KSK (Kexample.com.+007+24848).
The third command, dnssec-keygen, creates a successor key, using the exact same parameters (algorithms, key sizes,etc.) as the current KSK. The new key pair created in our example is Kexample.com.+007+23550.
The fourth and final command, dnssec-dsfromkey, creates a DS record from the new KSK (23550), using SHA-1
as the digest type. Again, in practice most people generate two DS records for both supported digest types (SHA-1 andSHA-256), but for our example here we are only using one to keep the output small and hopefully clearer.
Make sure the successor keys are readable by named.
The syslog message indicates when the next key checking event is. The log message looks like this:12.8. Recipes

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zone example.com/IN (signed): next key event: 01-Dec-2020 00:13:05.385

You can check the publish date of the key by looking at the key file:# cd /etc/bind/keys/example.com# cat Kexample.com.+007+23550.key; This is a key-signing key, keyid 23550, for example.com.
; Created: 20201130160024 (Thu Dec 1 00:00:24 2020); Publish: 20201202000000 (Fri Dec 2 08:00:00 2020); Activate: 20210101000000 (Sun Jan 1 08:00:00 2021)...

Since the publish date is set to the morning of December 2, and our example scenario takes place on December 1, thenext morning you will notice that your zone has gained a new DNSKEY record based on your new KSK, but with nocorresponding RRSIG yet. Below is the abbreviated output - with shortened DNSKEY and RRSIG - when querying theauthoritative name server, 192.168.1.13:$ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline...
;; ANSWER SECTION:
example.com.
300 IN DNSKEY 256 3 7 (AwEAAdYqAc...TiSlrma6Ef) ; ZSK; alg = NSEC3RSASHA1; key id = 29747
example.com.
300 IN DNSKEY 257 3 7 (AwEAAeTJ+w...O+Zy9j0m63) ; KSK; alg = NSEC3RSASHA1; key id = 24828
example.com.
300 IN DNSKEY 257 3 7 (AwEAAc1BQN...Wdc0qoH21H) ; KSK; alg = NSEC3RSASHA1; key id = 23550
example.com.
300 IN RRSIG DNSKEY 7 2 300 (20201206125617 20201107115617 24828 example.com.
4y1iPVJOrK...aC3iF9vgc= )example.com.
300 IN RRSIG DNSKEY 7 2 300 (20201206125617 20201107115617 29747 example.com.
g/gfmPjr+y...rt/S/xjPo= )...

Anytime after generating the DS record, you can upload it; it is not necessary to wait for the DNSKEY to be published inyour zone, since this new KSK is not active yet. You can do it immediately after the new DS record has been generated
on December 1, or you can wait until the next day after you have verified that the new DNSKEY record is added to thezone. Below are some screenshots from GoDaddy’s web-based interface, used to add a new DS record9 .
1. After logging in, click the green “Launch” button next to the domain name you want to manage.
2. Scroll down to the “DS Records” section and click “Manage.”
3. A dialog appears, displaying the current key (24828). Click “Add DS Record.”
4. Enter the Key ID, algorithm, digest type, and the digest, then click “Next.”
5. Address any errors and click “Finish.”
6. Both DS records are shown. Click “Save.”
9 The screenshots were taken from GoDaddy’s interface at the time the original version of this guide was published (2015). It may have changed

since then.

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Fig. 7: Upload DS Record Step #1

Fig. 8: Upload DS Record Step #2

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Fig. 9: Upload DS Record Step #3

Fig. 10: Upload DS Record Step #4

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Fig. 11: Upload DS Record Step #5

Fig. 12: Upload DS Record Step #6

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Finally, let’s verify that the registrar has published the new DS record. This may take anywhere from a few minutes to afew days, depending on your parent zone. You can verify whether your parent zone has published the new DS record by
querying for the DS record of your zone. In the example below, the Google public DNS server 8.8.8.8 is used:$ dig @8.8.8.8 example.com. DS...
;; ANSWER SECTION:
example.com.
21552
example.com.
21552

IN
IN

DS
DS

24828 7 1 D4A33E8DD550A9567B4C4971A34AD6C4B80A6AD323550 7 1 54FCF030AA1C79C0088FDEC1BD1C37DAA2E70DFB

You can also query your parent zone’s authoritative name servers directly to see if these records have been published. DS
records will not show up on your own authoritative zone, so you cannot query your own name servers for them. In thisrecipe, the parent zone is .com, so querying a few of the .com name servers is another appropriate verification.
Day of KSK Rollover
If you have followed the examples in this document, as described in Easy-Start Guide for Signing Authoritative Zones,
there is technically nothing you need to do manually on the actual day of the rollover. However, you should still keep an
eye on the zone to make sure new signature(s) are being generated by the new KSK (23550 in this example). The easiest
way is to query the authoritative name server 192.168.1.13 for the same DNSKEY and signatures, as you did a monthago:$ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline...
;; ANSWER SECTION:
example.com.
300 IN DNSKEY 256 3 7 (AwEAAdYqAc...TiSlrma6Ef) ; ZSK; alg = NSEC3RSASHA1; key id = 29747
example.com.
300 IN DNSKEY 257 3 7 (AwEAAeTJ+w...O+Zy9j0m63) ; KSK; alg = NSEC3RSASHA1; key id = 24828
example.com.
300 IN DNSKEY 257 3 7 (AwEAAc1BQN...Wdc0qoH21H) ; KSK; alg = NSEC3RSASHA1; key id = 23550
example.com.
300 IN RRSIG DNSKEY 7 2 300 (
20210201074900 20210101064900 23550 mydnssecgood.org.
S6zTbBTfvU...Ib5eXkbtE= )example.com.
300 IN RRSIG DNSKEY 7 2 300 (
20210105074900 20201206064900 29747 mydnssecgood.org.
VY5URQA2/d...OVKr1+KX8= )...

As you can see, the signature generated by the old KSK (24828) has disappeared, replaced by a new signature generated
from the new KSK (23550).

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One Month After KSK Rollover
While the removal of the old DNSKEY from the zone should be automated by named, the removal of the DS record
is manual. You should make sure the old DNSKEY record is gone from your zone first, by querying for the DNSKEY
records of the zone; this time we expect not to see the key with an ID of 24828:$ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline...
;; ANSWER SECTION:
example.com.
300 IN DNSKEY 256 3 7 (AwEAAdYqAc...TiSlrma6Ef) ; ZSK; alg = NSEC3RSASHA1; key id = 29747
example.com.
300 IN DNSKEY 257 3 7 (AwEAAc1BQN...Wdc0qoH21H) ; KSK; alg = NSEC3RSASHA1; key id = 23550
example.com.
300 IN RRSIG DNSKEY 7 2 300 (
20210208000000 20210105230000 23550 mydnssecgood.org.
Qw9Em3dDok...bNCS7KISw= )example.com.
300 IN RRSIG DNSKEY 7 2 300 (
20210208000000 20210105230000 29747 mydnssecgood.org.
OuelpIlpY9...XfsKupQgc= )...

Since the key with the ID 24828 is gone, you can now remove the old DS record for that key from our parent zone. Be
careful to remove the correct DS record. If you accidentally remove the new DS record(s) with key ID 23550, it could
lead to a problem called “security lameness,” as discussed in Security Lameness, and may cause users to be unable toresolve any names in the zone.
1. After logging in (again, GoDaddy.com in our example) and launching the domain, scroll down to the “DS Records”
section and click Manage.
2. A dialog appears, displaying both keys (24828 and 23550). Use the far right-hand X button to remove key 24828.
3. Key 24828 now appears crossed out; click “Save” to complete the removal.
Congratulations, the KSK rollover is complete! As for the actual key files (ending in .key and .private), they may
be deleted at this point, but they do not have to be.

12.8.3 NSEC and NSEC3
Migrating from NSEC to NSEC3This recipe describes how to transition from using NSEC to NSEC3, as described in Proof of Non-Existence (NSEC andNSEC3). This recipe assumes that the zones are already signed, and that named is configured according to the steps
described in Easy-Start Guide for Signing Authoritative Zones.
Warning: If your zone is signed with RSASHA1 (algorithm 5), you cannot migrate to NSEC3 without also performing an algorithm rollover to RSASHA1-NSEC3-SHA1 (algorithm 7), as described in Algorithm Rollovers. This
ensures that older validating resolvers that do not understand NSEC3 will fall back to treating the zone as unsecured(rather than “bogus”), as described in Section 2 of RFC 5155.
To enable NSEC3, update your dnssec-policy and add the desired NSEC3 parameters. The example below enables
NSEC3 for zones with the standard DNSSEC policy, using 0 additional iterations, no opt-out, and a zero-length salt:

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Fig. 13: Remove DS Record Step #1

Fig. 14: Remove DS Record Step #2

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Fig. 15: Remove DS Record Step #3

dnssec-policy "standard" {nsec3param iterations 0 optout no salt-length 0;};

Then reconfigure the server with rndc. You can tell that it worked if you see the following debug log messages:
Oct 21 13:47:21 received control channel command 'reconfig'
Oct 21 13:47:21 zone example.com/IN (signed): zone_addnsec3chain(1,CREATE,0,-)You can also verify that it worked by querying for a name that you know does not exist, and checking for the presence of
the NSEC3 record. For example:$ dig @192.168.1.13 thereisnowaythisexists.example.com. A +dnssec +multiline...
5A03TL362CS8VSIH69CVA4MJIKRHFQH3.example.com. 300 IN NSEC3 1 0 0 - (TQ9QBEGA6CROHEOC8KIH1A2C06IVQ5ER
NS SOA RRSIG DNSKEY NSEC3PARAM )...

Our example used four parameters: 1, 0, 0, and -, in order. 1 represents the algorithm, 0 represents the opt-out flag, 0represents the number of additional iterations, and - denotes no salt is used. To learn more about each of these parameters,
please see NSEC3PARAM.
Migrating from NSEC3 to NSEC
Migrating from NSEC3 back to NSEC is easy; just remove the nsec3param configuration option from yourdnssec-policy and reconfigure the name server. You can tell that it worked if you see these messages in the log:
named[14093]: received control channel command 'reconfig'
named[14093]: zone example.com/IN: zone_addnsec3chain(1,REMOVE,0,-)You can also query for a name that you know does not exist, and you should no longer see any traces of NSEC3 records.

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BIND 9 Administrator Reference Manual, Release 9.20.0$ dig @192.168.1.13 reieiergiuhewhiouwe.example.com. A +dnssec +multiline...
example.com.
...
ns1.example.com.
...

300 IN NSEC aaa.example.com. NS SOA RRSIG NSEC DNSKEY
300 IN NSEC web.example.com. A RRSIG NSECNSEC3 Opt-Out
This recipe discusses how to enable and disable NSEC3 opt-out, and how to show the results of each action. As discussed
in NSEC3 Opt-Out, NSEC3 opt-out is a feature that can help conserve resources on parent zones with many delegations
that have not yet been signed.
Warning: NSEC3 Opt-Out feature brings benefit only to _extremely_ large zones with lots of insecure delegations.
It’s use is counterproductive in all other cases as it decreases tamper-resistance of the zone and also decreases efficiencyof resolver cache (see RFC 8198).
In other words, don’t enable Opt-Out unless you are serving an equivalent of com. zone.
Because the NSEC3PARAM record does not keep track of whether opt-out is used, it is hard to check whether changes
need to be made to the NSEC3 chain if the flag is changed. Similar to changing the NSEC3 salt, your best option is
to change the value of optout together with another NSEC3 parameter, like iterations, and in a following step
restore the iterations value.
For this recipe we assume the zone example.com has the following four entries (for this example, it is not relevant
what record types these entries are):• ns1.example.com• ftp.example.com• www.example.com• web.example.com
And the zone example.com has five delegations to five subdomains, only one of which is signed and has a valid DS
RRset:• aaa.example.com, not signed• bbb.example.com, signed• ccc.example.com, not signed• ddd.example.com, not signed• eee.example.com, not signed
Before enabling NSEC3 opt-out, the zone example.com contains ten NSEC3 records; below is the list with the plain
text name before the actual NSEC3 record:• aaa.example.com: IFA1I3IE7EKCTPHM6R58URO3Q846I52M.example.com• bbb.example.com: ROJUF3VJSJO6LQ2LC1DNSJ5GBAUJPVHE.example.com• ccc.example.com: 0VPUT696LUVDPDS5NIHSHBH9KLV20V5K.example.com• ddd.example.com: UHPBD5U4HRGB84MLC2NQOVEFNAKJU0CA.example.com

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We can enable NSEC3 opt-out with the following configuration, changing the optout configuration value from no toyes:
dnssec-policy "standard" {nsec3param iterations 0 optout yes salt-length 0;};

After NSEC3 opt-out is enabled, the number of NSEC3 records is reduced. Notice that the unsigned delegations aaa,
ccc, ddd, and eee no longer have corresponding NSEC3 records.
• bbb.example.com: ROJUF3VJSJO6LQ2LC1DNSJ5GBAUJPVHE.example.com• ftp.example.com: 8P15KCUAT1RHCSDN46HBQVPI5T532IN1.example.com• ns1.example.com: GUFVRA2SFIO8RSFP7UO41E8AD1KR41FH.example.com• web.example.com: CVQ4LA4ALPQIAO2H3N2RB6IR8UHM91E7.example.com• www.example.com: MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK.example.com• example.com: ONIB9MGUB9H0RML3CDF5BGRJ59DKJHVK.example.com
To undo NSEC3 opt-out, change the configuration again:
dnssec-policy "standard" {nsec3param iterations 0 optout no salt-length 0;};

Note: NSEC3 hashes the plain text domain name, and we can compute our own hashes using the tool nsec3hash. For
example, to compute the hashed name for www.example.com using the parameters we listed above, we can execute
this command:# nsec3hash - 1 0 www.example.com.
MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK (salt=-, hash=1, iterations=0)

12.8.4 Reverting to Unsigned
This recipe describes how to revert from a signed zone (DNSSEC) back to an unsigned (DNS) zone.
Here is what named.conf looks like when it is signed:zone "example.com" IN {type primary;file "db/example.com.db";
dnssec-policy "default";};

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To indicate the reversion to unsigned, change the dnssec-policy line:
zone "example.com" IN {type primary;file "db/example.com.db";
dnssec-policy "insecure";};

Then use rndc reload to reload the zone.
The “insecure” policy is a built-in policy (like “default”). It makes sure the zone is still DNSSEC-maintained, to allow
for a graceful transition to unsigned. It also publishes the CDS and CDNSKEY DELETE records automatically at theappropriate time.
If the parent zone allows management of DS records via CDS/CDNSKEY, as described in RFC 8078, the DS record
should be removed from the parent automatically.
Otherwise, DS records can be removed via the registrar. Below is an example showing how to remove DS records using
the GoDaddy web-based interface:
1. After logging in, click the green “Launch” button next to the domain name you want to manage.

Fig. 16: Revert to Unsigned Step #1

2. Scroll down to the “DS Records” section and click Manage.

3. A dialog appears, displaying all current keys. Use the far right-hand X button to remove each key.

4. Click Save.

When the DS records have been removed from the parent zone, use rndc dnssec -checkds -key id withdrawn example.com to tell named that the DS is removed, and the remaining DNSSEC records will be removed ina timely manner. Or, if parental agents are configured, the DNSSEC records will be automatically removed after BIND
has seen that the parental agents no longer serve the DS RRset for this zone.
After a while, the zone is reverted back to the traditional, insecure DNS format. This can be verified by checking that all
DNSKEY and RRSIG records have been removed from the zone.
The dnssec-policy line can then be removed from named.conf and the zone reloaded. The zone will no longer
be subject to any DNSSEC maintenance.
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Fig. 17: Revert to Unsigned Step #2

Fig. 18: Revert to Unsigned Step #3

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Fig. 19: Revert to Unsigned Step #4

12.9 Commonly Asked Questions
Below are some common questions and (hopefully) some answers that help.
Do I need IPv6 to have DNSSEC?
No. DNSSEC can be deployed without IPv6.
Does DNSSEC encrypt my DNS traffic, so others cannot eavesdrop on my DNS queries?
No. Although cryptographic keys and digital signatures are used in DNSSEC, they only provide authenticity andintegrity, not privacy. Someone who sniffs network traffic can still see all the DNS queries and answers in plain
text; DNSSEC just makes it very difficult for the eavesdropper to alter or spoof the DNS responses. For protection
against eavesdropping, the preferred protocol is DNS-over-TLS. DNS-over-HTTPS can also do the job, but it ismore complex.
If I deploy DNS-over-TLS/HTTPS, can I skip deploying DNSSEC?
No. DNS-over-encrypted-transport stops eavesdroppers on a network, but it does not protect against cache poisoning and answer manipulation in other parts of the DNS resolution chain. In other words, these technologies
offer protection only for records when they are in transit between two machines; any compromised server can still
redirect traffic elsewhere (or simply eavesdrop). However, DNSSEC provides integrity and authenticity for DNS
records, even when these records are stored in caches and on disks.
Does DNSSEC protect the communication between my laptop and my name server?
Unfortunately, not at the moment. DNSSEC is designed to protect the communication between end clients (laptop)
and name servers; however, there are few applications or stub resolver libraries as of mid-2020 that take advantageof this capability.
Does DNSSEC secure zone transfers?
No. You should consider using TSIG to secure zone transfers among your name servers.
Does DNSSEC protect my network from malicious websites?
DNSSEC makes it much more difficult for attackers to spoof DNS responses or perform cache poisoning. It
cannot protect against users who visit a malicious website that an attacker owns and operates, or prevent users frommistyping a domain name; it will just become less likely that an attacker can hijack other domain names.
In other words, DNSSEC is designed to provide confidence that when a DNS response is received forwww.company.com over port 53, it really came from Company’s name servers and the answers are authentic.
But that does not mean the web server a user visits over port 80 or port 443 is necessarily safe.
If I enable DNSSEC validation, will it break DNS lookup, since most domain names do not yet use DNSSEC?
No, DNSSEC is backwards-compatible to “standard” DNS. A DNSSEC-enabled validating resolver can still lookup all of these domain names as it always has under standard DNS.
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There are four (4) categories of responses (see RFC 4035):
SecureDomains that have DNSSEC deployed correctly.
Insecure
Domains that have yet to deploy DNSSEC.
Bogus
Domains that have deployed DNSSEC but have done it incorrectly.
Indeterminate
Domains for which it is not possible to determine whether these domains use DNSSEC.
A DNSSEC-enabled validating resolver still resolves Secure and Insecure; only Bogus and Indeterminate result in a
SERVFAIL. As of mid-2022, roughly one-third of users worldwide are using DNSSEC validation on their recursive
name servers. Google public DNS (8.8.8.8) also has enabled DNSSEC validation.
Do I need to have special client software to use DNSSEC?
No. DNSSEC only changes the communication behavior among DNS servers, not between a DNS server (validating
resolver) and a client (stub resolver). With DNSSEC validation enabled on your recursive server, if a domain namedoes not pass the checks, an error message (typically SERVFAIL) is returned to clients; to most client software
today, it appears that the DNS query has failed or that the domain name does not exist.
Since DNSSEC uses public key cryptography, do I need Public Key Infrastructure (PKI) in order to use
DNSSEC?
No, DNSSEC does not depend on an existing PKI. Public keys are stored within the DNS hierarchy; the trustworthiness of each zone is guaranteed by its parent zone, all the way back to the root zone. A copy of the trust anchor
for the root zone is distributed with BIND 9.
Do I need to purchase SSL certificates from a Certificate Authority (CA) to use DNSSEC?
No. With DNSSEC, you generate and publish your own keys, and sign your own data as well. There is no need to
pay someone else to do it for you.
My parent zone does not support DNSSEC; can I still sign my zone?
Technically, yes, but you will not get the full benefit of DNSSEC, as other validating resolvers are not able tovalidate your zone data. Without the DS record(s) in your parent zone, other validating resolvers treat your zone
as an insecure (traditional) zone, and no actual verification is carried out. To the rest of the world, your zone still
appears to be insecure, and it will continue to be insecure until your parent zone can host the DS record(s) for you
and tell the rest of the world that your zone is signed.
Is DNSSEC the same thing as TSIG?
No. TSIG is typically used between primary and secondary name servers to secure zone transfers, while DNSSEC
secures DNS lookup by validating answers. Even if you enable DNSSEC, zone transfers are still not validated; tosecure the communication between your primary and secondary name servers, consider setting up TSIG or similar
secure channels.
How are keys copied from primary to secondary server(s)?
DNSSEC uses public cryptography, which results in two types of keys: public and private. The public keys arepart of the zone data, stored as DNSKEY record types. Thus the public keys are synchronized from primary to
secondary server(s) as part of the zone transfer. The private keys are not, and should not be, stored anywhere otherthan secured on the primary server. See Key Storage for more information on key storage options and considerations.
Can I use the same key for multiple zones?
Yes and no. Good security practice suggests that you should use unique key pairs for each zone, just as you shouldhave different passwords for your email account, social media login, and online banking credentials. On a technicallevel, it is completely feasible to reuse a key, but multiple zones are at risk if one key pair is compromised. However,
if you have hundreds or thousands of zones to administer, a single key pair for all might be less error-prone tomanage. You may choose to use the same approach as with password management: use unique passwords for yourbank accounts and shopping sites, but use a standard password for your not-very-important logins. First, categorize

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your zones: high-value zones (or zones that have specific key rollover requirements) get their own key pairs, whileother, more “generic” zones can use a single key pair for easier management. Note that at present (mid-2020), fully
automatic signing (using the dnssec-policy clause in your named configuration file) does not support reuseof keys except when the same zone appears in multiple views (see next question). To use the same key for multiple
zones, sign your zones using semi-automatic signing. Each zone wishing to use the key should point to the same
key directory.
How do I sign the different instances of a zone that appears in multiple views?
Add a dnssec-policy statement to each zone definition in the configuration file. To avoid problems when asingle computer accesses different instances of the zone while information is still in its cache (e.g., a laptop movingfrom your office to a customer site), you should sign all instances with the same key. This means setting the same
DNSSEC policy for all instances of the zone, and making sure that the key directory is the same for all instancesof the zone.
Will there be any problems if I change the DNSSEC policy for a zone?
If you are using fully automatic signing, no. Just change the parameters in the dnssec-policy statement andreload the configuration file. named makes a smooth transition to the new policy, ensuring that your zone remains
valid at all times.

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CHAPTERTHIRTEEN

A BRIEF HISTORY OF THE DNS AND BIND

Although the Domain Name System “officially” began in 1984 with the publication of RFC 920, the core of the new
system was described in 1983 in RFC 882 and RFC 883. From 1984 to 1987, the ARPAnet (the precursor to today’s
Internet) became a testbed of experimentation for developing the new naming/addressing scheme in a rapidly expanding,operational network environment. New RFCs were written and published in 1987 that modified the original documents
to incorporate improvements based on the working model. RFC 1034, “Domain Names-Concepts and Facilities,” andRFC 1035, “Domain Names-Implementation and Specification,” were published and became the standards upon which
all DNS implementations are built.
The first working domain name server, called “Jeeves,” was written in 1983-84 by Paul Mockapetris for operation on
DEC Tops-20 machines located at the University of Southern California’s Information Sciences Institute (USC-ISI) and
SRI International’s Network Information Center (SRI-NIC). A DNS server for Unix machines, the Berkeley Internet
Name Domain (BIND) package, was written soon after by a group of graduate students at the University of California at
Berkeley under a grant from the US Defense Advanced Research Projects Administration (DARPA).
Versions of BIND through 4.8.3 were maintained by the Computer Systems Research Group (CSRG) at UC Berkeley.
Douglas Terry, Mark Painter, David Riggle, and Songnian Zhou made up the initial BIND project team. After that,
additional work on the software package was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment Corporation
employee on loan to the CSRG, worked on BIND for 2 years, from 1985 to 1987. Many other people also contributed
to BIND development during that time: Doug Kingston, Craig Partridge, Smoot Carl-Mitchell, Mike Muuss, Jim Bloom,
and Mike Schwartz. BIND maintenance was subsequently handled by Mike Karels and Øivind Kure.
BIND versions 4.9 and 4.9.1 were released by Digital Equipment Corporation (which became Compaq Computer Corporation and eventually merged with Hewlett-Packard). Paul Vixie, then a DEC employee, became BIND’s primary
caretaker. He was assisted by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan Beecher, Andrew Partan,
Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis,
Christophe Wolfhugel, and others.
In 1994, BIND version 4.9.2 was sponsored by Vixie Enterprises.
tect/programmer.

Paul Vixie became BIND’s principal archi-

BIND versions from 4.9.3 onward have been developed and maintained by Internet Systems Consortium and its predecessor, the Internet Software Consortium, with support provided by ISC’s sponsors.
As co-architects/programmers, Bob Halley and Paul Vixie released the first production-ready version of BIND version 8
in May 1997.
BIND version 9 was released in September 2000 and is a major rewrite of nearly all aspects of the underlying BIND
architecture.
BIND versions 4 and 8 are officially deprecated. No additional development is done on BIND version 4 or BIND version
8.
BIND development work is made possible today by the sponsorship of corporations who purchase professional support
services from ISC (https://www.isc.org/contact/) and/or donate to our mission, and by the tireless efforts of numerous
individuals.

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CHAPTERFOURTEEN

GENERAL DNS REFERENCE INFORMATION

14.1 Requests for Comment (RFCs)
Specification documents for the Internet protocol suite, including the DNS, are published as part of the Request forComments (RFCs) series of technical notes. The standards themselves are defined by the Internet Engineering Task Force(IETF) and the Internet Engineering Steering Group (IESG). RFCs can be viewed online at: https://www.rfc-editor.org/.
While reading RFCs, please keep in mind that not all RFCs are standards, and also that the validity of documents doeschange over time. Every RFC needs to be interpreted in the context of other documents.
BIND 9 strives for strict compliance with IETF standards. To the best of our knowledge, BIND 9 complies with thefollowing RFCs, with the caveats and exceptions listed in the numbered notes below. Many of these RFCs were written
by current or former ISC staff members. The list is non-exhaustive.
Some of these RFCs, though DNS-related, are not concerned with implementing software.

14.1.1 Protocol Specifications
RFC 1034 - P. Mockapetris. Domain Names — Concepts and Facilities. November 1987.
RFC 1035 - P. Mockapetris. Domain Names — Implementation and Specification. November 1987.12
RFC 1183 - C. F. Everhart, L. A. Mamakos, R. Ullmann, P. Mockapetris. New DNS RR Definitions. October 1990.
RFC 1706 - B. Manning and R. Colella. DNS NSAP Resource Records. October 1994.
RFC 1712 - C. Farrell, M. Schulze, S. Pleitner, and D. Baldoni. DNS Encoding of Geographical Location. November
1994.
RFC 1876 - C. Davis, P. Vixie, T. Goodwin, and I. Dickinson. A Means for Expressing Location Information in the
Domain Name System. January 1996.
RFC 1982 - R. Elz and R. Bush. Serial Number Arithmetic. August 1996.
RFC 1995 - M. Ohta. Incremental Zone Transfer in DNS. August 1996.
RFC 1996 - P. Vixie. A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY). August 1996.
RFC 2136 - P. Vixie, S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates in the Domain Name System (DNS
UPDATE). April 1997.
RFC 2163 - A. Allocchio. Using the Internet DNS to Distribute MIXER Conformant Global Address Mapping (MCGAM).
January 1998.
RFC 2181 - R. Elz and R. Bush. Clarifications to the DNS Specification. July 1997.
1 Queries to zones that have failed to load return SERVFAIL rather than a non-authoritative response. This is considered a feature.
2 CLASS ANY queries are not supported. This is considered a feature.

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RFC 2230 - R. Atkinson. Key Exchange Delegation Record for the DNS. November 1997.
RFC 2308 - M. Andrews. Negative Caching of DNS Queries (DNS NCACHE). March 1998.
RFC 2539 - D. Eastlake, 3rd. Storage of Diffie-Hellman Keys in the Domain Name System (DNS). March 1999.
RFC 2782 - A. Gulbrandsen, P. Vixie, and L. Esibov. A DNS RR for Specifying the Location of Services (DNS SRV).
February 2000.
RFC 2930 - D. Eastlake, 3rd. Secret Key Establishment for DNS (TKEY RR). September 2000.
RFC 2931 - D. Eastlake, 3rd. DNS Request and Transaction Signatures (SIG(0)s). September 2000.3
RFC 3007 - B. Wellington. Secure Domain Name System (DNS) Dynamic Update. November 2000.
RFC 3110 - D. Eastlake, 3rd. RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS). May 2001.
RFC 3123 - P. Koch. A DNS RR Type for Lists of Address Prefixes (APL RR). June 2001.
RFC 3225 - D. Conrad. Indicating Resolver Support of DNSSEC. December 2001.
RFC 3226 - O. Gudmundsson. DNSSEC and IPv6 A6 Aware Server/Resolver Message Size Requirements. December
2001.
RFC 3363 - R. Bush, A. Durand, B. Fink, O. Gudmundsson, and T. Hain. Representing Internet Protocol Version 6 (IPv6)
Addresses in the Domain Name System (DNS). August 2002.15
RFC 3403 - M. Mealling. Dynamic Delegation Discovery System (DDDS). Part Three: The Domain Name System (DNS)
Database. October 2002.
RFC 3492 - A. Costello. Punycode: A Bootstring Encoding of Unicode for Internationalized Domain Names in Applications(IDNA). March 2003.
RFC 3493 - R. Gilligan, S. Thomson, J. Bound, J. McCann, and W. Stevens. Basic Socket Interface Extensions for IPv6.
March 2003.
RFC 3496 - A. G. Malis and T. Hsiao. Protocol Extension for Support of Asynchronous Transfer Mode (ATM) Service
Class-aware Multiprotocol Label Switching (MPLS) Traffic Engineering. March 2003.
RFC 3596 - S. Thomson, C. Huitema, V. Ksinant, and M. Souissi. DNS Extensions to Support IP Version 6. October
2003.
RFC 3597 - A. Gustafsson. Handling of Unknown DNS Resource Record (RR) Types. September 2003.
RFC 3645 - S. Kwan, P. Garg, J. Gilroy, L. Esibov, J. Westhead, and R. Hall. Generic Security Service Algorithm for
Secret Key Transaction Authentication for DNS (GSS-TSIG). October 2003.
RFC 4025 - M. Richardson. A Method for Storing IPsec Keying Material in DNS. March 2005.
RFC 4033 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. DNS Security Introduction and Requirements.
March 2005.
RFC 4034 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. Resource Records for the DNS Security Extensions.
March 2005.
RFC 4035 - R. Arends, R. Austein, M. Larson, D. Massey, and S. Rose. Protocol Modifications for the DNS Security
Extensions. March 2005.
RFC 4255 - J. Schlyter and W. Griffin. Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints. January 2006.
RFC 4343 - D. Eastlake, 3rd. Domain Name System (DNS) Case Insensitivity Clarification. January 2006.
RFC 4398 - S. Josefsson. Storing Certificates in the Domain Name System (DNS). March 2006.
3 When receiving a query signed with a SIG(0), the server is only able to verify the signature if it has the key in its local authoritative data; it cannot
do recursion or validation to retrieve unknown keys.
15 Section 4 is ignored.

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RFC 4470 - S. Weiler and J. Ihren. Minimally covering NSEC Records and DNSSEC On-line Signing. April 2006.6
RFC 4509 - W. Hardaker. Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs). May 2006.
RFC 4592 - E. Lewis. The Role of Wildcards in the Domain Name System. July 2006.
RFC 4635 - D. Eastlake, 3rd. HMAC SHA (Hashed Message Authentication Code, Secure Hash Algorithm) TSIG Algorithm
Identifiers. August 2006.
RFC 4701 - M. Stapp, T. Lemon, and A. Gustafsson. A DNS Resource Record (RR) for Encoding Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR). October 2006.
RFC 4955 - D. Blacka. DNS Security (DNSSEC) Experiments. July 2007.7
RFC 5001 - R. Austein. DNS Name Server Identifier (NSID) Option. August 2007.
RFC 5011 - M. StJohns. Automated Updates of DNS Security (DNSSEC) Trust Anchors.
RFC 5155 - B. Laurie, G. Sisson, R. Arends, and D. Blacka. DNS Security (DNSSEC) Hashed Authenticated Denial of
Existence. March 2008.
RFC 5205 - P. Nikander and J. Laganier. Host Identity Protocol (HIP) Domain Name System (DNS) Extension. April
2008.
RFC 5452 - A. Hubert and R. van Mook. Measures for Making DNS More Resilient Against Forged Answers. January
2009.8
RFC 5702 - J. Jansen. Use of SHA-2 Algorithms with RSA in DNSKEY and RRSIG Resource Records for DNSSEC. October
2009.
RFC 5891 - J. Klensin. Internationalized Domain Names in Applications (IDNA): Protocol. August 2010
RFC 5936 - E. Lewis and A. Hoenes, Ed. DNS Zone Transfer Protocol (AXFR). June 2010.
RFC 5952 - S. Kawamura and M. Kawashima. A Recommendation for IPv6 Address Text Representation. August 2010.
RFC 6052 - C. Bao, C. Huitema, M. Bagnulo, M. Boucadair, and X. Li. IPv6 Addressing of IPv4/IPv6 Translators.
October 2010.
RFC 6147 - M. Bagnulo, A. Sullivan, P. Matthews, and I. van Beijnum. DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers. April 2011.9
RFC 6604 - D. Eastlake, 3rd. xNAME RCODE and Status Bits Clarification. April 2012.
RFC 6605 - P. Hoffman and W. C. A. Wijngaards. Elliptic Curve Digital Signature Algorithm (DSA) for DNSSEC. April
2012.10
RFC 6672 - S. Rose and W. Wijngaards. DNAME Redirection in the DNS. June 2012.
RFC 6698 - P. Hoffman and J. Schlyter. The DNS-Based Authentication of Named Entities (DANE) Transport Layer
Security (TLS) Protocol: TLSA. August 2012.
RFC 6725 - S. Rose. DNS Security (DNSSEC) DNSKEY Algorithm IANA Registry Updates. August 2012.11
RFC 6742 - RJ Atkinson, SN Bhatti, U. St. Andrews, and S. Rose. DNS Resource Records for the Identifier-Locator
Network Protocol (ILNP). November 2012.
6 Minimally Covering NSEC records are accepted but not generated.
7 BIND 9 interoperates with correctly designed experiments.
8 named only uses ports to extend the ID space; addresses are not used.
9 Section 5.5 does not match reality. named uses the presence of DO=1 to detect if validation may be occurring. CD has no bearing on whether

validation occurs.
10 Compliance is conditional on the OpenSSL library being linked against a supporting ECDSA.
11 RSAMD5 support has been removed. See RFC 8624.

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RFC 6840 - S. Weiler, Ed., and D. Blacka, Ed. Clarifications and Implementation Notes for DNS Security (DNSSEC).
February 2013.12
RFC 6891 - J. Damas, M. Graff, and P. Vixie. Extension Mechanisms for DNS (EDNS(0)). April 2013.
RFC 7043 - J. Abley. Resource Records for EUI-48 and EUI-64 Addresses in the DNS. October 2013.
RFC 7050 - T. Savolainen, J. Korhonen, and D. Wing. Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis.
November 2013.20
RFC 7208 - S. Kitterman. Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1. April
2014.
RFC 7314 - M. Andrews. Extension Mechanisms for DNS (EDNS) EXPIRE Option. July 2014.
RFC 7344 - W. Kumari, O. Gudmundsson, and G. Barwood. Automating DNSSEC Delegation Trust Maintenance.
September 2014.13
RFC 7477 - W. Hardaker. Child-to-Parent Synchronization in DNS. March 2015.
RFC 7553 - P. Faltstrom and O. Kolkman. The Uniform Resource Identifier (URI) DNS Resource Record. June 2015.
RFC 7583 - S. Morris, J. Ihren, J. Dickinson, and W. Mekking. DNSSEC Key Rollover Timing Considerations. October
2015.
RFC 7766 - J. Dickinson, S. Dickinson, R. Bellis, A. Mankin, and D. Wessels. DNS Transport over TCP - Implementation
Requirements. March 2016.
RFC 7828 - P. Wouters, J. Abley, S. Dickinson, and R. Bellis. The edns-tcp-keepalive EDNS0 Option. April 2016.
RFC 7830 - A. Mayrhofer. The EDNS(0) Padding Option. May 2016.14
RFC 7858 - Z. Hu, L. Zhu, J. Heidemann, A. Mankin, D. Wessels, and P. Hoffman. Specification for DNS over Transport
Layer Security (TLS). May 2016.21
RFC 7929 - P. Wouters. DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP. August 2016.
RFC 8078 - O. Gudmundsson and P. Wouters. Managing DS Records from the Parent via CDS/CDNSKEY. March 2017.22
RFC 8080 - O. Sury and R. Edmonds. Edwards-Curve Digital Security Algorithm (EdDSA) for DNSSEC. February 2017.
RFC 8484 - P. Hoffman and P. McManus. DNS Queries over HTTPS (DoH). October 2018.21
RFC 8509 - G. Huston, J. Damas, W. Kumari. A Root Key Trust Anchor Sentinel for DNSSEC. December 2018.
RFC 8624 - P. Wouters and O. Sury. Algorithm Implementation Requirements and Usage Guidance for DNSSEC. June2019.
RFC 8659 - P. Hallam-Baker, R. Stradling, and J. Hoffman-Andrews. DNS Certification Authority Authorization (CAA)
Resource Record. November 2019.
RFC 8880 - S. Cheshire and D. Schinazi. Special Use Domain Name ‘ipv4only.arpa’. August 2020.
RFC 8945 - F. Dupont, S. Morris, P. Vixie, D. Eastlake 3rd, O. Gudmundsson, and B. Wellington. Secret Key Transaction
Authentication for DNS (TSIG). November 2020.
RFC 9103 - W. Toorop, S. Dickinson, S. Sahib, P. Aras, and A. Mankin. DNS Zone Transfer over TLS. August 2021.23
12 Section 5.9 - Always set CD=1 on queries. This is not done, as it prevents DNSSEC from working correctly through another recursive server.

When talking to a recursive server, the best algorithm is to send CD=0 and then send CD=1 iff SERVFAIL is returned, in case the recursive server
has a bad clock and/or bad trust anchor. Alternatively, one can send CD=1 then CD=0 on validation failure, in case the recursive server is under attack
or there is stale/bogus authoritative data.
20 RFC 7050 is updated by RFC 8880.
13 Updating of parent zones is not yet implemented.
14 named does not currently encrypt DNS requests, so the PAD option is accepted but not returned in responses.
21 Forwarding DNS queries over encrypted transports is not supported yet.
22 Updating of parent zones is not yet implemented.
23 Strict TLS and Mutual TLS authentication mechanisms are not supported yet.

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RFC 9432 - P. van Dijk, L. Peltan, O. Sury, W. Toorop, C.R. Monshouwer, P. Thomassen, A. Sargsyan. DNS Catalog
Zones. July 2023.
RFC 9460 - B. Schwartz, M. Bishop and E. Nygren, Service Binding and Parameter Specification via the DNS (SVCB andHTTPS Resource Records). November 2023.

14.1.2 Best Current Practice RFCs
RFC 2219 - M. Hamilton and R. Wright. Use of DNS Aliases for Network Services. October 1997.
RFC 2317 - H. Eidnes, G. de Groot, and P. Vixie. Classless IN-ADDR.ARPA Delegation. March 1998.
RFC 2606 - D. Eastlake, 3rd and A. Panitz. Reserved Top Level DNS Names. June 1999.16
RFC 3901 - A. Durand and J. Ihren. DNS IPv6 Transport Operational Guidelines. September 2004.
RFC 5625 - R. Bellis. DNS Proxy Implementation Guidelines. August 2009.
RFC 6303 - M. Andrews. Locally Served DNS Zones. July 2011.
RFC 7793 - M. Andrews. Adding 100.64.0.0/10 Prefixes to the IPv4 Locally-Served DNS Zones Registry. May 2016.
RFC 8906 - M. Andrews and R. Bellis. A Common Operational Problem in DNS Servers: Failure to Communicate.
September 2020.
RFC 9276 - W. Hardaker and V. Dukhovni. Guidance for NSEC3 Parameter Settings. August 2022.

14.1.3 For Your Information
RFC 1101 - P. Mockapetris. DNS Encoding of Network Names and Other Types. April 1989.
RFC 1123 - R. Braden. Requirements for Internet Hosts - Application and Support. October 1989.
RFC 1535 - E. Gavron. A Security Problem and Proposed Correction With Widely Deployed DNS Software. October
1993.
RFC 1536 - A. Kumar, J. Postel, C. Neuman, P. Danzig, and S. Miller. Common DNS Implementation Errors and
Suggested Fixes. October 1993.
RFC 1912 - D. Barr. Common DNS Operational and Configuration Errors. February 1996.
RFC 2874 - M. Crawford and C. Huitema. DNS Extensions to Support IPv6 Address Aggregation and Renumbering. July
2000.4
RFC 3833 - D. Atkins and R. Austein. Threat Analysis of the Domain Name System (DNS). August 2004.
RFC 4074 - Y. Morishita and T. Jinmei. Common Misbehavior Against DNS Queries for IPv6 Addresses. June 2005.
RFC 4431 - M. Andrews and S. Weiler. The DNSSEC Lookaside Validation (DLV) DNS Resource Record. February
2006.5
RFC 4892 - S. Woolf and D. Conrad. Requirements for a Mechanism Identifying a Name Server Instance. June 2007.
RFC 6781 - O. Kolkman, W. Mekking, and R. Gieben. DNSSEC Operational Practices, Version 2. December 2012.
RFC 7129 - R. Gieben and W. Mekking. Authenticated Denial of Existence in the DNS. February 2014.
RFC 8749 - W. Mekking and D. Mahoney. Moving DNSSEC Lookaside Validation (DLV) to Historic Status. March 2020.
16 This does not apply to DNS server implementations.
4 Compliance is with loading and serving of A6 records only. A6 records were moved to the experimental category by RFC 3363.
5 Compliance is with loading and serving of DLV records only. DLV records were moved to the historic category by RFC 8749.

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14.2 Notes
14.3 Internet Drafts
Internet Drafts (IDs) are rough-draft working documents of the Internet Engineering Task Force (IETF). They are, in
essence, RFCs in the preliminary stages of development. Implementors are cautioned not to regard IDs as archival, andthey should not be quoted or cited in any formal documents unless accompanied by the disclaimer that they are “works
in progress.” IDs have a lifespan of six months, after which they are deleted unless updated by their authors.

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CHAPTERFIFTEENMANUAL PAGES

15.1 arpaname - translate IP addresses to the corresponding ARPAnames
15.1.1 Synopsis
arpaname {ipaddress …}

15.1.2 Description
arpaname translates IP addresses (IPv4 and IPv6) to the corresponding IN-ADDR.ARPA or IP6.ARPA names.

15.1.3 See Also
BIND 9 Administrator Reference Manual.

15.2 ddns-confgen - TSIG key generation tool
15.2.1 Synopsis
ddns-confgen [-a algorithm] [-h] [-k keyname] [-q] [-s name] [-z zone]

15.2.2 Description
ddns-confgen is an utility that generates keys for use in TSIG signing. The resulting keys can be used, for example,
to secure dynamic DNS updates to a zone, or for the rndc command channel.
The key name can specified using -k parameter and defaults to ddns-key. The generated key is accompanied byconfiguration text and instructions that can be used with nsupdate and named when setting up dynamic DNS, including an example update-policy statement. (This usage is similar to the rndc-confgen command for setting up
command-channel security.)
Note that named itself can configure a local DDNS key for use with nsupdate -l; it does this when a zone isconfigured with update-policy local;. ddns-confgen is only needed when a more elaborate configurationis required: for instance, if nsupdate is to be used from a remote system.

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15.2.3 Options-a algorithm
This option specifies the algorithm to use for the TSIG key. Available choices are: hmac-md5, hmac-sha1, hmacsha224, hmac-sha256, hmac-sha384, and hmac-sha512. The default is hmac-sha256. Options are case-insensitive,
and the “hmac-” prefix may be omitted.
-hThis option prints a short summary of options and arguments.
-k keynameThis option specifies the key name of the DDNS authentication key. The default is ddns-key when neither the-s nor -z option is specified; otherwise, the default is ddns-key as a separate label followed by the argumentof the option, e.g., ddns-key.example.com. The key name must have the format of a valid domain name,consisting of letters, digits, hyphens, and periods.
-qThis option enables quiet mode, which prints only the key, with no explanatory text or usage examples. This isessentially identical to tsig-keygen.
-s nameThis option generates a configuration example to allow dynamic updates of a single hostname. The example
named.conf text shows how to set an update policy for the specified name using the “name” nametype. The default key name is ddns-key.name. Note that the “self” nametype cannot be used, since the name to be updated
may differ from the key name. This option cannot be used with the -z option.
-z zoneThis option generates a configuration example to allow dynamic updates of a zone. The example named.conf
text shows how to set an update policy for the specified zone using the “zonesub” nametype, allowing updates to all
subdomain names within that zone. This option cannot be used with the -s option.

15.2.4 See Also
nsupdate(1), named.conf(5), named(8), BIND 9 Administrator Reference Manual.

15.3 delv - DNS lookup and validation utility
15.3.1 Synopsis
delv [@server] [ [-4] | [-6] ] [-a anchor-file] [-b address] [-c class] [-d level] [-i] [-m] [-p port#] [-q name] [-t type] [-xaddr] [name] [type] [class] [queryopt…]
delv [-h]delv [-v]delv [queryopt…] [query…]

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15.3.2 Description
delv is a tool for sending DNS queries and validating the results, using the same internal resolver and validator logic as
named.
delv sends to a specified name server all queries needed to fetch and validate the requested data; this includes the original
requested query, subsequent queries to follow CNAME or DNAME chains, queries for DNSKEY, and DS records toestablish a chain of trust for DNSSEC validation. It does not perform iterative resolution, but simulates the behavior ofa name server configured for DNSSEC validating and forwarding.
By default, responses are validated using the built-in DNSSEC trust anchor for the root zone (“.”). Records returned bydelv are either fully validated or were not signed. If validation fails, an explanation of the failure is included in the
output; the validation process can be traced in detail. Because delv does not rely on an external server to carry out
validation, it can be used to check the validity of DNS responses in environments where local name servers may not be
trustworthy.
Unless it is told to query a specific name server, delv tries each of the servers listed in /etc/resolv.conf. If nousable server addresses are found, delv sends queries to the localhost addresses (127.0.0.1 for IPv4, ::1 for IPv6).
When no command-line arguments or options are given, delv performs an NS query for “.” (the root zone).

15.3.3 Simple Usage
A typical invocation of delv looks like:delv @server name typewhere:
serveris the name or IP address of the name server to query. This can be an IPv4 address in dotted-decimal notation or
an IPv6 address in colon-delimited notation. When the supplied server argument is a hostname, delv resolves
that name before querying that name server (note, however, that this initial lookup is not validated by DNSSEC).
If no server argument is provided, delv consults /etc/resolv.conf; if an address is found there, it queries
the name server at that address. If either of the -4 or -6 options is in use, then only addresses for the correspondingtransport are tried. If no usable addresses are found, delv sends queries to the localhost addresses (127.0.0.1 for
IPv4, ::1 for IPv6).
nameis the domain name to be looked up.
type
indicates what type of query is required - ANY, A, MX, etc. type can be any valid query type. If no typeargument is supplied, delv performs a lookup for an A record.

15.3.4 Options-a anchor-file
This option specifies a file from which to read an alternate DNSSEC root zone trust anchor.
By default, keys that do not match the root zone name (.) are ignored. If an alternate key name is desired, it can be
specified using the +root option.
Note: When reading trust anchors, delv treats trust-anchors, initial-key, and static-key identically. That is, for a managed key, it is the initial key that is trusted; RFC 5011 key management is not supported.

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delv does not consult the managed-keys database maintained by named. This means that if the default key built
in to delv is revoked, delv must be updated to a newer version in order to continue validating.
-b addressThis option sets the source IP address of the query to address. This must be a valid address on one of the host’s
network interfaces, or 0.0.0.0, or ::. An optional source port may be specified by appending #<port>-c class
This option sets the query class for the requested data. Currently, only class “IN” is supported in delv and anyother value is ignored.
-d levelThis option sets the systemwide debug level to level. The allowed range is from 0 to 99. The default is 0 (nodebugging). Debugging traces from delv become more verbose as the debug level increases. See the +mtrace,+rtrace, and +vtrace options below for additional debugging details.
-hThis option displays the delv help usage output and exits.
-iThis option sets insecure mode, which disables internal DNSSEC validation. (Note, however, that this does not
set the CD bit on upstream queries. If the server being queried is performing DNSSEC validation, then it does
not return invalid data; this can cause delv to time out. When it is necessary to examine invalid data to debug a
DNSSEC problem, use dig +cd.)-mThis option enables memory usage debugging.
-p port#This option specifies a destination port to use for queries, instead of the standard DNS port number 53. This option
is used with a name server that has been configured to listen for queries on a non-standard port number.
-q nameThis option sets the query name to name. While the query name can be specified without using the -q option, it
is sometimes necessary to disambiguate names from types or classes (for example, when looking up the name “ns”,
which could be misinterpreted as the type NS, or “ch”, which could be misinterpreted as class CH).
-t typeThis option sets the query type to type, which can be any valid query type supported in BIND 9 except for zonetransfer types AXFR and IXFR. As with -q, this is useful to distinguish query-name types or classes when they
are ambiguous. It is sometimes necessary to disambiguate names from types.
The default query type is “A”, unless the -x option is supplied to indicate a reverse lookup, in which case it is“PTR”.
-v
This option prints the delv version and exits.
-x addrThis option performs a reverse lookup, mapping an address to a name. addr is an IPv4 address in dotted-decimal
notation, or a colon-delimited IPv6 address. When -x is used, there is no need to provide the name or typearguments; delv automatically performs a lookup for a name like 11.12.13.10.in-addr.arpa and sets
the query type to PTR. IPv6 addresses are looked up using nibble format under the IP6.ARPA domain.
-4This option forces delv to only use IPv4.
-6
This option forces delv to only use IPv6.
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15.3.5 Query Options
delv provides a number of query options which affect the way results are displayed, and in some cases the way lookups
are performed.
Each query option is identified by a keyword preceded by a plus sign (+). Some keywords set or reset an option. Thesemay be preceded by the string no to negate the meaning of that keyword. Other keywords assign values to options likethe timeout interval. They have the form +keyword=value. The query options are:+cdflag, +nocdflag
This option controls whether to set the CD (checking disabled) bit in queries sent by delv. This may be usefulwhen troubleshooting DNSSEC problems from behind a validating resolver. A validating resolver blocks invalid
responses, making it difficult to retrieve them for analysis. Setting the CD flag on queries causes the resolver toreturn invalid responses, which delv can then validate internally and report the errors in detail.
+class, +noclassThis option controls whether to display the CLASS when printing a record. The default is to display the CLASS.
+hint=FILE, +nohint
This option specifies a filename from which to load root hints; this will be used to find the root name servers whenname server mode (delv +ns) is in use. If the option is not specified, built-in root hints will be used.
+ns, +nons
This option toggles name server mode. When this option is in use, the delv process instantiates a full recursive resolver, and uses that to look up the requested query name and type. Turning on this option also activates +mtrace,+strace and +rtrace, so that every iterative query will be logged, including the full response messages fromeach authoritatve server. These logged messages will be written to stdout rather than stderr as usual, so thatthe full trace can be captured more easily.
This is intended to be similar to the behavior of dig +trace, but because it uses the same code as named,
it much more accurately replicates the behavior of a recursive name server with a cold cache that is processing arecursive query.
+qmin[=MODE], +noqmin
When used with +ns, this option enables QNAME minimization mode. Valid options of MODE are relaxedand strict. By default, QNAME minimization is disabled. If +qmin is specified but MODE is omitted, thenrelaxed mode will be used.
+ttl, +nottl
This option controls whether to display the TTL when printing a record. The default is to display the TTL.
+rtrace, +nortrace
This option toggles resolver fetch logging. This reports the name and type of each query sent by delv in theprocess of carrying out the resolution and validation process, including the original query and all subsequent queries
to follow CNAMEs and to establish a chain of trust for DNSSEC validation.
This is equivalent to setting the debug level to 1 in the “resolver” logging category. Setting the systemwide debug
level to 1 using the -d option produces the same output, but affects other logging categories as well.
+mtrace, +nomtrace
This option toggles logging of messages received. This produces a detailed dump of the responses received bydelv in the process of carrying out the resolution and validation process.
This is equivalent to setting the debug level to 10 for the “packets” module of the “resolver” logging category.
Setting the systemwide debug level to 10 using the -d option produces the same output, but affects other logging
categories as well.

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This option toggles logging of messages sent. This produces a detailed dump of the queries sent by delv in theprocess of carrying out the resolution and validation process. Turning on this option also activates +mtrace.
This is equivalent to setting the debug level to 11 for the “packets” module of the “resolver” logging category.
Setting the systemwide debug level to 11 using the -d option produces the same output, but affects other logging
categories as well.
+vtrace, +novtrace
This option toggles validation logging. This shows the internal process of the validator as it determines whether ananswer is validly signed, unsigned, or invalid.
This is equivalent to setting the debug level to 3 for the “validator” module of the “dnssec” logging category. Setting
the systemwide debug level to 3 using the -d option produces the same output, but affects other logging categories
as well.
+short, +noshortThis option toggles between verbose and terse answers. The default is to print the answer in a verbose form.
+comments, +nocomments
This option toggles the display of comment lines in the output. The default is to print comments.
+rrcomments, +norrcomments
This option toggles the display of per-record comments in the output (for example, human-readable key information
about DNSKEY records). The default is to print per-record comments.
+crypto, +nocrypto
This option toggles the display of cryptographic fields in DNSSEC records. The contents of these fields are unnecessary to debug most DNSSEC validation failures and removing them makes it easier to see the common failures.
The default is to display the fields. When omitted, they are replaced by the string [omitted] or, in the DNSKEY
case, the key ID is displayed as the replacement, e.g. [ key id = value ].
+trust, +notrust
This option controls whether to display the trust level when printing a record. The default is to display the trustlevel.
+split[=W], +nosplit
This option splits long hex- or base64-formatted fields in resource records into chunks of W characters (where W isrounded up to the nearest multiple of 4). +nosplit or +split=0 causes fields not to be split at all. The default
is 56 characters, or 44 characters when multiline mode is active.
+all, +noall
This option sets or clears the display options +comments, +rrcomments, and +trust as a group.
+multiline, +nomultiline
This option prints long records (such as RRSIG, DNSKEY, and SOA records) in a verbose multi-line format withhuman-readable comments. The default is to print each record on a single line, to facilitate machine parsing of thedelv output.
+dnssec, +nodnssec
This option indicates whether to display RRSIG records in the delv output. The default is to do so. Note that(unlike in dig) this does not control whether to request DNSSEC records or to validate them. DNSSEC records
are always requested, and validation always occurs unless suppressed by the use of -i or +noroot.
+root[=ROOT], +norootThis option indicates whether to perform conventional DNSSEC validation, and if so, specifies the name of a trust
anchor. The default is to validate using a trust anchor of “.” (the root zone), for which there is a built-in key. If
specifying a different trust anchor, then -a must be used to specify a file containing the key.
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BIND 9 Administrator Reference Manual, Release 9.20.0+tcp, +notcp
This option controls whether to use TCP when sending queries. The default is to use UDP unless a truncatedresponse has been received.
+unknownformat, +nounknownformat
This option prints all RDATA in unknown RR-type presentation format (RFC 3597). The default is to print
RDATA for known types in the type’s presentation format.
+yaml, +noyaml
This option prints response data in YAML format.

15.3.6 Files/etc/resolv.conf

15.3.7 See Alsodig(1), named(8), RFC 4034, RFC 4035, RFC 4431, RFC 5074, RFC 5155.

15.4 dig - DNS lookup utility
15.4.1 Synopsis
dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m] [-p port#] [-q name] [-t type] [-v] [-x addr] [-y[hmac:]name:key] [ [-4] | [-6] ] [name] [type] [class] [queryopt…]
dig [-h]dig [global-queryopt…] [query…]

15.4.2 Description
dig is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are
returned from the name server(s) that were queried. Most DNS administrators use dig to troubleshoot DNS problems
because of its flexibility, ease of use, and clarity of output. Other lookup tools tend to have less functionality than dig.
Although dig is normally used with command-line arguments, it also has a batch mode of operation for reading lookup
requests from a file. A brief summary of its command-line arguments and options is printed when the -h option is given.
The BIND 9 implementation of dig allows multiple lookups to be issued from the command line.
Unless it is told to query a specific name server, dig tries each of the servers listed in /etc/resolv.conf. If nousable server addresses are found, dig sends the query to the local host.
When no command-line arguments or options are given, dig performs an NS query for “.” (the root).
It is possible to set per-user defaults for dig via ${HOME}/.digrc. This file is read and any options in it are applied
before the command-line arguments. The -r option disables this feature, for scripts that need predictable behavior.
The IN and CH class names overlap with the IN and CH top-level domain names. Either use the -t and -c options to
specify the type and class, use the -q to specify the domain name, or use “IN.” and “CH.” when looking up these top-leveldomains.

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15.4.3 Simple Usage
A typical invocation of dig looks like:dig @server name typewhere:
serveris the name or IP address of the name server to query. This can be an IPv4 address in dotted-decimal notation or
an IPv6 address in colon-delimited notation. When the supplied server argument is a hostname, dig resolves
that name before querying that name server.
If no server argument is provided, dig consults /etc/resolv.conf; if an address is found there, it queries
the name server at that address. If either of the -4 or -6 options are in use, then only addresses for the corresponding transport are tried. If no usable addresses are found, dig sends the query to the local host. The reply
from the name server that responds is displayed.
nameis the name of the resource record that is to be looked up.
type
indicates what type of query is required - ANY, A, MX, SIG, etc. type can be any valid query type. If no typeargument is supplied, dig performs a lookup for an A record.

15.4.4 Options-4
This option indicates that only IPv4 should be used.
-6This option indicates that only IPv6 should be used.
-b address[#port]
This option sets the source IP address of the query. The address must be a valid address on one of the host’s
network interfaces, or “0.0.0.0” or “::”. An optional port may be specified by appending #port.
-c class
This option sets the query class. The default class is IN; other classes are HS for Hesiod records or CH for
Chaosnet records.
-f fileThis option sets batch mode, in which dig reads a list of lookup requests to process from the given file. Eachline in the file should be organized in the same way it would be presented as a query to dig using the command-line
interface.
-hPrint a usage summary.
-k keyfile
This option tells dig to sign queries using TSIG or SIG(0) using a key read from the given file. Key files canbe generated using tsig-keygen. When using TSIG authentication with dig, the name server that is queriedneeds to know the key and algorithm that is being used. In BIND, this is done by providing appropriate key andserver statements in named.conf for TSIG and by looking up the KEY record in zone data for SIG(0).

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BIND 9 Administrator Reference Manual, Release 9.20.0-mThis option enables memory usage debugging.
-p portThis option sends the query to a non-standard port on the server, instead of the default port 53. This option is used
to test a name server that has been configured to listen for queries on a non-standard port number.
-q nameThis option specifies the domain name to query. This is useful to distinguish the name from other arguments.
-rThis option indicates that options from ${HOME}/.digrc should not be read. This is useful for scripts that needpredictable behavior.
-t typeThis option indicates the resource record type to query, which can be any valid query type. If it is a resource record
type supported in BIND 9, it can be given by the type mnemonic (such as NS or AAAA). The default query type isA, unless the -x option is supplied to indicate a reverse lookup. A zone transfer can be requested by specifying atype of AXFR. When an incremental zone transfer (IXFR) is required, set the type to ixfr=N. The incrementalzone transfer contains all changes made to the zone since the serial number in the zone’s SOA record was N.
All resource record types can be expressed as TYPEnn, where nn is the number of the type. If the resource record
type is not supported in BIND 9, the result is displayed as described in RFC 3597.
-uThis option indicates that print query times should be provided in microseconds instead of milliseconds.
-v
This option prints the version number and exits.
-x addrThis option sets simplified reverse lookups, for mapping addresses to names. The addr is an IPv4 address indotted-decimal notation, or a colon-delimited IPv6 address. When the -x option is used, there is no need toprovide the name, class, and type arguments. dig automatically performs a lookup for a name like 94.
2.0.192.in-addr.arpa and sets the query type and class to PTR and IN respectively. IPv6 addresses arelooked up using nibble format under the IP6.ARPA domain.
-y [hmac:]keyname:secretThis option signs queries using TSIG with the given authentication key. keyname is the name of the key, and secret is the base64-encoded shared secret. hmac is the name of the key algorithm; valid choices are hmac-md5,
hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384, or hmac-sha512. If hmac is not specified, the default is hmac-md5; if MD5 was disabled, the default is hmac-sha256.
Note: Only the -k option should be used, rather than the -y option, because with -y the shared secret is supplied as acommand-line argument in clear text. This may be visible in the output from ps1 or in a history file maintained by theuser’s shell.

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15.4.5 Query Options
dig provides a number of query options which affect the way in which lookups are made and the results displayed. Someof these set or reset flag bits in the query header, some determine which sections of the answer get printed, and others
determine the timeout and retry strategies.
Each query option is identified by a keyword preceded by a plus sign (+). Some keywords set or reset an option; these
may be preceded by the string no to negate the meaning of that keyword. Other keywords assign values to options, likethe timeout interval. They have the form +keyword=value. Keywords may be abbreviated, provided the abbreviationis unambiguous; for example, +cd is equivalent to +cdflag. The query options are:+aaflag, +noaaflag
This option is a synonym for +aaonly, +noaaonly.
+aaonly, +noaaonly
This option sets the aa flag in the query.
+additional, +noadditional
This option displays [or does not display] the additional section of a reply. The default is to display it.
+adflag, +noadflag
This option sets [or does not set] the AD (authentic data) bit in the query. This requests the server to return whether
all of the answer and authority sections have been validated as secure, according to the security policy of the server.
AD=1 indicates that all records have been validated as secure and the answer is not from a OPT-OUT range. AD=0
indicates that some part of the answer was insecure or not validated. This bit is set by default.
+all, +noall
This option sets or clears all display flags.
+answer, +noanswer
This option displays [or does not display] the answer section of a reply. The default is to display it.
+authority, +noauthority
This option displays [or does not display] the authority section of a reply. The default is to display it.
+badcookie, +nobadcookie
This option retries the lookup with a new server cookie if a BADCOOKIE response is received.
+besteffort, +nobesteffort
This option attempts to display the contents of messages which are malformed. The default is to not display malformed answers.
+bufsize[=B]This option sets the UDP message buffer size advertised using EDNS0 to B bytes. The maximum and minimum
sizes of this buffer are 65535 and 0, respectively. +bufsize restores the default buffer size.
+cd, +cdflag, +nocdflag
This option sets [or does not set] the CD (checking disabled) bit in the query. This requests the server to not
perform DNSSEC validation of responses.
+class, +noclassThis option displays [or does not display] the CLASS when printing the record.
+cmd, +nocmd
This option toggles the printing of the initial comment in the output, identifying the version of dig and the query
options that have been applied. This option always has a global effect; it cannot be set globally and then overridden
on a per-lookup basis. The default is to print this comment.

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BIND 9 Administrator Reference Manual, Release 9.20.0+comments, +nocomments
This option toggles the display of some comment lines in the output, with information about the packet header and
OPT pseudosection, and the names of the response section. The default is to print these comments.
Other types of comments in the output are not affected by this option, but can be controlled using other commandline switches. These include +cmd, +question, +stats, and +rrcomments.
+cookie=####, +nocookie
This option sends [or does not send] a COOKIE EDNS option, with an optional value. Replaying a COOKIE froma previous response allows the server to identify a previous client. The default is +cookie.
+cookie is also set when +trace is set to better emulate the default queries from a nameserver.
+crypto, +nocrypto
This option toggles the display of cryptographic fields in DNSSEC records. The contents of these fields are unnecessary for debugging most DNSSEC validation failures and removing them makes it easier to see the common
failures. The default is to display the fields. When omitted, they are replaced by the string [omitted] or, in the
DNSKEY case, the key ID is displayed as the replacement, e.g. [ key id = value ].
+defname, +nodefnameThis option, which is deprecated, is treated as a synonym for +search, +nosearch.
+dns64prefix, +nodns64prefix
Lookup IPV4ONLY.ARPA AAAA and print any DNS64 prefixes found.
+dnssec, +do, +nodnssec, +nodo
This option requests that DNSSEC records be sent by setting the DNSSEC OK (DO) bit in the OPT record in the
additional section of the query.
+domain=somename
This option sets the search list to contain the single domain somename, as if specified in a domain directive in/etc/resolv.conf, and enables search list processing as if the +search option were given.
+edns[=#], +noedns
This option specifies the EDNS version to query with. Valid values are 0 to 255. Setting the EDNS version causes
an EDNS query to be sent. +noedns clears the remembered EDNS version. EDNS is set to 0 by default.
+ednsflags[=#], +noednsflags
This option sets the must-be-zero EDNS flags bits (Z bits) to the specified value. Decimal, hex, and octal encodings
are accepted. Setting a named flag (e.g., DO) is silently ignored. By default, no Z bits are set.
+ednsnegotiation, +noednsnegotiation
This option enables/disables EDNS version negotiation. By default, EDNS version negotiation is enabled.
+ednsopt[=code[:value]], +noednsopt
This option specifies the EDNS option with code point code and an optional payload of value as a hexadecimalstring. code can be either an EDNS option name (for example, NSID or ECS) or an arbitrary numeric value.
+noednsopt clears the EDNS options to be sent.
+expire, +noexpire
This option sends an EDNS Expire option.
+fail, +nofailThis option indicates that named should try [or not try] the next server if a SERVFAIL is received. The default is
to not try the next server, which is the reverse of normal stub resolver behavior.

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BIND 9 Administrator Reference Manual, Release 9.20.0+fuzztime[=value], +nofuzztime
This option allows the signing time to be specified when generating signed messages. If a value is specified it is theseconds since 00:00:00 January 1, 1970 UTC ignoring leap seconds. If no value is specified 1646972129 (Fri 11
Mar 2022 04:15:29 UTC) is used. The default is +nofuzztime and the current time is used.
+header-only, +noheader-onlyThis option sends a query with a DNS header without a question section. The default is to add a question section.
The query type and query name are ignored when this is set.
+https[=value], +nohttps
This option indicates whether to use DNS over HTTPS (DoH) when querying name servers. When this option isin use, the port number defaults to 443. The HTTP POST request mode is used when sending the query.
If value is specified, it will be used as the HTTP endpoint in the query URI; the default is /dns-query. So,for example, dig @example.com +https will use the URI https://example.com/dns-query.
+https-get[=value], +nohttps-get
Similar to +https, except that the HTTP GET request mode is used when sending the query.
+https-post[=value], +nohttps-postSame as +https.
+http-plain[=value], +nohttp-plain
Similar to +https, except that HTTP queries will be sent over a non-encrypted channel. When this option is inuse, the port number defaults to 80 and the HTTP request mode is POST.
+http-plain-get[=value], +nohttp-plain-get
Similar to +http-plain, except that the HTTP request mode is GET.
+http-plain-post[=value], +nohttp-plain-postSame as +http-plain.
+identify, +noidentify
This option shows [or does not show] the IP address and port number that supplied the answer, when the +short
option is enabled. If short form answers are requested, the default is not to show the source address and port numberof the server that provided the answer.
+idn, +noidn
Enable or disable IDN processing. By default IDN is enabled for input query names, and for display when the
output is a terminal.
You can also turn off dig’s IDN processing by setting the IDN_DISABLE environment variable.
+ignore, +noignore
This option ignores [or does not ignore] truncation in UDP responses instead of retrying with TCP. By default,
TCP retries are performed.
+keepalive, +nokeepalive
This option sends [or does not send] an EDNS Keepalive option.
+keepopen, +nokeepopen
This option keeps [or does not keep] the TCP socket open between queries, and reuses it rather than creating a new
TCP socket for each lookup. The default is +nokeepopen.
+multiline, +nomultiline
This option prints [or does not print] records, like the SOA records, in a verbose multi-line format with humanreadable comments. The default is to print each record on a single line to facilitate machine parsing of the dig
output.

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BIND 9 Administrator Reference Manual, Release 9.20.0+ndots=D
This option sets the number of dots (D) that must appear in name for it to be considered absolute. The default
value is that defined using the ndots statement in /etc/resolv.conf, or 1 if no ndots statement is present.
Names with fewer dots are interpreted as relative names, and are searched for in the domains listed in the searchor domain directive in /etc/resolv.conf if +search is set.
+nsid, +nonsid
When enabled, this option includes an EDNS name server ID request when sending a query.
+nssearch, +nonssearch
When this option is set, dig attempts to find the authoritative name servers for the zone containing the name being
looked up, and display the SOA record that each name server has for the zone. Addresses of servers that did not
respond are also printed.
+onesoa, +noonesoa
When enabled, this option prints only one (starting) SOA record when performing an AXFR. The default is to print
both the starting and ending SOA records.
+opcode=value, +noopcode
When enabled, this option sets (restores) the DNS message opcode to the specified value. The default value is
QUERY (0).
+padding=value
This option pads the size of the query packet using the EDNS Padding option to blocks of value bytes. For
example, +padding=32 causes a 48-byte query to be padded to 64 bytes. The default block size is 0, which
disables padding; the maximum is 512. Values are ordinarily expected to be powers of two, such as 128; however,this is not mandatory. Responses to padded queries may also be padded, but only if the query uses TCP or DNSCOOKIE.
+proxy[=src_addr[#src_port]-dst_addr[#dst_port]], +noproxy
When this option is set, dig adds PROXYv2 headers to the queries. When source and destination addresses are
specified, the headers contain them and use the PROXY command. It means for the remote peer that the queries
were sent on behalf of another node and that the PROXYv2 header reflects the original connection endpoints. The
default source port is 0 and destination port is 53.
For encrypted DNS transports, to prevent accidental information leakage, encryption is applied to the PROXYv2
headers: the headers are sent right after the handshake process has been completed.
For plain DNS transports, no encryption is applied to the PROXYv2 headers.
If the addressees are omitted, PROXYv2 headers, that use the LOCAL command set, are added instead. For the
remote peer, that means that the queries were sent on purpose without being relayed, so the real connection endpoint
addresses must be used.
+proxy-plain[=src_addr[#src_port]-dst_addr[#dst_port], +noproxy-plain
The same as +[no]proxy, but instructs dig to send PROXYv2 headers ahead of any encryption, before any
handshake messages are sent. That makes dig behave exactly how it is described in the PROXY protocol specification, but not all software expects such behaviour.
Please consult the software documentation to find out if you need this option. (for example, dnsdist expects
encrypted PROXYv2 headers sent over TLS when encryption is used, while HAProxy and many other software
packages expect plain ones).
For plain DNS transports the option is effectively an alias for the +[no]proxy described above.
+qid=value
This option specifies the query ID to use when sending queries.

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BIND 9 Administrator Reference Manual, Release 9.20.0+qr, +noqr
This option toggles the display of the query message as it is sent. By default, the query is not printed.
+question, +noquestion
This option toggles the display of the question section of a query when an answer is returned. The default is to print
the question section as a comment.
+raflag, +noraflag
This option sets [or does not set] the RA (Recursion Available) bit in the query. The default is +noraflag. Thisbit is ignored by the server for QUERY.
+rdflag, +nordflag
This option is a synonym for +recurse, +norecurse.
+recurse, +norecurseThis option toggles the setting of the RD (recursion desired) bit in the query. This bit is set by default, which means
dig normally sends recursive queries. Recursion is automatically disabled when the +nssearch or +trace
query option is used.
+retry=T
This option sets the number of times to retry UDP and TCP queries to server to T instead of the default, 2. Unlike+tries, this does not include the initial query.
+rrcomments, +norrcomments
This option toggles the display of per-record comments in the output (for example, human-readable key information
about DNSKEY records). The default is not to print record comments unless multiline mode is active.
+search, +nosearchThis option uses [or does not use] the search list defined by the searchlist or domain directive in resolv.conf,
if any. The search list is not used by default.
ndots from resolv.conf (default 1), which may be overridden by +ndots, determines whether the name istreated as relative and hence whether a search is eventually performed.
+short, +noshortThis option toggles whether a terse answer is provided. The default is to print the answer in a verbose form. This
option always has a global effect; it cannot be set globally and then overridden on a per-lookup basis.
+showbadcookie, +noshowbadcookie
This option toggles whether to show the message containing the BADCOOKIE rcode before retrying the request
or not. The default is to not show the messages.
+showsearch, +noshowsearchThis option performs [or does not perform] a search showing intermediate results.
+split=W
This option splits long hex- or base64-formatted fields in resource records into chunks of W characters (where W isrounded up to the nearest multiple of 4). +nosplit or +split=0 causes fields not to be split at all. The default
is 56 characters, or 44 characters when multiline mode is active.
+stats, +nostats
This option toggles the printing of statistics: when the query was made, the size of the reply, etc. The default
behavior is to print the query statistics as a comment after each lookup.
+subnet=addr[/prefix-length], +nosubnet
This option sends [or does not send] an EDNS CLIENT-SUBNET option with the specified IP address or network
prefix.

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dig +subnet=0.0.0.0/0, or simply dig +subnet=0 for short, sends an EDNS CLIENT-SUBNET
option with an empty address and a source prefix-length of zero, which signals a resolver that the client’s address
information must not be used when resolving this query.
+tcflag, +notcflag
This option sets [or does not set] the TC (TrunCation) bit in the query. The default is +notcflag. This bit isignored by the server for QUERY.
+tcp, +notcp
This option indicates whether to use TCP when querying name servers. The default behavior is to use UDP unlessa type any or ixfr=N query is requested, in which case the default is TCP. AXFR queries always use TCP. To
prevent retry over TCP when TC=1 is returned from a UDP query, use +ignore.
+timeout=T
This option sets the timeout for a query to T seconds. The default timeout is 5 seconds. An attempt to set T to lessthan 1 is silently set to 1.
+tls, +notls
This option indicates whether to use DNS over TLS (DoT) when querying name servers. When this option is inuse, the port number defaults to 853.
+tls-ca[=file-name], +notls-ca
This option enables remote server TLS certificate validation for DNS transports, relying on TLS. Certificate authorities certificates are loaded from the specified PEM file (file-name). If the file is not specified, the default
certificates from the global certificates store are used.
+tls-certfile=file-name, +tls-keyfile=file-name, +notls-certfile,+notls-keyfile
These options set the state of certificate-based client authentication for DNS transports, relying on TLS. Bothcertificate chain file and private key file are expected to be in PEM format. Both options must be specified at thesame time.
+tls-hostname=hostname, +notls-hostnameThis option makes dig use the provided hostname during remote server TLS certificate verification. Otherwise,
the DNS server name is used. This option has no effect if +tls-ca is not specified.
+trace, +notrace
This option toggles tracing of the delegation path from the root name servers for the name being looked up. Tracing
is disabled by default. When tracing is enabled, dig makes iterative queries to resolve the name being looked up.
It follows referrals from the root servers, showing the answer from each server that was used to resolve the lookup.
If @server is also specified, it affects only the initial query for the root zone name servers.
+dnssec is set when +trace is set, to better emulate the default queries from a name server.
Note that the delv +ns option can also be used for tracing the resolution of a name from the root (see delv).
+tries=T
This option sets the number of times to try UDP and TCP queries to server to T instead of the default, 3. If T isless than or equal to zero, the number of tries is silently rounded up to 1.
+ttlid, +nottlid
This option displays [or does not display] the TTL when printing the record.
+ttlunits, +nottlunits
This option displays [or does not display] the TTL in friendly human-readable time units of s, m, h, d, and w,
representing seconds, minutes, hours, days, and weeks. This implies +ttlid.

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BIND 9 Administrator Reference Manual, Release 9.20.0+unknownformat, +nounknownformat
This option prints all RDATA in unknown RR type presentation format (RFC 3597). The default is to print
RDATA for known types in the type’s presentation format.
+vc, +novc
This option uses [or does not use] TCP when querying name servers. This alternate syntax to +tcp is provided
for backwards compatibility. The vc stands for “virtual circuit.”+yaml, +noyaml
When enabled, this option prints the responses (and, if +qr is in use, also the outgoing queries) in a detailed YAML
format.
+zflag, +nozflag
This option sets [or does not set] the last unassigned DNS header flag in a DNS query. This flag is off by default.

15.4.6 Multiple Queries
The BIND 9 implementation of dig supports specifying multiple queries on the command line (in addition to supportingthe -f batch file option). Each of those queries can be supplied with its own set of flags, options, and query options.
In this case, each query argument represents an individual query in the command-line syntax described above. Eachconsists of any of the standard options and flags, the name to be looked up, an optional query type and class, and any
query options that should be applied to that query.
A global set of query options, which should be applied to all queries, can also be supplied. These global query options
must precede the first tuple of name, class, type, options, flags, and query options supplied on the command line. Any
global query options (except +cmd and +short options) can be overridden by a query-specific set of query options. For
example:dig +qr www.isc.org any -x 127.0.0.1 isc.org ns +noqr

shows how dig can be used from the command line to make three lookups: an ANY query for www.isc.org, a reverse
lookup of 127.0.0.1, and a query for the NS records of isc.org. A global query option of +qr is applied, so that dig
shows the initial query it made for each lookup. The final query has a local query option of +noqr which means thatdig does not print the initial query when it looks up the NS records for isc.org.

15.4.7 Return Codes
dig return codes are:0
DNS response received, including NXDOMAIN status
1
Usage error
8
Couldn’t open batch file9
No reply from server
10
Internal error

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15.4.8 Files/etc/resolv.conf${HOME}/.digrc

15.4.9 See Alsodelv(1), host(1), named(8), dnssec-keygen(8), RFC 1035.

15.4.10 Bugs
There are probably too many query options.

15.5 dnssec-cds - change DS records for a child zone based on
CDS/CDNSKEY
15.5.1 Synopsis
dnssec-cds [-a alg…] [-c class] [-D] {-d dsset-file} {-f child-file} [-i**[extension]] [-s** start-time] [-T ttl] [-u] [-vlevel] [-V] {domain}

15.5.2 Description
The dnssec-cds command changes DS records at a delegation point based on CDS or CDNSKEY records publishedin the child zone. If both CDS and CDNSKEY records are present in the child zone, the CDS is preferred. This enables a child zone to inform its parent of upcoming changes to its key-signing keys (KSKs); by polling periodically withdnssec-cds, the parent can keep the DS records up-to-date and enable automatic rolling of KSKs.
Two input files are required. The -f child-file option specifies a file containing the child’s CDS and/or CDNSKEY
records, plus RRSIG and DNSKEY records so that they can be authenticated. The -d path option specifies the locationof a file containing the current DS records. For example, this could be a dsset- file generated by dnssec-signzone,or the output of dnssec-dsfromkey, or the output of a previous run of dnssec-cds.
The dnssec-cds command uses special DNSSEC validation logic specified by RFC 7344. It requires that the CDS
and/or CDNSKEY records be validly signed by a key represented in the existing DS records. This is typically the preexisting KSK.
For protection against replay attacks, the signatures on the child records must not be older than they were on a previous
run of dnssec-cds. Their age is obtained from the modification time of the dsset- file, or from the -s option.
To protect against breaking the delegation, dnssec-cds ensures that the DNSKEY RRset can be verified by every key
algorithm in the new DS RRset, and that the same set of keys are covered by every DS digest type.
By default, replacement DS records are written to the standard output; with the -i option the input file is overwritten inplace. The replacement DS records are the same as the existing records, when no change is required. The output can be
empty if the CDS/CDNSKEY records specify that the child zone wants to be insecure.
Warning: Be careful not to delete the DS records when dnssec-cds fails!

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Alternatively, :option`dnssec-cds -u` writes an nsupdate script to the standard output. The -u and -i options can beused together to maintain a dsset- file as well as emit an nsupdate script.

15.5.3 Options-a algorithm
When converting CDS records to DS records, this option specifies the acceptable digest algorithms. This option
can be repeated, so that multiple digest types are allowed. If none of the CDS records use an acceptable digest
type, dnssec-cds will try to use CDNSKEY records instead; if there are no CDNSKEY records, it reports anerror.
When converting CDNSKEY records to DS records, this option specifies the digest algorithm to use. It can be
repeated, so that multiple DS records are created for each CDNSKEY records.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These values are case-insensitive, and the hyphen
may be omitted. If no algorithm is specified, the default is SHA-256 only.
-c class
This option specifies the DNS class of the zones.
-D
This option generates DS records from CDNSKEY records if both CDS and CDNSKEY records are present in thechild zone. By default CDS records are preferred.
-d pathThis specifies the location of the parent DS records. The path can be the name of a file containing the DS records;
if it is a directory, dnssec-cds looks for a dsset- file for the domain inside the directory.
To protect against replay attacks, child records are rejected if they were signed earlier than the modification timeof the dsset- file. This can be adjusted with the -s option.
-f child-file
This option specifies the file containing the child’s CDS and/or CDNSKEY records, plus its DNSKEY records andthe covering RRSIG records, so that they can be authenticated.
The examples below describe how to generate this file.
-i extension
This option updates the dsset- file in place, instead of writing DS records to the standard output.
There must be no space between the -i and the extension. If no extension is provided, the old dsset- is discarded.
If an extension is present, a backup of the old dsset- file is kept with the extension appended to its filename.
To protect against replay attacks, the modification time of the dsset- file is set to match the signature inception
time of the child records, provided that it is later than the file’s current modification time.
-s start-timeThis option specifies the date and time after which RRSIG records become acceptable. This can be either anabsolute or a relative time. An absolute start time is indicated by a number in YYYYMMDDHHMMSS notation;
20170827133700 denotes 13:37:00 UTC on August 27th, 2017. A time relative to the dsset- file is indicatedwith -N, which is N seconds before the file modification time. A time relative to the current time is indicated with
now+N.
If no start-time is specified, the modification time of the dsset- file is used.
-T ttlThis option specifies a TTL to be used for new DS records. If not specified, the default is the TTL of the old DS
records. If they had no explicit TTL, the new DS records also have no explicit TTL.

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BIND 9 Administrator Reference Manual, Release 9.20.0-uThis option writes an nsupdate script to the standard output, instead of printing the new DS reords. The output
is empty if no change is needed.
Note: The TTL of new records needs to be specified: it can be done in the original dsset- file, with the -T
option, or using the nsupdate ttl command.
-V
This option prints version information.
-v levelThis option sets the debugging level. Level 1 is intended to be usefully verbose for general users; higher levels areintended for developers.
domainThis indicates the name of the delegation point/child zone apex.

15.5.4 Exit Status
The dnssec-cds command exits 0 on success, or non-zero if an error occurred.
If successful, the DS records may or may not need to be changed.

15.5.5 Examples
Before running dnssec-signzone, ensure that the delegations are up-to-date by running dnssec-cds on every
dsset- file.
To fetch the child records required by dnssec-cds, invoke dig as in the script below. It is acceptable if the dig fails,
since dnssec-cds performs all the necessary checking.
for f in dsset-*dod=${f#dsset-}
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |dnssec-cds -i -f /dev/stdin -d $f $d
done

When the parent zone is automatically signed by named, dnssec-cds can be used with nsupdate to maintain adelegation as follows. The dsset- file allows the script to avoid having to fetch and validate the parent DS records, andit maintains the replay attack protection time.
dig +dnssec +noall +answer $d DNSKEY $d CDNSKEY $d CDS |dnssec-cds -u -i -f /dev/stdin -d $f $d |nsupdate -l

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15.5.6 See Alsodig(1), dnssec-settime(8), dnssec-signzone(8), nsupdate(1), BIND 9 Administrator Reference
Manual, RFC 7344.

15.6 dnssec-dsfromkey - DNSSEC DS RR generation tool
15.6.1 Synopsis
dnssec-dsfromkey [ -1 | -2 | -a alg ] [ -C ] [-T TTL] [-v level] [-K directory] {keyfile}dnssec-dsfromkey [ -1 | -2 | -a alg ] [ -C ] [-T TTL] [-v level] [-c class] [-A] {-f file} [dnsname]dnssec-dsfromkey [ -1 | -2 | -a alg ] [ -C ] [-T TTL] [-v level] [-c class] [-K directory] {-s} {dnsname}dnssec-dsfromkey [ -h | -V ]15.6.2 Description
The dnssec-dsfromkey command outputs DS (Delegation Signer) resource records (RRs), or CDS (Child DS) RRs
with the -C option.
By default, only KSKs are converted (keys with flags = 257). The -A option includes ZSKs (flags = 256). Revoked keys
are never included.
The input keys can be specified in a number of ways:
By default, dnssec-dsfromkey reads a key file named in the format Knnnn.+aaa+iiiii.key, as generated bydnssec-keygen.
With the -f file option, dnssec-dsfromkey reads keys from a zone file or partial zone file (which can containjust the DNSKEY records).
With the -s option, dnssec-dsfromkey reads a keyset- file, as generated by dnssec-keygen -C.

15.6.3 Options-1
This option is an abbreviation for -a SHA1.
-2
This option is an abbreviation for -a SHA-256.
-a algorithm
This option specifies a digest algorithm to use when converting DNSKEY records to DS records. This option canbe repeated, so that multiple DS records are created for each DNSKEY record.
The algorithm must be one of SHA-1, SHA-256, or SHA-384. These values are case-insensitive, and the hyphen
may be omitted. If no algorithm is specified, the default is SHA-256.
-AThis option indicates that ZSKs are to be included when generating DS records. Without this option, only keys
which have the KSK flag set are converted to DS records and printed. This option is only useful in -f zone file
mode.

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BIND 9 Administrator Reference Manual, Release 9.20.0-c class
This option specifies the DNS class; the default is IN. This option is only useful in -s keyset or -f zone file mode.
-CThis option generates CDS records rather than DS records.
-f fileThis option sets zone file mode, in which the final dnsname argument of dnssec-dsfromkey is the DNS domainname of a zone whose master file can be read from file. If the zone name is the same as file, then it may beomitted.
If file is -, then the zone data is read from the standard input. This makes it possible to use the output of thedig command as input, as in:
dig dnskey example.com | dnssec-dsfromkey -f - example.com-hThis option prints usage information.
-K directoryThis option tells BIND 9 to look for key files or keyset- files in directory.
-s
This option enables keyset mode, in which the final dnsname argument from dnssec-dsfromkey is the DNS
domain name used to locate a keyset- file.
-T TTL
This option specifies the TTL of the DS records. By default the TTL is omitted.
-v levelThis option sets the debugging level.
-VThis option prints version information.

15.6.4 Example
To build the SHA-256 DS RR from the Kexample.com.+003+26160 keyfile, issue the following command:
dnssec-dsfromkey -2 Kexample.com.+003+26160
The command returns something similar to:

example.com. IN DS 26160 5 2 3A1EADA7A74B8D0BA86726B0C227AA85AB8BBD2B2004F41A868A54F0C5EA0B94

15.6.5 FilesThe keyfile can be designated by the key identification Knnnn.+aaa+iiiii or the full file name Knnnn.
+aaa+iiiii.key, as generated by dnssec-keygen.
The keyset file name is built from the directory, the string keyset-, and the dnsname.

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15.6.6 Caveat
A keyfile error may return “file not found,” even if the file exists.

15.6.7 See Also
dnssec-keygen(8), dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 3658 (DS RRs),
RFC 4509 (SHA-256 for DS RRs), RFC 6605 (SHA-384 for DS RRs), RFC 7344 (CDS and CDNSKEY RRs).

15.7 dnssec-importkey - import DNSKEY records from external systems so they can be managed
15.7.1 Synopsis
dnssec-importkey [-K directory] [-L ttl] [-P date/offset] [-P sync date/offset] [-D date/offset] [-D sync date/offset][-h] [-v level] [-V] {keyfile}dnssec-importkey {-f filename} [-K directory] [-L ttl] [-P date/offset] [-P sync date/offset] [-D date/offset] [-Dsync date/offset] [-h] [-v level] [-V] [dnsname]15.7.2 Description
dnssec-importkey reads a public DNSKEY record and generates a pair of .key/.private files. The DNSKEY record
may be read from an existing .key file, in which case a corresponding .private file is generated, or it may be read from anyother file or from the standard input, in which case both .key and .private files are generated.
The newly created .private file does not contain private key data, and cannot be used for signing. However, having a.private file makes it possible to set publication (-P) and deletion (-D) times for the key, which means the public key canbe added to and removed from the DNSKEY RRset on schedule even if the true private key is stored offline.

15.7.3 Options-f filename
This option indicates the zone file mode. Instead of a public keyfile name, the argument is the DNS domain nameof a zone master file, which can be read from filename. If the domain name is the same as filename, then it
may be omitted.
If filename is set to "-", then the zone data is read from the standard input.
-K directoryThis option sets the directory in which the key files are to reside.
-L ttlThis option sets the default TTL to use for this key when it is converted into a DNSKEY RR. This is the TTL
used when the key is imported into a zone, unless there was already a DNSKEY RRset in place, in which case theexisting TTL takes precedence. Setting the default TTL to 0 or none removes it from the key.
-hThis option emits a usage message and exits.

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BIND 9 Administrator Reference Manual, Release 9.20.0-v levelThis option sets the debugging level.
-VThis option prints version information.

15.7.4 Timing Options
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS. (which is the format used inside key
files), or ‘Day Mon DD HH:MM:SS YYYY’ (as printed by dnssec-settime -p), or UNIX epoch time (as printed
by dnssec-settime -up), or the literal now.
The argument can be followed by + or - and an offset from the given time. The literal now can be omitted before an
offset. The offset can be followed by one of the suffixes y, mo, w, d, h, or mi, so that it is computed in years (defined as
365 24-hour days, ignoring leap years), months (defined as 30 24-hour days), weeks, days, hours, or minutes, respectively.
Without a suffix, the offset is computed in seconds.
To explicitly prevent a date from being set, use none, never, or unset.
All these formats are case-insensitive.
-P date/offset
This option sets the date on which a key is to be published to the zone. After that date, the key is included in thezone but is not used to sign it.
sync date/offset
This option sets the date on which CDS and CDNSKEY records that match this key are to be published to
the zone.
-D date/offset
This option sets the date on which the key is to be deleted. After that date, the key is no longer included in thezone. (However, it may remain in the key repository.)
sync date/offset
This option sets the date on which the CDS and CDNSKEY records that match this key are to be deleted.

15.7.5 Files
A keyfile can be designed by the key identification Knnnn.+aaa+iiiii or the full file name Knnnn.+aaa+iiiii.
key, as generated by dnssec-keygen.

15.7.6 See Also
dnssec-keygen(8), dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 5011.

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15.8 dnssec-keyfromlabel - DNSSEC key generation tool
15.8.1 Synopsis
dnssec-keyfromlabel {-l label} [-3] [-a algorithm] [-A date/offset] [-c class] [-D date/offset] [-D sync date/offset][-E engine] [-f flag] [-G] [-I date/offset] [-i interval] [-k] [-K directory] [-L ttl] [-n nametype] [-P date/offset] [-P sync
date/offset] [-p protocol] [-R date/offset] [-S key] [-t type] [-v level] [-V] [-y] {name}15.8.2 Description
dnssec-keyfromlabel generates a pair of key files that reference a key object stored in a cryptographic hardware
service module (HSM). The private key file can be used for DNSSEC signing of zone data as if it were a conventionalsigning key created by dnssec-keygen, but the key material is stored within the HSM and the actual signing takes
place there.
The name of the key is specified on the command line. This must match the name of the zone for which the key is being
generated.

15.8.3 Options-a algorithm
This option selects the cryptographic algorithm. The value of algorithm must be one of RSASHA1,NSEC3RSASHA1, RSASHA256, RSASHA512, ECDSAP256SHA256, ECDSAP384SHA384, ED25519, orED448.
These values are case-insensitive. In some cases, abbreviations are supported, such as ECDSA256 for ECDSAP256SHA256 and ECDSA384 for ECDSAP384SHA384. If RSASHA1 is specified along with the -3 option,then NSEC3RSASHA1 is used instead.
This option is mandatory except when using the -S option, which copies the algorithm from the predecessory key.
Changed in version 9.12.0: The default value RSASHA1 for newly generated keys was removed.
-3This option uses an NSEC3-capable algorithm to generate a DNSSEC key. If this option is used with an algorithm
that has both NSEC and NSEC3 versions, then the NSEC3 version is used; for example, dnssec-keygen -3a
RSASHA1 specifies the NSEC3RSASHA1 algorithm.
-E engine
This option specifies the cryptographic hardware to use.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-l labelThis option specifies the label for a key pair in the crypto hardware.
When BIND 9 is built with OpenSSL-based PKCS#11 support, the label is an arbitrary string that identifies a particular key. It may be preceded by an optional OpenSSL engine name, followed by a colon, as inpkcs11:keylabel.
-n nametypeThis option specifies the owner type of the key. The value of nametype must either be ZONE (for a DNSSEC
zone key (KEY/DNSKEY)), HOST or ENTITY (for a key associated with a host (KEY)), USER (for a key associated with a user (KEY)), or OTHER (DNSKEY). These values are case-insensitive.
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BIND 9 Administrator Reference Manual, Release 9.20.0-CThis option enables compatibility mode, which generates an old-style key, without any metadata. By default,
dnssec-keyfromlabel includes the key’s creation date in the metadata stored with the private key; otherdates may be set there as well, including publication date, activation date, etc. Keys that include this data may be
incompatible with older versions of BIND; the -C option suppresses them.
-c class
This option indicates that the DNS record containing the key should have the specified class. If not specified, class
IN is used.
-f flag
This option sets the specified flag in the flag field of the KEY/DNSKEY record. The only recognized flags are
KSK (Key-Signing Key) and REVOKE.
-G
This option generates a key, but does not publish it or sign with it. This option is incompatible with -P and -A.
-hThis option prints a short summary of the options and arguments to dnssec-keyfromlabel.
-K directoryThis option sets the directory in which the key files are to be written.
-kThis option generates KEY records rather than DNSKEY records.
-L ttlThis option sets the default TTL to use for this key when it is converted into a DNSKEY RR. This is the TTL
used when the key is imported into a zone, unless there was already a DNSKEY RRset in place, in which case theexisting TTL would take precedence. Setting the default TTL to 0 or none removes it.
-p protocol
This option sets the protocol value for the key. The protocol is a number between 0 and 255. The default is 3
(DNSSEC). Other possible values for this argument are listed in RFC 2535 and its successors.
-S keyThis option generates a key as an explicit successor to an existing key. The name, algorithm, size, and type of the
key are set to match the predecessor. The activation date of the new key is set to the inactivation date of the existingone. The publication date is set to the activation date minus the prepublication interval, which defaults to 30 days.
-t typeThis option indicates the type of the key. type must be one of AUTHCONF, NOAUTHCONF, NOAUTH, or
NOCONF. The default is AUTHCONF. AUTH refers to the ability to authenticate data, and CONF to the ability
to encrypt data.
-v levelThis option sets the debugging level.
-VThis option prints version information.
-yThis option allows DNSSEC key files to be generated even if the key ID would collide with that of an existing key,in the event of either key being revoked. (This is only safe to enable if RFC 5011 trust anchor maintenance is not
used with either of the keys involved.)

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15.8.4 Timing Options
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS (which is the format used inside key
files), or ‘Day Mon DD HH:MM:SS YYYY’ (as printed by dnssec-settime -p), or UNIX epoch time (as printed
by dnssec-settime -up), or the literal now.
The argument can be followed by + or - and an offset from the given time. The literal now can be omitted before an
offset. The offset can be followed by one of the suffixes y, mo, w, d, h, or mi, so that it is computed in years (defined as
365 24-hour days, ignoring leap years), months (defined as 30 24-hour days), weeks, days, hours, or minutes, respectively.
Without a suffix, the offset is computed in seconds.
To explicitly prevent a date from being set, use none, never, or unset.
All these formats are case-insensitive.
-P date/offset
This option sets the date on which a key is to be published to the zone. After that date, the key is included in thezone but is not used to sign it. If not set, and if the -G option has not been used, the default is the current date.
sync date/offset
This option sets the date on which CDS and CDNSKEY records that match this key are to be published to
the zone.
-A date/offset
This option sets the date on which the key is to be activated. After that date, the key is included in the zone andused to sign it. If not set, and if the -G option has not been used, the default is the current date.
-R date/offset
This option sets the date on which the key is to be revoked. After that date, the key is flagged as revoked. It is
included in the zone and is used to sign it.
-I date/offset
This option sets the date on which the key is to be retired. After that date, the key is still included in the zone, but
it is not used to sign it.
-D date/offset
This option sets the date on which the key is to be deleted. After that date, the key is no longer included in thezone. (However, it may remain in the key repository.)
sync date/offset
This option sets the date on which the CDS and CDNSKEY records that match this key are to be deleted.
-i intervalThis option sets the prepublication interval for a key. If set, then the publication and activation dates must be
separated by at least this much time. If the activation date is specified but the publication date is not, the publication
date defaults to this much time before the activation date; conversely, if the publication date is specified but not theactivation date, activation is set to this much time after publication.
If the key is being created as an explicit successor to another key, then the default prepublication interval is 30 days;
otherwise it is zero.
As with date offsets, if the argument is followed by one of the suffixes y, mo, w, d, h, or mi, the interval is measured
in years, months, weeks, days, hours, or minutes, respectively. Without a suffix, the interval is measured in seconds.

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15.8.5 Generated Key Files
When dnssec-keyfromlabel completes successfully, it prints a string of the form Knnnn.+aaa+iiiii to thestandard output. This is an identification string for the key files it has generated.
• nnnn is the key name.
• aaa is the numeric representation of the algorithm.
• iiiii is the key identifier (or footprint).
dnssec-keyfromlabel creates two files, with names based on the printed string. Knnnn.+aaa+iiiii.key
contains the public key, and Knnnn.+aaa+iiiii.private contains the private key.
The .key file contains a DNS KEY record that can be inserted into a zone file (directly or with an $INCLUDE statement).
The .private file contains algorithm-specific fields. For obvious security reasons, this file does not have general read
permission.

15.8.6 See Also
dnssec-keygen(8), dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 4034, RFC 7512.

15.9 dnssec-keygen: DNSSEC key generation tool
15.9.1 Synopsis
dnssec-keygen [-3] [-A date/offset] [-a algorithm] [-b keysize] [-C] [-c class] [-D date/offset] [-d bits] [-D sync
date/offset] [-E engine] [-f flag] [-F] [-G] [-h] [-I date/offset] [-i interval] [-K directory] [-k policy] [-L ttl] [-l file] [-nnametype] [-P date/offset] [-P sync date/offset] [-p protocol] [-q] [-R date/offset] [-S key] [-s strength] [-T rrtype] [-ttype] [-V] [-v level] {name}15.9.2 Description
dnssec-keygen generates keys for DNSSEC (Secure DNS), as defined in RFC 2535 and RFC 4034.
The name of the key is specified on the command line. For DNSSEC keys, this must match the name of the zone forwhich the key is being generated.

15.9.3 Options-3
This option uses an NSEC3-capable algorithm to generate a DNSSEC key. If this option is used with an algorithm
that has both NSEC and NSEC3 versions, then the NSEC3 version is selected; for example, dnssec-keygen-3 -a RSASHA1 specifies the NSEC3RSASHA1 algorithm.
-a algorithm
This option selects the cryptographic algorithm. For DNSSEC keys, the value of algorithm must be oneof RSASHA1, NSEC3RSASHA1, RSASHA256, RSASHA512, ECDSAP256SHA256, ECDSAP384SHA384,
ED25519, or ED448.

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These values are case-insensitive. In some cases, abbreviations are supported, such as ECDSA256 for ECDSAP256SHA256 and ECDSA384 for ECDSAP384SHA384. If RSASHA1 is specified along with the -3 option,
NSEC3RSASHA1 is used instead.
This parameter must be specified except when using the -S option, which copies the algorithm from the predecessor
key.
In prior releases, HMAC algorithms could be generated for use as TSIG keys, but that feature was removed in
BIND 9.13.0. Use tsig-keygen to generate TSIG keys.
-b keysize
This option specifies the number of bits in the key. The choice of key size depends on the algorithm used: RSA
keys must be between 1024 and 4096 bits; Diffie-Hellman keys must be between 128 and 4096 bits. Elliptic curvealgorithms do not need this parameter.
If the key size is not specified, some algorithms have pre-defined defaults. For example, RSA keys for use as
DNSSEC zone-signing keys have a default size of 1024 bits; RSA keys for use as key-signing keys (KSKs, generated
with -f KSK) default to 2048 bits.
-C
This option enables compatibility mode, which generates an old-style key, without any timing metadata. By default,
dnssec-keygen includes the key’s creation date in the metadata stored with the private key; other dates may be
set there as well, including publication date, activation date, etc. Keys that include this data may be incompatible
with older versions of BIND; the -C option suppresses them.
-c class
This option indicates that the DNS record containing the key should have the specified class. If not specified, class
IN is used.
-d bits
This option specifies the key size in bits. For the algorithms RSASHA1, NSEC3RSASA1, RSASHA256, and
RSASHA512 the key size must be between 1024 and 4096 bits; DH size is between 128 and 4096 bits. This option
is ignored for algorithms ECDSAP256SHA256, ECDSAP384SHA384, ED25519, and ED448.
-E engine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-f flag
This option sets the specified flag in the flag field of the KEY/DNSKEY record. The only recognized flags are ZSK(Zone-Signing Key), KSK (Key-Signing Key) and REVOKE.
Note that ZSK is not a physical flag in the DNSKEY record, it is merely used to explicitly tell that you want tocreate a ZSK. Setting -f in conjunction with -k will result in generating keys that only match the given role set
with this option.
-F
This options turns on FIPS (US Federal Information Processing Standards) mode if the underlying crytographic
library supports running in FIPS mode.
-G
This option generates a key, but does not publish it or sign with it. This option is incompatible with -P and -A.
-hThis option prints a short summary of the options and arguments to dnssec-keygen.

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BIND 9 Administrator Reference Manual, Release 9.20.0-K directoryThis option sets the directory in which the key files are to be written.
-k policy
This option creates keys for a specific dnssec-policy. If a policy uses multiple keys, dnssec-keygengenerates multiple keys. This also creates a “.state” file to keep track of the key state.
This option creates keys according to the dnssec-policy configuration, hence it cannot be used at the sametime as many of the other options that dnssec-keygen provides.
-L ttlThis option sets the default TTL to use for this key when it is converted into a DNSKEY RR. This is the TTL
used when the key is imported into a zone, unless there was already a DNSKEY RRset in place, in which case theexisting TTL takes precedence. If this value is not set and there is no existing DNSKEY RRset, the TTL defaults
to the SOA TTL. Setting the default TTL to 0 or none is the same as leaving it unset.
-l fileThis option provides a configuration file that contains a dnssec-policy statement (matching the policy set with-k).
-n nametypeThis option specifies the owner type of the key. The value of nametype must either be ZONE (for a DNSSEC
zone key (KEY/DNSKEY)), HOST or ENTITY (for a key associated with a host (KEY)), USER (for a key associated with a user (KEY)), or OTHER (DNSKEY). These values are case-insensitive. The default is ZONE for
DNSKEY generation.
-p protocol
This option sets the protocol value for the generated key, for use with -T KEY. The protocol is a number between
0 and 255. The default is 3 (DNSSEC). Other possible values for this argument are listed in RFC 2535 and its
successors.
-q
This option sets quiet mode, which suppresses unnecessary output, including progress indication. Without thisoption, when dnssec-keygen is run interactively to generate an RSA or DSA key pair, it prints a string ofsymbols to stderr indicating the progress of the key generation. A . indicates that a random number has beenfound which passed an initial sieve test; + means a number has passed a single round of the Miller-Rabin primality
test; and a space ( ) means that the number has passed all the tests and is a satisfactory key.
-S keyThis option creates a new key which is an explicit successor to an existing key. The name, algorithm, size, and typeof the key are set to match the existing key. The activation date of the new key is set to the inactivation date of theexisting one. The publication date is set to the activation date minus the prepublication interval, which defaults to
30 days.
-s strength
This option specifies the strength value of the key. The strength is a number between 0 and 15, and currently has
no defined purpose in DNSSEC.
-T rrtypeThis option specifies the resource record type to use for the key. rrtype must be either DNSKEY or KEY. The
default is DNSKEY when using a DNSSEC algorithm, but it can be overridden to KEY for use with SIG(0).
-t typeThis option indicates the type of the key for use with -T KEY. type must be one of AUTHCONF, NOAUTHCONF, NOAUTH, or NOCONF. The default is AUTHCONF. AUTH refers to the ability to authenticate data,
and CONF to the ability to encrypt data.

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BIND 9 Administrator Reference Manual, Release 9.20.0-VThis option prints version information.
-v levelThis option sets the debugging level.

15.9.4 Timing Options
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS (which is the format used inside key
files), or ‘Day Mon DD HH:MM:SS YYYY’ (as printed by dnssec-settime -p), or UNIX epoch time (as printed
by dnssec-settime -up), or the literal now.
The argument can be followed by + or - and an offset from the given time. The literal now can be omitted before an
offset. The offset can be followed by one of the suffixes y, mo, w, d, h, or mi, so that it is computed in years (defined as
365 24-hour days, ignoring leap years), months (defined as 30 24-hour days), weeks, days, hours, or minutes, respectively.
Without a suffix, the offset is computed in seconds.
To unset a date, use none, never, or unset.
-P date/offset
This option sets the date on which a key is to be published to the zone. After that date, the key is included in thezone but is not used to sign it. If not set, and if the -G option has not been used, the default is the current date.
sync date/offset
This option sets the date on which CDS and CDNSKEY records that match this key are to be published to
the zone.
-A date/offset
This option sets the date on which the key is to be activated. After that date, the key is included in the zone andused to sign it. If not set, and if the -G option has not been used, the default is the current date. If set, and -P is
not set, the publication date is set to the activation date minus the prepublication interval.
-R date/offset
This option sets the date on which the key is to be revoked. After that date, the key is flagged as revoked. It is
included in the zone and is used to sign it.
-I date/offset
This option sets the date on which the key is to be retired. After that date, the key is still included in the zone, but
it is not used to sign it.
-D date/offset
This option sets the date on which the key is to be deleted. After that date, the key is no longer included in thezone. (However, it may remain in the key repository.)
sync date/offset
This option sets the date on which the CDS and CDNSKEY records that match this key are to be deleted.
-i intervalThis option sets the prepublication interval for a key. If set, then the publication and activation dates must be
separated by at least this much time. If the activation date is specified but the publication date is not, the publication
date defaults to this much time before the activation date; conversely, if the publication date is specified but not theactivation date, activation is set to this much time after publication.
If the key is being created as an explicit successor to another key, then the default prepublication interval is 30 days;
otherwise it is zero.
As with date offsets, if the argument is followed by one of the suffixes y, mo, w, d, h, or mi, the interval is measured
in years, months, weeks, days, hours, or minutes, respectively. Without a suffix, the interval is measured in seconds.
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15.9.5 Generated Keys
When dnssec-keygen completes successfully, it prints a string of the form Knnnn.+aaa+iiiii to the standard
output. This is an identification string for the key it has generated.
• nnnn is the key name.
• aaa is the numeric representation of the algorithm.
• iiiii is the key identifier (or footprint).
dnssec-keygen creates two files, with names based on the printed string. Knnnn.+aaa+iiiii.key contains the
public key, and Knnnn.+aaa+iiiii.private contains the private key.
The .key file contains a DNSKEY or KEY record. When a zone is being signed by named or dnssec-signzone-S, DNSKEY records are included automatically. In other cases, the .key file can be inserted into a zone file manuallyor with an $INCLUDE statement.
The .private file contains algorithm-specific fields. For obvious security reasons, this file does not have general read
permission.

15.9.6 Example
To generate an ECDSAP256SHA256 zone-signing key for the zone example.com, issue the command:
dnssec-keygen -a ECDSAP256SHA256 example.com
The command prints a string of the form:
Kexample.com.+013+26160
In this example, dnssec-keygen creates the files Kexample.com.+013+26160.key and Kexample.com.
+013+26160.private.
To generate a matching key-signing key, issue the command:
dnssec-keygen -a ECDSAP256SHA256 -f KSK example.com

15.9.7 See Also
dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 2539, RFC 2845, RFC 4034.

15.10 dnssec-ksr - Create signed key response (SKR) files for offline
KSK setups
15.10.1 Synopsis
dnssec-ksr [-E engine] [-e date/offset] [-F] [-h] [-i date/offset] [-K directory] [-k policy] [-l file] [-V] [-v level]{command} {zone}

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15.10.2 Description
The dnssec-ksr can be used to issue several commands that are needed to generate presigned RRsets for a zone
where the private key file of the Key Signing Key (KSK) is typically offline. This requires Zone Signing Keys (ZSKs) tobe pregenerated, and the DNSKEY, CDNSKEY, and CDS RRsets to be already signed in advance.
The latter is done by creating Key Signing Requests (KSRs) that can be imported to the environment where the KSK isavailable. Once there, this program can create Signed Key Responses (SKRs) that can be loaded by an authoritative DNS
server.

15.10.3 Options-E engine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-e date/offset
This option sets the end date for which keys or SKRs need to be generated (depending on the command).
-F
This options turns on FIPS (US Federal Information Processing Standards) mode if the underlying crytographic
library supports running in FIPS mode.
-hThis option prints a short summary of the options and arguments to dnssec-ksr.
-i date/offset
This option sets the start date for which keys or SKRs need to be generated (depending on the command).
-K directoryThis option sets the directory in which the key files are to be read or written (depending on the command).
-k policy
This option sets the specific dnssec-policy for which keys need to be generated, or signed.
-l fileThis option provides a configuration file that contains a dnssec-policy statement (matching the policy set with-k).
-V
This option prints version information.
-v levelThis option sets the debugging level. Level 1 is intended to be usefully verbose for general users; higher levels areintended for developers.
command
The KSR command to be executed. See below for the available commands.
zone
The name of the zone for which the KSR command is being executed.

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15.10.4 Commands
keygenPregenerate a number of zone signing keys (ZSKs), given a DNSSEC policy and an interval. The number ofgenerated keys depends on the interval and the ZSK lifetime.
requestCreate a Key Signing Request (KSR), given a DNSSEC policy and an interval. This will generate a file with a number of key bundles, where each bundle contains the currently published ZSKs (according to the timing metadata).
sign
Sign a Key Signing Request (KSR), given a DNSSEC policy and an interval, creating a Signed Key Response(SKR). This will add the corresponding DNSKEY, CDS, and CDNSKEY records for the KSK that is being used
for signing.

15.10.5 Exit Status
The dnssec-ksr command exits 0 on success, or non-zero if an error occurred.

15.10.6 Examples
When you need to generate keys for the zone “example.com” for the next year, given a dnssec-policy named “mypolicy”:
dnssec-ksr -i now -e +1y -k mypolicy -l named.conf keygen example.com

Creating a KSR for the same zone and period can be done with:dnssec-ksr -i now -e +1y -k mypolicy -l named.conf request example.com > ksr.txt

Typically you would now transfer the KSR to the system that has access to the KSK.
Signing the KSR created above can be done with:dnssec-ksr -i now -e +1y -k kskpolicy -l named.conf -f ksr.txt sign example.com

Make sure that the DNSSEC parameters in kskpolicy match those in mypolicy.

15.10.7 See Also
dnssec-keygen(8), dnssec-signzone(8), BIND 9 Administrator Reference Manual.

15.11 dnssec-revoke - set the REVOKED bit on a DNSSEC key
15.11.1 Synopsis
dnssec-revoke [-hr] [-v level] [-V] [-K directory] [-E engine] [-f] [-R] {keyfile}

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15.11.2 Description
dnssec-revoke reads a DNSSEC key file, sets the REVOKED bit on the key as defined in RFC 5011, and creates a
new pair of key files containing the now-revoked key.

15.11.3 Options-hThis option emits a usage message and exits.
-K directoryThis option sets the directory in which the key files are to reside.
-r
This option indicates to remove the original keyset files after writing the new keyset files.
-v levelThis option sets the debugging level.
-VThis option prints version information.
-E engine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-f
This option indicates a forced overwrite and causes dnssec-revoke to write the new key pair, even if a filealready exists matching the algorithm and key ID of the revoked key.
-R
This option prints the key tag of the key with the REVOKE bit set, but does not revoke the key.

15.11.4 See Also
dnssec-keygen(8), BIND 9 Administrator Reference Manual, RFC 5011.

15.12 dnssec-settime: set the key timing metadata for a DNSSEC key
15.12.1 Synopsis
dnssec-settime [-f] [-K directory] [-L ttl] [-P date/offset] [-P ds date/offset] [-P sync date/offset] [-A date/offset][-R date/offset] [-I date/offset] [-D date/offset] [-D ds date/offset] [-D sync date/offset] [-S key] [-i interval] [-h] [-V][-v level] [-E engine] {keyfile} [-s] [-g state] [-d state date/offset] [-k state date/offset] [-r state date/offset] [-z state
date/offset]

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15.12.2 Description
dnssec-settime reads a DNSSEC private key file and sets the key timing metadata as specified by the -P, -A, -R,-I, and -D options. The metadata can then be used by dnssec-signzone or other signing software to determine
when a key is to be published, whether it should be used for signing a zone, etc.
If none of these options is set on the command line, dnssec-settime simply prints the key timing metadata alreadystored in the key.
When key metadata fields are changed, both files of a key pair (Knnnn.+aaa+iiiii.key and Knnnn.
+aaa+iiiii.private) are regenerated.
Metadata fields are stored in the private file. A human-readable description of the metadata is also placed in comments inthe key file. The private file’s permissions are always set to be inaccessible to anyone other than the owner (mode 0600).
When working with state files, it is possible to update the timing metadata in those files as well with -s. With this option,
it is also possible to update key states with -d (DS), -k (DNSKEY), -r (RRSIG of KSK), or -z (RRSIG of ZSK).
Allowed states are HIDDEN, RUMOURED, OMNIPRESENT, and UNRETENTIVE.
The goal state of the key can also be set with -g. This should be either HIDDEN or OMNIPRESENT, representing
whether the key should be removed from the zone or published.
It is NOT RECOMMENDED to manipulate state files manually, except for testing purposes.

15.12.3 Options-fThis option forces an update of an old-format key with no metadata fields.
Without this option,
dnssec-settime fails when attempting to update a legacy key. With this option, the key is recreated in the
new format, but with the original key data retained. The key’s creation date is set to the present time. If no othervalues are specified, then the key’s publication and activation dates are also set to the present time.
-K directoryThis option sets the directory in which the key files are to reside.
-L ttlThis option sets the default TTL to use for this key when it is converted into a DNSKEY RR. This is the TTL
used when the key is imported into a zone, unless there was already a DNSKEY RRset in place, in which case theexisting TTL takes precedence. If this value is not set and there is no existing DNSKEY RRset, the TTL defaults
to the SOA TTL. Setting the default TTL to 0 or none removes it from the key.
-hThis option emits a usage message and exits.
-V
This option prints version information.
-v levelThis option sets the debugging level.
-E engine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).

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15.12.4 Timing Options
Dates can be expressed in the format YYYYMMDD or YYYYMMDDHHMMSS (which is the format used inside key
files), or ‘Day Mon DD HH:MM:SS YYYY’ (as printed by dnssec-settime -p), or UNIX epoch time (as printed
by dnssec-settime -up), or the literal now.
The argument can be followed by + or - and an offset from the given time. The literal now can be omitted before an
offset. The offset can be followed by one of the suffixes y, mo, w, d, h, or mi, so that it is computed in years (defined as
365 24-hour days, ignoring leap years), months (defined as 30 24-hour days), weeks, days, hours, or minutes, respectively.
Without a suffix, the offset is computed in seconds.
To unset a date, use none, never, or unset.
All these formats are case-insensitive.
-P date/offset
This option sets the date on which a key is to be published to the zone. After that date, the key is included in thezone but is not used to sign it.
ds date/offset
This option sets the date on which DS records that match this key have been seen in the parent zone.
sync date/offset
This option sets the date on which CDS and CDNSKEY records that match this key are to be published to
the zone.
-A date/offset
This option sets the date on which the key is to be activated. After that date, the key is included in the zone andused to sign it.
-R date/offset
This option sets the date on which the key is to be revoked. After that date, the key is flagged as revoked. It is
included in the zone and is used to sign it.
-I date/offset
This option sets the date on which the key is to be retired. After that date, the key is still included in the zone, but
it is not used to sign it.
-D date/offset
This option sets the date on which the key is to be deleted. After that date, the key is no longer included in thezone. (However, it may remain in the key repository.)ds date/offset
This option sets the date on which the DS records that match this key have been seen removed from the parent
zone.
sync date/offset
This option sets the date on which the CDS and CDNSKEY records that match this key are to be deleted.
-S predecessor key
This option selects a key for which the key being modified is an explicit successor. The name, algorithm, size,
and type of the predecessor key must exactly match those of the key being modified. The activation date of thesuccessor key is set to the inactivation date of the predecessor. The publication date is set to the activation dateminus the prepublication interval, which defaults to 30 days.
-i intervalThis option sets the prepublication interval for a key. If set, then the publication and activation dates must be
separated by at least this much time. If the activation date is specified but the publication date is not, the publication

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date defaults to this much time before the activation date; conversely, if the publication date is specified but not theactivation date, activation is set to this much time after publication.
If the key is being created as an explicit successor to another key, then the default prepublication interval is 30 days;
otherwise it is zero.
As with date offsets, if the argument is followed by one of the suffixes y, mo, w, d, h, or mi, the interval is measured
in years, months, weeks, days, hours, or minutes, respectively. Without a suffix, the interval is measured in seconds.

15.12.5 Key State Options
To test dnssec-policy it may be necessary to construct keys with artificial state information; these options are used by thetesting framework for that purpose, but should never be used in production.
Known key states are HIDDEN, RUMOURED, OMNIPRESENT, and UNRETENTIVE.
-s
This option indicates that when setting key timing data, the state file should also be updated.
-g state
This option sets the goal state for this key. Must be HIDDEN or OMNIPRESENT.
-d state date/offset
This option sets the DS state for this key as of the specified date, offset from the current date.
-k state date/offset
This option sets the DNSKEY state for this key as of the specified date, offset from the current date.
-r state date/offset
This option sets the RRSIG (KSK) state for this key as of the specified date, offset from the current date.
-z state date/offset
This option sets the RRSIG (ZSK) state for this key as of the specified date, offset from the current date.

15.12.6 Printing Options
dnssec-settime can also be used to print the timing metadata associated with a key.
-uThis option indicates that times should be printed in Unix epoch format.
-p C/P/Pds/Psync/A/R/I/D/Dds/Dsync/all
This option prints a specific metadata value or set of metadata values. The -p option may be followed by one ormore of the following letters or strings to indicate which value or values to print: C for the creation date, P for
the publication date, Pds` for the DS publication date, ``Psync for the CDS and CDNSKEY
publication date, A for the activation date, R for the revocation date, I for the inactivation date, D for the deletiondate, Dds for the DS deletion date, and Dsync for the CDS and CDNSKEY deletion date. To print all of themetadata, use all.

15.12. dnssec-settime: set the key timing metadata for a DNSSEC key

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15.12.7 See Also
dnssec-keygen(8), dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 5011.

15.13 dnssec-signzone - DNSSEC zone signing tool
15.13.1 Synopsis
dnssec-signzone [-a] [-c class] [-d directory] [-D] [-E engine] [-e end-time] [-f output-file] [-F] [-g] [-G syncrecords] [-h] [-i interval] [-I input-format] [-j jitter] [-J filename] [-K directory] [-k key] [-L serial] [-M maxttl] [-N
soa-serial-format] [-o origin] [-O output-format] [-P] [-Q] [-q] [-R] [-S] [-s start-time] [-T ttl] [-t] [-u] [-v level] [-V][-X extended end-time] [-x] [-z] [-3 salt] [-H iterations] [-A] {zonefile} [key…]

15.13.2 Description
dnssec-signzone signs a zone; it generates NSEC and RRSIG records and produces a signed version of the zone.
The security status of delegations from the signed zone (that is, whether the child zones are secure) is determined by thepresence or absence of a keyset file for each child zone.

15.13.3 Options-aThis option verifies all generated signatures.
-c class
This option specifies the DNS class of the zone.
-C
This option sets compatibility mode, in which a keyset-zonename file is generated in addition todsset-zonename when signing a zone, for use by older versions of dnssec-signzone.
-d directoryThis option indicates the directory where BIND 9 should look for dsset- or keyset- files.
-D
This option indicates that only those record types automatically managed by dnssec-signzone, i.e., RRSIG,NSEC, NSEC3 and NSEC3PARAM records, should be included in the output. If smart signing (-S) is used,
DNSKEY records are also included. The resulting file can be included in the original zone file with $INCLUDE.
This option cannot be combined with -O raw or serial-number updating.
-E engine
This option specifies the hardware to use for cryptographic operations, such as a secure key store used for signing,when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-F
This options turns on FIPS (US Federal Information Processing Standards) mode if the underlying crytographic
library supports running in FIPS mode.

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BIND 9 Administrator Reference Manual, Release 9.20.0-gThis option indicates that DS records for child zones should be generated from a dsset- or keyset- file.
Existing DS records are removed.
-G sync-records
This option indicates which CDS and CDNSKEY records should be generated. sync-records is acomma-separated string with the following allowed items: cdnskey, and cds:<digest-type>, wheredigest-type is an allowed algorithm such as SHA-256 (2), or SHA-384 (4). Only works in combination
with smart signing (-S).
-J filename
This option tells dnssec-signzone to read the journal from the given file when loading the zone file.
-K directoryThis option specifies the directory to search for DNSSEC keys. If not specified, it defaults to the current directory.
-k keyThis option tells BIND 9 to treat the specified key as a key-signing key, ignoring any key flags. This option may be
specified multiple times.
-M maxttl
This option sets the maximum TTL for the signed zone. Any TTL higher than maxttl in the input zone is reduced
to maxttl in the output. This provides certainty as to the largest possible TTL in the signed zone, which is useful
to know when rolling keys. The maxttl is the longest possible time before signatures that have been retrievedby resolvers expire from resolver caches. Zones that are signed with this option should be configured to use amatching max-zone-ttl in named.conf. (Note: This option is incompatible with -D, because it modifies
non-DNSSEC data in the output zone.)-s start-timeThis option specifies the date and time when the generated RRSIG records become valid. This can be either anabsolute or relative time. An absolute start time is indicated by a number in YYYYMMDDHHMMSS notation;
20000530144500 denotes 14:45:00 UTC on May 30th, 2000. A relative start time is indicated by +N, which is N
seconds from the current time. If no start-time is specified, the current time minus 1 hour (to allow for clockskew) is used.
-e end-timeThis option specifies the date and time when the generated RRSIG records expire. As with start-time, anabsolute time is indicated in YYYYMMDDHHMMSS notation. A time relative to the start time is indicated with+N, which is N seconds from the start time. A time relative to the current time is indicated with now+N. If no
end-time is specified, 30 days from the start time is the default. end-time must be later than start-time.
-X extended end-timeThis option specifies the date and time when the generated RRSIG records for the DNSKEY RRset expire. This
is to be used in cases when the DNSKEY signatures need to persist longer than signatures on other records; e.g.,when the private component of the KSK is kept offline and the KSK signature is to be refreshed manually.
As with end-time, an absolute time is indicated in YYYYMMDDHHMMSS notation. A time relative to thestart time is indicated with +N, which is N seconds from the start time. A time relative to the current time isindicated with now+N. If no extended end-time is specified, the value of end-time is used as the default.
(end-time, in turn, defaults to 30 days from the start time.) extended end-time must be later thanstart-time.
-f output-file
This option indicates the name of the output file containing the signed zone. The default is to append .signed
to the input filename. If output-file is set to -, then the signed zone is written to the standard output, with adefault output format of full.

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BIND 9 Administrator Reference Manual, Release 9.20.0-hThis option prints a short summary of the options and arguments to dnssec-signzone.
-V
This option prints version information.
-i intervalThis option indicates that, when a previously signed zone is passed as input, records may be re-signed. The interval option specifies the cycle interval as an offset from the current time, in seconds. If a RRSIG record
expires after the cycle interval, it is retained; otherwise, it is considered to be expiring soon and it is replaced.
The default cycle interval is one quarter of the difference between the signature end and start times. So if neither
end-time nor start-time is specified, dnssec-signzone generates signatures that are valid for 30 days,
with a cycle interval of 7.5 days. Therefore, if any existing RRSIG records are due to expire in less than 7.5 days,
they are replaced.
-I input-format
This option sets the format of the input zone file. Possible formats are text (the default), and raw. This option is
primarily intended to be used for dynamic signed zones, so that the dumped zone file in a non-text format containing
updates can be signed directly. This option is not useful for non-dynamic zones.
-j jitter
When signing a zone with a fixed signature lifetime, all RRSIG records issued at the time of signing expire simultaneously. If the zone is incrementally signed, i.e., a previously signed zone is passed as input to the signer, all expired
signatures must be regenerated at approximately the same time. The jitter option specifies a jitter window thatis used to randomize the signature expire time, thus spreading incremental signature regeneration over time.
Signature lifetime jitter also, to some extent, benefits validators and servers by spreading out cache expiration, i.e.,
if large numbers of RRSIGs do not expire at the same time from all caches, there is less congestion than if all
validators need to refetch at around the same time.
-L serial
When writing a signed zone to “raw” format, this option sets the “source serial” value in the header to the specified
serial number. (This is expected to be used primarily for testing purposes.)-n ncpus
This option specifies the number of threads to use. By default, one thread is started for each detected CPU.
-N soa-serial-format
This option sets the SOA serial number format of the signed zone. Possible formats are keep (the default),
increment, unixtime, and date.
keepThis format indicates that the SOA serial number should not be modified.
incrementThis format increments the SOA serial number using RFC 1982 arithmetic.
unixtime
This format sets the SOA serial number to the number of seconds since the beginning of the Unix epoch,
unless the serial number is already greater than or equal to that value, in which case it is simply incremented
by one.
dateThis format sets the SOA serial number to today’s date, in YYYYMMDDNN format, unless the serial number
is already greater than or equal to that value, in which case it is simply incremented by one.

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BIND 9 Administrator Reference Manual, Release 9.20.0-o origin
This option sets the zone origin. If not specified, the name of the zone file is assumed to be the origin.
-O output-format
This option sets the format of the output file containing the signed zone. Possible formats are text (the default),which is the standard textual representation of the zone; full, which is text output in a format suitable for processing by external scripts; and raw and raw=N, which store the zone in binary formats for rapid loading by named.
raw=N specifies the format version of the raw zone file: if N is 0, the raw file can be read by any version of named;
if N is 1, the file can be read by release 9.9.0 or higher. The default is 1.
-P
This option disables post-sign verification tests.
The post-sign verification tests ensure that for each algorithm in use there is at least one non-revoked self-signed
KSK key, that all revoked KSK keys are self-signed, and that all records in the zone are signed by the algorithm.
This option skips these tests.
-Q
This option removes signatures from keys that are no longer active.
Normally, when a previously signed zone is passed as input to the signer, and a DNSKEY record has been removed
and replaced with a new one, signatures from the old key that are still within their validity period are retained.
This allows the zone to continue to validate with cached copies of the old DNSKEY RRset. The -Q option forces
dnssec-signzone to remove signatures from keys that are no longer active. This enables ZSK rollover using
the procedure described in RFC 6781#4.1.1.1 (“Pre-Publish Key Rollover”).
-qThis option enables quiet mode, which suppresses unnecessary output.
Without this option, whendnssec-signzone is run it prints three pieces of information to standard output: the number of keys in use; thealgorithms used to verify the zone was signed correctly and other status information; and the filename containing
the signed zone. With the option that output is suppressed, leaving only the filename.
-R
This option removes signatures from keys that are no longer published.
This option is similar to -Q, except it forces dnssec-signzone to remove signatures from keys that are nolonger published. This enables ZSK rollover using the procedure described in RFC 6781#4.1.1.2 (“Double Signature Zone Signing Key Rollover”).
-S
This option enables smart signing, which instructs dnssec-signzone to search the key repository for keys thatmatch the zone being signed, and to include them in the zone if appropriate.
When a key is found, its timing metadata is examined to determine how it should be used, according to the following
rules. Each successive rule takes priority over the prior ones:
If no timing metadata has been set for the key, the key is published in the zone and used to sign thezone.
If the key’s publication date is set and is in the past, the key is published in the zone.
If the key’s activation date is set and is in the past, the key is published (regardless of publication date)and used to sign the zone.
If the key’s revocation date is set and is in the past, and the key is published, then the key is revoked,
and the revoked key is used to sign the zone.
If either the key’s unpublication or deletion date is set and in the past, the key is NOT published or used
to sign the zone, regardless of any other metadata.

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If the key’s sync publication date is set and is in the past, synchronization records (type CDS and/or
CDNSKEY) are created.
If the key’s sync deletion date is set and is in the past, synchronization records (type CDS and/or
CDNSKEY) are removed.
-T ttlThis option specifies a TTL to be used for new DNSKEY records imported into the zone from the key repository. If
not specified, the default is the TTL value from the zone’s SOA record. This option is ignored when signing without-S, since DNSKEY records are not imported from the key repository in that case. It is also ignored if there are
any pre-existing DNSKEY records at the zone apex, in which case new records’ TTL values are set to match them,or if any of the imported DNSKEY records had a default TTL value. In the event of a conflict between TTL values
in imported keys, the shortest one is used.
-tThis option prints statistics at completion.
-uThis option updates the NSEC/NSEC3 chain when re-signing a previously signed zone. With this option, a zone
signed with NSEC can be switched to NSEC3, or a zone signed with NSEC3 can be switched to NSEC or to NSEC3
with different parameters. Without this option, dnssec-signzone retains the existing chain when re-signing.
-v levelThis option sets the debugging level.
-x
This option indicates that BIND 9 should only sign the DNSKEY, CDNSKEY, and CDS RRsets with key-signingkeys, and should omit signatures from zone-signing keys.
-zThis option indicates that BIND 9 should ignore the KSK flag on keys when determining what to sign. This causes
KSK-flagged keys to sign all records, not just the DNSKEY RRset.
-3 salt
This option generates an NSEC3 chain with the given hex-encoded salt. A dash (-) can be used to indicate that nosalt is to be used when generating the NSEC3 chain.
Note: -3 - is the recommended configuration. Adding salt provides no practical benefits. See RFC 9276.
-H iterations
This option indicates that, when generating an NSEC3 chain, BIND 9 should use this many iterations. The default
is 0.
Warning: Values greater than 0 cause interoperability issues and also increase the risk of CPU-exhausting
DoS attacks. See RFC 9276.
-A
This option indicates that, when generating an NSEC3 chain, BIND 9 should set the OPTOUT flag on all NSEC3
records and should not generate NSEC3 records for insecure delegations.
Warning: Do not use this option unless all its implications are fully understood. This option is intended only
for extremely large zones (comparable to com.) with sparse secure delegations. See RFC 9276.

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BIND 9 Administrator Reference Manual, Release 9.20.0-AAThis option turns the OPTOUT flag off for all records. This is useful when using the -u option to modify an
NSEC3 chain which previously had OPTOUT set.
zonefile
This option sets the file containing the zone to be signed.
keyThis option specifies which keys should be used to sign the zone. If no keys are specified, the zone is examined for
DNSKEY records at the zone apex. If these records are found and there are matching private keys in the current
directory, they are used for signing.

15.13.4 Example
The following command signs the example.com zone with the ECDSAP256SHA256 key generated bydnssec-keygen (Kexample.com.+013+17247). Because the -S option is not being used, the zone’s keys must be in
the master file (db.example.com). This invocation looks for dsset files in the current directory, so that DS records
can be imported from them (-g).
% dnssec-signzone -g -o example.com db.example.com \Kexample.com.+013+17247
db.example.com.signed%

In the above example, dnssec-signzone creates the file db.example.com.signed. This file should be referenced in a zone statement in the named.conf file.
This example re-signs a previously signed zone with default parameters. The private keys are assumed to be in the current
directory.
% cp db.example.com.signed db.example.com% dnssec-signzone -o example.com db.example.com
db.example.com.signed%

15.13.5 See Also
dnssec-keygen(8), BIND 9 Administrator Reference Manual, RFC 4033, RFC 6781.

15.14 dnssec-verify - DNSSEC zone verification tool
15.14.1 Synopsis
dnssec-verify [-c class] [-E engine] [-I input-format] [-J filename] [-o origin] [-q] [-v level] [-V] [-x] [-z] {zonefile}

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15.14.2 Description
dnssec-verify verifies that a zone is fully signed for each algorithm found in the DNSKEY RRset for the zone, andthat the NSEC/NSEC3 chains are complete.

15.14.3 Options-c class
This option specifies the DNS class of the zone.
-E engine
This option specifies the cryptographic hardware to use, when applicable.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-I input-format
This option sets the format of the input zone file. Possible formats are text (the default) and raw. This option is
primarily intended to be used for dynamic signed zones, so that the dumped zone file in a non-text format containing
updates can be verified independently. This option is not useful for non-dynamic zones.
-J filename
This option tells dnssec-verify to read the journal from the given file when loading the zone file.
-o origin
This option indicates the zone origin. If not specified, the name of the zone file is assumed to be the origin.
-v levelThis option sets the debugging level.
-VThis option prints version information.
-q
This option sets quiet mode, which suppresses output. Without this option, when dnssec-verify is run it prints
to standard output the number of keys in use, the algorithms used to verify the zone was signed correctly, and otherstatus information. With this option, all non-error output is suppressed, and only the exit code indicates success.
-x
This option verifies only that the DNSKEY RRset is signed with key-signing keys. Without this flag, it is assumed
that the DNSKEY RRset is signed by all active keys. When this flag is set, it is not an error if the DNSKEY RRset
is not signed by zone-signing keys. This corresponds to the -x option in dnssec-signzone.
-zThis option indicates that the KSK flag on the keys should be ignored when determining whether the zone is correctly
signed. Without this flag, it is assumed that there is a non-revoked, self-signed DNSKEY with the KSK flag set
for each algorithm, and that RRsets other than DNSKEY RRset are signed with a different DNSKEY without the
KSK flag set.
With this flag set, BIND 9 only requires that for each algorithm, there be at least one non-revoked, self-signed
DNSKEY, regardless of the KSK flag state, and that other RRsets be signed by a non-revoked key for the samealgorithm that includes the self-signed key; the same key may be used for both purposes. This corresponds to the-z option in dnssec-signzone.
zonefile
This option indicates the file containing the zone to be signed.

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15.14.4 See Also
dnssec-signzone(8), BIND 9 Administrator Reference Manual, RFC 4033.

15.15 dnstap-read - print dnstap data in human-readable form
15.15.1 Synopsis
dnstap-read [-m] [-p] [-x] [-y] {file}

15.15.2 Description
dnstap-read reads dnstap data from a specified file and prints it in a human-readable format. By default, dnstap
data is printed in a short summary format, but if the -y option is specified, a longer and more detailed YAML format isused.

15.15.3 Options-mThis option indicates trace memory allocations, and is used for debugging memory leaks.
-pThis option prints the text form of the DNS message that was encapsulated in the dnstap frame, after printing
the dnstap data.
-tThis option prints long timestamps with millisecond precision.
-x
This option prints a hex dump of the wire form of the DNS message that was encapsulated in the dnstap frame,
after printing the dnstap data.
-yThis option prints dnstap data in a detailed YAML format.

15.15.4 See Also
named(8), rndc(8), BIND 9 Administrator Reference Manual.

15.16 filter-aaaa.so - filter AAAA in DNS responses when A is present
15.16.1 Synopsis
plugin query “filter-aaaa.so” [{ parameters }];15.15. dnstap-read - print dnstap data in human-readable form

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15.16.2 Description
filter-aaaa.so is a query plugin module for named, enabling named to omit some IPv6 addresses when responding to clients.
Until BIND 9.12, this feature was implemented natively in named and enabled with the filter-aaaa ACL and thefilter-aaaa-on-v4 and filter-aaaa-on-v6 options. These options are no longer available in named.conf
but can be passed as parameters to the filter-aaaa.so plugin, for example:
plugin query "filter-aaaa.so" {filter-aaaa-on-v4 yes;filter-aaaa-on-v6 yes;filter-aaaa { 192.0.2.1; 2001:db8:2::1; };};This module is intended to aid transition from IPv4 to IPv6 by withholding IPv6 addresses from DNS clients which are
not connected to the IPv6 Internet, when the name being looked up has an IPv4 address available. Use of this module is
not recommended unless absolutely necessary.
Note: This mechanism can erroneously cause other servers not to give AAAA records to their clients. If a recursing
server with both IPv6 and IPv4 network connections queries an authoritative server using this mechanism via IPv4, it isdenied AAAA records even if its client is using IPv6.

15.16.3 Options
filter-aaaa
This option specifies a list of client addresses for which AAAA filtering is to be applied. The default is any.
filter-aaaa-on-v4
If set to yes, this option indicates that the DNS client is at an IPv4 address, in filter-aaaa. If the response
does not include DNSSEC signatures, then all AAAA records are deleted from the response. This filtering applies
to all responses, not only authoritative ones.
If set to break-dnssec, then AAAA records are deleted even when DNSSEC is enabled. As suggested by thename, this causes the response to fail to verify, because the DNSSEC protocol is designed to detect deletions.
This mechanism can erroneously cause other servers not to give AAAA records to their clients. If a recursing serverwith both IPv6 and IPv4 network connections queries an authoritative server using this mechanism via IPv4, it isdenied AAAA records even if its client is using IPv6.
filter-aaaa-on-v6
This option is identical to filter-aaaa-on-v4, except that it filters AAAA responses to queries from IPv6
clients instead of IPv4 clients. To filter all responses, set both options to yes.

15.16.4 See Also
BIND 9 Administrator Reference Manual.

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15.17 host - DNS lookup utility
15.17.1 Synopsis
host [-aACdlnrsTUwv] [-c class] [-N ndots] [-p port] [-R number] [-t type] [-W wait] [-m flag] [ [-4] | [-6] ] [-v] [-V]
{name} [server]

15.17.2 Description
host is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa.
When no arguments or options are given, host prints a short summary of its command-line arguments and options.
name is the domain name that is to be looked up. It can also be a dotted-decimal IPv4 address or a colon-delimited IPv6
address, in which case host by default performs a reverse lookup for that address. server is an optional argument
which is either the name or IP address of the name server that host should query instead of the server or servers listed
in /etc/resolv.conf.

15.17.3 Options-4
This option specifies that only IPv4 should be used for query transport. See also the -6 option.
-6
This option specifies that only IPv6 should be used for query transport. See also the -4 option.
-a
The -a (“all”) option is normally equivalent to -v -t ANY. It also affects the behavior of the -l list zone option.
-A
The -A (“almost all”) option is equivalent to -a, except that RRSIG, NSEC, and NSEC3 records are omitted fromthe output.
-c class
This option specifies the query class, which can be used to lookup HS (Hesiod) or CH (Chaosnet) class resource
records. The default class is IN (Internet).
-C
This option indicates that named should check consistency, meaning that host queries the SOA records for zone
name from all the listed authoritative name servers for that zone. The list of name servers is defined by the NS
records that are found for the zone.
-dThis option prints debugging traces, and is equivalent to the -v verbose option.
-lThis option tells named to list the zone, meaning the host command performs a zone transfer of zone name andprints out the NS, PTR, and address records (A/AAAA).
Together, the -l -a options print all records in the zone.

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BIND 9 Administrator Reference Manual, Release 9.20.0-N ndotsThis option specifies the number of dots (ndots) that have to be in name for it to be considered absolute. The
default value is that defined using the ndots statement in /etc/resolv.conf, or 1 if no ndots statement
is present. Names with fewer dots are interpreted as relative names, and are searched for in the domains listed in
the search or domain directive in /etc/resolv.conf.
-p portThis option specifies the port to query on the server. The default is 53.
-rThis option specifies a non-recursive query; setting this option clears the RD (recursion desired) bit in the query.
This means that the name server receiving the query does not attempt to resolve name. The -r option enables
host to mimic the behavior of a name server by making non-recursive queries, and expecting to receive answers
to those queries that can be referrals to other name servers.
-R numberThis option specifies the number of retries for UDP queries. If number is negative or zero, the number of retries
is silently set to 1. The default value is 1, or the value of the attempts option in /etc/resolv.conf, if set.
-s
This option tells named not to send the query to the next nameserver if any server responds with a SERVFAIL
response, which is the reverse of normal stub resolver behavior.
-t typeThis option specifies the query type. The type argument can be any recognized query type: CNAME, NS, SOA,
TXT, DNSKEY, AXFR, etc.
When no query type is specified, host automatically selects an appropriate query type. By default, it looks for A,
AAAA, and MX records. If the -C option is given, queries are made for SOA records. If name is a dotted-decimal
IPv4 address or colon-delimited IPv6 address, host queries for PTR records.
If a query type of IXFR is chosen, the starting serial number can be specified by appending an equals sign (=),
followed by the starting serial number, e.g., -t IXFR=12345678.
-T, -UThis option specifies TCP or UDP. By default, host uses UDP when making queries; the -T option makes it use
a TCP connection when querying the name server. TCP is automatically selected for queries that require it, such aszone transfer (AXFR) requests. Type ANY queries default to TCP, but can be forced to use UDP initially via -U.
-m flag
This option sets memory usage debugging: the flag can be record, usage, or trace. The -m option can be
specified more than once to set multiple flags.
-v
This option sets verbose output, and is equivalent to the -d debug option. Verbose output can also be enabled by
setting the debug option in /etc/resolv.conf.
-V
This option prints the version number and exits.
-w
This option sets “wait forever”: the query timeout is set to the maximum possible. See also the -W option.
-W waitThis options sets the length of the wait timeout, indicating that named should wait for up to wait seconds for a
reply. If wait is less than 1, the wait interval is set to 1 second.

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By default, host waits for 5 seconds for UDP responses and 10 seconds for TCP connections. These defaults canbe overridden by the timeout option in /etc/resolv.conf.
See also the -w option.

15.17.4 IDN Support
If host has been built with IDN (internationalized domain name) support, it can accept and display non-ASCII domainnames. host appropriately converts character encoding of a domain name before sending a request to a DNS serveror displaying a reply from the server. To turn off IDN support, define the IDN_DISABLE environment variable. IDN
support is disabled if the variable is set when host runs.

15.17.5 Files/etc/resolv.conf

15.17.6 See Alsodig(1), named(8).

15.18 mdig - DNS pipelined lookup utility
15.18.1 Synopsis
mdig {@server} [-f filename] [-h] [-v] [ [-4] | [-6] ] [-m] [-b address] [-p port#] [-c class] [-t type] [-i] [-x addr][plusopt…]
mdig {-h}mdig [@server] {global-opt…} { {local-opt…} {query} …}

15.18.2 Description
mdig is a multiple/pipelined query version of dig: instead of waiting for a response after sending each query, it begins
by sending all queries. Responses are displayed in the order in which they are received, not in the order the corresponding
queries were sent.
mdig options are a subset of the dig options, and are divided into “anywhere options,” which can occur anywhere,“global options,” which must occur before the query name (or they are ignored with a warning), and “local options,”
which apply to the next query on the command line.
The @server option is a mandatory global option. It is the name or IP address of the name server to query. (Unlike
dig, this value is not retrieved from /etc/resolv.conf.) It can be an IPv4 address in dotted-decimal notation, an
IPv6 address in colon-delimited notation, or a hostname. When the supplied server argument is a hostname, mdig
resolves that name before querying the name server.
mdig provides a number of query options which affect the way in which lookups are made and the results displayed.
Some of these set or reset flag bits in the query header, some determine which sections of the answer get printed, andothers determine the timeout and retry strategies.

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Each query option is identified by a keyword preceded by a plus sign (+). Some keywords set or reset an option. Thesemay be preceded by the string no to negate the meaning of that keyword. Other keywords assign values to options likethe timeout interval. They have the form +keyword=value.

15.18.3 Anywhere Options-fThis option makes mdig operate in batch mode by reading a list of lookup requests to process from the file
filename. The file contains a number of queries, one per line. Each entry in the file should be organized in
the same way they would be presented as queries to mdig using the command-line interface.
-hThis option causes mdig to print detailed help information, with the full list of options, and exit.
-v
This option causes mdig to print the version number and exit.

15.18.4 Global Options-4
This option forces mdig to only use IPv4 query transport.
-6This option forces mdig to only use IPv6 query transport.
-b addressThis option sets the source IP address of the query to address. This must be a valid address on one of the host’s
network interfaces or “0.0.0.0” or “::”. An optional port may be specified by appending “#<port>”-mThis option enables memory usage debugging.
-p port#This option is used when a non-standard port number is to be queried. port# is the port number that mdig sends
its queries to, instead of the standard DNS port number 53. This option is used to test a name server that has been
configured to listen for queries on a non-standard port number.
The global query options are:+additional, +noadditional
This option displays [or does not display] the additional section of a reply. The default is to display it.
+all, +noall
This option sets or clears all display flags.
+answer, +noanswer
This option displays [or does not display] the answer section of a reply. The default is to display it.
+authority, +noauthority
This option displays [or does not display] the authority section of a reply. The default is to display it.
+besteffort, +nobesteffort
This option attempts to display [or does not display] the contents of messages which are malformed. The default
is to not display malformed answers.

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BIND 9 Administrator Reference Manual, Release 9.20.0+burstThis option delays queries until the start of the next second.
+cl, +nocl
This option displays [or does not display] the CLASS when printing the record.
+comments, +nocomments
This option toggles the display of comment lines in the output. The default is to print comments.
+continue, +nocontinue
This option toggles continuation on errors (e.g. timeouts).
+crypto, +nocrypto
This option toggles the display of cryptographic fields in DNSSEC records. The contents of these fields are unnecessary to debug most DNSSEC validation failures and removing them makes it easier to see the common failures.
The default is to display the fields. When omitted, they are replaced by the string “[omitted]”; in the DNSKEY
case, the key ID is displayed as the replacement, e.g., [ key id = value ].
+multiline, +nomultiline
This option toggles printing of records, like the SOA records, in a verbose multi-line format with human-readable
comments. The default is to print each record on a single line, to facilitate machine parsing of the mdig output.
+question, +noquestion
This option prints [or does not print] the question section of a query when an answer is returned. The default is toprint the question section as a comment.
+rrcomments, +norrcomments
This option toggles the display of per-record comments in the output (for example, human-readable key information
about DNSKEY records). The default is not to print record comments unless multiline mode is active.
+short, +noshortThis option provides [or does not provide] a terse answer. The default is to print the answer in a verbose form.
+split=W
This option splits long hex- or base64-formatted fields in resource records into chunks of W characters (where W isrounded up to the nearest multiple of 4). +nosplit or +split=0 causes fields not to be split. The default is 56
characters, or 44 characters when multiline mode is active.
+tcp, +notcp
This option uses [or does not use] TCP when querying name servers. The default behavior is to use UDP.
+ttlid, +nottlid
This option displays [or does not display] the TTL when printing the record.
+ttlunits, +nottlunits
This option displays [or does not display] the TTL in friendly human-readable time units of “s”, “m”, “h”, “d”, and“w”, representing seconds, minutes, hours, days, and weeks. This implies +ttlid.
+vc, +novc
This option uses [or does not use] TCP when querying name servers. This alternate syntax to +tcp is provided
for backwards compatibility. The vc stands for “virtual circuit”.

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15.18.5 Local Options-c class
This option sets the query class to class. It can be any valid query class which is supported in BIND 9. The
default query class is “IN”.
-t typeThis option sets the query type to type. It can be any valid query type which is supported in BIND 9. The default
query type is “A”, unless the -x option is supplied to indicate a reverse lookup with the “PTR” query type.
-x addr
Reverse lookups - mapping addresses to names - are simplified by this option. addr is an IPv4 address in dotteddecimal notation, or a colon-delimited IPv6 address. mdig automatically performs a lookup for a query namelike 11.12.13.10.in-addr.arpa and sets the query type and class to PTR and IN respectively. By default,
IPv6 addresses are looked up using nibble format under the IP6.ARPA domain.
The local query options are:+aaflag, +noaaflag
This is a synonym for +aaonly, +noaaonly.
+aaonly, +noaaonly
This sets the aa flag in the query.
+adflag, +noadflag
This sets [or does not set] the AD (authentic data) bit in the query. This requests the server to return whether all of
the answer and authority sections have all been validated as secure, according to the security policy of the server.
AD=1 indicates that all records have been validated as secure and the answer is not from a OPT-OUT range. AD=0
indicates that some part of the answer was insecure or not validated. This bit is set by default.
+bufsize=B
This sets the UDP message buffer size advertised using EDNS0 to B bytes. The maximum and minimum sizes ofthis buffer are 65535 and 0 respectively. Values outside this range are rounded up or down appropriately. Values
other than zero cause a EDNS query to be sent.
+cdflag, +nocdflag
This sets [or does not set] the CD (checking disabled) bit in the query. This requests the server to not perform
DNSSEC validation of responses.
+cookie=####, +nocookie
This sends [or does not send] a COOKIE EDNS option, with an optional value. Replaying a COOKIE from aprevious response allows the server to identify a previous client. The default is +nocookie.
+dnssec, +nodnssec
This requests that DNSSEC records be sent by setting the DNSSEC OK (DO) bit in the OPT record in the additional
section of the query.
+edns[=#], +noedns
This specifies [or does not specify] the EDNS version to query with. Valid values are 0 to 255. Setting the EDNS
version causes an EDNS query to be sent. +noedns clears the remembered EDNS version. EDNS is set to 0 by
default.
+ednsflags[=#], +noednsflags
This sets the must-be-zero EDNS flag bits (Z bits) to the specified value. Decimal, hex, and octal encodings are
accepted. Setting a named flag (e.g. DO) is silently ignored. By default, no Z bits are set.

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BIND 9 Administrator Reference Manual, Release 9.20.0+ednsopt[=code[:value]], +noednsopt
This specifies [or does not specify] an EDNS option with code point code and an optional payload of value asa hexadecimal string. +noednsopt clears the EDNS options to be sent.
+expire, +noexpire
This toggles sending of an EDNS Expire option.
+nsid, +nonsid
This toggles inclusion of an EDNS name server ID request when sending a query.
+recurse, +norecurseThis toggles the setting of the RD (recursion desired) bit in the query. This bit is set by default, which means mdig
normally sends recursive queries.
+retry=T
This sets the number of times to retry UDP queries to server to T instead of the default, 2. Unlike +tries, thisdoes not include the initial query.
+subnet=addr[/prefix-length], +nosubnet
This sends [or does not send] an EDNS Client Subnet option with the specified IP address or network prefix.
mdig +subnet=0.0.0.0/0, or simply mdig +subnet=0
This sends an EDNS client-subnet option with an empty address and a source prefix-length of zero, which signals
a resolver that the client’s address information must not be used when resolving this query.
+timeout=T
This sets the timeout for a query to T seconds. The default timeout is 5 seconds for UDP transport and 10 for TCP.
An attempt to set T to less than 1 results in a query timeout of 1 second being applied.
+tries=T
This sets the number of times to try UDP queries to server to T instead of the default, 3. If T is less than or equal
to zero, the number of tries is silently rounded up to 1.
+udptimeout=T
This sets the timeout between UDP query retries to T.
+unknownformat, +nounknownformat
This prints [or does not print] all RDATA in unknown RR-type presentation format (see RFC 3597). The default
is to print RDATA for known types in the type’s presentation format.
+yaml, +noyaml
This toggles printing of the responses in a detailed YAML format.
+zflag, +nozflag
This sets [or does not set] the last unassigned DNS header flag in a DNS query. This flag is off by default.

15.18.6 See Alsodig(1), RFC 1035.

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15.19 named-checkconf - named configuration file syntax checking
tool
15.19.1 Synopsis
named-checkconf [-achjlvz] [-p [-x ]] [-t directory] {filename}15.19.2 Description
named-checkconf checks the syntax, but not the semantics, of a named configuration file. The file, along with all
files included by it, is parsed and checked for syntax errors. If no file is specified, /etc/named.conf is read by default.
Note: files that named reads in separate parser contexts, such as rndc.conf or rndc.key, are not automatically read by named-checkconf. Configuration errors in these files may cause named to fail to run, even if
named-checkconf was successful. However, named-checkconf can be run on these files explicitly.

15.19.3 Options-aDon’t check the dnssec-policy’s DNSSEC key algorithms against those supported by the crypto provider. This isuseful when checking a named.conf intended to be run on another machine with possibly a different set of supported
DNSSEC key algorithms.
-hThis option prints the usage summary and exits.
-jWhen loading a zonefile, this option instructs named to read the journal if it exists.
-lThis option lists all the configured zones. Each line of output contains the zone name, class (e.g. IN), view, andtype (e.g. primary or secondary).
-cThis option specifies that only the “core” configuration should be checked. This suppresses the loading of plugin
modules, and causes all parameters to plugin statements to be ignored.
-iThis option ignores warnings on deprecated options.
-pThis option prints out the named.conf and included files in canonical form if no errors were detected. See also
the -x option.
-t directoryThis option instructs named to chroot to directory, so that include directives in the configuration file areprocessed as if run by a similarly chrooted named.
-v
This option prints the version of the named-checkconf program and exits.

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BIND 9 Administrator Reference Manual, Release 9.20.0-xWhen printing the configuration files in canonical form, this option obscures shared secrets by replacing themwith strings of question marks (?). This allows the contents of named.conf and related files to be shared - forexample, when submitting bug reports - without compromising private data. This option cannot be used without-p.
-zThis option performs a test load of all zones of type primary found in named.conf.
filename
This indicates the name of the configuration file to be checked. If not specified, it defaults to /etc/named.conf.

15.19.4 Return Values
named-checkconf returns an exit status of 1 if errors were detected and 0 otherwise.

15.19.5 See Also
named(8), named-checkzone(8), BIND 9 Administrator Reference Manual.

15.20 named-checkzone - zone file validation tool
15.20.1 Synopsis
named-checkzone [-d] [-h] [-j] [-q] [-v] [-c class] [-C mode] [-f format] [-F format] [-J filename] [-i mode] [-kmode] [-m mode] [-M mode] [-n mode] [-l ttl] [-L serial] [-o filename] [-r mode] [-s style] [-S mode] [-t directory] [-Tmode] [-w directory] [-D] [-W mode] {zonename} {filename}15.20.2 Description
named-checkzone checks the syntax and integrity of a zone file. It performs the same checks as named does whenloading a zone. This makes named-checkzone useful for checking zone files before configuring them into a nameserver.

15.20.3 Options-dThis option enables debugging.
-hThis option prints the usage summary and exits.
-qThis option sets quiet mode, which only sets an exit code to indicate successful or failed completion.
-v
This option prints the version of the named-checkzone program and exits.

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BIND 9 Administrator Reference Manual, Release 9.20.0-jWhen loading a zone file, this option tells named to read the journal if it exists. The journal file name is assumed
to be the zone file name with the string .jnl appended.
-J filename
When loading the zone file, this option tells named to read the journal from the given file, if it exists. This implies-j.
-c class
This option specifies the class of the zone. If not specified, IN is assumed.
-C modeThis option controls check mode on zone files when loading. Possible modes are check-svcb:fail andcheck-svcb:ignore.
check-svcb:fail turns on additional checks on _dns SVCB records and check-svcb:ignore disables
these checks. The default is check-svcb:fail.
-i modeThis option performs post-load zone integrity checks. Possible modes are full (the default), full-sibling,
local, local-sibling, and none.
Mode full checks that MX records refer to A or AAAA records (both in-zone and out-of-zone hostnames).
Mode local only checks MX records which refer to in-zone hostnames.
Mode full checks that SRV records refer to A or AAAA records (both in-zone and out-of-zone hostnames).
Mode local only checks SRV records which refer to in-zone hostnames.
Mode full checks that delegation NS records refer to A or AAAA records (both in-zone and out-of-zone hostnames). It also checks that glue address records in the zone match those advertised by the child. Mode local
only checks NS records which refer to in-zone hostnames or verifies that some required glue exists, i.e., when thename server is in a child zone.
Modes full-sibling and local-sibling disable sibling glue checks, but are otherwise the same as fulland local, respectively.
Mode none disables the checks.
-f format
This option specifies the format of the zone file. Possible formats are text (the default), and raw.
-F format
This option specifies the format of the output file specified. For named-checkzone, this does not have any
effect unless it dumps the zone contents.
Possible formats are text (the default), which is the standard textual representation of the zone, and raw and
raw=N, which store the zone in a binary format for rapid loading by named. raw=N specifies the format versionof the raw zone file: if N is 0, the raw file can be read by any version of named; if N is 1, the file can only be readby release 9.9.0 or higher. The default is 1.
-k modeThis option performs check-names checks with the specified failure mode. Possible modes are fail, warn
(the default), and ignore.
-l ttlThis option sets a maximum permissible TTL for the input file. Any record with a TTL higher than this valuecauses the zone to be rejected. This is similar to using the max-zone-ttl option in named.conf.

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BIND 9 Administrator Reference Manual, Release 9.20.0-L serial
When compiling a zone to raw format, this option sets the “source serial” value in the header to the specified serial
number. This is expected to be used primarily for testing purposes.
-m modeThis option specifies whether MX records should be checked to see if they are addresses. Possible modes are fail,warn (the default), and ignore.
-M modeThis option checks whether a MX record refers to a CNAME. Possible modes are fail, warn (the default), andignore.
-n modeThis option specifies whether NS records should be checked to see if they are addresses. Possible modes are fail,warn (the default), and ignore.
-o filename
This option writes the zone output to filename. If filename is -, then the zone output is written to standard
output.
-r modeThis option checks for records that are treated as different by DNSSEC but are semantically equal in plain DNS.
Possible modes are fail, warn (the default), and ignore.
-s style
This option specifies the style of the dumped zone file. Possible styles are full (the default) and relative.
The full format is most suitable for processing automatically by a separate script. The relative format is morehuman-readable and is thus suitable for editing by hand. This does not have any effect unless it dumps the zone
contents. It also does not have any meaning if the output format is not text.
-S modeThis option checks whether an SRV record refers to a CNAME. Possible modes are fail, warn (the default),
and ignore.
-t directoryThis option tells named to chroot to directory, so that include directives in the configuration file are processed as if run by a similarly chrooted named.
-T modeThis option checks whether Sender Policy Framework (SPF) records exist and issues a warning if an SPF-formatted
TXT record is not also present. Possible modes are warn (the default) and ignore.
-w directoryThis option instructs named to chdir to directory, so that relative filenames in master file $INCLUDE directives work. This is similar to the directory clause in named.conf.
-D
This option dumps the zone file in canonical format.
-W modeThis option specifies whether to check for non-terminal wildcards. Non-terminal wildcards are almost always theresult of a failure to understand the wildcard matching algorithm (RFC 4592). Possible modes are warn (thedefault) and ignore.
zonename
This indicates the domain name of the zone being checked.

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filename
This is the name of the zone file.

15.20.4 Return Values
named-checkzone returns an exit status of 1 if errors were detected and 0 otherwise.

15.20.5 See Also
named(8), named-checkconf(8), named-compilezone(8), RFC 1035, BIND 9 Administrator Reference
Manual.

15.21 named-compilezone - zone file converting tool
15.21.1 Synopsis
named-compilezone [-d] [-h] [-j] [-q] [-v] [-c class] [-C mode] [-f format] [-F format] [-J filename] [-i mode] [-kmode] [-m mode] [-M mode] [-n mode] [-l ttl] [-L serial] [-r mode] [-s style] [-S mode] [-t directory] [-T mode] [-w
directory] [-D] [-W mode] {-o filename} {zonename} {filename}15.21.2 Description
named-compilezone checks the syntax and integrity of a zone file, and dumps the zone contents to a specified filein a specified format.
Unlike named-checkzone, zone contents are not strictly checked by default. If the output is to be used as an actualzone file to be loaded by named, then the check levels should be manually configured to be at least as strict as thosespecified in the named configuration file.
Running named-checkzone on the input prior to compiling will ensure that the zone compiles with the default requirements of named.

15.21.3 Options-dThis option enables debugging.
-hThis option prints the usage summary and exits.
-qThis option sets quiet mode, which only sets an exit code to indicate successful or failed completion.
-v
This option prints the version of the named-checkzone program and exits.
-jWhen loading a zone file, this option tells named to read the journal if it exists. The journal file name is assumed
to be the zone file name with the string .jnl appended.

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BIND 9 Administrator Reference Manual, Release 9.20.0-J filename
When loading the zone file, this option tells named to read the journal from the given file, if it exists. This implies-j.
-c class
This option specifies the class of the zone. If not specified, IN is assumed.
-C modeThis option controls check mode on zone files when loading. Possible modes are check-svcb:fail andcheck-svcb:ignore.
check-svcb:fail turns on additional checks on _dns SVCB records and check-svcb:ignore disables
these checks. The default is check-svcb:ignore.
-i modeThis option performs post-load zone integrity checks. Possible modes are full, full-sibling, local,
local-sibling, and none (the default).
Mode full checks that MX records refer to A or AAAA records (both in-zone and out-of-zone hostnames).
Mode local only checks MX records which refer to in-zone hostnames.
Mode full checks that SRV records refer to A or AAAA records (both in-zone and out-of-zone hostnames).
Mode local only checks SRV records which refer to in-zone hostnames.
Mode full checks that delegation NS records refer to A or AAAA records (both in-zone and out-of-zone hostnames). It also checks that glue address records in the zone match those advertised by the child. Mode local
only checks NS records which refer to in-zone hostnames or verifies that some required glue exists, i.e., when thename server is in a child zone.
Modes full-sibling and local-sibling disable sibling glue checks, but are otherwise the same as fulland local, respectively.
Mode none disables the checks.
-f format
This option specifies the format of the zone file. Possible formats are text (the default), and raw.
-F format
This option specifies the format of the output file specified. For named-checkzone, this does not have any
effect unless it dumps the zone contents.
Possible formats are text (the default), which is the standard textual representation of the zone, and raw and
raw=N, which store the zone in a binary format for rapid loading by named. raw=N specifies the format versionof the raw zone file: if N is 0, the raw file can be read by any version of named; if N is 1, the file can only be readby release 9.9.0 or higher. The default is 1.
-k modeThis option performs check-names checks with the specified failure mode. Possible modes are fail, warn,
and ignore (the default).
-l ttlThis option sets a maximum permissible TTL for the input file. Any record with a TTL higher than this valuecauses the zone to be rejected. This is similar to using the max-zone-ttl option in named.conf.
-L serial
When compiling a zone to raw format, this option sets the “source serial” value in the header to the specified serial
number. This is expected to be used primarily for testing purposes.

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BIND 9 Administrator Reference Manual, Release 9.20.0-m modeThis option specifies whether MX records should be checked to see if they are addresses. Possible modes are fail,warn, and ignore (the default).
-M modeThis option checks whether a MX record refers to a CNAME. Possible modes are fail, warn, and ignore (thedefault).
-n modeThis option specifies whether NS records should be checked to see if they are addresses. Possible modes are fail,warn, and ignore (the default).
-o filename
This option writes the zone output to filename. If filename is -, then the zone output is written to standard
output. This is mandatory for named-compilezone.
-r modeThis option checks for records that are treated as different by DNSSEC but are semantically equal in plain DNS.
Possible modes are fail, warn, and ignore (the default).
-s style
This option specifies the style of the dumped zone file. Possible styles are full (the default) and relative.
The full format is most suitable for processing automatically by a separate script. The relative format is morehuman-readable and is thus suitable for editing by hand.
-S modeThis option checks whether an SRV record refers to a CNAME. Possible modes are fail, warn, and ignore(the default).
-t directoryThis option tells named to chroot to directory, so that include directives in the configuration file are processed as if run by a similarly chrooted named.
-T modeThis option checks whether Sender Policy Framework (SPF) records exist and issues a warning if an SPF-formatted
TXT record is not also present. Possible modes are warn and ignore (the default).
-w directoryThis option instructs named to chdir to directory, so that relative filenames in master file $INCLUDE directives work. This is similar to the directory clause in named.conf.
-D
This option dumps the zone file in canonical format. This is always enabled for named-compilezone.
-W modeThis option specifies whether to check for non-terminal wildcards. Non-terminal wildcards are almost always theresult of a failure to understand the wildcard matching algorithm (RFC 4592). Possible modes are warn andignore (the default).
zonename
This indicates the domain name of the zone being checked.
filename
This is the name of the zone file.

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15.21.4 Return Values
named-compilezone returns an exit status of 1 if errors were detected and 0 otherwise.

15.21.5 See Also
named(8), named-checkconf(8), named-checkzone(8), RFC 1035, BIND 9 Administrator Reference
Manual.

15.22 named-journalprint - print zone journal in human-readableform
15.22.1 Synopsis
named-journalprint [-c serial] [-dux] {journal}

15.22.2 Description
named-journalprint scans the contents of a zone journal file, printing it in a human-readable form, or, optionally,
converting it to a different journal file format.
Journal files are automatically created by named when changes are made to dynamic zones (e.g., by nsupdate). They
record each addition or deletion of a resource record, in binary format, allowing the changes to be re-applied to the zone
when the server is restarted after a shutdown or crash. By default, the name of the journal file is formed by appending
the extension .jnl to the name of the corresponding zone file.
named-journalprint converts the contents of a given journal file into a human-readable text format. Each line
begins with add or del, to indicate whether the record was added or deleted, and continues with the resource record in
master-file format.
The -c (compact) option provides a mechanism to reduce the size of a journal by removing (most/all) transactions prior
to the specified serial number. Note: this option must not be used while named is running, and can cause data loss if thezone file has not been updated to contain the data being removed from the journal. Use with extreme caution.
The -x option causes additional data about the journal file to be printed at the beginning of the output and before eachgroup of changes.
The -u (upgrade) and -d (downgrade) options recreate the journal file with a modified format version. The existing
journal file is replaced. -d writes out the journal in the format used by versions of BIND up to 9.16.11; -u writes it out
in the format used by versions since 9.16.13. (9.16.12 is omitted due to a journal-formatting bug in that release.) Notethat these options must not be used while named is running.

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15.22.3 See Also
named(8), nsupdate(1), BIND 9 Administrator Reference Manual.

15.23 named-nzd2nzf - convert an NZD database to NZF text format
15.23.1 Synopsis
named-nzd2nzf {filename}15.23.2 Description
named-nzd2nzf converts an NZD database to NZF format and prints it to standard output. This can be used to review
the configuration of zones that were added to named via rndc addzone. It can also be used to restore the old fileformat when rolling back from a newer version of BIND to an older version.

15.23.3 Arguments
filename
This is the name of the .nzd file whose contents should be printed.

15.23.4 See Also
BIND 9 Administrator Reference Manual.

15.24 named-rrchecker - syntax checker for individual DNS resource
records
15.24.1 Synopsis
named-rrchecker [-h] [-o origin] [-p] [-u] [-C] [-T] [-P]

15.24.2 Description
named-rrchecker reads a individual DNS resource record from standard input and checks whether it is syntacticallycorrect.

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15.24.3 Options-hThis option prints out the help menu.
-o origin
This option specifies the origin to be used when interpreting the record.
-pThis option prints out the resulting record in canonical form. If there is no canonical form defined, the record is
printed in unknown record format.
-uThis option prints out the resulting record in unknown record form.
-C, -T, -P
These options print out the known class, standard type, and private type mnemonics, respectively.

15.24.4 See Also
RFC 1034, RFC 1035, named(8).

15.25 named.conf - configuration file for named
15.25.1 Synopsis
named.conf

15.25.2 Description
named.conf is the configuration file for named.
For complete documentation about the configuration statements, please refer to the Configuration Reference section in
the BIND 9 Administrator Reference Manual.
Statements are enclosed in braces and terminated with a semi-colon. Clauses in the statements are also semi-colon
terminated. The usual comment styles are supported:
C style: /* */C++ style: // to end of line
Unix style: # to end of lineacl <string> { <address_match_element>; ... }; // may occur multiple times
controls {inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] allow,→{ <address_match_element>; ... } [ keys { <string>; ... } ] [ read-only <boolean> ];,→ // may occur multiple times
unix <quoted_string> perm <integer> owner <integer> group <integer> [ keys {,→<string>; ... } ] [ read-only <boolean> ]; // may occur multiple times}; // may occur multiple times(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)dlz <string> {database <string>;
search <boolean>;}; // may occur multiple times
dnssec-policy <string> {cdnskey <boolean>;
cds-digest-types { <string>; ... };dnskey-ttl <duration>;
inline-signing <boolean>;keys { ( csk | ksk | zsk ) [ key-directory | key-store <string> ] lifetime,→<duration_or_unlimited> algorithm <string> [ <integer> ]; ... };max-zone-ttl <duration>;
nsec3param [ iterations <integer> ] [ optout <boolean> ] [ salt-length,→<integer> ];parent-ds-ttl <duration>;parent-propagation-delay <duration>;publish-safety <duration>;purge-keys <duration>;retire-safety <duration>;signatures-jitter <duration>;signatures-refresh <duration>;signatures-validity <duration>;signatures-validity-dnskey <duration>;zone-propagation-delay <duration>;}; // may occur multiple times
dyndb <string> <quoted_string> { <unspecified-text> }; // may occur multiple times
http <string> {endpoints { <quoted_string>; ... };listener-clients <integer>;streams-per-connection <integer>;}; // may occur multiple times
key <string> {algorithm <string>;
secret <string>;}; // may occur multiple times
key-store <string> {directory <string>;
pkcs11-uri <quoted_string>;}; // may occur multiple times
logging {category <string> { <string>; ... }; // may occur multiple times
channel <string> {buffered <boolean>;file <quoted_string> [ versions ( unlimited | <integer> ) ] [ size,→<size> ] [ suffix ( increment | timestamp ) ];null;
print-category <boolean>;print-severity <boolean>;print-time ( iso8601 | iso8601-utc | local | <boolean> );severity <log_severity>;(continues on next page)502

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managed-keys { <string> ( static-key | initial-key | static-ds | initial-ds ),→<integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times,␣
,→deprecatedoptions {allow-new-zones <boolean>;allow-notify { <address_match_element>; ... };allow-proxy { <address_match_element>; ... }; // experimental
allow-proxy-on { <address_match_element>; ... }; // experimental
allow-query { <address_match_element>; ... };allow-query-cache { <address_match_element>; ... };allow-query-cache-on { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-recursion { <address_match_element>; ... };allow-recursion-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6␣
,→( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };answer-cookie <boolean>;
attach-cache <string>;
auth-nxdomain <boolean>;
automatic-interface-scan <boolean>;
avoid-v4-udp-ports { <portrange>; ... }; // deprecatedavoid-v6-udp-ports { <portrange>; ... }; // deprecatedbindkeys-file <quoted_string>; // test only
blackhole { <address_match_element>; ... };catalog-zones { zone <string> [ default-primaries [ port <integer> ] [ source␣,→( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers>␣
,→| <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key,→<string> ] [ tls <string> ]; ... } ] [ zone-directory <quoted_string> ] [ in-memory,→<boolean> ] [ min-update-interval <duration> ]; ... };check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( primary | master | secondary | slave | response ) ( fail | warn␣
,→| ignore ); // may occur multiple times
check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;clients-per-query <integer>;cookie-algorithm ( siphash24 );cookie-secret <string>; // may occur multiple times
deny-answer-addresses { <address_match_element>; ... } [ except-from {,→<string>; ... } ];deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];(continues on next page)

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dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddirectory <quoted_string>;
disable-algorithms <string> { <string>; ... }; // may occur multiple times
disable-ds-digests <string> { <string>; ... }; // may occur multiple times
disable-empty-zone <string>; // may occur multiple times
dns64 <netprefix> {break-dnssec <boolean>;clients { <address_match_element>; ... };exclude { <address_match_element>; ... };mapped { <address_match_element>; ... };recursive-only <boolean>;suffix <ipv6_address>;}; // may occur multiple times
dns64-contact <string>;
dns64-server <string>;
dnskey-sig-validity <integer>; // obsolete
dnsrps-enable <boolean>; // not configured
dnsrps-library <quoted_string>; // not configured
dnsrps-options { <unspecified-text> }; // not configured
dnssec-accept-expired <boolean>;dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-must-be-secure <string> <boolean>; // may occur multiple times,␣
,→deprecateddnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
dnssec-validation ( yes | no | auto );dnstap { ( all | auth | client | forwarder | resolver | update ) [ ( query |␣,→response ) ]; ... }; // not configured
dnstap-identity ( <quoted_string> | none | hostname ); // not configured
dnstap-output ( file | unix ) <quoted_string> [ size ( unlimited | <size> ) ]␣,→[ versions ( unlimited | <integer> ) ] [ suffix ( increment | timestamp ) ]; // not␣,→configured
dnstap-version ( <quoted_string> | none ); // not configured
dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer> ]␣
,→| <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };dump-file <quoted_string>;
edns-udp-size <integer>;
empty-contact <string>;
empty-server <string>;
empty-zones-enable <boolean>;fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
fetches-per-server <integer> [ ( drop | fail ) ];fetches-per-zone <integer> [ ( drop | fail ) ];flush-zones-on-shutdown <boolean>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };fstrm-set-buffer-hint <integer>; // not configured
fstrm-set-flush-timeout <integer>; // not configured
fstrm-set-input-queue-size <integer>; // not configured
fstrm-set-output-notify-threshold <integer>; // not configured
fstrm-set-output-queue-model ( mpsc | spsc ); // not configured
fstrm-set-output-queue-size <integer>; // not configured
fstrm-set-reopen-interval <duration>; // not configured(continues on next page)504

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geoip-directory ( <quoted_string> | none );heartbeat-interval <integer>; // deprecatedhostname ( <quoted_string> | none );http-listener-clients <integer>;
http-port <integer>;
http-streams-per-connection <integer>;https-port <integer>;interface-interval <duration>;
ipv4only-contact <string>;
ipv4only-enable <boolean>;
ipv4only-server <string>;
ixfr-from-differences ( primary | master | secondary | slave | <boolean> );keep-response-order { <address_match_element>; ... }; // obsolete
key-directory <quoted_string>;lame-ttl <duration>;
listen-on [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http,→<string> ] { <address_match_element>; ... }; // may occur multiple times
listen-on-v6 [ port <integer> ] [ proxy <string> ] [ tls <string> ] [ http,→<string> ] { <address_match_element>; ... }; // may occur multiple times
lmdb-mapsize <sizeval>;managed-keys-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );match-mapped-addresses <boolean>;max-cache-size ( default | unlimited | <sizeval> | <percentage> );max-cache-ttl <duration>;max-clients-per-query <integer>;max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-ncache-ttl <duration>;max-records <integer>;max-records-per-type <integer>;max-recursion-depth <integer>;max-recursion-queries <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-rsa-exponent-size <integer>;max-stale-ttl <duration>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-udp-size <integer>;max-validation-failures-per-fetch <integer>; // experimental
max-validations-per-fetch <integer>; // experimental
max-zone-ttl ( unlimited | <duration> ); // deprecatedmemstatistics <boolean>;memstatistics-file <quoted_string>;
message-compression <boolean>;min-cache-ttl <duration>;
min-ncache-ttl <duration>;min-refresh-time <integer>;min-retry-time <integer>;minimal-any <boolean>;minimal-responses ( no-auth | no-auth-recursive | <boolean> );multi-master <boolean>;(continues on next page)

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new-zones-directory <quoted_string>;
no-case-compress { <address_match_element>; ... };nocookie-udp-size <integer>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-rate <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
nta-lifetime <duration>;
nta-recheck <duration>;
nxdomain-redirect <string>;
parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );pid-file ( <quoted_string> | none );port <integer>;preferred-glue <string>;
prefetch <integer> [ <integer> ];provide-ixfr <boolean>;qname-minimization ( strict | relaxed | disabled | off );query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );querylog <boolean>;rate-limit {all-per-second <integer>;errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;log-only <boolean>;max-table-size <integer>;min-table-size <integer>;nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;referrals-per-second <integer>;
responses-per-second <integer>;slip <integer>;
window <integer>;};recursing-file <quoted_string>;
recursion <boolean>;recursive-clients <integer>;request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-server-cookie <boolean>;resolver-query-timeout <integer>;
resolver-use-dns64 <boolean>;
response-padding { <address_match_element>; ... } block-size <integer>;
response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [ max,→policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname |␣,→disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only <quoted_,→string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable,→<boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [ break-dnssec <boolean>␣
,→] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ min-ns-dots(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)<integer> ] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [␣,→qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable <boolean>␣
,→] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [ dnsrps-options {,→<unspecified-text> } ];reuseport <boolean>;root-key-sentinel <boolean>;rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string> ],→<string> <string>; ... };secroots-file <quoted_string>;
send-cookie <boolean>;serial-query-rate <integer>;
serial-update-method ( date | increment | unixtime );server-id ( <quoted_string> | none | hostname );servfail-ttl <duration>;session-keyalg <string>;
session-keyfile ( <quoted_string> | none );session-keyname <string>;
sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
sig0checks-quota <integer>; // experimental
sig0checks-quota-exempt { <address_match_element>; ... }; // experimental
sortlist { <address_match_element>; ... }; // deprecatedstale-answer-client-timeout ( disabled | off | <integer> );stale-answer-enable <boolean>;stale-answer-ttl <duration>;stale-cache-enable <boolean>;stale-refresh-time <duration>;startup-notify-rate <integer>;statistics-file <quoted_string>;
synth-from-dnssec <boolean>;
tcp-advertised-timeout <integer>;
tcp-clients <integer>;
tcp-idle-timeout <integer>;
tcp-initial-timeout <integer>;
tcp-keepalive-timeout <integer>;
tcp-listen-queue <integer>;tcp-receive-buffer <integer>;tcp-send-buffer <integer>;tkey-domain <quoted_string>;
tkey-gssapi-credential <quoted_string>;
tkey-gssapi-keytab <quoted_string>;
tls-port <integer>;transfer-format ( many-answers | one-answer );transfer-message-size <integer>;transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers-in <integer>;transfers-out <integer>;transfers-per-ns <integer>;trust-anchor-telemetry <boolean>;try-tcp-refresh <boolean>;
udp-receive-buffer <integer>;
udp-send-buffer <integer>;
update-check-ksk <boolean>; // obsolete
update-quota <integer>;,→(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)use-v4-udp-ports { <portrange>; ... }; // deprecateduse-v6-udp-ports { <portrange>; ... }; // deprecatedv6-bias <integer>;validate-except { <string>; ... };version ( <quoted_string> | none );zero-no-soa-ttl <boolean>;zero-no-soa-ttl-cache <boolean>;zone-statistics ( full | terse | none | <boolean> );};parental-agents <string> [ port <integer> ] [ source ( <ipv4_address> | * ) ] [␣,→source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port,→<integer> ] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ];,→ ... }; // may occur multiple times
plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur multiple times
primaries <string> [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 (,→<ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... }; //␣
,→may occur multiple times
server <netprefix> {bogus <boolean>;edns <boolean>;edns-udp-size <integer>;edns-version <integer>;keys <server_key>;
max-udp-size <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );padding <integer>;provide-ixfr <boolean>;query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-cookie <boolean>;send-cookie <boolean>;
tcp-keepalive <boolean>;
tcp-only <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers <integer>;}; // may occur multiple times
statistics-channels {inet ( <ipv4_address> | <ipv6_address> | * ) [ port ( <integer> | * ) ] [␣,→allow { <address_match_element>; ... } ]; // may occur multiple times}; // may occur multiple times
tls <string> {ca-file <quoted_string>;
cert-file <quoted_string>;
cipher-suites <string>;(continues on next page)

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ciphers <string>;
dhparam-file <quoted_string>;
key-file <quoted_string>;
prefer-server-ciphers <boolean>;
protocols { <string>; ... };remote-hostname <quoted_string>;
session-tickets <boolean>;}; // may occur multiple times
trust-anchors { <string> ( static-key | initial-key | static-ds | initial-ds ),→<integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times
trusted-keys { <string> <integer> <integer> <integer> <quoted_string>; ... }; // may␣,→occur multiple times, deprecatedview <string> [ <class> ] {allow-new-zones <boolean>;allow-notify { <address_match_element>; ... };allow-proxy { <address_match_element>; ... }; // experimental
allow-proxy-on { <address_match_element>; ... }; // experimental
allow-query { <address_match_element>; ... };allow-query-cache { <address_match_element>; ... };allow-query-cache-on { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-recursion { <address_match_element>; ... };allow-recursion-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6␣
,→( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };attach-cache <string>;
auth-nxdomain <boolean>;catalog-zones { zone <string> [ default-primaries [ port <integer> ] [ source␣,→( <ipv4_address> | * ) ] [ source-v6 ( <ipv6_address> | * ) ] { ( <remote-servers>␣
,→| <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ) [ key,→<string> ] [ tls <string> ]; ... } ] [ zone-directory <quoted_string> ] [ in-memory,→<boolean> ] [ min-update-interval <duration> ]; ... };check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( primary | master | secondary | slave | response ) ( fail | warn␣
,→| ignore ); // may occur multiple times
check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;clients-per-query <integer>;deny-answer-addresses { <address_match_element>; ... } [ except-from {,→<string>; ... } ];deny-answer-aliases { <string>; ... } [ except-from { <string>; ... } ];dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecated(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)disable-algorithms <string> { <string>; ... }; // may occur multiple times
disable-ds-digests <string> { <string>; ... }; // may occur multiple times
disable-empty-zone <string>; // may occur multiple times
dlz <string> {database <string>;
search <boolean>;}; // may occur multiple times
dns64 <netprefix> {break-dnssec <boolean>;clients { <address_match_element>; ... };exclude { <address_match_element>; ... };mapped { <address_match_element>; ... };recursive-only <boolean>;suffix <ipv6_address>;}; // may occur multiple times
dns64-contact <string>;
dns64-server <string>;
dnskey-sig-validity <integer>; // obsolete
dnsrps-enable <boolean>; // not configured
dnsrps-options { <unspecified-text> }; // not configured
dnssec-accept-expired <boolean>;dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-must-be-secure <string> <boolean>; // may occur multiple times,␣
,→deprecateddnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
dnssec-validation ( yes | no | auto );dnstap { ( all | auth | client | forwarder | resolver | update ) [ ( query |␣,→response ) ]; ... }; // not configured
dual-stack-servers [ port <integer> ] { ( <quoted_string> [ port <integer> ]␣
,→| <ipv4_address> [ port <integer> ] | <ipv6_address> [ port <integer> ] ); ... };dyndb <string> <quoted_string> { <unspecified-text> }; // may occur multiple␣
,→times
edns-udp-size <integer>;
empty-contact <string>;
empty-server <string>;
empty-zones-enable <boolean>;fetch-quota-params <integer> <fixedpoint> <fixedpoint> <fixedpoint>;
fetches-per-server <integer> [ ( drop | fail ) ];fetches-per-zone <integer> [ ( drop | fail ) ];forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };ipv4only-contact <string>;
ipv4only-enable <boolean>;
ipv4only-server <string>;
ixfr-from-differences ( primary | master | secondary | slave | <boolean> );key <string> {algorithm <string>;
secret <string>;}; // may occur multiple times
key-directory <quoted_string>;lame-ttl <duration>;
lmdb-mapsize <sizeval>;managed-keys { <string> ( static-key | initial-key | static-ds | initial-ds )(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)<integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times,␣
,→deprecatedmasterfile-format ( raw | text );masterfile-style ( full | relative );match-clients { <address_match_element>; ... };match-destinations { <address_match_element>; ... };match-recursive-only <boolean>;max-cache-size ( default | unlimited | <sizeval> | <percentage> );max-cache-ttl <duration>;max-clients-per-query <integer>;max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-ncache-ttl <duration>;max-records <integer>;max-records-per-type <integer>;max-recursion-depth <integer>;max-recursion-queries <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-stale-ttl <duration>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-udp-size <integer>;max-validation-failures-per-fetch <integer>; // experimental
max-validations-per-fetch <integer>; // experimental
max-zone-ttl ( unlimited | <duration> ); // deprecatedmessage-compression <boolean>;min-cache-ttl <duration>;
min-ncache-ttl <duration>;min-refresh-time <integer>;min-retry-time <integer>;minimal-any <boolean>;minimal-responses ( no-auth | no-auth-recursive | <boolean> );multi-master <boolean>;
new-zones-directory <quoted_string>;
no-case-compress { <address_match_element>; ... };nocookie-udp-size <integer>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
nta-lifetime <duration>;
nta-recheck <duration>;
nxdomain-redirect <string>;
parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );plugin ( query ) <string> [ { <unspecified-text> } ]; // may occur multiple␣
,→times
preferred-glue <string>;
prefetch <integer> [ <integer> ];provide-ixfr <boolean>;qname-minimization ( strict | relaxed | disabled | off );,→(continues on next page)

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query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );rate-limit {all-per-second <integer>;errors-per-second <integer>;
exempt-clients { <address_match_element>; ... };ipv4-prefix-length <integer>;
ipv6-prefix-length <integer>;log-only <boolean>;max-table-size <integer>;min-table-size <integer>;nodata-per-second <integer>;
nxdomains-per-second <integer>;
qps-scale <integer>;referrals-per-second <integer>;
responses-per-second <integer>;slip <integer>;
window <integer>;};recursion <boolean>;request-expire <boolean>;request-ixfr <boolean>;request-nsid <boolean>;require-server-cookie <boolean>;resolver-query-timeout <integer>;
resolver-use-dns64 <boolean>;
response-padding { <address_match_element>; ... } block-size <integer>;
response-policy { zone <string> [ add-soa <boolean> ] [ log <boolean> ] [ max,→policy-ttl <duration> ] [ min-update-interval <duration> ] [ policy ( cname |␣,→disabled | drop | given | no-op | nodata | nxdomain | passthru | tcp-only <quoted_,→string> ) ] [ recursive-only <boolean> ] [ nsip-enable <boolean> ] [ nsdname-enable,→<boolean> ] [ ede <string> ]; ... } [ add-soa <boolean> ] [ break-dnssec <boolean>␣
,→] [ max-policy-ttl <duration> ] [ min-update-interval <duration> ] [ min-ns-dots,→<integer> ] [ nsip-wait-recurse <boolean> ] [ nsdname-wait-recurse <boolean> ] [␣,→qname-wait-recurse <boolean> ] [ recursive-only <boolean> ] [ nsip-enable <boolean>␣
,→] [ nsdname-enable <boolean> ] [ dnsrps-enable <boolean> ] [ dnsrps-options {,→<unspecified-text> } ];root-key-sentinel <boolean>;rrset-order { [ class <string> ] [ type <string> ] [ name <quoted_string> ],→<string> <string>; ... };send-cookie <boolean>;serial-update-method ( date | increment | unixtime );server <netprefix> {bogus <boolean>;edns <boolean>;edns-udp-size <integer>;edns-version <integer>;keys <server_key>;
max-udp-size <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );padding <integer>;provide-ixfr <boolean>;query-source [ address ] ( <ipv4_address> | * );query-source-v6 [ address ] ( <ipv6_address> | * );request-expire <boolean>;request-ixfr <boolean>;(continues on next page)

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request-nsid <boolean>;require-cookie <boolean>;send-cookie <boolean>;
tcp-keepalive <boolean>;
tcp-only <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );transfers <integer>;}; // may occur multiple times
servfail-ttl <duration>;sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
sortlist { <address_match_element>; ... }; // deprecatedstale-answer-client-timeout ( disabled | off | <integer> );stale-answer-enable <boolean>;stale-answer-ttl <duration>;stale-cache-enable <boolean>;stale-refresh-time <duration>;synth-from-dnssec <boolean>;transfer-format ( many-answers | one-answer );transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );trust-anchor-telemetry <boolean>;trust-anchors { <string> ( static-key | initial-key | static-ds | initial-ds␣
,→) <integer> <integer> <integer> <quoted_string>; ... }; // may occur multiple times
trusted-keys { <string> <integer> <integer> <integer> <quoted_string>; ... };␣
,→// may occur multiple times, deprecatedtry-tcp-refresh <boolean>;
update-check-ksk <boolean>; // obsolete
v6-bias <integer>;validate-except { <string>; ... };zero-no-soa-ttl <boolean>;zero-no-soa-ttl-cache <boolean>;zone-statistics ( full | terse | none | <boolean> );}; // may occur multiple times

Any of these zone statements can also be set inside the view statement.
zone <string> [ <class> ] {type primary;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6␣
,→( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };check-dup-records ( fail | warn | ignore );check-integrity <boolean>;check-mx ( fail | warn | ignore );check-mx-cname ( fail | warn | ignore );check-names ( fail | warn | ignore );(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)check-sibling <boolean>;check-spf ( warn | ignore );check-srv-cname ( fail | warn | ignore );check-svcb <boolean>;check-wildcard <boolean>;checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete
dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-secure-to-insecure <boolean>; // obsolete
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-transfer-idle-out <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatednotify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer>␣
,→] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );serial-update-method ( date | increment | unixtime );sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsolete
update-check-ksk <boolean>; // obsolete
update-policy ( local | { ( deny | grant ) <string> ( 6to4-self | external |␣,→krb5-self | krb5-selfsub | krb5-subdomain | krb5-subdomain-self-rhs | ms-self | ms,→selfsub | ms-subdomain | ms-subdomain-self-rhs | name | self | selfsub | selfwild |␣,→subdomain | tcp-self | wildcard | zonesub ) [ <string> ] <rrtypelist>; ... } );zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)};
zone <string> [ <class> ] {type secondary;allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6␣
,→( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };check-names ( fail | warn | ignore );checkds ( explicit | <boolean> );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecateddlz <string>;
dnskey-sig-validity <integer>; // obsolete
dnssec-dnskey-kskonly <boolean>; // obsolete
dnssec-loadkeys-interval <integer>;dnssec-policy <string>;
dnssec-update-mode ( maintain | no-resign ); // obsolete
file <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };inline-signing <boolean>;ixfr-from-differences <boolean>;journal <quoted_string>;
key-directory <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );notify-to-soa <boolean>;nsec3-test-zone <boolean>; // test only
parental-agents [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source,→v6 ( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer>␣
(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)] | <ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };parental-source ( <ipv4_address> | * );parental-source-v6 ( <ipv6_address> | * );primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 (,→<ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;sig-signing-nodes <integer>;sig-signing-signatures <integer>;sig-signing-type <integer>;
sig-validity-interval <integer> [ <integer> ]; // obsoletetransfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;
update-check-ksk <boolean>; // obsolete
zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};,→zone <string> [ <class> ] {type mirror;
allow-notify { <address_match_element>; ... };allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };allow-transfer [ port <integer> ] [ transport <string> ] { <address_match_,→element>; ... };allow-update-forwarding { <address_match_element>; ... };also-notify [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6␣
,→( <ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };check-names ( fail | warn | ignore );database <string>;
file <quoted_string>;
ixfr-from-differences <boolean>;journal <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-ixfr-ratio ( unlimited | <percentage> );max-journal-size ( default | unlimited | <sizeval> );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-idle-out <integer>;max-transfer-time-in <integer>;max-transfer-time-out <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;
notify ( explicit | master-only | primary-only | <boolean> );notify-delay <integer>;
notify-source ( <ipv4_address> | * );notify-source-v6 ( <ipv6_address> | * );(continues on next page)

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primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 (,→<ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };request-expire <boolean>;request-ixfr <boolean>;transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );try-tcp-refresh <boolean>;zero-no-soa-ttl <boolean>;zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type forward;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };};zone <string> [ <class> ] {type hint;
check-names ( fail | warn | ignore );file <quoted_string>;};zone <string> [ <class> ] {type redirect;
allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };dlz <string>;
file <quoted_string>;
masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;max-zone-ttl ( unlimited | <duration> ); // deprecatedprimaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 (,→<ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type static-stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };max-records <integer>;max-records-per-type <integer>;max-types-per-name <integer>;server-addresses { ( <ipv4_address> | <ipv6_address> ); ... };server-names { <string>; ... };(continues on next page)

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BIND 9 Administrator Reference Manual, Release 9.20.0(continued from previous page)zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {type stub;allow-query { <address_match_element>; ... };allow-query-on { <address_match_element>; ... };check-names ( fail | warn | ignore );database <string>;
dialup ( notify | notify-passive | passive | refresh | <boolean> ); //␣
,→deprecatedfile <quoted_string>;
forward ( first | only );forwarders [ port <integer> ] [ tls <string> ] { ( <ipv4_address> | <ipv6_,→address> ) [ port <integer> ] [ tls <string> ]; ... };masterfile-format ( raw | text );masterfile-style ( full | relative );max-records <integer>;max-records-per-type <integer>;max-refresh-time <integer>;max-retry-time <integer>;max-transfer-idle-in <integer>;max-transfer-time-in <integer>;max-types-per-name <integer>;min-refresh-time <integer>;min-retry-time <integer>;
multi-master <boolean>;primaries [ port <integer> ] [ source ( <ipv4_address> | * ) ] [ source-v6 (,→<ipv6_address> | * ) ] { ( <remote-servers> | <ipv4_address> [ port <integer> ] |,→<ipv6_address> [ port <integer> ] ) [ key <string> ] [ tls <string> ]; ... };transfer-source ( <ipv4_address> | * );transfer-source-v6 ( <ipv6_address> | * );zone-statistics ( full | terse | none | <boolean> );};zone <string> [ <class> ] {in-view <string>;};

15.25.3 Files/etc/named.conf

15.25.4 See Also
named(8), named-checkconf(8), rndc(8), rndc-confgen(8), tsig-keygen(8), BIND 9 Administrator Reference Manual.

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15.26 named - Internet domain name server
15.26.1 Synopsis
named [ [-4] | [-6] ] [-c config-file] [-C] [-d debug-level] [-D string] [-E engine-name] [-f] [-g] [-L logfile] [-M option][-m flag] [-n #cpus] [-p port] [-s] [-t directory] [-u user] [-v] [-V] ]15.26.2 Description
named is a Domain Name System (DNS) server, part of the BIND 9 distribution from ISC. For more information on
the DNS, see RFC 1033, RFC 1034, and RFC 1035.
When invoked without arguments, named reads the default configuration file /etc/named.conf, reads any initial
data, and listens for queries.

15.26.3 Options-4
This option tells named to use only IPv4, even if the host machine is capable of IPv6. -4 and -6 are mutually
exclusive.
-6
This option tells named to use only IPv6, even if the host machine is capable of IPv4. -4 and -6 are mutually
exclusive.
-c config-file
This option tells named to use config-file as its configuration file instead of the default, /etc/named.
conf. To ensure that the configuration file can be reloaded after the server has changed its working directory due
to to a possible directory option in the configuration file, config-file should be an absolute pathname.
-C
This option prints out the default built-in configuration and exits.
NOTE: This is for debugging purposes only and is not an accurate representation of the actual configuration usedby named at runtime.
-d debug-level
This option sets the daemon’s debug level to debug-level. Debugging traces from named become moreverbose as the debug level increases.
-D stringThis option specifies a string that is used to identify a instance of named in a process listing. The contents ofstring are not examined.
-E engine-name
When applicable, this option specifies the hardware to use for cryptographic operations, such as a secure key store
used for signing.
When BIND 9 is built with OpenSSL, this needs to be set to the OpenSSL engine identifier that drives the cryptographic accelerator or hardware service module (usually pkcs11).
-f
This option runs the server in the foreground (i.e., do not daemonize).

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BIND 9 Administrator Reference Manual, Release 9.20.0-FThis options turns on FIPS (US Federal Information Processing Standards) mode if the underlying crytographic
library supports running in FIPS mode.
-gThis option runs the server in the foreground and forces all logging to stderr.
-L logfile
This option sets the log to the file logfile by default, instead of the system log.
-M option
This option sets the default (comma-separated) memory context options. The possible flags are:• fill: fill blocks of memory with tag values when they are allocated or freed, to assist debugging of memory
problems; this is the implicit default if named has been compiled with --enable-developer.
• nofill: disable the behavior enabled by fill; this is the implicit default unless named has been compiled
with --enable-developer.
-m flag
This option turns on memory usage debugging flags. Possible flags are usage, trace, record, size, andmctx. These correspond to the ISC_MEM_DEBUGXXXX flags described in <isc/mem.h>.
-n #cpus
This option creates #cpus worker threads to take advantage of multiple CPUs. If not specified, named tries todetermine the number of CPUs present and creates one thread per CPU. If it is unable to determine the number ofCPUs, a single worker thread is created.
-p value
This option specifies the port(s) on which the server will listen for queries. If value is of the form <portnum>
or dns=<portnum>, the server will listen for DNS queries on portnum; if not not specified, the default is port
53. If value is of the form tls=<portnum>, the server will listen for TLS queries on portnum; the default is853. If value is of the form https=<portnum>, the server will listen for HTTPS queries on portnum; thedefault is 443. If value is of the form http=<portnum>, the server will listen for HTTP queries on portnum;
the default is 80.
-sThis option writes memory usage statistics to stdout on exit.
Note: This option is mainly of interest to BIND 9 developers and may be removed or changed in a future release.
-t directoryThis option tells named to chroot to directory after processing the command-line arguments, but before
reading the configuration file.
Warning: This option should be used in conjunction with the -u option, as chrooting a process running as root
doesn’t enhance security on most systems; the way chroot is defined allows a process with root privileges to escapea chroot jail.
-U #listeners
This option has been removed. Attempts to use it now result in a warning.

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BIND 9 Administrator Reference Manual, Release 9.20.0-u userThis option sets the setuid to user after completing privileged operations, such as creating sockets that listen on
privileged ports.
Note: On Linux, named uses the kernel’s capability mechanism to drop all root privileges except the ability to bind toa privileged port and set process resource limits. Unfortunately, this means that the -u option only works when named isrun on kernel 2.2.18 or later, or kernel 2.3.99-pre3 or later, since previous kernels did not allow privileges to be retained
after setuid.
-v
This option reports the version number and exits.
-V
This option reports the version number, build options, supported cryptographics algorithms, and exits.
-X lock-file
This option has been removed and using it will cause a fatal error.

15.26.4 Signals
In routine operation, signals should not be used to control the nameserver; rndc should be used instead.
SIGHUP
This signal forces a reload of the server.
SIGINT, SIGTERM
These signals shut down the server.
The result of sending any other signals to the server is undefined.

15.26.5 Configuration
The named configuration file is too complex to describe in detail here. A complete description is provided in the BIND
9 Administrator Reference Manual.
named inherits the umask (file creation mode mask) from the parent process. If files created by named, such as journal
files, need to have custom permissions, the umask should be set explicitly in the script used to start the named process.

15.26.6 Files/etc/named.conf
The default configuration file.
/run/named.pid
The default process-id file.

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15.26.7 See Also
RFC 1033, RFC 1034, RFC 1035, named-checkconf(8), named-checkzone(8), rndc(8), named.
conf(5), BIND 9 Administrator Reference Manual.

15.27 nsec3hash - generate NSEC3 hash15.27.1 Synopsis
nsec3hash {salt} {algorithm} {iterations} {domain}
nsec3hash -r {algorithm} {flags} {iterations} {salt} {domain}

15.27.2 Description
nsec3hash generates an NSEC3 hash based on a set of NSEC3 parameters. This can be used to check the validity of
NSEC3 records in a signed zone.
If this command is invoked as nsec3hash -r, it takes arguments in order, matching the first four fields of an NSEC3
record followed by the domain name: algorithm, flags, iterations, salt, domain. This makes it convenient
to copy and paste a portion of an NSEC3 or NSEC3PARAM record into a command line to confirm the correctness ofan NSEC3 hash.

15.27.3 Arguments
saltThis is the salt provided to the hash algorithm.
algorithm
This is a number indicating the hash algorithm. Currently the only supported hash algorithm for NSEC3 is SHA-1,
which is indicated by the number 1; consequently “1” is the only useful value for this argument.
flagsThis is provided for compatibility with NSEC3 record presentation format, but is ignored since the flags do notaffect the hash.
iterations
This is the number of additional times the hash should be performed.
domainThis is the domain name to be hashed.

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15.27.4 See Also
BIND 9 Administrator Reference Manual, RFC 5155.

15.28 nslookup - query Internet name servers interactively
15.28.1 Synopsis
nslookup [-option] [name | -] [server]

15.28.2 Description
nslookup is a program to query Internet domain name servers. nslookup has two modes: interactive and noninteractive. Interactive mode allows the user to query name servers for information about various hosts and domains or
to print a list of hosts in a domain. Non-interactive mode prints just the name and requested information for a host or
domain.

15.28.3 Arguments
Interactive mode is entered in the following cases:
a. when no arguments are given (the default name server is used);b. when the first argument is a hyphen (-) and the second argument is the host name or Internet address of a nameserver.
Non-interactive mode is used when the name or Internet address of the host to be looked up is given as the first argument.
The optional second argument specifies the host name or address of a name server.
Options can also be specified on the command line if they precede the arguments and are prefixed with a hyphen. For
example, to change the default query type to host information, with an initial timeout of 10 seconds, type:nslookup -query=hinfo-timeout=10

The -version option causes nslookup to print the version number and immediately exit.

15.28.4 Interactive Commands
host [server]
This command looks up information for host using the current default server or using server, if specified. If
host is an Internet address and the query type is A or PTR, the name of the host is returned. If host is a nameand does not have a trailing period (.), the search list is used to qualify the name.
To look up a host not in the current domain, append a period to the name.
server domain | lserver domain
These commands change the default server to domain; lserver uses the initial server to look up information
about domain, while server uses the current default server. If an authoritative answer cannot be found, thenames of servers that might have the answer are returned.
rootThis command is not implemented.

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fingerThis command is not implemented.
lsThis command is not implemented.
viewThis command is not implemented.
helpThis command is not implemented.
?
This command is not implemented.
exitThis command exits the program.
set keyword[=value]
This command is used to change state information that affects the lookups. Valid keywords are:all
This keyword prints the current values of the frequently used options to set. Information about the current
default server and host is also printed.
class=value
This keyword changes the query class to one of:IN
the Internet classCH
the Chaos classHS
the Hesiod class
ANY
wildcard
The class specifies the protocol group of the information. The default is IN; the abbreviation for this keyword
is cl.
nodebug
This keyword turns on or off the display of the full response packet, and any intermediate response packets,
when searching. The default for this keyword is nodebug; the abbreviation for this keyword is [no]deb.
nod2This keyword turns debugging mode on or off. This displays more about what nslookup is doing. The default
is nod2.
domain=name
This keyword sets the search list to name.
nosearch
If the lookup request contains at least one period, but does not end with a trailing period, this keyword appends
the domain names in the domain search list to the request until an answer is received. The default is search.
port=value
This keyword changes the default TCP/UDP name server port to value from its default, port 53. The
abbreviation for this keyword is po.

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querytype=value | type=value
This keyword changes the type of the information query to value. The defaults are A and then AAAA; theabbreviations for these keywords are q and ty.
Please note that it is only possible to specify one query type. Only the default behavior looks up both whenan alternative is not specified.
norecurseThis keyword tells the name server to query other servers if it does not have the information. The default isrecurse; the abbreviation for this keyword is [no]rec.
ndots=numberThis keyword sets the number of dots (label separators) in a domain that disables searching. Absolute names
always stop searching.
retry=numberThis keyword sets the number of retries to number.
timeout=numberThis keyword changes the initial timeout interval to wait for a reply to number, in seconds.
novc
This keyword indicates that a virtual circuit should always be used when sending requests to the server. novc
is the default.
nofailThis keyword tries the next nameserver if a nameserver responds with SERVFAIL or a referral (nofail), or
terminates the query (fail) on such a response. The default is nofail.

15.28.5 Return Values
nslookup returns with an exit status of 1 if any query failed, and 0 otherwise.

15.28.6 IDN Support
If nslookup has been built with IDN (internationalized domain name) support, it can accept and display non-ASCII
domain names. nslookup appropriately converts character encoding of a domain name before sending a request toa DNS server or displaying a reply from the server. To turn off IDN support, define the IDN_DISABLE environment
variable. IDN support is disabled if the variable is set when nslookup runs, or when the standard output is not a tty.

15.28.7 Files/etc/resolv.conf

15.28.8 See Alsodig(1), host(1), named(8).

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15.29 nsupdate - dynamic DNS update utility
15.29.1 Synopsis
nsupdate [-d] [-D] [-i] [-L level] [ [-g] | [-o] | [-l] | [-y [hmac:]keyname:secret] | [-k keyfile] ] [ [-S] [-K tlskeyfile][-E tlscertfile] [-A tlscafile] [-H tlshostname] [-O] ] [-t timeout] [-u udptimeout] [-r udpretries] [-v] [-T] [-P] [-V] [ [-4]
| [-6] ] [filename]15.29.2 Description
nsupdate is used to submit Dynamic DNS Update requests, as defined in RFC 2136, to a name server. This allows
resource records to be added or removed from a zone without manually editing the zone file. A single update request cancontain requests to add or remove more than one resource record.
Zones that are under dynamic control via nsupdate or a DHCP server should not be edited by hand. Manual edits
could conflict with dynamic updates and cause data to be lost.
The resource records that are dynamically added or removed with nsupdate must be in the same zone. Requests aresent to the zone’s primary server, which is identified by the MNAME field of the zone’s SOA record.
Transaction signatures can be used to authenticate the Dynamic DNS updates. These use the TSIG resource record typedescribed in RFC 2845, the SIG(0) record described in RFC 2535 and RFC 2931, or GSS-TSIG as described in RFC
3645.
TSIG relies on a shared secret that should only be known to nsupdate and the name server. For instance, suitable key
and server statements are added to /etc/named.conf so that the name server can associate the appropriate secretkey and algorithm with the IP address of the client application that is using TSIG authentication. ddns-confgen can
generate suitable configuration fragments. nsupdate uses the -y or -k options to provide the TSIG shared secret;these options are mutually exclusive.
SIG(0) uses public key cryptography. To use a SIG(0) key, the public key must be stored in a KEY record in a zone
served by the name server.
GSS-TSIG uses Kerberos credentials. Standard GSS-TSIG mode is switched on with the -g flag. A non-standardscompliant variant of GSS-TSIG used by Windows 2000 can be switched on with the -o flag.

15.29.3 Options-4
This option sets use of IPv4 only.
-6This option sets use of IPv6 only.
-A tlscafile
This option specifies the file of the certificate authorities (CA) certificates (in PEM format) in order to verify theremote server TLS certificate when using DNS-over-TLS (DoT), to achieve Strict or Mutual TLS. When used,
it will override the certificates from the global certificates store, which are otherwise used by default when -S isenabled. This option can not be used in conjuction with -O, and it implies -S.
-C
Overrides the default resolv.conf file. This is only intended for testing.

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BIND 9 Administrator Reference Manual, Release 9.20.0-dThis option sets debug mode, which provides tracing information about the update requests that are made and thereplies received from the name server.
-D
This option sets extra debug mode.
-E tlscertfile
This option sets the certificate(s) file for authentication for the DNS-over-TLS (DoT) transport to the remote server.
The certificate chain file is expected to be in PEM format. This option implies -S, and can only be used with -K.
-gThis option enables standard GSS-TSIG mode.
-H tlshostnameThis option makes nsupdate use the provided hostname during remote server TLS certificate verification. Otherwise, the DNS server name is used. This option implies -S.
-i
This option forces interactive mode, even when standard input is not a terminal.
-k keyfile
This option indicates the file containing the TSIG authentication key. Keyfiles may be in two formats: a single filecontaining a named.conf-format key statement, which may be generated automatically by ddns-confgen;or a pair of files whose names are of the format K{name}.+157.+{random}.key and K{name}.+157.
+{random}.private, which can be generated by dnssec-keygen. The -k option can also be used to
specify a SIG(0) key used to authenticate Dynamic DNS update requests. In this case, the key specified is not an
HMAC-MD5 key.
-K tlskeyfile
This option sets the key file for authenticated encryption for the DNS-over-TLS (DoT) transport with the remote
server. The private key file is expected to be in PEM format. This option implies -S, and can only be used with-E.
-lThis option sets local-host only mode, which sets the server address to localhost (disabling the server so that theserver address cannot be overridden). Connections to the local server use a TSIG key found in /run/session.
key, which is automatically generated by named if any local primary zone has set update-policy tolocal. The location of this key file can be overridden with the -k option.
-L levelThis option sets the logging debug level. If zero, logging is disabled.
-oThis option is deprecated. Previously, it enabled a non-standards-compliant variant of GSS-TSIG that was used byWindows 2000. Since that OS is now long past its end of life, this option is now treated as a synonym for -g.
-O
This option enables Opportunistic TLS. When used, the remote peer’s TLS certificate will not be verified. This
option should be used for debugging purposes only, and it is not recommended to use it in production. This option
can not be used in conjuction with -A, and it implies -S.
-p portThis option sets the port to use for connections to a name server. The default is 53.

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BIND 9 Administrator Reference Manual, Release 9.20.0-PThis option prints the list of private BIND-specific resource record types whose format is understood by nsupdate. See also the -T option.
-r udpretries
This option sets the number of UDP retries. The default is 3. If zero, only one update request is made.
-S
This option indicates whether to use DNS-over-TLS (DoT) when querying name servers specified by server
servername port syntax in the input file, and the primary server discovered through a SOA request. When the-K and -E options are used, then the specified TLS client certificate and private key pair are used for authentication(Mutual TLS). This option implies -v.
-t timeout
This option sets the maximum time an update request can take before it is aborted. The default is 300 seconds.
If zero, the timeout is disabled for TCP mode. For UDP mode, the option -u takes precedence over this option,
unless the option -u is set to zero, in which case the interval is computed from the -t timeout interval and thenumber of UDP retries. For UDP mode, the timeout can not be disabled, and will be rounded up to 1 second incase if both -t and -u are set to zero.
-T
This option prints the list of IANA standard resource record types whose format is understood by nsupdate.
nsupdate exits after the lists are printed. The -T option can be combined with the -P option.
Other types can be entered using TYPEXXXXX where XXXXX is the decimal value of the type with no leading
zeros. The rdata, if present, is parsed using the UNKNOWN rdata format, (<backslash> <hash> <space> <length><space> <hexstring>).
-u udptimeout
This option sets the UDP retry interval. The default is 3 seconds. If zero, the interval is computed from the timeout
interval and number of UDP retries.
-v
This option specifies that TCP should be used even for small update requests. By default, nsupdate uses UDP
to send update requests to the name server unless they are too large to fit in a UDP request, in which case TCP isused. TCP may be preferable when a batch of update requests is made.
-V
This option prints the version number and exits.
-y [hmac:]keyname:secretThis option sets the literal TSIG authentication key. keyname is the name of the key, and secret is the base64
encoded shared secret. hmac is the name of the key algorithm; valid choices are hmac-md5, hmac-sha1,
hmac-sha224, hmac-sha256, hmac-sha384, or hmac-sha512. If hmac is not specified, the default is
hmac-md5, or if MD5 was disabled, hmac-sha256.
NOTE: Use of the -y option is discouraged because the shared secret is supplied as a command-line argument inclear text. This may be visible in the output from ps1 or in a history file maintained by the user’s shell.

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15.29.4 Input Format
nsupdate reads input from filename or standard input. Each command is supplied on exactly one line of input. Somecommands are for administrative purposes; others are either update instructions or prerequisite checks on the contents ofthe zone. These checks set conditions that some name or set of resource records (RRset) either exists or is absent fromthe zone. These conditions must be met if the entire update request is to succeed. Updates are rejected if the tests for theprerequisite conditions fail.
Every update request consists of zero or more prerequisites and zero or more updates. This allows a suitably authenticatedupdate request to proceed if some specified resource records are either present or missing from the zone. A blank input
line (or the send command) causes the accumulated commands to be sent as one Dynamic DNS update request to thename server.
The command formats and their meanings are as follows:
server servername port
This command sends all dynamic update requests to the name server servername. When no server statement isprovided, nsupdate sends updates to the primary server of the correct zone. The MNAME field of that zone’s
SOA record identify the primary server for that zone. port is the port number on servername where thedynamic update requests are sent. If no port number is specified, the default DNS port number of 53 is used.
Note: This command has no effect when GSS-TSIG is in use.
local address port
This command sends all dynamic update requests using the local address. When no local statement is provided,
nsupdate sends updates using an address and port chosen by the system. port can also be used to force requests
to come from a specific port. If no port number is specified, the system assigns one.
zone zonename
This command specifies that all updates are to be made to the zone zonename. If no zone statement is provided,
nsupdate attempts to determine the correct zone to update based on the rest of the input.
class classname
This command specifies the default class. If no class is specified, the default class is IN.
ttl seconds
This command specifies the default time-to-live, in seconds, for records to be added. The value none clears thedefault TTL.
key hmac:keyname secretThis command specifies that all updates are to be TSIG-signed using the keyname-secret pair. If hmac is
specified, it sets the signing algorithm in use. The default is hmac-md5; if MD5 was disabled, the default is
hmac-sha256. The key command overrides any key specified on the command line via -y or -k.
gsstsig
This command uses GSS-TSIG to sign the updates. This is equivalent to specifying -g on the command line.
oldgsstsig
This command is deprecated and will be removed in a future release. Previously, it caused nsupdate to use theWindows 2000 version of GSS-TSIG to sign updates. It is now treated as a synonym for gsstsig.
realm [realm_name]
When using GSS-TSIG, this command specifies the use of realm_name rather than the default realm in krb5.
conf. If no realm is specified, the saved realm is cleared.
check-names [boolean]This command turns on or off check-names processing on records to be added. Check-names has no effect on

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prerequisites or records to be deleted. By default check-names processing is on. If check-names processing fails,
the record is not added to the UPDATE message.
check-svbc [boolean]This command turns on or off check-svcb processing on records to be added. Check-svcb has no effect on prerequisites or records to be deleted. By default check-svcb processing is on. If check-svcb processing fails, the record
is not added to the UPDATE message.
lease time [keytime]
Set the EDNS Update Lease (UL) option to value to time and optionally also set the key lease time to keytime
in seconds. If time is none the lease times are cleared.
prereq nxdomain domain-nameThis command requires that no resource record of any type exist with the name domain-name.
prereq yxdomain domain-nameThis command requires that domain-name exist (as at least one resource record, of any type).
prereq nxrrset domain-name class typeThis command requires that no resource record exist of the specified type, class, and domain-name. Ifclass is omitted, IN (Internet) is assumed.
prereq yxrrset domain-name class typeThis command requires that a resource record of the specified type, class and domain-name exist. If classis omitted, IN (internet) is assumed.
prereq yxrrset domain-name class type data
With this command, the data from each set of prerequisites of this form sharing a common type, class,and domain-name are combined to form a set of RRs. This set of RRs must exactly match the set of RRs
existing in the zone at the given type, class, and domain-name. The data are written in the standard text
representation of the resource record’s RDATA.
update delete domain-name ttl class type data
This command deletes any resource records named domain-name. If type and data are provided, only matching resource records are removed. The Internet class is assumed if class is not supplied. The ttl is ignored,
and is only allowed for compatibility.
update add domain-name ttl class type data
This command adds a new resource record with the specified ttl, class, and data.
show
This command displays the current message, containing all of the prerequisites and updates specified since the last
send.
send
This command sends the current message. This is equivalent to entering a blank line.
answerThis command displays the answer.
debugThis command turns on debugging.
versionThis command prints the version number.
helpThis command prints a list of commands.
Lines beginning with a semicolon (;) are comments and are ignored.

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15.29.5 Examples
The examples below show how nsupdate can be used to insert and delete resource records from the example.com
zone. Notice that the input in each example contains a trailing blank line, so that a group of commands is sent as one
dynamic update request to the primary name server for example.com.
# nsupdate> update delete oldhost.example.com A> update add newhost.example.com 86400 A 172.16.1.1> sendAny A records for oldhost.example.com are deleted, and an A record for newhost.example.com with IP
address 172.16.1.1 is added. The newly added record has a TTL of 1 day (86400 seconds).
# nsupdate> prereq nxdomain nickname.example.com> update add nickname.example.com 86400 CNAME somehost.example.com> sendThe prerequisite condition tells the name server to verify that there are no resource records of any type for nickname.
example.com. If there are, the update request fails. If this name does not exist, a CNAME for it is added. This
ensures that when the CNAME is added, it cannot conflict with the long-standing rule in RFC 1034 that a name must notexist as any other record type if it exists as a CNAME. (The rule has been updated for DNSSEC in RFC 2535 to allow
CNAMEs to have RRSIG, DNSKEY, and NSEC records.)

15.29.6 Files/etc/resolv.conf
Used to identify the default name server/run/session.key
Sets the default TSIG key for use in local-only mode
K{name}.+157.+{random}.key
Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.
K{name}.+157.+{random}.private
Base-64 encoding of the HMAC-MD5 key created by dnssec-keygen.

15.29.7 See Also
RFC 2136, RFC 3007, RFC 2104, RFC 2845, RFC 1034, RFC 2535, RFC 2931, named(8),dnssec-keygen(8), tsig-keygen(8).

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15.29.8 Bugs
The TSIG key is redundantly stored in two separate files. This is a consequence of nsupdate using the DST library for
its cryptographic operations, and may change in future releases.

15.30 rndc-confgen - rndc key generation tool
15.30.1 Synopsis
rndc-confgen [-a] [-A algorithm] [-b keysize] [-c keyfile] [-h] [-k keyname] [-p port] [-s address] [-t chrootdir] [-uuser]

15.30.2 Description
rndc-confgen generates configuration files for rndc. It can be used as a convenient alternative to writing the rndc.
conf file and the corresponding controls and key statements in named.conf by hand. Alternatively, it can be runwith the -a option to set up a rndc.key file and avoid the need for a rndc.conf file and a controls statement
altogether.

15.30.3 Options-aThis option sets automatic rndc configuration, which creates a file /etc/rndc.key that is read by both rndc
and named on startup. The rndc.key file defines a default command channel and authentication key allowing
rndc to communicate with named on the local host with no further configuration.
If a more elaborate configuration than that generated by rndc-confgen -a is required, for example if rndc is
to be used remotely, run rndc-confgen without the -a option and set up rndc.conf and named.conf as
directed.
-A algorithm
This option specifies the algorithm to use for the TSIG key. Available choices are: hmac-md5, hmac-sha1, hmacsha224, hmac-sha256, hmac-sha384, and hmac-sha512. The default is hmac-sha256.
-b keysize
This option specifies the size of the authentication key in bits. The size must be between 1 and 512 bits; the default
is the hash size.
-c keyfile
This option is used with the -a option to specify an alternate location for rndc.key.
-hThis option prints a short summary of the options and arguments to rndc-confgen.
-k keynameThis option specifies the key name of the rndc authentication key. This must be a valid domain name. The default
is rndc-key.
-p portThis option specifies the command channel port where named listens for connections from rndc. The default is
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BIND 9 Administrator Reference Manual, Release 9.20.0-qThis option prevets printing the written path in automatic configuration mode.
-s addressThis option specifies the IP address where named listens for command-channel connections from rndc. The
default is the loopback address 127.0.0.1.
-t chrootdir
This option is used with the -a option to specify a directory where named runs chrooted. An additional copy of
the rndc.key is written relative to this directory, so that it is found by the chrooted named.
-u userThis option is used with the -a option to set the owner of the generated rndc.key file. If -t is also specified,
only the file in the chroot area has its owner changed.

15.30.4 Examples
To allow rndc to be used with no manual configuration, run:rndc-confgen -a
To print a sample rndc.conf file and the corresponding controls and key statements to be manually inserted into
named.conf, run:rndc-confgen15.30.5 See Alsorndc(8), rndc.conf(5), named(8), BIND 9 Administrator Reference Manual.

15.31 rndc.conf - rndc configuration file
15.31.1 Synopsis
rndc.conf

15.31.2 Description
rndc.conf is the configuration file for rndc, the BIND 9 name server control utility. This file has a similar structureand syntax to named.conf. Statements are enclosed in braces and terminated with a semi-colon. Clauses in thestatements are also semi-colon terminated. The usual comment styles are supported:
C style: /* */C++ style: // to end of line
Unix style: # to end of line
rndc.conf is much simpler than named.conf. The file uses three statements: an options statement, a server statement, and a key statement.
The options statement contains five clauses. The default-server clause is followed by the name or address ofa name server. This host is used when no name server is given as an argument to rndc. The default-key clause isfollowed by the name of a key, which is identified by a key statement. If no keyid is provided on the rndc command
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line, and no key clause is found in a matching server statement, this default key is used to authenticate the server’s
commands and responses. The default-port clause is followed by the port to connect to on the remote name server.
If no port option is provided on the rndc command line, and no port clause is found in a matching server statement,
this default port is used to connect. The default-source-address and default-source-address-v6
clauses can be used to set the IPv4 and IPv6 source addresses respectively.
After the server keyword, the server statement includes a string which is the hostname or address for a name server.
The statement has three possible clauses: key, port, and addresses. The key name must match the name of a
key statement in the file. The port number specifies the port to connect to. If an addresses clause is supplied, theseaddresses are used instead of the server name. Each address can take an optional port. If an source-address or
source-address-v6 is supplied, it is used to specify the IPv4 and IPv6 source address, respectively.
The key statement begins with an identifying string, the name of the key. The statement has two clauses. algorithm
identifies the authentication algorithm for rndc to use; currently only HMAC-MD5 (for compatibility), HMAC-SHA1,
HMAC-SHA224, HMAC-SHA256 (default), HMAC-SHA384, and HMAC-SHA512 are supported. This is followed bya secret clause which contains the base-64 encoding of the algorithm’s authentication key. The base-64 string is enclosed
in double quotes.
There are two common ways to generate the base-64 string for the secret. The BIND 9 program rndc-confgen canbe used to generate a random key, or the mmencode program, also known as mimencode, can be used to generatea base-64 string from known input. mmencode does not ship with BIND 9 but is available on many systems. See the
Example section for sample command lines for each.

15.31.3 Example
options {default-server
default-key};

localhost;samplekey;

server localhost {keysamplekey;};
server testserver {key
testkey;
addresses{ localhost port 5353; };};key samplekey {algorithm
secret};hmac-sha256;"6FMfj43Osz4lyb24OIe2iGEz9lf1llJO+lz";

key testkey {algorithm
hmac-sha256;
secret"R3HI8P6BKw9ZwXwN3VZKuQ==";};In the above example, rndc by default uses the server at localhost (127.0.0.1) and the key called “samplekey”. Commands
to the localhost server use the “samplekey” key, which must also be defined in the server’s configuration file with the same
name and secret. The key statement indicates that “samplekey” uses the HMAC-SHA256 algorithm and its secret clausecontains the base-64 encoding of the HMAC-SHA256 secret enclosed in double quotes.
If rndc -s testserver is used, then rndc connects to the server on localhost port 5353 using the key “testkey”.

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To generate a random secret with rndc-confgen:rndc-confgen
A complete rndc.conf file, including the randomly generated key, is written to the standard output. Commented-out
key and controls statements for named.conf are also printed.
To generate a base-64 secret with mmencode:echo "known plaintext for a secret" | mmencode

15.31.4 Name Server Configuration
The name server must be configured to accept rndc connections and to recognize the key specified in the rndc.conf
file, using the controls statement in named.conf. See the sections on the controls statement in the BIND 9 Administrator Reference Manual for details.

15.31.5 See Alsorndc(8), rndc-confgen(8), mmencode(1), BIND 9 Administrator Reference Manual.

15.32 rndc - name server control utility
15.32.1 Synopsis
rndc [-b source-address] [-c config-file] [-k key-file] [-s server] [-p port] [-q] [-r] [-V] [-y server_key] [[-4] | [-6]]{command}15.32.2 Description
rndc controls the operation of a name server. If rndc is invoked with no command line options or arguments, it prints
a short summary of the supported commands and the available options and their arguments.
rndc communicates with the name server over a TCP connection, sending commands authenticated with digital signatures. In the current versions of rndc and named, the only supported authentication algorithms are HMAC-MD5 (forcompatibility), HMAC-SHA1, HMAC-SHA224, HMAC-SHA256 (default), HMAC-SHA384, and HMAC-SHA512.
They use a shared secret on each end of the connection, which provides TSIG-style authentication for the command request and the name server’s response. All commands sent over the channel must be signed by a server_key known to theserver.
rndc reads a configuration file to determine how to contact the name server and decide what algorithm and key it shoulduse.

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15.32.3 Options-4
This option indicates use of IPv4 only.
-6This option indicates use of IPv6 only.
-b source-addressThis option indicates source-address as the source address for the connection to the server. Multiple instances
are permitted, to allow setting of both the IPv4 and IPv6 source addresses.
-c config-file
This option indicates config-file as the configuration file instead of the default, /etc/rndc.conf.
-k key-file
This option indicates key-file as the key file instead of the default, /etc/rndc.key. The key in /etc/
rndc.key is used to authenticate commands sent to the server if the config-file does not exist.
-s server
server is the name or address of the server which matches a server statement in the configuration file for rndc.
If no server is supplied on the command line, the host named by the default-server clause in the options statementof the rndc configuration file is used.
-p portThis option instructs BIND 9 to send commands to TCP port port instead of its default control channel port, 953.
-qThis option sets quiet mode, where message text returned by the server is not printed unless there is an error.
-rThis option instructs rndc to print the result code returned by named after executing the requested command(e.g., ISC_R_SUCCESS, ISC_R_FAILURE, etc.).
-t timeout
This option sets the idle timeout period for rndc to timeout seconds. The default is 60 seconds, and the
maximum settable value is 86400 seconds (1 day). If set to 0, there is no timeout.
-V
This option enables verbose logging.
-y server_key
This option indicates use of the key server_key from the configuration file. For control message validation to
succeed, server_key must be known by named with the same algorithm and secret string. If no server_key
is specified, rndc first looks for a key clause in the server statement of the server being used, or if no serverstatement is present for that host, then in the default-key clause of the options statement. Note that the configuration
file contains shared secrets which are used to send authenticated control commands to name servers, and should
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15.32.4 Commands
A list of commands supported by rndc can be seen by running rndc without arguments.
Currently supported commands are:addzone zone [class [view]] configuration
This command adds a zone while the server is running. This command requires the allow-new-zones option
to be set to yes. The configuration string specified on the command line is the zone configuration text that would
ordinarily be placed in named.conf.
The configuration is saved in a file called viewname.nzf (or, if named is compiled with liblmdb, an LMDB
database file called viewname.nzd). viewname is the name of the view, unless the view name contains characters that are incompatible with use as a file name, in which case a cryptographic hash of the view name is usedinstead. When named is restarted, the file is loaded into the view configuration so that zones that were added canpersist after a restart.
This sample addzone command adds the zone example.com to the default view:rndc addzone example.com '{ type primary; file "example.com.db"; };'(Note the brackets around and semi-colon after the zone configuration text.)
See also rndc delzone and rndc modzone.
delzone [-clean] zone [class [view]]
This command deletes a zone while the server is running.
If the -clean argument is specified, the zone’s master file (and journal file, if any) are deleted along with thezone. Without the -clean option, zone files must be deleted manually. (If the zone is of type secondary or
stub, the files needing to be removed are reported in the output of the rndc delzone command.)If the zone was originally added via rndc addzone, then it is removed permanently. However, if it was originallyconfigured in named.conf, then that original configuration remains in place; when the server is restarted orreconfigured, the zone is recreated. To remove it permanently, it must also be removed from named.conf.
See also rndc addzone and rndc modzone.
dnssec (-status | -rollover -key id [-alg algorithm] [-when time] | -checkds [-key id [-alg algorithm]] [-when time]lished | withdrawn)) zone [class [view]]

pub-This command allows you to interact with the “dnssec-policy” of a given zone.
rndc dnssec -status show the DNSSEC signing state for the specified zone.
rndc dnssec -rollover allows you to schedule key rollover for a specific key (overriding the original key
lifetime).
rndc dnssec -checkds informs named that the DS for a specified zone’s key-signing key has been confirmed
to be published in, or withdrawn from, the parent zone. This is required in order to complete a KSK rollover. The-key id and -alg algorithm arguments can be used to specify a particular KSK, if necessary; if there is
only one key acting as a KSK for the zone, these arguments can be omitted. The time of publication or withdrawal
for the DS is set to the current time by default, but can be overridden to a specific time with the argument -whentime, where time is expressed in YYYYMMDDHHMMSS notation.
dnstap (-reopen | -roll [number])This command closes and re-opens DNSTAP output files.
rndc dnstap -reopen allows the output file to be renamed externally, so that named can truncate andre-open it.

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rndc dnstap -roll causes the output file to be rolled automatically, similar to log files. The most recent
output file has “.0” appended to its name; the previous most recent output file is moved to “.1”, and so on. If
number is specified, then the number of backup log files is limited to that number.
dumpdb [-all | -cache | -zones | -adb | -bad | -expired | -fail] [view ...]
This command dumps the server’s caches (default) and/or zones to the dump file for the specified views. If no viewis specified, all views are dumped. (See the dump-file option in the BIND 9 Administrator Reference Manual.)
fetchlimit [view]
This command dumps a list of servers that are currently being rate-limited as a result of fetches-per-server
settings, and a list of domain names that are currently being rate-limited as a result of fetches-per-zone
settings.
flushThis command flushes the server’s cache.
flushname name [view]
This command flushes the given name from the view’s DNS cache and, if applicable, from the view’s nameserver
address database, bad server cache, and SERVFAIL cache.
flushtree name [view]
This command flushes the given name, and all of its subdomains, from the view’s DNS cache, address database,bad server cache, and SERVFAIL cache.
freeze [zone [class [view]]]
This command suspends updates to a dynamic zone. If no zone is specified, then all zones are suspended. This
allows manual edits to be made to a zone normally updated by dynamic update, and causes changes in the journal
file to be synced into the master file. All dynamic update attempts are refused while the zone is frozen.
See also rndc thaw.
halt [-p]This command stops the server immediately. Recent changes made through dynamic update or IXFR are not saved
to the master files, but are rolled forward from the journal files when the server is restarted. If -p is specified,named’s process ID is returned. This allows an external process to determine when named has completed halting.
See also rndc stop.
loadkeys [zone [class [view]]]
This command fetches all DNSSEC keys for the given zone from the key directory. If they are within their publication period, they are merged into the zone’s DNSKEY RRset. Unlike rndc sign, however, the zone is not
immediately re-signed by the new keys, but is allowed to incrementally re-sign over time.
This command requires that the zone be configured with a dnssec-policy, and also requires the zone to be
configured to allow dynamic DNS. (See “Dynamic Update Policies” in the Administrator Reference Manual for
more details.)
managed-keys (status | refresh | sync | destroy) [class [view]]
This command inspects and controls the “managed-keys” database which handles RFC 5011 DNSSEC trust anchor
maintenance. If a view is specified, these commands are applied to that view; otherwise, they are applied to all
views.
• When run with the status keyword, this prints the current status of the managed-keys database.
• When run with the refresh keyword, this forces an immediate refresh query to be sent for all the managed
keys, updating the managed-keys database if any new keys are found, without waiting the normal refreshinterval.

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BIND 9 Administrator Reference Manual, Release 9.20.0• When run with the sync keyword, this forces an immediate dump of the managed-keys database to disk (inthe file managed-keys.bind or (viewname.mkeys). This synchronizes the database with its journal
file, so that the database’s current contents can be inspected visually.
• When run with the destroy keyword, the managed-keys database is shut down and deleted, and all key
maintenance is terminated. This command should be used only with extreme caution.
Existing keys that are already trusted are not deleted from memory; DNSSEC validation can continue after
this command is used. However, key maintenance operations cease until named is restarted or reconfigured,and all existing key maintenance states are deleted.
Running rndc reconfig or restarting named immediately after this command causes key maintenanceto be reinitialized from scratch, just as if the server were being started for the first time. This is primarily
intended for testing, but it may also be used, for example, to jumpstart the acquisition of new keys in theevent of a trust anchor rollover, or as a brute-force repair for key maintenance problems.
modzone zone [class [view]] configuration
This command modifies the configuration of a zone while the server is running. This command requires theallow-new-zones option to be set to yes. As with addzone, the configuration string specified on thecommand line is the zone configuration text that would ordinarily be placed in named.conf.
If the zone was originally added via rndc addzone, the configuration changes are recorded permanently and arestill in effect after the server is restarted or reconfigured. However, if it was originally configured in named.conf,
then that original configuration remains in place; when the server is restarted or reconfigured, the zone reverts to
its original configuration. To make the changes permanent, it must also be modified in named.conf.
See also rndc addzone and rndc delzone.
notify zone [class [view]]
This command resends NOTIFY messages for the zone.
notraceThis command sets the server’s debugging level to 0.
See also rndc trace.
nta [(-class class | -dump | -force | -remove | -lifetime duration)] domain [view]
This command sets a DNSSEC negative trust anchor (NTA) for domain, with a lifetime of duration. The
default lifetime is configured in named.conf via the nta-lifetime option, and defaults to one hour. The
lifetime cannot exceed one week.
A negative trust anchor selectively disables DNSSEC validation for zones that are known to be failing because of
misconfiguration rather than an attack. When data to be validated is at or below an active NTA (and above any otherconfigured trust anchors), named aborts the DNSSEC validation process and treats the data as insecure rather thanbogus. This continues until the NTA’s lifetime has elapsed.
NTAs persist across restarts of the named server. The NTAs for a view are saved in a file called name.nta,
where name is the name of the view; if it contains characters that are incompatible with use as a file name, a
cryptographic hash is generated from the name of the view.
An existing NTA can be removed by using the -remove option.
An NTA’s lifetime can be specified with the -lifetime option. TTL-style suffixes can be used to specify the
lifetime in seconds, minutes, or hours. If the specified NTA already exists, its lifetime is updated to the new value.
Setting lifetime to zero is equivalent to -remove.
If -dump is used, any other arguments are ignored and a list of existing NTAs is printed. Note that this may
include NTAs that are expired but have not yet been cleaned up.
Normally, named periodically tests to see whether data below an NTA can now be validated (see thenta-recheck option in the Administrator Reference Manual for details). If data can be validated, then the
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NTA is regarded as no longer necessary and is allowed to expire early. The -force parameter overrides thisbehavior and forces an NTA to persist for its entire lifetime, regardless of whether data could be validated if the
NTA were not present.
The view class can be specified with -class. The default is class IN, which is the only class for which DNSSEC
is currently supported.
All of these options can be shortened, i.e., to -l, -r, -d, -f, and -c.
Unrecognized options are treated as errors. To refer to a domain or view name that begins with a hyphen, use adouble-hyphen (–) on the command line to indicate the end of options.
querylog [(on | off)]
This command enables or disables query logging. For backward compatibility, this command can also be usedwithout an argument to toggle query logging on and off.
Query logging can also be enabled by explicitly directing the queries category to a channel in the logging section of named.conf, or by specifying querylog yes; in the options section of named.conf.
reconfig
This command reloads the configuration file and loads new zones, but does not reload existing zone files even if
they have changed. This is faster than a full rndc reload when there is a large number of zones, because it
avoids the need to examine the modification times of the zone files.
recursingThis command dumps the list of queries named is currently recursing on, and the list of domains to which iterative
queries are currently being sent.
The first list includes all unique clients that are waiting for recursion to complete, including the query that is awaitinga response and the timestamp (seconds since the Unix epoch) of when named started processing this client query.
The second list comprises of domains for which there are active (or recently active) fetches in progress. It reports thenumber of active fetches for each domain and the number of queries that have been passed (allowed) or dropped(spilled) as a result of the fetches-per-zone limit. (Note: these counters are not cumulative over time;
whenever the number of active fetches for a domain drops to zero, the counter for that domain is deleted, and thenext time a fetch is sent to that domain, it is recreated with the counters set to zero).
refresh zone [class [view]]
This command schedules zone maintenance for the given zone.
reloadThis command reloads the configuration file and zones.
zone [class [view]]
If a zone is specified, this command reloads only the given zone. If no zone is specified, the reloading happens
asynchronously.
retransfer zone [class [view]]
This command retransfers the given secondary zone from the primary server.
If the zone is configured to use inline-signing, the signed version of the zone is discarded; after the retransferof the unsigned version is complete, the signed version is regenerated with new signatures.
scanThis command scans the list of available network interfaces for changes, without performing a full rndc reconfig or waiting for the interface-interval timer.

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secroots [-] [view ...]
This command dumps the security roots (i.e., trust anchors configured via trust-anchors, or the
managed-keys or trusted-keys statements [both deprecated], or dnssec-validation auto) andnegative trust anchors for the specified views. If no view is specified, all views are dumped. Security roots indicate
whether they are configured as trusted keys, managed keys, or initializing managed keys (managed keys that have
not yet been updated by a successful key refresh query).
If the first argument is -, then the output is returned via the rndc response channel and printed to the standard
output. Otherwise, it is written to the secroots dump file, which defaults to named.secroots, but can beoverridden via the secroots-file option in named.conf.
See also rndc managed-keys.
serve-stale (on | off | reset | status) [class [view]]
This command enables, disables, resets, or reports the current status of the serving of stale answers as configured
in named.conf.
If serving of stale answers is disabled by rndc-serve-stale off, then it remains disabled even if named isreloaded or reconfigured. rndc serve-stale reset restores the setting as configured in named.conf.
rndc serve-stale status reports whether caching and serving of stale answers is currently enabled or
disabled. It also reports the values of stale-answer-ttl and max-stale-ttl.
showzone zone [class [view]]
This command prints the configuration of a running zone.
See also rndc zonestatus.
sign zone [class [view]]
This command fetches all DNSSEC keys for the given zone from the key directory (see the key-directory
option in the BIND 9 Administrator Reference Manual). If they are within their publication period, they are merged
into the zone’s DNSKEY RRset. If the DNSKEY RRset is changed, then the zone is automatically re-signed with
the new key set.
This command requires that the zone be configured with a dnssec-policy, and also requires the zone to be
configured to allow dynamic DNS. (See “Dynamic Update Policies” in the Administrator Reference Manual for
more details.)
See also rndc loadkeys.
signing [(-list | -clear keyid/algorithm | -clear all | -nsec3param (parameters | none) | -serial value) zone [class [view]]
This command lists, edits, or removes the DNSSEC signing-state records for the specified zone. The status ofongoing DNSSEC operations, such as signing or generating NSEC3 chains, is stored in the zone in the form of
DNS resource records of type sig-signing-type. rndc signing -list converts these records intoa human-readable form, indicating which keys are currently signing or have finished signing the zone, and which
NSEC3 chains are being created or removed.
rndc signing -clear can remove a single key (specified in the same format that rndc signing -list
uses to display it), or all keys. In either case, only completed keys are removed; any record indicating that a key has
not yet finished signing the zone is retained.
rndc signing -nsec3param sets the NSEC3 parameters for a zone. This is the only supported mechanism for using NSEC3 with inline-signing zones. Parameters are specified in the same format as an
NSEC3PARAM resource record: hash algorithm, flags, iterations, and salt, in that order.
Currently, the only defined value for hash algorithm is 1, representing SHA-1. The flags may be set to 0
or 1, depending on whether the opt-out bit in the NSEC3 chain should be set. iterations defines the numberof additional times to apply the algorithm when generating an NSEC3 hash. The salt is a string of data expressed

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in hexadecimal, a hyphen (-) if no salt is to be used, or the keyword auto, which causes named to generate a
random 64-bit salt.
The only recommended configuration is rndc signing -nsec3param 1 0 0 - zone, i.e. no salt, no
additional iterations, no opt-out.
Warning: Do not use extra iterations, salt, or opt-out unless all their implications are fully understood. A
higher number of iterations causes interoperability problems and opens servers to CPU-exhausting DoS attacks.
rndc signing -nsec3param none removes an existing NSEC3 chain and replaces it with NSEC.
rndc signing -serial value sets the serial number of the zone to value. If the value would cause
the serial number to go backwards, it is rejected. The primary use of this parameter is to set the serial number on
inline signed zones.
stats
This command writes server statistics to the statistics file. (See the statistics-file option in the BIND 9
Administrator Reference Manual.)
statusThis command displays the status of the server. Note that the number of zones includes the internal bind/CH
zone and the default ./IN hint zone, if there is no explicit root zone configured.
stop -pThis command stops the server, making sure any recent changes made through dynamic update or IXFR are firstsaved to the master files of the updated zones. If -p is specified, named’s process ID is returned. This allows anexternal process to determine when named has completed stopping.
See also rndc halt.
sync -clean [zone [class [view]]]
This command syncs changes in the journal file for a dynamic zone to the master file. If the “-clean” option is
specified, the journal file is also removed. If no zone is specified, then all zones are synced.
tcp-timeouts [initial idle keepalive advertised]
When called without arguments, this command displays the current values of the tcp-initial-timeout,
tcp-idle-timeout, tcp-keepalive-timeout, and tcp-advertised-timeout options. Whencalled with arguments, these values are updated. This allows an administrator to make rapid adjustments when undera denial-of-service (DoS) attack. See the descriptions of these options in the BIND 9 Administrator Reference
Manual for details of their use.
thaw [zone [class [view]]]
This command enables updates to a frozen dynamic zone. If no zone is specified, then all frozen zones are enabled. This causes the server to reload the zone from disk, and re-enables dynamic updates after the load hascompleted. After a zone is thawed, dynamic updates are no longer refused. If the zone has changed and theixfr-from-differences option is in use, the journal file is updated to reflect changes in the zone. Otherwise, if the zone has changed, any existing journal file is removed. If no zone is specified, the reloading happens
asynchronously.
See also rndc freeze.
trace [level]
If no level is specified, this command increments the server’s debugging level by one.
level
If specified, this command sets the server’s debugging level to the provided value.

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See also rndc notrace.
validation (on | off | status) [view ...]
This command enables, disables, or checks the current status of DNSSEC validation. By default, validation isenabled.
The cache is flushed when validation is turned on or off to avoid using data that might differ between states.
zonestatus zone [class [view]]
This command displays the current status of the given zone, including the master file name and any include files fromwhich it was loaded, when it was most recently loaded, the current serial number, the number of nodes, whether
the zone supports dynamic updates, whether the zone is DNSSEC signed, whether it uses automatic DNSSEC key
management or inline signing, and the scheduled refresh or expiry times for the zone.
See also rndc showzone.
rndc commands that specify zone names, such as reload retransfer, or zonestatus, can be ambiguous whenapplied to zones of type redirect. Redirect zones are always called ., and can be confused with zones of type hint
or with secondary copies of the root zone. To specify a redirect zone, use the special zone name -redirect, without
a trailing period. (With a trailing period, this would specify a zone called “-redirect”.)

15.32.5 Limitations
There is currently no way to provide the shared secret for a server_key without using the configuration file.
Several error messages could be clearer.

15.32.6 See Also
rndc.conf(5), rndc-confgen(8), named(8), named.conf(5), BIND 9 Administrator Reference Manual.

15.33 tsig-keygen - TSIG key generation tool
15.33.1 Synopsis
tsig-keygen [-a algorithm] [-h] [name]15.33.2 Description
tsig-keygen is an utility that generates keys for use with TSIG (Transaction Signatures) as defined in RFC 2845. The
resulting keys can be used, for example, to secure dynamic DNS updates to a zone, or for the rndc command channel.
A domain name can be specified on the command line to be used as the name of the generated key. If no name is specified,the default is tsig-key.

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15.33.3 Options-a algorithm
This option specifies the algorithm to use for the TSIG key. Available choices are: hmac-md5, hmac-sha1, hmacsha224, hmac-sha256, hmac-sha384, and hmac-sha512. The default is hmac-sha256. Options are case-insensitive,
and the “hmac-” prefix may be omitted.
-hThis option prints a short summary of options and arguments.

15.33.4 See Also
nsupdate(1), named.conf(5), named(8), BIND 9 Administrator Reference Manual.

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INDEX

Symbols+aaflag
dig command line option, 448
mdig command line option, 490+aaonly
dig command line option, 448
mdig command line option, 490+additional
dig command line option, 448
mdig command line option, 488+adflag
dig command line option, 448
mdig command line option, 490+alldelv command line option, 444
dig command line option, 448
mdig command line option, 488+answerdig command line option, 448
mdig command line option, 488+authority
dig command line option, 448
mdig command line option, 488+badcookie
dig command line option, 448+besteffort
dig command line option, 448
mdig command line option, 488+bufsizedig command line option, 448
mdig command line option, 490+burstmdig command line option, 488+cd
dig command line option, 448+cdflagdelv command line option, 443
dig command line option, 448
mdig command line option, 490+clmdig command line option, 489+classdelv command line option, 443
dig command line option, 448+cmd
dig command line option, 448+comments
delv command line option, 444
dig command line option, 448
mdig command line option, 489+continue
mdig command line option, 489+cookie
dig command line option, 449
mdig command line option, 490+cryptodelv command line option, 444
dig command line option, 449
mdig command line option, 489+defname
dig command line option, 449+dns64prefix
dig command line option, 449+dnssecdelv command line option, 444
dig command line option, 449
mdig command line option, 490+dodig command line option, 449+domaindig command line option, 449+edns
dig command line option, 449
mdig command line option, 490+ednsflags
dig command line option, 449
mdig command line option, 490+ednsnegotiation
dig command line option, 449+ednsopt
dig command line option, 449
mdig command line option, 490+expiredig command line option, 449

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mdig command line option, 491+faildig command line option, 449+fuzztime
dig command line option, 449+header-only
dig command line option, 450+hintdelv command line option, 443+http-plain
dig command line option, 450+http-plain-get
dig command line option, 450+http-plain-post
dig command line option, 450+httpsdig command line option, 450+https-get
dig command line option, 450+https-post
dig command line option, 450+identify
dig command line option, 450+idn
dig command line option, 450+ignoredig command line option, 450+keepalive
dig command line option, 450+keepopen
dig command line option, 450+mtracedelv command line option, 443+multiline
delv command line option, 444
dig command line option, 450
mdig command line option, 489+ndotsdig command line option, 450+noaaflag
dig command line option, 448
mdig command line option, 490+noaaonly
dig command line option, 448
mdig command line option, 490+noadditional
dig command line option, 448
mdig command line option, 488+noadflag
dig command line option, 448
mdig command line option, 490+noalldelv command line option, 444
dig command line option, 448
546

mdig command line option, 488+noanswer
dig command line option, 448
mdig command line option, 488+noauthority
dig command line option, 448
mdig command line option, 488+nobadcookie
dig command line option, 448+nobesteffort
dig command line option, 448
mdig command line option, 488+nocdflagdelv command line option, 443
dig command line option, 448
mdig command line option, 490+nocl
mdig command line option, 489+noclassdelv command line option, 443
dig command line option, 448+nocmddig command line option, 448+nocomments
delv command line option, 444
dig command line option, 448
mdig command line option, 489+nocontinue
mdig command line option, 489+nocookie
dig command line option, 449
mdig command line option, 490+nocryptodelv command line option, 444
dig command line option, 449
mdig command line option, 489+nodefname
dig command line option, 449+nodns64prefix
dig command line option, 449+nodnssec
delv command line option, 444
dig command line option, 449
mdig command line option, 490+nodo
dig command line option, 449+noedns
dig command line option, 449
mdig command line option, 490+noednsflags
dig command line option, 449
mdig command line option, 490+noednsnegotiation
dig command line option, 449
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BIND 9 Administrator Reference Manual, Release 9.20.0+noednsopt
dig command line option, 449
mdig command line option, 490+noexpire
dig command line option, 449
mdig command line option, 491+nofaildig command line option, 449+nofuzztime
dig command line option, 449+noheader-only
dig command line option, 450+nohint
delv command line option, 443+nohttp-plain
dig command line option, 450+nohttp-plain-get
dig command line option, 450+nohttp-plain-post
dig command line option, 450+nohttps
dig command line option, 450+nohttps-get
dig command line option, 450+nohttps-post
dig command line option, 450+noidentify
dig command line option, 450+noidndig command line option, 450+noignore
dig command line option, 450+nokeepalive
dig command line option, 450+nokeepopen
dig command line option, 450+nomtracedelv command line option, 443+nomultiline
delv command line option, 444
dig command line option, 450
mdig command line option, 489+nonsdelv command line option, 443+nonsid
dig command line option, 451
mdig command line option, 491+nonssearchdig command line option, 451+noonesoa
dig command line option, 451+noopcode
dig command line option, 451+noproxyIndex

dig command line option, 451+noproxy-plain
dig command line option, 451+noqmindelv command line option, 443+noqr
dig command line option, 451+noquestion
dig command line option, 452
mdig command line option, 489+noraflag
dig command line option, 452+nordflag
dig command line option, 452+norecurse
dig command line option, 452
mdig command line option, 491+norootdelv command line option, 444+norrcomments
delv command line option, 444
dig command line option, 452
mdig command line option, 489+nortracedelv command line option, 443+nosearchdig command line option, 452+noshortdelv command line option, 444
dig command line option, 452
mdig command line option, 489+noshowbadcookie
dig command line option, 452+noshowsearchdig command line option, 452+nosplit
delv command line option, 444+nostats
dig command line option, 452+nostracedelv command line option, 443+nosubnet
dig command line option, 452
mdig command line option, 491+notcflag
dig command line option, 453+notcpdelv command line option, 445
dig command line option, 453
mdig command line option, 489+notlsdig command line option, 453+notls-ca
dig command line option, 453
547

BIND 9 Administrator Reference Manual, Release 9.20.0+notls-certfile
dig command line option, 453+notls-hostname
dig command line option, 453+notls-keyfile
dig command line option, 453+notrace
dig command line option, 453+notrust
delv command line option, 444+nottldelv command line option, 443+nottlid
dig command line option, 453
mdig command line option, 489+nottlunits
dig command line option, 453
mdig command line option, 489+nounknownformat
delv command line option, 445
dig command line option, 453
mdig command line option, 491+novc
dig command line option, 454
mdig command line option, 489+novtracedelv command line option, 444+noyamldelv command line option, 445
dig command line option, 454
mdig command line option, 491+nozflagdig command line option, 454
mdig command line option, 491+nsdelv command line option, 443+nsid
dig command line option, 451
mdig command line option, 491+nssearchdig command line option, 451+onesoa
dig command line option, 451+opcodedig command line option, 451+padding
dig command line option, 451+proxydig command line option, 451+proxy-plain
dig command line option, 451+qid
dig command line option, 451
+qmin
548

delv command line option, 443+qr
dig command line option, 451+question
dig command line option, 452
mdig command line option, 489+raflag
dig command line option, 452+rdflag
dig command line option, 452+recurse
dig command line option, 452
mdig command line option, 491+retrydig command line option, 452
mdig command line option, 491+root
delv command line option, 444+rrcomments
delv command line option, 444
dig command line option, 452
mdig command line option, 489+rtracedelv command line option, 443+searchdig command line option, 452+shortdelv command line option, 444
dig command line option, 452
mdig command line option, 489+showbadcookie
dig command line option, 452+showsearchdig command line option, 452+splitdelv command line option, 444
dig command line option, 452
mdig command line option, 489+statsdig command line option, 452+stracedelv command line option, 443+subnetdig command line option, 452
mdig command line option, 491+tcflag
dig command line option, 453+tcp
delv command line option, 445
dig command line option, 453
mdig command line option, 489+timeout
dig command line option, 453
mdig command line option, 491
Index

BIND 9 Administrator Reference Manual, Release 9.20.0+tls
dig command line option, 453+tls-cadig command line option, 453+tls-certfile
dig command line option, 453+tls-hostname
dig command line option, 453+tls-keyfile
dig command line option, 453+tracedig command line option, 453+triesdig command line option, 453
mdig command line option, 491+trustdelv command line option, 444+ttl
delv command line option, 443+ttliddig command line option, 453
mdig command line option, 489+ttlunits
dig command line option, 453
mdig command line option, 489+udptimeout
mdig command line option, 491+unknownformat
delv command line option, 445
dig command line option, 453
mdig command line option, 491+vc
dig command line option, 454
mdig command line option, 489+vtracedelv command line option, 444+yamldelv command line option, 445
dig command line option, 454
mdig command line option, 491+zflagdig command line option, 454
mdig command line option, 491$TTL, 33
-1dnssec-dsfromkey command line option, 458-2dnssec-dsfromkey command line option, 458-3dnssec-keyfromlabel command line
option, 462

Index

dnssec-keygen command line option,
465
dnssec-signzone command line option,
480-4
delv command line option, 442
dig command line option, 446
host command line option, 485
mdig command line option, 488
named command line option, 519
nsupdate command line option, 526
rndc command line option, 536-6
delv command line option, 442
dig command line option, 446
host command line option, 485
mdig command line option, 488
named command line option, 519
nsupdate command line option, 526
rndc command line option, 536-A
dnssec-dsfromkey command line option, 458
dnssec-keyfromlabel command line
option, 464
dnssec-keygen command line option,468
dnssec-settime command line option,474
dnssec-signzone command line option,
480
host command line option, 485
nsupdate command line option, 526
rndc-confgen command line option, 532-AA
dnssec-signzone command line option,
480-C
dnssec-dsfromkey command line option, 459
dnssec-keyfromlabel command line
option, 462
dnssec-keygen command line option,466
dnssec-signzone command line option,
476
host command line option, 485
named command line option, 519
named-checkzone command line option,494
named-compilezone command line option, 497
named-rrchecker command line option,
501
549

BIND 9 Administrator Reference Manual, Release 9.20.0

nsupdate command line option, 526-Ddnssec-signzone command line option,
480
nsupdate command line option, 527-H

dnssec-cds command line option, 456
dnssec-importkey command line op- -Ition, 461
dnssec-keyfromlabel command line
dnssec-keyfromlabel command line
option, 464
option, 464
dnssec-keygen command line option,
dnssec-keygen command line option,
468
468
dnssec-settime command line option,
dnssec-settime command line option,474
474
dnssec-signzone command line option,
dnssec-signzone command line option,
478
476
dnssec-verify command line option,
named command line option, 519
482
named-checkzone command line option, -J
495
dnssec-signzone command line option,
named-compilezone command line op477
dnssec-verify command line option,
tion, 498
nsupdate command line option, 527
482
named-checkzone command line option,
dnssec-keyfromlabel command line494
named-compilezone command line opoption, 462
dnssec-keygen command line option,
tion, 496
466
-K
dnssec-dsfromkey command line opdnssec-ksr command line option, 470
tion, 459
dnssec-revoke command line option,472
dnssec-importkey command line option, 460
dnssec-settime command line option,473
dnssec-keyfromlabel command line
dnssec-signzone command line option,
option, 463
476
dnssec-keygen command line option,
dnssec-verify command line option,466
482
dnssec-ksr command line option, 470
named command line option, 519
dnssec-revoke command line option,
nsupdate command line option, 527
472
dnssec-settime command line option,
dnssec-keygen command line option,
473
466
dnssec-signzone command line option,
dnssec-ksr command line option, 470477
dnssec-signzone command line option,
nsupdate command line option, 527
476-L
named command line option, 519
dnssec-importkey command line opnamed-checkzone command line option,
tion, 460
494
dnssec-keyfromlabel command line
named-compilezone command line opoption, 463
dnssec-keygen command line option,
tion, 497
467
dnssec-settime command line option,
dnssec-keyfromlabel command line
473
option, 463
dnssec-keygen command line option,
dnssec-signzone command line option,
466
478
dnssec-signzone command line option,
named command line option, 520
477
named-checkzone command line option,
494

550

Index

-E

-F

-G

BIND 9 Administrator Reference Manual, Release 9.20.0

named-compilezone command line option, 497
nsupdate command line option, 527
-M

-N

-O

-P

-Q

-R

-S

474
dnssec-signzone command line option,479
named-checkzone command line option,495
named-compilezone command line option, 498
nsupdate command line option, 528

dnssec-signzone command line option,477
named command line option, 520
named-checkzone command line option,495-T
named-compilezone command line opdnssec-cds command line option, 456
dnssec-dsfromkey command line option, 498
tion, 459
dnssec-signzone command line option,
dnssec-keygen command line option,
478
467
host command line option, 485
dnssec-signzone command line option,
480
dnssec-signzone command line option,
host command line option, 486
479
named-checkzone command line option,
nsupdate command line option, 527
495
named-compilezone command line opdnssec-importkey command line option, 498
named-rrchecker command line option,
tion, 461
dnssec-keyfromlabel command line
501
option, 464
nsupdate command line option, 528
dnssec-keygen command line option, -U
host command line option, 486
468
dnssec-settime command line option,
named command line option, 520
474-V
dnssec-signzone command line option,
dnssec-cds command line option, 457
479
dnssec-dsfromkey command line opnamed-rrchecker command line option,
tion, 459
501
dnssec-importkey command line opnsupdate command line option, 527
tion, 461
dnssec-keyfromlabel command line
dnssec-signzone command line option,
option, 463
479
dnssec-keygen command line option,467
dnssec-keyfromlabel command line
dnssec-ksr command line option, 470
option, 464
dnssec-revoke command line option,
dnssec-keygen command line option,472
468
dnssec-settime command line option,
dnssec-revoke command line option,
473
472
dnssec-signzone command line option,
dnssec-settime command line option,
478
474
dnssec-verify command line option,
dnssec-signzone command line option,
482
479
host command line option, 486
host command line option, 486
named command line option, 521
nsupdate command line option, 528
dnssec-keyfromlabel command line
rndc command line option, 536
option, 463-W
dnssec-keygen command line option,
host command line option, 486
467
named-checkzone command line option,
dnssec-settime command line option,
495

Index

551

BIND 9 Administrator Reference Manual, Release 9.20.0

named-compilezone command line option, 498-X-ddnssec-signzone command line option,477
named command line option, 521-arndc command line option, 536
rndc-confgen command line option, 532
delv command line option, 442
dnssec-cds command line option, 456
dnssec-keygen command line option,466
dnssec-settime command line option,
475
dnssec-signzone command line option,
476
host command line option, 485
named command line option, 519
named-checkzone command line option,493
named-compilezone command line option, 496
nsupdate command line option, 526

ddns-confgen command line option, 440delv command line option, 441
dnssec-cds command line option, 456
dnssec-dsfromkey command line option, 458
dnssec-keyfromlabel command line
option, 462
dnssec-keygen command line option,
465
dnssec-signzone command line option,
476
host command line option, 485-enamed-checkconf command line option,
dnssec-ksr command line option, 470492
dnssec-signzone command line option,
rndc-confgen command line option, 532
477
tsig-keygen command line option, 544 -f-b
dig command line option, 446
delv command line option, 442
dnssec-cds command line option, 456
dig command line option, 446
dnssec-dsfromkey command line opdnssec-keygen command line option,
tion, 459
466
dnssec-importkey command line opmdig command line option, 488
tion, 460
rndc command line option, 536
dnssec-keyfromlabel command line
rndc-confgen command line option, 532
option, 463-cdnssec-keygen command line option,delv command line option, 442
466
dig command line option, 446
dnssec-revoke command line option,
dnssec-cds command line option, 456
472
dnssec-dsfromkey command line opdnssec-settime command line option,
tion, 458
473
dnssec-keyfromlabel command line
dnssec-signzone command line option,
option, 463
477
dnssec-keygen command line option,
mdig command line option, 488
466
named command line option, 519
dnssec-signzone command line option,
named-checkzone command line option,476
494
dnssec-verify command line option,
named-compilezone command line op482
tion, 497
host command line option, 485-gmdig command line option, 490
dnssec-settime command line option,
named command line option, 519
475
named-checkconf command line option,
dnssec-signzone command line option,492
476
named-checkzone command line option,
named command line option, 520
494
nsupdate command line option, 527
named-compilezone command line op- -htion, 497
ddns-confgen command line option, 440
552

Index

BIND 9 Administrator Reference Manual, Release 9.20.0

delv command line option, 442
named-compilezone command line opdig command line option, 446
tion, 496
dnssec-dsfromkey command line op- -ktion, 459
ddns-confgen command line option, 440
dnssec-importkey command line opdig command line option, 446
tion, 460
dnssec-keyfromlabel command line
dnssec-keyfromlabel command line
option, 463
option, 463
dnssec-keygen command line option,
dnssec-keygen command line option,467
466
dnssec-ksr command line option, 470
dnssec-ksr command line option, 470
dnssec-settime command line option,
dnssec-revoke command line option,475
472
dnssec-signzone command line option,
dnssec-settime command line option,477
473
named-checkzone command line option,
dnssec-signzone command line option,494
477
named-compilezone command line opmdig command line option, 488
tion, 497
named-checkconf command line option,
nsupdate command line option, 527492
rndc command line option, 536
named-checkzone command line option,
rndc-confgen command line option, 532
493-l
named-compilezone command line opdnssec-keyfromlabel command line
tion, 496
option, 462
named-rrchecker command line option,
dnssec-keygen command line option,
501
467
rndc-confgen command line option, 532
dnssec-ksr command line option, 470
tsig-keygen command line option, 544
host command line option, 485-inamed-checkconf command line option,delv command line option, 442
492
dnssec-cds command line option, 456
named-checkzone command line option,
dnssec-keyfromlabel command line
494
option, 464
named-compilezone command line opdnssec-keygen command line option,
tion, 497
468
nsupdate command line option, 527
dnssec-ksr command line option, 470-mdelv command line option, 442
dnssec-settime command line option,474
dig command line option, 446
dnssec-signzone command line option,
dnstap-read command line option, 483
478
host command line option, 486
named-checkconf command line option,
mdig command line option, 488
492
named command line option, 520
named-checkzone command line option,
named-checkzone command line option,494
495
named-compilezone command line opnamed-compilezone command line option, 497
tion, 497
nsupdate command line option, 527-n-jdnssec-keyfromlabel command line
dnssec-signzone command line option,
option, 462
478
dnssec-keygen command line option,
named-checkconf command line option,467
492
dnssec-signzone command line option,
named-checkzone command line option,
478
493
named command line option, 520
Index

553

BIND 9 Administrator Reference Manual, Release 9.20.0

named-checkzone command line option,495
named-compilezone command line option, 498-odnssec-revoke command line option,472
dnssec-settime command line option,
475
host command line option, 486
named-checkzone command line option,495
named-compilezone command line option, 498
nsupdate command line option, 528
rndc command line option, 536

dnssec-signzone command line option,478
dnssec-verify command line option,
482
named-checkzone command line option,495
named-compilezone command line op- -stion, 498
ddns-confgen command line option, 440
named-rrchecker command line option,
dnssec-cds command line option, 456
501
dnssec-dsfromkey command line opnsupdate command line option, 527
tion, 459-p
dnssec-keygen command line option,
467
delv command line option, 442
dig command line option, 447
dnssec-settime command line option,
dnssec-keyfromlabel command line
475
option, 463
dnssec-signzone command line option,
dnssec-keygen command line option,
477
467
host command line option, 486
dnssec-settime command line option,
named command line option, 520
475
named-checkzone command line option,
dnstap-read command line option, 483
495
host command line option, 486
named-compilezone command line option, 498
mdig command line option, 488
named command line option, 520
rndc command line option, 536
named-checkconf command line option,
rndc-confgen command line option, 533
492-t
named-rrchecker command line option,delv command line option, 442
501
dig command line option, 447
nsupdate command line option, 527
dnssec-keyfromlabel command line
rndc command line option, 536
option, 463
rndc-confgen command line option, 532
dnssec-keygen command line option,-q467
ddns-confgen command line option, 440
dnssec-signzone command line option,delv command line option, 442
480
dig command line option, 447
dnstap-read command line option, 483
dnssec-keygen command line option,
host command line option, 486
467
mdig command line option, 490
dnssec-signzone command line option,
named command line option, 520
479
named-checkconf command line option,
dnssec-verify command line option,
492
482
named-checkzone command line option,
named-checkzone command line option,495
493
named-compilezone command line opnamed-compilezone command line option, 498
tion, 496
nsupdate command line option, 528
rndc command line option, 536
rndc command line option, 536
rndc-confgen command line option, 532
rndc-confgen command line option, 533-r-udig command line option, 447
dig command line option, 447
554

Index

BIND 9 Administrator Reference Manual, Release 9.20.0

dnssec-cds command line option, 456
dnstap-read command line option, 483
dnssec-settime command line option,
mdig command line option, 490
475
named-checkconf command line option,
dnssec-signzone command line option,
492
480
-y
named command line option, 520
dig command line option, 447
named-rrchecker command line option,
dnssec-keyfromlabel command line
501
option, 463
nsupdate command line option, 528
dnstap-read command line option, 483
rndc-confgen command line option, 533
nsupdate command line option, 528-v
rndc command line option, 536
delv command line option, 442-zddns-confgen command line option, 440
dig command line option, 447
dnssec-cds command line option, 457
dnssec-settime command line option,
dnssec-dsfromkey command line op475
dnssec-signzone command line option,
tion, 459
dnssec-importkey command line op480
dnssec-verify command line option,
tion, 460
dnssec-keyfromlabel command line
482
option, 463
named-checkconf command line option,
dnssec-keygen command line option,
493
468
A
dnssec-ksr command line option, 470
dnssec-revoke command line option, acl_name, 91472
address_match_element, 90
dnssec-settime command line option, address_match_list, 91
473
addzonednssec-signzone command line option,
rndc command line option, 537
480
Algorithm, 399
dnssec-verify command line option, algorithm482
nsec3hash command line option, 522
host command line option, 486
arpanamemdig command line option, 488
manual page, 439
named command line option, 521
named-checkconf command line option, B
492
Block, 87
named-checkzone command line option, Bogus, 429
493
boolean, 91
named-compilezone command line option, 496C
nsupdate command line option, 528
CH, 32-wclass, 31
host command line option, 486
Comment, 87
named-checkzone command line option,
495
D
named-compilezone command line op- ddns-confgention, 498
manual page, 439-x
ddns-confgen command line option
delv command line option, 442-a, 440
dig command line option, 447-h, 440dnssec-signzone command line option,-k, 440480-q, 440dnssec-verify command line option,-s, 440482-z, 440
Index

555

BIND 9 Administrator Reference Manual, Release 9.20.0

delv
manual page, 440delv command line option+all, 444
+cdflag, 443+class, 443+comments, 444+crypto, 444+dnssec, 444+hint, 443+mtrace, 443+multiline, 444+noall, 444+nocdflag, 443+noclass, 443+nocomments, 444+nocrypto, 444+nodnssec, 444+nohint, 443+nomtrace, 443+nomultiline, 444+nons, 443+noqmin, 443+noroot, 444+norrcomments, 444+nortrace, 443+noshort, 444+nosplit, 444+nostrace, 443+notcp, 445+notrust, 444+nottl, 443+nounknownformat, 445+novtrace, 444+noyaml, 445+ns, 443+qmin, 443+root, 444+rrcomments, 444+rtrace, 443+short, 444+split, 444+strace, 443+tcp, 445
+trust, 444+ttl, 443
+unknownformat, 445+vtrace, 444+yaml, 445-4, 442-6, 442-a, 441-b, 442-c, 442556-d, 442-h, 442-i, 442-m, 442-p, 442-q, 442-t, 442-v, 442-x, 442
name, 441
server, 441
type, 441
delzonerndc command line option, 537
digmanual page, 445
dig command line option+aaflag, 448+aaonly, 448+additional, 448+adflag, 448+all, 448
+answer, 448+authority, 448+badcookie, 448+besteffort, 448+bufsize, 448+cd, 448+cdflag, 448+class, 448+cmd, 448
+comments, 448+cookie, 449+crypto, 449+defname, 449+dns64prefix, 449+dnssec, 449+do, 449+domain, 449+edns, 449+ednsflags, 449+ednsnegotiation, 449+ednsopt, 449+expire, 449+fail, 449+fuzztime, 449+header-only, 450+http-plain, 450+http-plain-get, 450+http-plain-post, 450+https, 450+https-get, 450+https-post, 450+identify, 450
Index

BIND 9 Administrator Reference Manual, Release 9.20.0+idn, 450
+ignore, 450+keepalive, 450+keepopen, 450+multiline, 450+ndots, 450+noaaflag, 448+noaaonly, 448+noadditional, 448+noadflag, 448+noall, 448+noanswer, 448+noauthority, 448+nobadcookie, 448+nobesteffort, 448+nocdflag, 448+noclass, 448+nocmd, 448+nocomments, 448+nocookie, 449+nocrypto, 449+nodefname, 449+nodns64prefix, 449+nodnssec, 449+nodo, 449+noedns, 449+noednsflags, 449+noednsnegotiation, 449+noednsopt, 449+noexpire, 449+nofail, 449+nofuzztime, 449+noheader-only, 450+nohttp-plain, 450+nohttp-plain-get, 450+nohttp-plain-post, 450+nohttps, 450+nohttps-get, 450+nohttps-post, 450+noidentify, 450+noidn, 450+noignore, 450+nokeepalive, 450+nokeepopen, 450+nomultiline, 450+nonsid, 451+nonssearch, 451+noonesoa, 451+noopcode, 451+noproxy, 451+noproxy-plain, 451+noqr, 451+noquestion, 452+noraflag, 452
Index+nordflag, 452+norecurse, 452+norrcomments, 452+nosearch, 452+noshort, 452+noshowbadcookie, 452+noshowsearch, 452+nostats, 452+nosubnet, 452+notcflag, 453+notcp, 453+notls, 453+notls-ca, 453+notls-certfile, 453+notls-hostname, 453+notls-keyfile, 453+notrace, 453+nottlid, 453+nottlunits, 453+nounknownformat, 453+novc, 454+noyaml, 454+nozflag, 454+nsid, 451+nssearch, 451+onesoa, 451+opcode, 451+padding, 451+proxy, 451+proxy-plain, 451+qid, 451
+qr, 451+question, 452+raflag, 452+rdflag, 452+recurse, 452+retry, 452+rrcomments, 452+search, 452+short, 452+showbadcookie, 452+showsearch, 452+split, 452+stats, 452+subnet, 452+tcflag, 453+tcp, 453
+timeout, 453+tls, 453
+tls-ca, 453+tls-certfile, 453+tls-hostname, 453+tls-keyfile, 453+trace, 453
557

BIND 9 Administrator Reference Manual, Release 9.20.0+tries, 453+ttlid, 453+ttlunits, 453+unknownformat, 453+vc, 454+yaml, 454+zflag, 454-4, 446-6, 446-b, 446-c, 446-f, 446-h, 446-k, 446-m, 446-p, 447-q, 447-r, 447-t, 447-u, 447-v, 447-x, 447-y, 447
name, 446
server, 446
type, 446
dnssecrndc command line option, 537
dnssec-cds
manual page, 455
dnssec-cds command line option-D, 456-T, 456-V, 457-a, 456-c, 456-d, 456-f, 456-i, 456-s, 456-u, 456-v, 457
dnssec-dsfromkey
manual page, 458
dnssec-dsfromkey command line option-1, 458-2, 458-A, 458-C, 459-K, 459-T, 459-V, 459-a, 458-c, 458
558-f, 459-h, 459-s, 459-v, 459
dnssec-importkey
manual page, 460
dnssec-importkey command line option-D, 461-K, 460-L, 460-P, 461-V, 461-f, 460-h, 460-v, 460
dnssec-importkey--D command line option
sync, 461
dnssec-importkey--P command line option
sync, 461
dnssec-keyfromlabel
manual page, 461
dnssec-keyfromlabel command line option-3, 462-A, 464-C, 462-D, 464-E, 462-G, 463-I, 464-K, 463-L, 463-P, 464-R, 464-S, 463-V, 463-a, 462-c, 463-f, 463-h, 463-i, 464-k, 463-l, 462-n, 462-p, 463-t, 463-v, 463-y, 463dnssec-keyfromlabel--D command line option
sync, 464
dnssec-keyfromlabel--P command line option
sync, 464
dnssec-keygen
Index

BIND 9 Administrator Reference Manual, Release 9.20.0

manual page, 465
dnssec-keygen command line option-3, 465-A, 468-C, 466-D, 468-E, 466-F, 466-G, 466-I, 468-K, 466-L, 467-P, 468-R, 468-S, 467-T, 467-V, 467-a, 465-b, 466-c, 466-d, 466-f, 466-h, 466-i, 468-k, 467-l, 467-n, 467-p, 467-q, 467-s, 467-t, 467-v, 468
dnssec-keygen--D command line option
sync, 468
dnssec-keygen--P command line option
sync, 468
dnssec-ksr
manual page, 469
dnssec-ksr command line option-E, 470-F, 470-K, 470-V, 470-e, 470-h, 470-i, 470-k, 470-l, 470-v, 470
keygen, 471
request, 471
sign, 471
dnssec-revoke
manual page, 471
Index

dnssec-revoke command line option-E, 472-K, 472-R, 472-V, 472-f, 472-h, 472-r, 472-v, 472dnssec-settime
manual page, 472
dnssec-settime command line option-A, 474-D, 474-E, 473-I, 474-K, 473-L, 473-P, 474-R, 474-S, 474-V, 473-d, 475-f, 473-g, 475-h, 473-i, 474-k, 475-p, 475-r, 475-s, 475-u, 475-v, 473-z, 475
dnssec-settime--D command line option
ds, 474
sync, 474
dnssec-settime--P command line option
ds, 474
sync, 474
dnssec-signzone
manual page, 476
dnssec-signzone command line option-3, 480-A, 480-AA, 480-C, 476-D, 476-E, 476-F, 476-G, 477-H, 480-I, 478-J, 477559

BIND 9 Administrator Reference Manual, Release 9.20.0-K, 477-L, 478-M, 477-N, 478-O, 479-P, 479-Q, 479-R, 479-S, 479-T, 480-V, 478-X, 477-a, 476-c, 476-d, 476-e, 477-f, 477-g, 476-h, 477-i, 478-j, 478-k, 477-n, 478-o, 478-q, 479-s, 477-t, 480-u, 480-v, 480-x, 480-z, 480
key, 481
zonefile, 481
dnssec-verify
manual page, 481
dnssec-verify command line option-E, 482-I, 482-J, 482-V, 482-c, 482-o, 482-q, 482-v, 482-x, 482-z, 482
zonefile, 482
dnstaprndc command line option, 537
dnstap-readmanual page, 483
dnstap-read command line option-m, 483-p, 483560-t, 483-x, 483-y, 483
domainnsec3hash command line option, 522
domain_name, 91
ds
dnssec-settime--D command line option, 474
dnssec-settime--P command line option, 474
dumpdbrndc command line option, 538
duration, 91

Ffetchlimit
rndc command line option, 538
filenamenamed-checkconf command line option,493
named-checkzone command line option,495
named-compilezone command line option, 498
named-nzd2nzf command line option,
500
filter-aaaa
manual page, 483
fixedpoint, 91
flags
nsec3hash command line option, 522
flush
rndc command line option, 538
flushnamerndc command line option, 538
flushtree
rndc command line option, 538
freezerndc command line option, 538

G
GitLab[GL !6752], 342[GL #1128], 343[GL #1129], 343[GL #1176], 344[GL #1879], 345[GL #1967], 347[GL #2147], 344[GL #2295], 343[GL #2360], 344[GL #2486], 343[GL #2710], 343
Index

BIND 9 Administrator Reference Manual, Release 9.20.0[GL #2918], 345[GL #3140], 344[GL #3374], 347[GL #3410], 343[GL #3423], 347[GL #3504], 342[GL #3508], 347[GL #3512], 342[GL #3525], 347[GL #3527], 347[GL #3567], 346[GL #3570], 347[GL #3576], 343[GL #3583], 346[GL #3661], 346[GL #3664], 345[GL #3672], 344[GL #3676], 345, 347[GL #3677], 346[GL #3686], 344[GL #3714], 344[GL #3718], 347[GL #3726], 342[GL #3729], 344[GL #3762], 343[GL #3789], 344[GL #3837], 343[GL #3842], 343, 347[GL #3883], 343[GL #3901], 346[GL #3903], 345[GL #3904], 345[GL #3905], 345[GL #3934], 346[GL #3953], 345[GL #4001], 347[GL #4002], 347[GL #4012], 345[GL #4041], 344[GL #4045], 346[GL #4046], 343[GL #4050], 343[GL #4170], 343[GL #4185], 346[GL #4194], 346[GL #4209], 346[GL #4241], 343[GL #4296], 344[GL #4311], 344[GL #4349], 346[GL #4363], 346[GL #4364], 346[GL #4367], 346[GL #4373], 346
Index[GL #4388], 342[GL #4391], 345[GL #4405], 344[GL #4411], 347[GL #4416], 347[GL #4421], 345[GL #4446], 345[GL #4447], 344[GL #4523], 344[GL #4593], 345[GL #4614], 347[GL #4668], 344[GL #4680], 346[GL #4728], 346[GL #4793], 342, 348[GL #608], 343[GL #665], 344

H
halt
rndc command line option, 538
hostmanual page, 484
host command line option-4, 485-6, 485-A, 485-C, 485-N, 485-R, 486-T, 486-U, 486-V, 486-W, 486-a, 485-c, 485-d, 485-l, 485-m, 486-p, 486-r, 486-s, 486-t, 486-v, 486-w, 486
HS, 32I
IN, 32
Indeterminate, 429
Insecure, 429
integer, 91
ip_address, 91
ipv4_address, 91
561

BIND 9 Administrator Reference Manual, Release 9.20.0

ipv6_address, 91
Iterations, 399
iterations
nsec3hash command line option, 522

tsig-keygen, 543
mdigmanual page, 487
mdig command line option+aaflag, 490
K+aaonly, 490+additional, 488
key+adflag, 490
dnssec-signzone command line option,+all, 488
481
+answer, 488
keygen+authority, 488
dnssec-ksr command line option, 471+besteffort, 488+bufsize, 490
L+burst, 488
level+cdflag, 490
rndc-trace command line option, 542+cl, 489
loadkeys+comments, 489
rndc command line option, 538+continue, 489+cookie, 490
M+crypto, 489
managed-keys+dnssec, 490
rndc command line option, 538+edns, 490
manual page+ednsflags, 490
arpaname, 439+ednsopt, 490
ddns-confgen, 439+expire, 491
delv, 440
+multiline, 489
dig, 445+noaaflag, 490
dnssec-cds, 455+noaaonly, 490
dnssec-dsfromkey, 458+noadditional, 488
dnssec-importkey, 460+noadflag, 490
dnssec-keyfromlabel, 461+noall, 488
dnssec-keygen, 465+noanswer, 488
dnssec-ksr, 469+noauthority, 488
dnssec-revoke, 471+nobesteffort, 488
dnssec-settime, 472+nocdflag, 490
dnssec-signzone, 476+nocl, 489
dnssec-verify, 481+nocomments, 489
dnstap-read, 483+nocontinue, 489
filter-aaaa, 483+nocookie, 490
host, 484
+nocrypto, 489
mdig, 487
+nodnssec, 490
named, 518+noedns, 490
named.conf, 501+noednsflags, 490
named-checkconf, 491+noednsopt, 490
named-checkzone, 493+noexpire, 491
named-compilezone, 496+nomultiline, 489
named-journalprint, 499+nonsid, 491
named-nzd2nzf, 500+noquestion, 489
named-rrchecker, 500+norecurse, 491
nsec3hash, 522+norrcomments, 489
nslookup, 523+noshort, 489
nsupdate, 525+nosubnet, 491
rndc, 535
+notcp, 489
rndc.conf, 533+nottlid, 489
rndc-confgen, 532
562

Index

BIND 9 Administrator Reference Manual, Release 9.20.0+nottlunits, 489+nounknownformat, 491+novc, 489+noyaml, 491+nozflag, 491+nsid, 491+question, 489+recurse, 491+retry, 491+rrcomments, 489+short, 489+split, 489+subnet, 491+tcp, 489
+timeout, 491+tries, 491+ttlid, 489+ttlunits, 489+udptimeout, 491+unknownformat, 491+vc, 489+yaml, 491+zflag, 491-4, 488-6, 488-b, 488-c, 490-f, 488-h, 488-m, 488-p, 488-t, 490-v, 488-x, 490
modzonerndc command line option, 539

N
namedelv command line option, 441
dig command line option, 446
namedmanual page, 518
named command line option-4, 519-6, 519-C, 519-D, 519-E, 519-F, 519-L, 520-M, 520-U, 520-V, 521
Index-X, 521-c, 519-d, 519-f, 519-g, 520-m, 520-n, 520-p, 520-s, 520-t, 520-u, 520-v, 521
named.conf
manual page, 501
named-checkconf
manual page, 491
named-checkconf command line option-a, 492-c, 492-h, 492-i, 492-j, 492-l, 492-p, 492-t, 492-v, 492-x, 492-z, 493
filename, 493
named-checkzone
manual page, 493
named-checkzone command line option-C, 494-D, 495-F, 494-J, 494-L, 494-M, 495-S, 495-T, 495-W, 495-c, 494-d, 493-f, 494-h, 493-i, 494-j, 493-k, 494-l, 494-m, 495-n, 495-o, 495-q, 493-r, 495
563

BIND 9 Administrator Reference Manual, Release 9.20.0-s, 495-t, 495-v, 493-w, 495
filename, 495
zonename, 495
named-compilezone
manual page, 496
named-compilezone command line option-C, 497-D, 498-F, 497-J, 496-L, 497-M, 498-S, 498-T, 498-W, 498-c, 497-d, 496-f, 497-h, 496-i, 497-j, 496-k, 497-l, 497-m, 497-n, 498-o, 498-q, 496-r, 498-s, 498-t, 498-v, 496-w, 498
filename, 498
zonename, 498
named-journalprint
manual page, 499
named-nzd2nzf
manual page, 500
named-nzd2nzf command line option
filename, 500
named-rrchecker
manual page, 500
named-rrchecker command line option-C, 501-P, 501-T, 501-h, 501-o, 501-p, 501-u, 501
netprefix, 92
564

notifyrndc command line option, 539
notracerndc command line option, 539
NSEC3 Hashing Algorithm, 399
nsec3hashmanual page, 522
nsec3hash command line option
algorithm, 522
domain, 522
flags, 522
iterations, 522
salt, 522
nslookupmanual page, 523
nsupdate
manual page, 525
nsupdate command line option-4, 526-6, 526-A, 526-C, 526-D, 527-E, 527-H, 527-K, 527-L, 527-O, 527-P, 527-S, 528-T, 528-V, 528-d, 526-g, 527-i, 527-k, 527-l, 527-o, 527-p, 527-r, 528-t, 528-u, 528-v, 528-y, 528
nta
rndc command line option, 539

O
Opt-out, 399
owner name, 31

Ppercentage, 92
port, 92
Index

BIND 9 Administrator Reference Manual, Release 9.20.0

portrange, 92

Qquerylog
rndc command line option, 540

R
RDATA, 31
reconfig
rndc command line option, 540
recursingrndc command line option, 540
refreshrndc command line option, 540
reloadrndc command line option, 540
remote-servers, 92
requestdnssec-ksr command line option, 471
retransfer
rndc command line option, 540
RFC
RFC 1033, 519, 522
RFC 1034, 7, 31, 32, 104, 146, 154, 431, 433, 501,
519, 522, 531
RFC 1035, 7, 34, 35, 431, 433, 455, 491, 496, 499,
501, 519, 522
RFC 1101, 437
RFC 1123, 135, 145, 437
RFC 1183, 433
RFC 1535, 437
RFC 1536, 437
RFC 1706, 433
RFC 1712, 433
RFC 1796, 433
RFC 1876, 433
RFC 1912, 437
RFC 1918, 24, 58, 186, 194, 241
RFC 1982, 433, 478
RFC 1995, 58, 73, 433
RFC 1996, 18, 58, 73, 74, 433
RFC 2104, 531
RFC 2136, 57, 433, 526, 531
RFC 2163, 433
RFC 2181, 433
RFC 2193, 24
RFC 2219, 437
RFC 2230, 434
RFC 2308, 33, 35, 434
RFC 2317, 36, 437
RFC 2535, 86, 463, 465, 467, 526, 531
RFC 2539, 434, 469
RFC 2606, 437
RFC 2671, 204, 262, 305
Index

RFC 2782, 434
RFC 2845, 84, 469, 526, 531, 543
RFC 2874, 437
RFC 2930, 434
RFC 2931, 86, 434, 526, 531
RFC 3007, 57, 434, 531
RFC 3056, 252
RFC 3110, 434
RFC 3123, 68, 434
RFC 3225, 434
RFC 3226, 434
RFC 3339, 91
RFC 3363, 61, 62, 434, 437
RFC 3403, 434
RFC 3492, 434
RFC 3493, 434
RFC 3496, 434
RFC 3542, 13
RFC 3548, 41
RFC 3596, 434
RFC 3597, 434, 445, 447, 454, 491
RFC 3645, 434, 526
RFC 3658, 460
RFC 3833, 437
RFC 3901, 437
RFC 3986, 213
RFC 4025, 434
RFC 4033, 434, 481, 483
RFC 4034, 434, 445, 465, 469
RFC 4035, 429, 434, 445
RFC 4074, 437
RFC 4193, 186
RFC 4255, 434
RFC 4343, 434
RFC 4398, 434
RFC 4431, 437, 445
RFC 4470, 399, 435
RFC 4509, 435, 460
RFC 4592, 71, 435, 495, 498
RFC 4635, 435
RFC 4701, 435
RFC 4892, 437
RFC 4955, 435
RFC 5001, 435
RFC 5011, 50, 93, 215, 386, 435, 441, 461, 463,
472, 476, 538
RFC 5074, 445
RFC 5077, 211
RFC 5155, 421, 435, 445, 523
RFC 5205, 435
RFC 5452, 435
RFC 5625, 437
RFC 5702, 435
RFC 5737, 24, 186
565

BIND 9 Administrator Reference Manual, Release 9.20.0

RFC 5891, 435
RFC 5936, 435
RFC 5952, 435
RFC 6052, 126, 435
RFC 6147, 435
RFC 6303, 437
RFC 6598, 24, 186
RFC 6604, 435
RFC 6605, 435, 460
RFC 6672, 435
RFC 6698, 408, 435
RFC 6725, 435
RFC 6742, 435
RFC 6781, 437, 481
RFC 6781#4.1.1.1, 479
RFC 6781#4.1.1.2, 479
RFC 6840, 436
RFC 6891, 204, 436
RFC 7043, 436
RFC 7050, 436
RFC 7129, 398, 437
RFC 7208, 436
RFC 7314, 436
RFC 7344, 49, 382, 383, 436, 455, 458, 460
RFC 7477, 436
RFC 7512, 54, 98, 465
RFC 7553, 436
RFC 7583, 349, 407, 436
RFC 7672, 408
RFC 7766, 344, 436
RFC 7793, 437
RFC 7816, 120
RFC 7828, 436
RFC 7830, 436
RFC 7858, 436
RFC 7929, 408, 436
RFC 8078, 382, 426, 436
RFC 8080, 436
RFC 8198, 148, 282, 291, 400, 424
RFC 821, 145
RFC 8484, 338, 436
RFC 8509, 134, 436
RFC 8624, 435, 436
RFC 8659, 436
RFC 8749, 437
RFC 8767, 140
RFC 8806, 240
RFC 882, 431
RFC 883, 431
RFC 8880, 436
RFC 8901, 47, 343
RFC 8906, 437
RFC 8914, 197, 343
RFC 8945, 436
566

RFC 9103, 211, 436
RFC 920, 431
RFC 9276, 220, 346, 399, 400, 437, 480
RFC 9432, 65, 437
RFC 9460, 437
RFC 952, 145
rndc
manual page, 535
rndc command line option-4, 536-6, 536-V, 536-b, 536-c, 536-k, 536-p, 536-q, 536-r, 536-s, 536-t, 536-y, 536
addzone, 537delzone, 537
dnssec, 537
dnstap, 537
dumpdb, 538
fetchlimit, 538
flush, 538
flushname, 538
flushtree, 538
freeze, 538
halt, 538
loadkeys, 538
managed-keys, 538
modzone, 539
notify, 539
notrace, 539
nta, 539
querylog, 540
reconfig, 540
recursing, 540
refresh, 540
reload, 540
retransfer, 540
scan, 540
secroots, 540
serve-stale, 541
showzone, 541
sign, 541
signing, 541
stats, 542
status, 542
stop, 542
sync, 542
Index

BIND 9 Administrator Reference Manual, Release 9.20.0

tcp-timeouts, 542
thaw, 542
trace, 542
validation, 543
zonestatus, 543
rndc.conf
manual page, 533
rndc-confgen
manual page, 532
rndc-confgen command line option-A, 532-a, 532-b, 532-c, 532-h, 532-k, 532-p, 532-q, 532-s, 533-t, 533-u, 533
rndc-reload command line optionzone, 540
rndc-trace command line option
level, 542
RR TTLs, 33
RR type, 31

S
Salt, 399
salt
nsec3hash command line option, 522
scanrndc command line option, 540
secroots
rndc command line option, 540
Secure, 429
serve-stale
rndc command line option, 541
serverdelv command line option, 441
dig command line option, 446
server_key, 92
showzone
rndc command line option, 541
signdnssec-ksr command line option, 471
rndc command line option, 541
signingrndc command line option, 541
size, 92
sizeval, 92
SOA minimum, 33
Statement, 87
Index

stats
rndc command line option, 542
statusrndc command line option, 542
stop
rndc command line option, 542
sync
dnssec-importkey--D command line
option, 461
dnssec-importkey--P command line
option, 461
dnssec-keyfromlabel--D command line
option, 464
dnssec-keyfromlabel--P command line
option, 464
dnssec-keygen--D command line option, 468
dnssec-keygen--P command line option, 468
dnssec-settime--D command line option, 474
dnssec-settime--P command line option, 474
rndc command line option, 542

T
tcp-timeouts
rndc command line option, 542
thaw
rndc command line option, 542
tls_id, 92
trace
rndc command line option, 542
tsig-keygenmanual page, 543
tsig-keygen command line option-a, 544-h, 544
TTL, 31
type
delv command line option, 441
dig command line option, 446

Vvalidation
rndc command line option, 543

Z
zone
rndc-reload command line option, 540
zonefile
dnssec-signzone command line option,
481

567

BIND 9 Administrator Reference Manual, Release 9.20.0

dnssec-verify command line option,
482
zonenamenamed-checkzone command line option,495
named-compilezone command line option, 498
zonestatus
rndc command line option, 543

568

Index