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result in a common instantiation of an authoritative server on the WAN and inner interface.  Other mechanisms may also be used. <del> 3.2. This section details the interfaces and channels of the DM, that is the Control Channel, the Synchronization Channel and the Distribution Channel. The Control Channel and the Synchronization Channel are the interfaces used between the HNA and the Outsourcing Infrastructure. The entity within the Outsourcing Infrastructure responsible to handle these communications is the DM and communications between the HNA and the DM SHOULD be protected and mutually authenticated.  While section sec-ctrl-security discusses in more depth the different security protocols that could be used to secure, this specification RECOMMENDS the use of TLS with mutually authentication based on certificates to secure the channel between the HNA and the DM. The Control Channel is used to set up the Synchronization Channel. We assume that the HNA initiates the Control Channel connection with the DM and as such has a prior knowledge of the DM identity (X509 certificate), the IP address and port to use and protocol to set secure session.  We also assume the DM has knowledge of the identity of the HNA (X509 certificate) as well as the Registered Homenet Domain.  For more detail to see how this can be achieved, please see section hna-provisioning. The information exchanged between the HNA and the DM is using DNS messages.  DNS messages can be protected using various kind of transport layers, among others, UDP:53/DTLS, TLS/TCP:53, HTTPS:443. There was consideration to using a standard TSIG RFC2845 or SIG(0) RFC2931 to perform a dynamic DNS update to the DM.  There are a number of issues with this.  The main one is that the Dynamic DNS update would also update the parent zone's (NS, DS and associated A or AAAA records) while the goal is to update the Distribution Master's configuration files.  The visible NS records SHOULD remain pointing at the cloud provider's anycast addresses.  Revealing the address of the HNA in the DNS is not desirable.  Please see section sec-chain-of-trust for more details. This specification also assumes: * the DM serves both the Control Channel and Synchronization Channel on a single IP address, single port and with a single transport protocol.  * the HNA uses a single IP address for both the Control and Synchronization channel by default.  However, the HNA MAY use distinct IP addresses - see section sec-synch and section {sec-sync-info}} for more details. The Distribution Channel is internal to the Outsourcing Infrastructure and as such is not the primary concern of this specification. </del>  <del> 4. The DM Control Channel is used by the HNA and the Outsourcing Infrastructure to exchange information related to the configuration of the delegation which includes: 4.1. When the HNA builds the public zone, it must include information that it retrieves from the DM relating to how the zone is to be published. The information includes at least names and IP addresses of the Public Authoritative Name Servers.  In term of RRset information this includes: the MNAME of the SOA, the NS and associated A and AAA RRsets of the name servers. Optionally the Outsourcing Infrastructure MAY also provide operational parameters such as other fields of SOA (SERIAL, RNAME, REFRESH, RETRY, EXPIRE and MINIMUM).  As the information is necessary for the HNA to proceed and the information is associated to the Outsourcing Infrastructure, this information exchange is mandatory. 4.2. The HNA SHOULD provide the hash of the KSK (DS RRset), so the that Outsourcing Infrastructure provides this value to the parent zone.  A common deployment use case is that the Outsourcing Infrastructure is the registrar of the Registered Homenet Domain, and as such, its relationship with the registry of the parent zone enables it to update the parent zone.  When such relation exists, the HNA should be able to request the Outsourcing Infrastructure to update the DS RRset in the parent zone.  A direct update is especially necessary to initialize the chain of trust. Though the HNA may also later directly update the values of the DS via the Control Channel, it is RECOMMENDED to use other mechanisms such as CDS and CDNSKEY RFC7344 for transparent updates during key roll overs. As some deployment may not provide an Outsourcing Infrastructure that will be able to update the DS in the parent zone, this information exchange is OPTIONAL. By accepting the DS, the DM commits in taking care of advertising the DS to the parent zone.  Upon refusal, the DM clearly indicates it does not have the capacity to proceed to the update. 4.3. That information sets the primary/secondary relation between the HNA and the DM.  The HNA works as a primary authoritative DNS server, and MUST provide the corresponding IP address. The specified IP address on the HNA side and the currently used IP address of the DM defines the IP addresses involved in the Synchronization Channel.  Ports and transport protocol are the same as those used by the Control Channel.  By default, the same IP address used by the HNA is considered by the DM.  Exchange of this information is OPTIONAL. 4.4. The purpose of the previous sections were to exchange information in order to set a delegation.  The HNA MUST also be able to delete a delegation with a specific DM.  Upon an instruction of deleting the delegation, the DM MUST stop serving the Public Homenet Zone. 4.5. There are multiple ways these information could be exchanged between the HNA and the DM.  This specification defines a mechanism that re- use the DNS exchanges format.  The intention is to reuse standard libraries especially to check the format of the exchanged fields as well as to minimize the additional libraries needed for the HNA.  The re-use of DNS exchanges achieves these goals.  Note that while information is provided using DNS exchanges, the exchanged information is not expected to be set in any zone file, instead this information is expected to be processed appropriately. The Control Channel is not expected to be a long term session.  After a predefined timer the Control Channel is expected to be terminated. The Control Channel MAY Be re-opened at any time later. The provisioning process SHOULD provide a method of securing the control channel, so that the content of messages can be authenticated.  This authentication MAY be based on certificates for both the DM and each HNA.  The DM may also create the initial configuration for the delegation zone in the parent zone during the provisioning process. 4.5.1. The information provided by the DM to the HNA is retrieved by the HNA with a AXFR exchange.  The AXFR message enables the response to contain any type of RRsets.  The response might be extended in the future if additional information will be needed.  Alternatively, the information provided by the HNA to the DM is pushed by the HNA via a DNS update exchange. To retrieve the necessary information to build the Public Homenet Zone, the HNA MUST send an DNS request of type AXFR associated to the Registered Homenet Domain.  The DM MUST respond with a zone template. The zone template MUST contain a RRset of type SOA, one or multiple RRset of type NS and zero or more RRset of type A or AAAA. The SOA RR is used to indicate to the HNA the value of the MNAME of the Public Homenet Zone.  The NAME of the SOA RR MUST be the Registered Homenet Domain.  The MNAME value of the SOA RDATA is the value provided by the Outsourcing Infrastructure to the HNA.  Other RDATA values (RNAME, REFRESH, RETRY, EXPIRE and MINIMUM) are provided by the Outsourcing Infrastructure as suggestions.  The NS RRsets are used to carry the Public Authoritative Servers of the Outsourcing Infrastructure.  Their associated NAME MUST be the Registered Homenet Domain.  The TTL and RDATA are those expected to be published on the Public Homenet Zone.  The RRsets of Type A and AAAA MUST have their NAME matching the NSDNAME of one of the NS RRsets. Upon receiving the response, the HNA MUST validate format and properties of the SOA, NS and A or AAAA RRsets.  If an error occurs, the HNA MUST stop proceeding and MUST report an error.  Otherwise, the HNA builds the Public Homenet Zone by setting the MNAME value of the SOA as indicated by the SOA provided by the AXFR response.  The HNA SHOULD set the value of NAME, REFRESH, RETRY, EXPIRE and MINIMUM of the SOA to those provided by the AXFR response.  The HNA MUST insert the NS and corresponding A or AAAA RRset in its Public Homenet Zone.  The HNA MUST ignore other RRsets.  If an error message is returned by the DM, the HNA MUST proceed as a regular DNS resolution. Error messages SHOULD be logged for further analysis.  If the resolution does not succeed, the outsourcing operation is aborted and the HNA MUST close the Control Channel. 4.5.2. To provide the DS RRset to initialize the DNSSEC chain of trust the HNA MAY send a DNS UPDATE RFC2136 message.  The NAME in the SOA MUST be set to the parent zone of the Registered Homenet Domain - that is where the DS records should be inserted.  The DS RRset MUST be placed in the Update section of the UPDATE query, and the NAME SHOULD be set to the Registered Homenet Domain.  The RDATA of the DS RR SHOULD correspond to the DS record to be inserted in the parent zone. A NOERROR response from the MD is a commitment to update the parent zone with the provided DS.  An error indicates the MD will not update the DS, and other method should be used by the HNA. 4.5.3. To provide the IP address of the primary, the HNA MAY send a DNS UPDATE message.  The NAME in the SOA MUST be the parent zone of the Registered Homenet Domain.  The Update section MUST be a RRset of Type NS.  The RDATA MUST be a RRset of type A or AAAA that designates the IP addresses associated to the primary.  There may be multiple IP addresses.  These IP addresses MUST be provided in the additional section.  The reason to provide these IP addresses is that it is NOT RECOMMENDED to publish these IP addresses.  As a result, it is not expected to resolve them. A NOERROR response indicates the DM has configured the secondary and is committed to serve as a secondary.  An error indicates the DM is not configured as a secondary. The regular DNS error message SHOULD be returned to the HNA when an error occurs.  In particular a FORMERR is returned when a format error is found, this includes when unexpected RRSets are added or when RRsets are missing.  A SERVFAIL error is returned when a internal error is encountered.  A NOTZONE error is returned when update and Zone sections are not coherent, a NOTAUTH error is returned when the DM is not authoritative for the Zone section.  A REFUSED error is returned when the DM refuses to proceed to the configuration and the requested action. 4.5.4. To instruct to delete the delegation the HNA MAY send a DNS UPDATE Delete message.  The NAME in the SOA MUST be the parent zone of the Registered Homenet Domain.  The Update section MUST be a RRset of Type NS.  The NAME associated to the NS RRSet MUST be the Registered Domain Name.  As indicated by RFC2136 section 2.5.2 the delete instruction is set by setting the TTL to 0, the CLass to ANY, the RDLENGTH to 0 and the RDATA MUST be empty. 4.6. The control channel between the HNA and the DM MUST be secured at both the HNA and the DM. Secure protocols (like TLS RFC8446 / DTLS I-D.ietf-tls-dtls13) SHOULD be used to secure the transactions between the DM and the HNA. The advantage of TLS/DTLS is that this technology is widely deployed, and most of the devices already embed TLS/DTLS libraries, possibly also taking advantage of hardware acceleration.  Further, TLS/DTLS provides authentication facilities and can use certificates to mutually authenticate the DM and HNA at the application layer, including available API.  On the other hand, using TLS/DTLS requires implementing DNS exchanges over TLS/DTLS, as well as a new service port. The HNA SHOULD authenticate inbound connections from the DM using standard mechanisms, such as a public certificate with baked-in root certificates on the HNA, or via DANE {!RFC6698}}.  The HNA is expected to be provisioned with a connection to the DM by the manufacturer, or during some user-initiated onboarding process, see hna-provisioning. The DM SHOULD authenticate the HNA and check that inbound messages are from the appropriate client.  The DM MAY use a self-signed CA certificate mechanism per HNA, or public certificates for this purpose. IPsec RFC4301 and IKEv2 RFC7296 were considered.  They would need to operate in transport mode, and the authenticated end points would need to be visible to the applications, and this is not commonly available at the time of this writing. A pure DNS solution using TSIG and/or SIG(0) to authenticate message was also considered.  hna-provisioning envisions one mechanism would involve the end user, with a browser, signing up to a service provider, with a resulting OAUTH2 token to be provided to the HNA.  A way to translate this OAUTH2 token from HTTPS web space to DNS SIG(0) space seems overly problematic, and so the enrollment protocol using web APIs was determined to be easier to implement at scale. Note also that authentication of message exchanges between the HNA and the DM SHOULD NOT use the external IP address of the HNA to index the appropriate keys.  As detailed in sec-renumbering, the IP addresses of the DM and the Hidden Primary are subject to change, for example while the network is being renumbered.  This means that the necessary keys to authenticate transaction SHOULD NOT be indexed using the IP address, and SHOULD be resilient to IP address changes. This should apply to any OAUTH2 token produced as envisioned by hna- provisioning. 4.7. The Hidden Primary Server on the HNA differs from a regular authoritative server for the home network due to: Interface Binding: the Hidden Primary Server will almost certainly listen on the WAN Interface, whereas a regular authoritative server for the home network would listen on the internal home network interface. Limited exchanges: the purpose of the Hidden Primary Server is to synchronize with the DM, not to serve any zones to end users, or the public Internet. As a result, exchanges are performed with specific nodes (the DM). Further, exchange types are limited.  The only legitimate exchanges are: NOTIFY initiated by the Hidden Primary and IXFR or AXFR exchanges initiated by the DM.  On the other hand, regular authoritative servers would respond to any hosts, and any DNS query would be processed.  The HNA SHOULD filter IXFR/AXFR traffic and drop traffic not initiated by the DM.  The HNA MUST listen for DNS on TCP and UDP and MUST at least allow SOA lookups of the Homenet Zone. 5. The DM Synchronization Channel is used for communication between the HNA and the DM for synchronizing the Public Homenet Zone.  Note that the Control Channel and the Synchronization Channel are by construction different channels even though there they MAY use the same IP addresses.  In fact the Control Channel is set between the HNA working as a client using port YYYY (a high range port) toward a service provided by the MD at port XX (well known port).  On the other hand, the Synchronization Channel is set between the DM working as a client using port ZZZZ ( a high range port) toward a service a service provided by the HNA at port XX.  As a result, even though the same couple of IP addresses may be involved the Control Channel and the Synchronization Channel are always distinct channels. Uploading and dynamically updating the zone file on the DM can be seen as zone provisioning between the HNA (Hidden Primary) and the DM (Secondary Server).  This can be handled via AXFR + DNS UPDATE. This document RECOMMENDS use of a primary / secondary mechanism instead of the use of DNS UPDATE.  The primary / secondary mechanism is RECOMMENDED as it scales better and avoids DoS attacks.  Note that even when UPDATE messages are used, these messages are using a distinct channel as those used to set the configuration. Note that there is no standard way to distribute a DNS primary between multiple devices.  As a result, if multiple devices are candidate for hosting the Hidden Primary, some specific mechanisms should be designed so the home network only selects a single HNA for the Hidden Primary.  Selection mechanisms based on HNCP RFC7788 are good candidates. The HNA acts as a Hidden Primary Server, which is a regular authoritative DNS Server listening on the WAN interface. The DM is configured as a secondary for the Homenet Domain Name. This secondary configuration has been previously agreed between the end user and the provider of the Outsourcing Infrastructure as part of either the provisioning or due to receipt of UPDATE messages on the DM Control Channel. The Homenet Reverse Zone MAY also be updated either with DNS UPDATE RFC2136 or using a primary / secondary synchronization. 5.1. The Synchronization Channel used standard DNS request. First the primary notifies the secondary that the zone must be updated and eaves the secondary to proceed with the update when possible/ convenient. Then, a NOTIFY message is sent by the primary, which is a small packet that is less likely to load the secondary. Finally, the AXFR RFC1034 or IXFR RFC1995 query performed by the secondary is a small packet sent over TCP (section 4.2 RFC5936), which mitigates reflection attacks using a forged NOTIFY. The AXFR request from the DM to the HNA SHOULD be secured.  DNS over TLS RFC7858 is RECOMMENDED. When using TLS, the HNA MAY authenticate inbound connections from the DM using standard mechanisms, such as a public certificate with baked-in root certificates on the HNA, or via DANE {!RFC6698}} The HNA MAY apply a simple IP filter on inbound AXFR requests to ensure they only arrive from the DM Synchronization Channel.  In this case, the HNA SHOULD regularly check (via DNS resolution) that the address of the DM in the filter is still valid. 6. The DM Distribution Channel is used for communication between the DM and the Public Authoritative Servers.  The architecture and communication used for the DM Distribution Channels is outside the scope of this document, and there are many existing solutions available e.g. rsynch, DNS AXFR, REST, DB copy. 7. This section details security policies related to the Hidden Primary / Secondary synchronization. The Hidden Primary, as described in this document SHOULD drop any queries from the home network.  This could be implemented via port binding and/or firewall rules.  The precise mechanism deployed is out of scope of this document.  The Hidden Primary SHOULD drop any DNS queries arriving on the WAN interface that are not issued from the DM.  The Hidden Primary SHOULD drop any outgoing packets other than DNS NOTIFY query, SOA response, IXFR response or AXFR responses.  The Hidden Primary SHOULD drop any incoming packets other than DNS NOTIFY response, SOA query, IXFR query or AXFR query.  The Hidden Primary SHOULD drop any non protected IXFR or AXFR exchange,depending on how the synchronization is secured. 8. RFC7368 in Section 3.7.3 recommends DNSSEC to be deployed on both the authoritative server and the resolver.  The resolver side is out of scope of this document, and only the authoritative part of the server is considered. This document assumes the HNA signs the Public Homenet Zone. Secure delegation is achieved only if the DS RRset is properly set in the parent zone.  Secure delegation is performed by the HNA or the Outsourcing Infrastructures. The DS RRset can be updated manually with nsupdate for example.  This requires the HNA or the Outsourcing Infrastructure to be authenticated by the DNS server hosting the parent of the Public Homenet Zone.  Such a trust channel between the HNA and the parent DNS server may be hard to maintain with HNAs, and thus may be easier to establish with the Outsourcing Infrastructure.  In fact, the Public Authoritative Server(s) may use Automating DNSSEC Delegation Trust Maintenance RFC7344. 9. The Public Homenet Zone is associated to a Registered Homenet Domain and the ownership of that domain requires a specific registration from the end user as well as the HNA being provisioned with some authentication credentials .  Such steps are mandatory unless the Outsourcing Infrastructure has some other means to authenticate the HNA.  Such situation may occur, for example, when the ISP provides the Homenet Domain as well as the Outsourcing Infrastructure.  In this case, the HNA may be authenticated by the physical link layer, in which case the authentication of the HNA may be performed without additional provisioning of the HNA.  While this may be not so common for the Public Homenet Zone, this situation is expected to be quite common for the Reverse Homenet Zone. More specifically, a common case is that the upstream ISP provides the IPv6 prefix to the Homenet with a IA_PD RFC8415 option and manages the Outsourcing Infrastructure of the associated reverse zone.  This leave place for setting up automatically the relation between HNA and the Outsourcing infrastructure as described in I- D.ietf-homenet-naming-architecture-dhc-options. With this relation automatically configured, the synchronization between the Home network and the Outsourcing infrastructure happens similarly as for the Public Homenet Zone described earlier in this document. Note that for home networks hosted by multiple ISPs, each ISP provides only the Outsourcing Infrastructure of the reverse zones associated to the delegated prefix.  It is also likely that the DNS exchanges will need to be performed on dedicated interfaces as to be accepted by the ISP.  More specifically, the reverse zone associated to prefix 1 will not be possible to be performs by the HNA using an IP address that belongs to prefix 2.  Such constraints does not raise major concerns either for hot standby or load sharing configuration. With IPv6, the domain space for IP addresses is so large that reverse zone may be confronted with scalability issues.  How the reverse zone is generated is out of scope of this document.  I-D.howard-dnsop- ip6rdns provides guidance on how to address scalability issues. 10. This document does not deal with how the HNA is provisioned with a trusted relationship to the Distribution Master for the forward zone. This section details what needs to be provisioned into the HNA and serves as a requirements statement for mechanisms.  The HNA needs to be provisioned with: the Registered Domain (e.g., myhome.isp.example ) the contact info for the Distribution Master (DM), including the DNS name (FQDN), possibly including the IP literal, and a certificate (or anchor) to be used to authenticate the service the DM transport protocol and port (the default is DNS over TLS, on port 853) the HNA credentials used by the DM for its authentication. The HNA will need to select an IP address for communication for the Synchronization Channel.  This is typically the outside WAN address of the router, but could be an IPv6 LAN address in the case of a home with multiple ISPs (and multiple border routers).  This is communicated in section BLAH when the NS and A record is communicated. The above parameters MUST be be provisionined for ISP-specific reverse zones, as per I-D.ietf-homenet-naming-architecture-dhc- options.  ISP-specific forward zones MAY also be provisioned using I- D.ietf-homenet-naming-architecture-dhc-options, but zones which are not related to a specific ISP zone (such as with a DNS provider) must be provisioned through other means. Similarly, it the HNA is provided by a registrar, the HNA may be given configured to end user. In the absence of specific pre-established relation, these pieces of information may be entered manually by the end user.  In order to ease the configuration from the end user the following scheme may be implemented. The HNA may present the end user a web interface where it provides the end user the ability to indicate the Registered Domain or the registrar for example a preselected list.  Once the regsitrar has been selected, the HNA redirects the end user to that registrar in order to receive a access token.  The access token will enable the HNA to retrieve the DM parameters associated to the Registered Domain.  These parameters will include the credentials used by the HNA to establish the Control and Synchronization Channels. Such architecture limits the necessary steps to configure the HNA from the end user. 11. This section details how renumbering is handled by the Hidden Primary server or the DM.  Both types of renumbering are discussed i.e. "make-before-break" and "break-before-make". In the make-before-break renumbering scenario, the new prefix is advertised, the network is configured to prepare the transition to the new prefix.  During a period of time, the two prefixes old and new coexist, before the old prefix is completely removed.  In the break-before-make renumbering scenario, the new prefix is advertised making the old prefix obsolete. Renumbering has been extensively described in RFC4192 and analyzed in RFC7010 and the reader is expected to be familiar with them before reading this section. 11.1. In a renumbering scenario, the Hidden Primary is informed it is being renumbered.  In most cases, this occurs because the whole home network is being renumbered.  As a result, the Public Homenet Zone will also be updated.  Although the new and old IP addresses may be stored in the Public Homenet Zone, we recommend that only the newly reachable IP addresses be published. To avoid reachability disruption, IP connectivity information provided by the DNS SHOULD be coherent with the IP plane.  In our case, this means the old IP address SHOULD NOT be provided via the DNS when it is not reachable anymore.  Let for example TTL be the TTL associated with a RRset of the Public Homenet Zone, it may be cached for TTL seconds.  Let T_NEW be the time the new IP address replaces the old IP address in the Homenet Zone, and T_OLD_UNREACHABLE the time the old IP is not reachable anymore. In the case of the make-before-break, seamless reachability is provided as long as T_OLD_UNREACHABLE - T_NEW > 2 * TTL.  If this is not satisfied, then devices associated with the old IP address in the home network may become unreachable for 2 * TTL - (T_OLD_UNREACHABLE - T_NEW).  In the case of a break-before-make, T_OLD_UNREACHABLE = T_NEW, and the device may become unreachable up to 2 * TTL. Once the Public Homenet Zone file has been updated on the Hidden Primary, the Hidden Primary needs to inform the Outsourcing Infrastructure that the Public Homenet Zone has been updated and that the IP address to use to retrieve the updated zone has also been updated.  Both notifications are performed using regular DNS exchanges.  Mechanisms to update an IP address provided by lower layers with protocols like SCTP RFC4960, MOBIKE RFC4555 are not considered in this document. The Hidden Primary SHOULD inform the DM that the Public Homenet Zone has been updated by sending a NOTIFY payload with the new IP address. In addition, this NOTIFY payload SHOULD be authenticated using SIG(0) or TSIG.  When the DM receives the NOTIFY payload, it MUST authenticate it.  Note that the cryptographic key used for the authentication SHOULD be indexed by the Registered Homenet Domain contained in the NOTIFY payload as well as the RRSIG.  In other words, the IP address SHOULD NOT be used as an index.  If authentication succeeds, the DM MUST also notice the IP address has been modified and perform a reachability check before updating its primary configuration.  The routability check MAY performed by sending a SOA request to the Hidden Primary using the source IP address of the NOTIFY.  This exchange is also secured, and if an authenticated response is received from the Hidden Primary with the new IP address, the DM SHOULD update its configuration file and retrieve the Public Homenet Zone using an AXFR or a IXFR exchange. Note that the primary reason for providing the IP address is that the Hidden Primary is not publicly announced in the DNS.  If the Hidden Primary were publicly announced in the DNS, then the IP address update could have been performed using the DNS as described in sec- secondary. 11.2. </del>  <del> Renumbering of the Distribution Master results in it changing its IP address.  As the DM is a secondary, the destination of DNS NOTIFY payloads MUST be changed, and any configuration/firewalling that restricts DNS AXFR/IXFR operations MUST be updated. If the DM is configured in the Hidden Primary configuration file using a FQDN, then the update of the IP address is performed by DNS. More specifically, before sending the NOTIFY, the Hidden Primary performs a DNS resolution to retrieve the IP address of the secondary. As described in sec-primary, the DM DNS information SHOULD be coherent with the IP plane.  The TTL of the Distribution Master name SHOULD be adjusted appropriately prior to changing the IP address. Some DNS infrastructure uses the IP address to designate the secondary, in which case, other mechanisms must be found.  The reason for using IP addresses instead of names is generally to reach an internal interface that is not designated by a FQDN, and to avoid potential bootstrap problems.  Such scenarios are considered as out of scope in the case of home networks. 12. Outsourcing the DNS Authoritative service from the HNA to a third party raises a few privacy related concerns. The Public Homenet Zone lists the names of services hosted in the home network.  Combined with blocking of AXFR queries, the use of NSEC3 RFC5155 (vs NSEC RFC4034) prevents an attacker from being able to walk the zone, to discover all the names.  However, the attacker may be able to walk the reverse DNS zone, or use other reconnaissance techniques to learn this information as described in RFC7707. In general a home owner is expected only to publish names for which there is some need to be able to reference externally.  Publication of the name does not imply that the service is necessarily reachable from any or all parts of the Internet.  RFC7084 mandates that the outgoing-only policy RFC6092 be available, and in many cases it is configured by default.  A well designed User Interface would combine a policy for making a service public by a name with a policy on who may access it. In many cases, the home owner wishes to publish names for services that only they will be able to access.  The access control may consist of an IP source address range, or access may be restricted via some VPN functionality.  The purpose of publishing the name is so that the service may be access by the same name both within the home, and outside the home.  Sending traffic to the relevant IPv6 address causes the relevant VPN policy to be enacted upon. While the problem of getting access to internal names has been solved in Enterprise configurations with a split-DNS, and such a thing could be done in the home, many recent improvements to VPN user interfaces make it more likely that an individual might have multiple connections configured.  For instance, an adult child checking on the state of a home automation system for a parent. In addition to the Public Homenet Zone, pervasive DNS monitoring can also monitor the traffic associated with the Public Homenet Zone. This traffic may provide an indication of the services an end user accesses, plus how and when they use these services.  Although, caching may obfuscate this information inside the home network, it is likely that outside your home network this information will not be cached. 13. The Homenet Naming Architecture described in this document solves exposing the HNA's DNS service as a DoS attack vector. 13.1. The HNA DM channels are specified to include their own security mechanisms that are designed to provide the minimum attack surface, and to authenticate transactions where necessary. Note that in the case of the Reverse Homenet Zone, the data is less subject to attacks than in the Public Homenet Zone.  In addition, the HNA and the DM MAY belong to the same administrative domain, i.e. the ISP.  More specifically, the WAN interface is located in the ISP network.  As a result, if provisioned using DHCPv6, the security credential may not even transit in the home network.  On the other hand, if the HNA is not hosted at the border of the home network, the credential may rely on the security associated to DHCPv6.  Even if HNA and DM are in the same administrative domain it is strongly RECOMMENDED to use a secure channel. The security of these channels heavily relies on TLS and the DM or RDM is authenticated by its certificate.  To ensure the multiple TLS session are are continuously authenticating the same entity, TLS may take advantage of second factor authentication as described in RFC8672. 13.2. This document describes how an end user can make their services and devices from his home network reachable on the Internet by using names rather than IP addresses.  This exposes the home network to attackers, since names are expected to include less entropy than IP addresses.  In fact, with IP addresses, the Interface Identifier is 64 bits long leading to up to 2^64 possibilities for a given subnetwork.  This is not to mention that the subnet prefix is also of 64 bits long, thus providing up to 2^64 possibilities.  On the other hand, names used either for the home network domain or for the devices present less entropy (livebox, router, printer, nicolas, jennifer, ...) and thus potentially exposes the devices to dictionary attacks. 13.3. IP addresses may be used to locate a device, a host or a service. However, home networks are not expected to be assigned a time invariant prefix by ISPs.  As a result, observing IP addresses only provides some ephemeral information about who is accessing the service.  On the other hand, names are not expected to be as volatile as IP addresses.  As a result, logging names over time may be more valuable than logging IP addresses, especially to profile an end user's characteristics. PTR provides a way to bind an IP address to a name.  In that sense, responding to PTR DNS queries may affect the end user's privacy.  For that reason end users may choose not to respond to PTR DNS queries and MAY instead return a NXDOMAIN response. 13.4. An attacker performs a reflection attack when it sends traffic to one or more intermediary nodes (reflectors), that in turn send back response traffic to the victim.  Motivations for using an intermediary node might be anonymity of the attacker, as well as amplification of the traffic.  Typically, when the intermediary node is a DNSSEC server, the attacker sends a DNSSEC query and the victim is likely to receive a DNSSEC response.  This section analyzes how the different components may be involved as a reflector in a reflection attack.  sec-reflection-hidden-primary considers the Hidden Primary, sec-reflection-public-auth-name-server-set the Synchronization Server, and sec-reflection-public-primary the Public Authoritative Server(s). 13.5. With the specified architecture, the Hidden Primary is only expected to receive DNS queries of type SOA, AXFR or IXFR.  This section analyzes how these DNS queries may be used by an attacker to perform a reflection attack. DNS queries of type AXFR and IXFR use TCP and as such are less subject to reflection attacks.  This makes SOA queries the only remaining practical vector of attacks for reflection attacks, based on UDP. SOA queries are not associated with a large amplification factor compared to queries of type "ANY" or to query of non existing FQDNs. This reduces the probability a DNS query of type SOA will be involved in a DDoS attack. SOA queries are expected to follow a very specific pattern, which makes rate limiting techniques an efficient way to limit such attacks, and associated impact on the naming service of the home network. Motivations for such a flood might be a reflection attack, but could also be a resource exhaustion attack performed against the Hidden Primary.  The Hidden Primary only expects to exchange traffic with the DM, that is its associated secondary.  Even though secondary servers may be renumbered as mentioned in sec-renumbering, the Hidden Primary is likely to perform a DNSSEC resolution and find out the associated secondary's IP addresses in use.  As a result, the Hidden Primary is likely to limit the origin of its incoming traffic based on the origin IP address. With filtering rules based on IP address, SOA flooding attacks are limited to forged packets with the IP address of the secondary server.  In other words, the only victims are the Hidden Primary itself or the secondary.  There is a need for the Hidden Primary to limit that flood to limit the impact of the reflection attack on the secondary, and to limit the resource needed to carry on the traffic by the HNA hosting the Hidden Primary.  On the other hand, mitigation should be performed appropriately, so as to limit the impact on the legitimate SOA sent by the secondary. The main reason for the DM sending a SOA query is to update the SOA RRset after the TTL expires, to check the serial number upon the receipt of a NOTIFY query from the Hidden Primary, or to re-send the SOA request when the response has not been received.  When a flood of SOA queries is received by the Hidden Primary, the Hidden Primary may assume it is involved in an attack. There are few legitimate time slots when the secondary is expected to send a SOA query.  Suppose T_NOTIFY is the time a NOTIFY is sent by the Hidden Primary, T_SOA the last time the SOA has been queried, TTL the TTL associated to the SOA, and T_REFRESH the refresh time defined in the SOA RRset.  The specific time SOA queries are expected can be for example T_NOTIFY, T_SOA + 2/3 TTL, T_SOA + TTL, T_SOA + T_REFRESH., and.  Outside a few minutes following these specific time slots, the probability that the HNA discards a legitimate SOA query is very low.  Within these time slots, the probability the secondary may have its legitimate query rejected is higher.  If a legitimate SOA is discarded, the secondary will re-send SOA query every "retry time" second until "expire time" seconds occurs, where "retry time" and "expire time" have been defined in the SOA. As a result, it is RECOMMENDED to set rate limiting policies to protect HNA resources.  If a flood lasts more than the expired time defined by the SOA, it is RECOMMENDED to re-initiate a synchronization between the Hidden Primary and the secondaries. 13.6. The DM acts as a secondary coupled with the Hidden Primary.  The secondary expects to receive NOTIFY query, SOA responses, AXFR and IXFR responses from the Hidden Primary. Sending a NOTIFY query to the secondary generates a NOTIFY response as well as initiating an SOA query exchange from the secondary to the Hidden Primary.  As mentioned in RFC1996, this is a known "benign denial of service attack".  As a result, the DM SHOULD enforce rate limiting on sending SOA queries and NOTIFY responses to the Hidden Primary.  Most likely, when the secondary is flooded with valid and signed NOTIFY queries, it is under a replay attack which is discussed in sec-replay-attack.  The key thing here is that the secondary is likely to be designed to be able to process much more traffic than the Hidden Primary hosted on a HNA. This paragraph details how the secondary may limit the NOTIFY queries.  Because the Hidden Primary may be renumbered, the secondary SHOULD NOT perform permanent IP filtering based on IP addresses.  In addition, a given secondary may be shared among multiple Hidden Primaries which make filtering rules based on IP harder to set.  The time at which a NOTIFY is sent by the Hidden Primary is not predictable.  However, a flood of NOTIFY messages may be easily detected, as a NOTIFY originated from a given Homenet Zone is expected to have a very limited number of unique source IP addresses, even when renumbering is occurring.  As a result, the secondary, MAY rate limit incoming NOTIFY queries. On the Hidden Primary side, it is recommended that the Hidden Primary sends a NOTIFY as long as the zone has not been updated by the secondary.  Multiple SOA queries may indicate the secondary is under attack. 13.7. Reflection attacks involving the Public Authoritative Server(s) are similar to attacks on any Outsourcing Infrastructure.  This is not specific to the architecture described in this document, and thus are considered as out of scope. In fact, one motivation of the architecture described in this document is to expose the Public Authoritative Server(s) to attacks instead of the HNA, as it is believed that the Public Authoritative Server(s) will be better able to defend itself. 13.8. The purpose of flooding attacks is mostly resource exhaustion, where the resource can be bandwidth, memory, or CPU for example. One goal of the architecture described in this document is to limit the surface of attack on the HNA.  This is done by outsourcing the DNS service to the Public Authoritative Server(s).  By doing so, the HNA limits its DNS interactions between the Hidden Primary and the DM.  This limits the number of entities the HNA interacts with as well as the scope of DNS exchanges - NOTIFY, SOA, AXFR, IXFR. The use of an authenticated channel with SIG(0) or TSIG between the HNA and the DM, enables detection of illegitimate DNS queries, so appropriate action may be taken - like dropping the queries.  If signatures are validated, then most likely, the HNA is under a replay attack, as detailed in In order to limit the resource required for authentication, it is recommended to use TSIG that uses symmetric cryptography over SIG(0) that uses asymmetric cryptography. 13.9. Replay attacks consist of an attacker either resending or delaying a legitimate message that has been sent by an authorized user or process.  As the Hidden Primary and the DM use an authenticated channel, replay attacks are mostly expected to use forged DNS queries in order to provide valid traffic. From the perspective of an attacker, using a correctly authenticated DNS query may not be detected as an attack and thus may generate a response.  Generating and sending a response consumes more resources than either dropping the query by the defender, or generating the query by the attacker, and thus could be used for resource exhaustion attacks.  In addition, as the authentication is performed at the DNS layer, the source IP address could be impersonated in order to perform a reflection attack. sec-reflection-attack details how to mitigate reflection attacks and sec-flooding-attack details how to mitigate resource exhaustion. Both sections assume a context of DoS with a flood of DNS queries. This section suggests a way to limit the attack surface of replay attacks. As SIG(0) and TSIG use inception and expiration time, the time frame for replay attack is limited.  SIG(0) and TSIG recommends a fudge value of 5 minutes.  This value has been set as a compromise between possibly loose time synchronization between devices and the valid lifetime of the message.  As a result, better time synchronization policies could reduce the time window of the attack. 14. </del>  This document has no actions for IANA. <del> 15. </del>  The authors wish to thank Philippe Lemordant for its contributions on the early versions of the draft; Ole Troan for pointing out issues HNA and low power devices; Olafur Gudmundsson for clarifying DNSSEC capabilities of small devices; Simon Kelley for its feedback as dnsmasq implementer; Andrew Sullivan, Mark Andrew, Ted Lemon, Mikael <del> Abrahamson, Michael Richardson and Ray Bellis for their feedback on handling different views as well as clarifying the impact of outsourcing the zone signing operation outside the HNA; Mark Andrew and Peter Koch for clarifying the renumbering. </del> 

Reviewer comments:
…ng to
Section 12 needs to be fleshed out.
OOps, I rewrote Privacy Considerations since that was section 12.

Revised text:
result in a common instantiation of an authoritative server on the WAN and inner interface.  Other mechanisms may also be used.  <ins> { "dm_notify" : "2001:db8:1f15:62e:21c::2", "dm_acl" : "2001:db8:1f15:62e:21c::/64", "dm_ctrl" : "192.168.1.18", "dm_port" : "4433", "ns_list" : [ "ns1.publicdns.example", "ns2.publicdns.example"], "zone" : "daniel.homenetdns.example", "auth_method" : "certificate", "hna_certificate":"---BEGIN CERTIFICATE---nMIIDTjCCAjYCFGy....", "hna_key" : "---BEGIN RSA PRIVATE KEY---nMIIEowIBAAKCAQE...." } ~~~~ </ins>  <ins> Here goes a YANG MODULE description of the above. </ins>  <ins> 4. </ins> This document has no actions for IANA.  <ins> 5. </ins> The authors wish to thank Philippe Lemordant for its contributions on the early versions of the draft; Ole Troan for pointing out issues HNA and low power devices; Olafur Gudmundsson for clarifying DNSSEC capabilities of small devices; Simon Kelley for its feedback as dnsmasq implementer; Andrew Sullivan, Mark Andrew, Ted Lemon, Mikael  <ins> Abrahamson, and Ray Bellis for their feedback on handling different views as well as clarifying the impact of outsourcing the zone signing operation outside the HNA; Mark Andrew and Peter Koch for clarifying the renumbering. </ins>