# Data Networking/Fall 2014/Priya/DNS

The Domain Name server or Domain Name Service fuctions as the Domain Name resolved to find out the IP address that relates to a particular system Paul Mockapetris drafted the Domain Name System at the University of California at Irvine in 1983. The Domain Name read from right to left, with each level of the hierarchy divided by periods(.) Indicating the Top level domain followed by sub-domain and host name in the domain name seperated by periods (.)
Domain Name System (DNS) is a protocol for Transmission Control Protocol/Internet Protocol networks, defined by the Requests for Comments (RFCs) DNS rfc 1034 rfc 1035
DNS is distributed database that contains mappings of DNS domain names to IP address.
client wants IP for www.neunetworks.com; client queries root server to find com DNS server client queries .com DNS server to get neunetworks.com DNS server client queries neunetworks.com DNS server to get IP address for www.neunetworks.com
The DNS client can make two basic types of queries namely Recursive and Iterative. The following list describes the difference between these two query types.
Recursive queries: When the client issues a Recursive DNS query, the server responds with either the IP address of the Requested host name or an error message indicating that the domain name doesn’t exist and the load is on the server which is contacted on the name server.
Iterative queries: When a DNS client issues an iterative query then the IP address is known returns the IP address of the requested host name. If the server doesn’t know the address, it returns a referral, which is the address of a DNS server that should be contacted to get the IP address. The client can then issue an iterative query to the server to which it was referred and load is on the local DNS server

## Resource Records

Resource Records (RRs) are the data elements which contain the structure and content of namespace . All the DNS operations are written in terms of resource records. The most important fields in a Resource Record are Name, Class, Type, and Data
Inorder to resolve names the servers consult zones. The zones stores resource records which use the resource information related with the DNS domain.
Types of Resource records:
i. A Resource Records
The A Resource record maps FQDN to an IP address
ii. NS Resource Record:(Name Server)
The NS Resource record specifies the host which needs to be authoritative for the class and domain and indicates Master and Slave servers for the zone specified in the SOA resource record
iii. MX Resource Records
The Mail exchange (MX) resource record specifies a mail exchange server for a DNS domain name.
iv.CNAME Resource Records
The canonical name (CNAME) resource record which indicates the primary name or canonical for the alias in the specified FQDN
v.PTR (Pointer Resource records)
The PTR is used to construct the domain in-addr.arpa and Convert the IP address to FQDN which is used in reverse lookup functional opposite to A Resource records.
vi.SOA (Start of Authority) Resource Record:
The SOA RR indicates the starting of DNS zone which is the first record in the name server of the domain in which is present.
The DNS message exchange is as shown below
There are different types of DNS -Softwares can be viewed in detail