The Domain Name System is a distributed database with hierarchical structure and serve the basis for name resolution process in TCP/IP network.

The process of DNS resolution involves converting a hostname (such as www.example.com) into a computer-friendly IP address (such as 1.2.3.4).  Just as we require a street address to find a particular home in the same way  IP address is necessary to find a particular Internet device.

When a user wants to load a webpage, a translation must occur between what a user types into their web browser (example.com) and the machine-friendly address necessary to locate the example.com webpage.

 Domain Name System (DNS) converts the name of a Web site to an IP address and vice-versa. The reverse process is called Reverse Domain System (RDNS).

Key Components of DNS

1. Domain name space
2.  Zones
3.  Nameservers
4.  Resolver

1. Domain Names Space -

Domain Name Space  is defined such that the names of all similar components must be similarly structured, but similarly identifiable. The full DNS name must point to a particular address.

The fully qualified domain name (FQDN) of the host mail is mail.google.com. No two hosts can have the same FQDN.

2. Zones -

All top-level domains, and many domains at the second and lower levels, are broken into zones.

3. Name Servers -

The programs that store information about the domain namespace are called nameservers. Nameservers generally have complete information about some part of the domain namespace, called a zone

       - Primary name server (Master)

       - Secondary name server (Slave)

4. Resolver -

Resolvers are the clients that access nameservers. Programs running on a host that need information from the domain namespace use the resolver. The resolver  handles:

Querying a nameserver.

Interpreting responses (which may be resource records or an error).

Returning the information to the programs that requested it.

 In BIND, the resolver is a set of library routines that is linked to programs.

Ex. gethostbyname() in standard socket library in C prog.   Language

Resolver Configuration

• /etc/nsswitch

         - hosts: dns files

• /etc/resolv.conf

          - On Clients

            search example.com

            nameserver 1.2.3.24

          - On Server

            nameserver 127.0.0.1