Domain name system

Domain Name System (DNS) Server

Domain Name System (DNS) Server

The Domain Name System (DNS) is the crucial glue that keeps computer networks in harmony by converting human−friendly host names to the numerical IP addresses computers require to communicate with each other. DNS is one of the largest and most important distributed databases the world depends on by serving billions of DNS requests daily for public IP addresses. Most public DNS servers today are run by larger ISPs and commercial companies but private DNS servers can also be useful for private home networks.

Like the telephone system, every device attached to the Internet has a unique number, its IP address. Also like the telephone system, there is a directory service to help you find those numbers called DNS.

If you have someone’s name and address you can call a directory service, give them the details you know and they will (usually) give you the telephone number to call them. Likewise, if you know a server’s host name (maybe http://www.google.co.in) you can give that name to a DNS server and it will give you the IP address of that server.

The format of a domain name

Domain name system

Like a physical address, Internet domain names are hierarchical (only a little stricter), so while your address might look like:

  • House name : Parliament
  • Town             : Delhi
  • County          : Delhi
  • Country         : India

An Internet domain name looks like:

  • Host name                    www
  • Domain                         google
  • Second level domain     co
  • Top-level domain          In, uk, us

A database is made up of records and the DNS is a database. Therefore, common resource record types in the DNS database are:

  • A – Host’s IP address. Address record allowing a computer name to be translated into an IP address. Each computer must have this record for its IP address to be located. These names are not assigned for clients that have dynamically assigned IP addresses but are a must for locating servers with static IP addresses.
  • PTR – Host’s domain name, host identified by its IP address.
  • CNAME – Host’s canonical name allows additional names or aliases to be used to locate
    a computer.
  • MX – Host’s or domain’s mail exchanger.
  • NS – Host’s or domain’s name server(s).
  • SOA – Indicates authority for the domain (Start of Authority)
  • TXT – Generic text record
  • SRV – Service location record
  • RP – Responsible person
  • HINFO – Host information record with CPU type and operating system.

The package which is used in Linux for performing DNS activity is BIND (Berkeley Internet Name Domain).

Profile for DNS Server

  • Usage                     : To Resolve IP into host name and vice-versa
  • Package                 : bind, caching-name
  • Script                     : /etc/init.d/named
  • Port                        : 53
  • Configuration File : /etc/named.conf
  • Document root     : /var/named/
  • Daemon                 : named

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