Monday, January 09, 2006

How DNS Works

DNS - Domain Name System is used to resolve domain name like to IP - 10.10.93.x.

Rules of DNS

The Rules as Defined in (RFC 952)

Names can be up to 24 Characters long
Names should be more than 1 character long
Names may contain letters, numbers, dashes and dots.
Names Should start with a letter
Names should not end with a dash or dot.


First Level -

The root of a domain name system is represented by a dot ( . )

Root - This is Managed by Internic

There are 14 root servers around the world mentioned in /var/named/

Second Level -

Second Level Domain name is Managed by Registrars like ( .net, .com, .org, .us)

Third Level -

Third level Domain are managed by whomever registers them through Registrars for eg. (

Some Important Files

Bind - The Utility for DNS



This is the main configuration file where you add the Master, Slave servers.

Master Server - Primary Name Server.

Slave Server - Secondary Name Server.

In Case the Master Fails then Slave resolves.

/var/named - Default place where zone files are stored.

[root@mybox named]# cat
$ttl 38400 IN SOA (
38400 ) IN NS IN A IN A

Note the above lines should be seperated by way of Tab


Hint file (cache file)(/var/named/ It actually provides the name of root server which gets activated in case the machine name, which is to be searched, is not there in user defined zone (discussed below).

The copy of same can be obatined from internic... Very rarely it changes

localhost file (/var/named.local): All configuration have a local domain Database for resolving address to the host name localhost.

Zone: Basically a zone that keeps the information about the domain database

Reverse Zone file: This is responsible for mapping Ipaddress to host names, which is exactly the opposite of what the zone file does.

In previous post I have given complete configuration of DNS on LINUX

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