Domain Name Service

The Internet is the "network of networks" worldwide that speak the TCP/IP protocols. Each computer on the Internet (or any TCP/IP network) must have an address, e.g. 129.79.17.63. An Internet Protocol (IP) address or Internet address may also have one or more names, e.g. 129.79.17.63 is also known as teak.uwsg.indiana.edu. The computer name of a host, when completely specified, is known as a Fully Qualified Domain Name (FQDN).

Although the Internet address is actually used by applications to open connections to machines on the Internet, people prefer to use computer names rather than numbers. The Domain Name database coordinates a look up of a computer name and finds the corresponding Internet number.

This is done by a set of name servers that keep track of computer names and the corresponding Internet addresses. These servers have the ability to store and report more than just the computer name.

There isn't one central server, there are lots of interlocking servers that form a tree, with separate branches for each of the major divisions; like com, or edu.

How it works

The look up of a computer name such as teak.uwsg.indiana.edu goes through these steps:

Sends a request to central (root) server that keeps track of educational institutions. The root server would reply with the names and Internet addresses of several domain servers for "edu". There are redundant domain servers in case of a single server failure.
Sends a request to the "edu" domain server for the "indiana" domain server. That server will reply with names and Internet addresses of servers for the "indiana" domain. It's a well practiced tradition to have at least one server that is not physically at the indiana domain in case of catastrophic failure at that site.
Sends a request to the server for "uwsg". That server replies with the names and Internet addresses of servers for the "uwsg" domain.
Finally, asks one of the uwsg servers about the computer named "teak". The result would be the Internet address for teak.uwsg.indiana.edu.

Each of these levels is referred to as a "domain": the "edu" domain the "indiana.edu" domain . The entire name is called a fully qualified domain name; such as "teak.uwsg.indiana.edu" or "pete.graphics.scamper.com".

This example demonstrates how DNS works. However, domain servers store requested information. This process is known as caching. This enables the bypass of several of the above steps.

This illustration , created by Glenn Stevens, provides a pictorial example of the domain look up process.

Implementation

Client machines wishing to use DNS must be configured to consult local nameservers, rather than look only the local /etc/hosts file. There are several methods employed. Most commonly there is a configuration file that directs the use of DNS, usually /etc/nsswitch.conf. The DNS configuration file /etc/resolv.conf indicates your local domain and others that you wish to consult and lists nameservers to contact when looking up Internet addresses for computer names.

Platform specific configuration files

SunOS 4.1.X: Standard C libraries can be modified to allow DNS lookups.
Solaris 2.X: The file /etc/nsswitch.conf must be updated.
Digital Unix: The file /etc/svc.conf must be updated.
SGI IRIX: The hostresorder directive is added to the /etc/resolv.conf file.
HPUX 10.X: The file /etc/nsswitch.conf must be updated.
Linux: The /etc/host.conf file lists the services to be used and the order which to check those services.

For more essential information please review the DNS guide , also recommended is the Bind FAQ. Optionally, review the information available from the DNS Resources Directory and the Linux DNS HOWTO

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