Domain Name System

Naming Concepts
Once a kernel is configured for TCP/IP (the current UNIX default setting), the network interface is set properly, and the routing table is established, the system is ready for a network communication.

A number of extremely useful network applications and services are available so that the system
may benefit from the network configuration. In the past, UNIX considered networking an option; today, networking is an integral part of any UNIX installation. Networking and network−based applications are booming today; however, it is not realistic to expect each network service to be a default part of UNIX. The UNIX philosophy is to remain open to all newcomers, and, thanks to thisconcept and other related issues, UNIX is supporting networking very well.

UNIX is actually the main supporting platform for most network services.
The significance of different network applications and services varies; some network services are
conditio sine qua non for other network services, while other services are optional, and are used
only by a very small segment of the UNIX community. Some network applications are important
from an administration point of view, and we will refer to those network services as the core network services.
Core network services are usually an integral part of each modern UNIX installation, and we will
focus on them.
Among all the core network services, perhaps the most important one is the name service.

Host Names and Addresses
Each UNIX system on the network is uniquely identified by at least one IP address, and this is
sufficient for systems. The machines understand these addresses very well, and they communicate among themselves without any problem. In fact, they only understand the numerical IP addresses.
However, it is not very convenient for users, who are human beings, to use numerical IP addresses (four not−logically related numbers), although there are no restrictions. For example, a user wishing to telnet to the host with IP address 128.124.128.14 can do that by entering the following command:

telnet 128.122.128.14

And it will work well.
But when a user wishes to telnet to many different hosts, it would be quite hard to remember all of the required IP addresses. Users are accustomed to using another identification mechanism,
names, to identify someone or something. The name service, officially named Domain Name
Service (DNS), also known as Domain Name System helps in implementing this mechanism in
network communications.
It is much easier for a user to establish the above telnet session using the
following command:

telnet acf4.nyu.edu

And it will also work well.
DNS is basically a distributed database of host information, which, besides host names and IP
addresses, also includes some other useful information about hosts on the network. DNS makes
this information available to all hosts, i.e., all users, on the network whenever they need it.