Domain Name System in Computer Network

Domain Name System

  • Domain Name System is an Internet service that translates domain names into IP addresses.
  • The DNS has a distributed database that resides on multiple machines on the Internet.
  • DNS has some protocols that allow the client and servers to communicate with each other.
  • When the Internet was small, mapping was done by using hosts.txt file.
  • The host file was located at host's disk and updated periodically from a master host file.
  • When any program or any user wanted to map  domain name to an address, the host consulted the host file and found the mapping.
  • Now Internet is not small, it is impossible to have only one host file to relate every address with a name and vice versa.
  • The solution used today is to divide the host file into smaller parts and store each part on a different computer.
  • In this method, the host that needs mapping can call the closest computer holding the needed information.
  • This method is used in Domain Name System (DNS).

Name space

  • The names assigned to the machines must be carefully selected from a name space with complete control over the binding between the names and IP addresses.
  • There are two types of name spaces: Flat name spaces and Hierarchical names.

Flat name spaces

  • In a flat name space, a name is a sequence of characters without structure.
  • A name in this space is assigned to an address.
  • The names were convenient and short.
  • A flat name space cannot be used in a large system such as the internet because it must be centrally controlled to avoid ambiguity and duplication.

Hierarchical Name Space

  • In hierarchical name space, each name consists of several parts.
  • First part defines the nature of the organization, second part defines the name of an organization, third part defines department of the organization, and so on.
  • In hierarchical name space, the authority to assign and control the name spaces can be decentralized.
  • Authority for names in each partition is passed to each designated agent.
hierarchy dsn

DNS in the Internet

  • DNS is a protocol that can be used in different platform.
  • Domain Name Space is divided into different sections in the Internet: Generic domain, country domain and inverse domain.
dns in internet

Generic Domains

The generic domains define registered hosts according to their generic behavior.

Generic domain labels are as stated below:

1. Country Domains
  • Country domain uses two character country abbreviations.
  • Second labels can be more specific, national designation.
  • For example, for Australia the country domain is “au”, Inida is .in, UK is .uk etc.
country domain

2. Inverse Domains
  • Inverse domain is used to map an address to a name.
  • For example, a client send a request to the server for performing a particular task, server finds a list of authorized client.  The list contains only IP addresses of the client.
  • The server sends a query to the DNS server to map an address to a name to determine if the client is on the authorized list.
  • This query is called an inverse query.
  • This query is handled by first level node called arpa.
inverse domain