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.

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.

Generic 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.

• 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.