A computer connected to the Internet must have a unique address in order to communicate across the Internet. Internet Protocol (IP) address is assigned uniquely to every computer connected to the Internet. IP address is provided by the ISP whose services you use to connect your computer to the Internet. IP address is a string of numbers consisting of four parts, where each part is a number between 0 and 255. An IP address looks like 201.54.122.107. Since IP addresses are numeric, it is difficult to remember everyone’s IP address. So, instead of numeric IP address, domain name is used.
Domain name is a text name (string of words) corresponding to the numeric IP address of a computer on the Internet. Domain names are used for the convenience of the user. A domain name combines a group of hosts on the Internet (e.g. Yahoo, Google, MSN etc.), and a top-level domain. Some examples of top-level domain are as follows:
· com—for commercial organizations,
· Edu—for educational institutions,
· net—for gateways and administrative hosts,
· org—for non-profit organizations,
· co—for companies, and
· ac—for academics
Some examples of domain name are google.com, isoc.org, center.edu and vsnl.net.
Additionally, top-level domain is also provided based on the two-letter Internet country code. For example, in for India, uk for United Kingdom, au for Australia etc. Example of such domain names are du.ac.in, ibm.co.in etc.
In order to translate numeric IP address that identifies a computer on the Internet to a domain name that is convenient for the user to remember, a mapping is needed between the IP addresses and domain names. Domain Name System (DNS) server is a computer having a database that stores the IP addresses and their domain names. Whenever a user uses the domain name, DNS translates it into its corresponding IP address, to access the computer on Internet. For example, DNS translates google.com to the IP address of the computer that houses Google.
