Domain name

 

What is a domain name? Why do we need domain name?

A domain name is the unique name of a computer on the Internet that distinguishes it from the other systems on the network. They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".

Every website, email account, etc, on the Internet is hosted on at least one computer (server). Each server has a unique IP address which is nothing but a set of numbers, such as "207.142.131.235" . To access a particular internet service, one can specify its IP address in an appropriate application, such as an FTP client; however because it is difficult to remember numbers, an IP address can be associated with a fully qualified host name (a domain name), such as "www.wikipedia.org". Domain names also provide a persistent address for some service when it is necessary to move to a different server, which would have a different IP address.

Each set of letters and numbers between the dots is called a label in parlance of the domain name service (DNS). There are some rules about the size and make up of labels. Each must start with a letter or number, and then may be made up of letters, numbers, and hyphens, to a maximum of 63 characters. These are the rules imposed by the way names are looked up ("resolved") by DNS. Some top level domains (see below) impose more rules, like a minimum length, on some labels. Fully qualified names are sometimes written with a final dot.

Translating numeric addresses to alphabetical ones, domain names allow Internet users to localize and visit websites. Additionally since more than one IP address can be assigned to a domain name, and more than one domain name assigned to an IP address, one server can have multiple roles, and one role can be spread among multiple servers.

 

Examples

The following examples illustrates the difference between a URL and a domain name:

URL: http://www.example.com/

Server name: www.example.com

Domain name: example.com

Subdomain: www

Domain: example

Top level domain: com

As a general rule, the IP address and the server name are interchangeable. For most internet services, the server will not have any way to know which was used. The big exception to this is for web addresses. The explosion of interest in the web means that there are far more websites than servers. To accommodate this the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way one server, with one IP address, can provide different sites for different domain names.

For example, the server at 192.0.34.166 handles all of the following sites:

www.example.com

www.example.net

www.example.org

Top-level domains

Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of general names, or a ISO-3166 two character country code.

Examples of (gTLD) extensions are:

• .com
• .net
• .org
• .info
• .biz
• .name
• .museum
• .travel

Examples of country code top-level domain (ccTLD) extensions are:

• .us
• .uk (not an ISO-3166 code, but used anyway)
• .fr
• .es
• .de
• .it
• .jp
• .ie
• .tv
• .co.uk