A name that identifies one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL http://www.webhostplazza.com/, the domain name is webhostplazza.com.

Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains. For example:

·         gov - Government agencies

·         edu - Educational institutions

·         org - Organizations (nonprofit)

·         mil - Military

·         com - commercial business

·         net - Network organizations

·         ca - Canada

·         th - Thailand

Because the Internet is based on IP addresses not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.

The term domain name has multiple related meanings:

·         A hostname that identifies a computer or computers on the Internet. These names appear as a component of a Web site's URL, e.g. en.wikipedia.org.

·         Registered domain names, which are obtained from domain name registrars.

·         Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domain names like .com, or the names used by the Session Initiation Protocol (VoIP), or Domain Keys.

Parts of a Domain name

A domain name usually consists of two or more parts (technically labels), which are conventionally written separated by dots, such as example.com.

·        The rightmost label conveys the top-level domain (for example, the address www.example.com has the top-level domain com).

·         Each label to the left specifies a subdivision, or subdomain of the domain above it. Note: “subdomain” expresses relative dependence, not absolute dependence. For example: example.com is a subdomain of the comdomain, and www.example.com is a subdomain of the domain example.com. In theory, this subdivision can go down 127 levels. Each label can contain up to 63 octets. The whole domain name may not exceed a total length of 253 octets. In practice, some domain registries may have shorter limits.

·         A hostname refers to a domain name that has one or more associated IP addresses; ie: the 'www.example.com' and 'example.com' domains are both hostnames, however, the 'com' domain is not.

The main purpose of a domain name is to provide recognizable names to mostly numerically addressed Internet resources. This abstraction allows any resource (e.g., website) to be moved to a different physical location in the address topology of the network, globally or locally in an intranet, in effect changing the IP address.

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:

·         URL: http://www.example.net/index.html

·         Domain name: www.example.net

·         Registered domain name: example.net

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. However, the explosion of interest in the Web means that there are far more Web sites 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. This feature goes under the name virtual hosting and is commonly used by web.

For example, as referenced in RFC 2606 (Reserved Top Level DNS Names), the server at IP address 208.77.188.166 handles all of the following sites:

·         example.com

·         www.example.com

·         example.net

·         www.example.net

·         example.org

·         www.example.org

When a request is made, the data corresponding to the hostname requested is provided to the user.