Internet Domain Extensions

Domain extensions on the Internet are often called top level domains (TLDs). To understand the concept of TLDs and domain extensions requires a brief explanation of Internet domains in general.

Internet Domain Names

A domain name is a string used to name Web sites and other servers on computer networks. On the Internet, these strings are managed by the Domain Name System (DNS). The DNS uses a system of multi-level strings separated by dots ('.') to organize domain names. For example, the Web site

compnetworking.about.com

uses three levels of naming. The levels are listed in order of lowest to highest when reading from left to right. In this example, the first substring ('compnetworking') represents one specific Web site or sub-domain. Then, the second substring ('about') represents a organizational domain that points to a Web site but also contains numerous other sub-sites (sub-domains). Finally, the third substring ('.com') represents a top level domain (TLD) that encompasses numerous organizations worldwide.

TLDs - Common Domain Extensions

.com is the most commonly used top-level domain extension on the Internet. Many others exist, however. These other six TLDs were part of the original Internet specifications for domain extensions:

• .edu
• .gov
• .int
• .mil
• .net
• .org

In recent years, many new TLDs have been deployed on the Internet. Some of these are intended for broad use worldwide, while others are designed to serve special interest groups. Though not as popular as the original TLDs listed above, you may also encounter some of these newer domain extensions when browsing the Web:

• .biz
• .info
• .jobs
• .mobi
• .name
• .tel

The ICANN organization ultimately oversees the process of managing Internet domains including new TLD extensions.

About Country Domain Extensions

Besides the generic TLDs listed above, the Internet also maintains domain extensions for each country to help organize Web sites within each nation. These extensions are named according to worldwide standard two-letter country codes similar to those used by the postal system. Examples of country code TLDs include:

• .br (Brazil)
• .ca (Canada)
• .cn (mainland China)
• .fr (France)
• .in (India)
• .jp (Japan)
• .ru (Russian Federation)