Domain Names

Computers on the Internet are referenced using IP addresses, which are comprised of a series of four numbers separated by periods (always called dots). Each number is an 8-bit integer (a number from 0-255). For example, the IP address of my Web server at Neural Applications is 198.137.221.9 (verbalized as "one-ninety-eight dot one-thirty-seven dot two-twenty-one dot nine"). However, because addresses composed of nothing but numbers are difficult for humans to remember, in 1983 the University of Wisconsin developed the Domain Name Server (DNS), which was then introduced to the Net during the following year. DNS automatically and invisibly translates names composed of real words into their numeric IP addresses, which makes the Net a lot more user-friendly. To use the same example cited above, the DNS address of Neural's Web server is www.neural.com (pronounced "double-u double-u double-u dot neural dot cahm"). There is no formula for calculating an IP address from a domain name-the correlation must be established by looking one or the other up in a table. Domain names consist of two or more parts, separated by periods (always, in Internet parlance, pronounced dot). Generally speaking, the leftmost part of the name is the most specific, with sections further to the right more general. A computer may have more than one domain name assigned to it, but any given domain name will "resolve" into only one specific IP address (which is unique for each machine). Usually, all the machines on one network will share a right-hand and middle domain name portion. For example, you might see computers at one site with the names: server.grizzly.com mars.grizzly.com www.grizzly.com The leftmost portion of a domain name may indicate its purpose; for example, www. for a Web server or mail. for a mail server. The rightmost portion of a domain name often indicates the type of site it lives on. The most common domain name extensions are:
.com	Commercial site
.edu	Educational site
.gov	Government site
.mil	Military site
.net	Network service provider
.org	Organization
Other (generally two-letter) extensions indicate a site's country of origin, such as .ca for Canada, .de for Germany, or .fr for France.