LIS 525 - Domain Names

A domain name is a name that identifies one or more IP addresses. Domain names are used in URLs as well as in e-mail addresses. For example, in the URL, the domain name is; other elements illustrated are the protocol (http://), the host name (www), and the path (/univsec/handbook/).

Every domain name has a suffix (such as .gov, .edu, or .ca) that indicates which top level domain (TLD) it belongs to. There are a limited number of TLDs, although the number has recently been increased. The part of the domain name before the dot is the Second Level Domain (SLD).

Because IP addresses are used to route data through the Internet, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses. For example, the host name plus domain name translates into If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

Before checking domain names on other servers, a computer may check a local list for IP numbers. For example, Microsoft TCP/IP for Windows looks at a plain-text file hosts (typically found in windows\system32\drivers\etc\), which the user can edit to provide customized aliases or to block access to certain servers.

Domain names and host names are used because people can more easily recognize and remember meaningful words than long strings of numerals, and because they can be reassigned to new machines (with different IP addresses).

Getting your own domain name has advantages and disadvantages.
Advantages Disadvantages
  • Easier for users to remember than host-domain-path (such as
  • More impressive (looks less like a personal site)
  • Transportable to another hosting service
  • Must be registered with appropriate service, normally for a small yearly fee.
  • The name you want may already be taken; you may have to pay a lot (or sue) to obtain it.
  • You may lose the domain name unexpectedly because of registrar incompetence.
  • DNS records must be maintained on a server.

Letters and numbers are valid characters in a Web address, as are hyphens except at the beginning or end. Special characters may not be used (apart from the period, which has a special meaning). Technically, the maximum number of characters is 256 (including the TLD), but individual registration services usually impose lower limits, such as 25 or 67 characters.

Applicants for domain names must ensure that they have the right to use the domain names and that the registration or use of the domain name does not violate intellectual property or other rights, is not defamatory, and does not contravene any applicable laws. Registration services may also require that the name be put into service as a functional and reliable Internet address, that registration not be used for hoarding or for excessive protection of trademarks, or that the use is appropriate to the scope of the TLD.

In the past, to have a host name, a computer had to have a fixed IP address. Thus, users of cable modem and dialup services, with dynamically assigned IP addresses, for example, had difficulty in running their machines as servers. But a new service called dynamic domain name system aliasing actively tracks changes to a subscriber's dynamic IP address. The query first goes to the dynamic DNS server which hands out the destination's current address.

Some Guidelines for Choosing a Domain Name

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Last updated October 26, 2007.
This page maintained by Prof. Tim Craven
E-mail (text/plain only):
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7