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Domains

Getting where you want to go can often be one of the more difficult aspects of using networks. The variety of ways that places are named will probably leave a blank stare on your face at first. Don't fret; there is a method to this apparent madness.

If someone were to ask for a home address, they would probably expect a street, apartment, city, state, and zip code. That's all the information the post office needs to deliver mail in a reasonably speedy fashion. Likewise, computer addresses have a structure to them. The general form is:

 a person's email address on a computer: user@somewhere.domain
 a computer's name: somewhere.domain
 

The user portion is usually the person's account name on the system, though it doesn't have to be. somewhere.domain tells you the name of a system or location, and what kind of organization it is. The trailing domain is often one of the following:

com

Usually a company or other commercial institution or organization, like Convex Computers (`convex.com').

edu

An educational institution, e.g. New York University, named `nyu.edu'.

gov

A government site; for example, NASA is `nasa.gov'.

mil

A military site, like the Air Force (`af.mil').

net

Gateways and other administrative hosts for a network (it does not mean all of the hosts in a network).(1) One such gateway is `near.net'.

org

invisible.xbm This is a domain reserved for private organizations, who don't comfortably fit in the other classes of domains. One example is the Electronic Frontier Foundation (see section The Electronic Frontier Foundation), named `eff.org'.

Each country also has its own top-level domain. For example, the us domain includes each of the fifty states. Other countries represented with domains include:

au

Australia

ca

Canada

fr

France

uk

The United Kingdom. These also have sub-domains of things like `ac.uk' for academic sites and `co.uk' for commercial ones.

invisible.xbm The proper terminology for a site's domain name (somewhere.domain above) is its Fully Qualified Domain Name (FQDN). It is usually selected to give a clear indication of the site's organization or sponsoring agent. For example, the Massachusetts Institute of Technology's FQDN is `mit.edu'; similarly, Apple Computer's domain name is `apple.com'. While such obvious names are usually the norm, there are the occasional exceptions that are ambiguous enough to mislead--like `vt.edu', which on first impulse one might surmise is an educational institution of some sort in Vermont; not so. It's actually the domain name for Virginia Tech. In most cases it's relatively easy to glean the meaning of a domain name--such confusion is far from the norm.

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Copyright © 1998, Software Engineering Laboratory
National Technical University of Athens