What Are Top-Level Domains (TLDs)?
Dec 13th, 2009 01:10
Scott Mandarich, Joe Bloggs, chat alarab, dman, Laurent Chouinard, Kagan (Kai) MacTane,
A Top-Level Domain (TLD) is one of the highest-level domains on the
Internet, usually represented by the last two or three letters of an
address, URL, or domain name. For example, consider the following
addresses (some of which are hostnames, some of which are URLs, and
of which are email addresses):
In the above list, the TLDs are, in order: .com, .edu, .uk, .us, and
.tw. The example.com domain is a subset of the .com TLD. The host
www.demon.co.uk is a member of the domain demon.co.uk, which is a
of the .co.uk domain, which in turn is a subset of the .uk TLD.
TLDs can be grouped into two major groups: _Geographic_ domains and
_Organizational_ domains. These are also referred to as "country
and "role domains", since the geographic domains are based on national
borders, and the organizational domains are based on the "role" an
organization plays in the Uninted States.
The U.S. organizational domains are the following six, all containing
.com COMmercial entities: businesses, shops, merchants, etc.
.edu EDUcational institutions (accredited higher learning
centers only; public grade schools go under .gov)
.org Non-profit ORGanizations: charities, lobbying groups,
.net NETworking providers: ISPs; major access providers;
groups that maintain backbone routes and cables; etc.
.gov GOVernmental (non-military) bodies: Congress; state
governments; Cabinet departments such as the DoE,
DoD, HUD, etc.; NASA, the IRS, and similar stuff.
.mil MILitary divisions: the Army, Navy, Air Force, Marines,
and so forth.
These categories used to be pretty firm. In recent years, however, the
people responsible for registering the .com, .net, and .org domains
(Network Solutions, Inc.) have been very lax abbout enforcing those
standards, so nearly anyone can get a domain registered in any of
three TLDs. The .edu, .gov, and .mil TLDs, however, are still strictly
controlled to ensure that only qualifying organizations can register
domains within them.
Country codes, on the other hand, are far more numerous. They all use
two-letter abbreviations, based on ISO 3166 (an international standard
for abbreviating country names). Here are a few that are useful to
(please don't get angry at me if I didn't include your country!), and
which will help give you the flavor of them:
.ch Switzerland (Confederaziun Helvetica)
.de Germany (Deutschland)
.uk United Kingdom
.us United States
A complete list of country codes can be found at
other places on the Web.
There are a few countries which have elected to make domain names
their TLDs available to outsiders, generally for the purpose of
up names that "look like standard English". Prominent among these are
Tonga (.to), which has allowed servers such as go.to and come.to,
Armenia (.am), for the i.am server, and Sao Tome and Principe (.st),
allowing hosts like sesame.st, fascination.st, and the like.
Oddly, country code TLDs are sometimes more stable than the countries
they represent! There is still a .su (Soviet Union) TLD in use on the
Internet, because when the Soviet Union collapsed, there were some
machines whose new ownership was unclear. Eventually, rather than
them to, for instance, .ru, .by (Belarus) or .az (Azerbaijan), it was
decided to simply leave them designated as being in the .su domain.
Finally, there are two "special" TLDs, each with four letters: .arpa
.nato. The .arpa domain stands for "Advanced Research Projects
a division of the U.S. government that funded much of the early
development of what eventually became the Internet. The .arpa TLD is
mostly unused now, except for the in-addr.arpa domain, which is used
maintain a database of reverse lookups for DNS servers. (DNS, the
Name System, is used to translate host names into IP addresses and
The .nato domain is for use by NATO, the North Atlantic Treaty
There is also a .int Top-Level domain, intended for international
organizations. Very few actually use the .int domain, as most
either use a .com domain, or country-specific domains wherever they
have businesses in. The Internet Assigned Numbers Authority is
responsible for for .int TLD, and currently accepts registrations.