Domain names

A ``domain name'' is the section of a mail address that appears to the right of the at (@) character, for example, mynet.com. The domain name describes the site where a machine is located and generally includes the machine (host) name, a department (optionally), and the site's organization or country. MMDF uses the domain name to deliver the message to the appropriate location. Domain names can be either upper or lowercase; MMDF is case-insensitive when evaluating domain names. Note that the domain name uniquely identifies a machine, but not the path by which messages reach that machine.

This is the convention for specifying domains:

hostname.subdomain.top-level

If the domain includes a department, the convention is:

hostname.local.subdomain.top-level

Here is a description of each of the domain levels:

Top-Level Domain

A top-level domain is an officially registered name that describes the purpose of a group of institutions or a code that is associated with a country.

You can only use registered top-level and subdomain names if you have registered your organization with SRI International. For information on registering your domain, see ``Registering domain names''. If you have not registered with SRI, use the UUCP top-level domain.

In the United States, the common top-level domains on the Internet are:

COM

commercial institutions

code

country code

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NOTE: The International Standards Organization (ISO) standard 3166 defines the country codes. For example, US is the country code for the United States, AU for Australia, DK for Denmark, and JP for Japan.

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EDU

educational and research institutions

GOV

government institutions

MIL

military institutions

NET

network

ORG

organization (generic)

UUCP

a domain name where users transmit information between cooperating neighbor machines via UUCP

Subdomain

An officially registered name that describes a company, department, or any subgroup under a top-level domain; sco is an example of a subdomain in the domain COM.

Local Domain

A name recognized only within an organization that has meaning only within that organization; a department name such as engr is an example of a local domain.