What Is a Domain Identifier?

by David Dunning

A domain identifier, otherwise known as a primary domain name or top-level domain name, is the rightmost portion of the common, word-based identifier for a group of computers, known as the domain name. For example, in a fully qualified domain name, such as www.ehow.com, www is the host, ehow is the second-level domain name and .com is the domain identifier.

Domain Name System

The Domain Name System (DNS) is an Internet protocol, or set of rules, which translates human-readable domain names, such as ehow.com, into machine-readable Internet Protocol addresses. The DNS uses a hierarchical, tree-like structure with a single root node at the top of the tree and seven nodes, each containing a domain identifier, below the root.


The seven generic, three character, domain identifiers are .com, which identifies commercial enterprises, .edu, which identifies educational establishments, .gov, which identifies U.S. government agencies and .int, .mil, .net, .org, which identify international and military domains, network providers, such as Internet service providers, and organizations of any kind respectively. Domain names can be registered in the .com, .net and .org domains without restriction, but restrictions apply to the other top-level domains. Furthermore, two character domain identifiers, known as country code top-levels, have been established for over 250 countries and external territories. The top-level domains are delegated to managers, who operate them in accordance with the cultural, economic, linguistic and legal circumstances in the country designated by the domain identifier.


A fully qualified domain name can contain up to 67 characters, including alphanumeric characters, hyphens and periods used to separate the host, second-level domain name and domain identifier. Nowadays, domain identifiers are controlled by a non-profit, international corporation, known as the Internet Corporation for Assigned Names and Numbers (ICANN), which was formed in 1998. Domain identifiers were originally proposed, however, as long ago as 1984, in a document known as Request for Comments (RFC) 920, published by the Network Working Group.


Domain identifiers were introduced as a means of providing an addressing system when the number of computers connected to the Internet became too great to handle with simple computers names. Domains need not be constrained by geography, topography or technology. The hosts in a single domain do not need to have common hardware, software or protocols, but domain names break down the administration of the Internet into smaller units, which can be managed more easily and responsibly.

About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.