Technical Library

Domain Name System

Introduction

Integration

The Domain Name System is a distributed hierarchical system for resolving host names into IP addresses. The DNS has a root domain at the top of the hierarchy and directly under are the top-level domains. The root of the tree has no name. All siblings of a domain must have unique names. Children of a domain are called subdomains of the parent.

                            ROOT 

           ___________________|________________________
           |    |    |    |       |    |    |    |    |
          COM  EDU  GOV  MIL      NET  ORG  INT  US  ARPA

The information is distributed among thousands of name servers. The root name servers only have complete information about the top-level domains. No servers have complete information about all domains, but the root name servers have pointers to the servers for the second level domains. This gives them complete access to the information about all domains by querying its list of name servers.

Top-Level Domains

Descriptions of each main top-level domain that divide up the Internet Name Space are given below.

COM

Any commercial, for-profit business may register in the COM domain. This is the most common type of domain being registered today. Although a full domain name may be up to 63 characters, the InterNIC recommends 12 characters or less in the portion preceding the "dot". Any alphanumeric character is allowed. Hyphens are permitted, but only for interior characters (no name may start or end with a hyphen).

May I register more than one domain for the same company?

Because the COM domain is becoming so heavily populated, the InterNIC has developed certain guidelines for registering multiple domain names. More than one domain may be registered if you can provide a reasonable business justification. Without an explanation, the InterNIC will return an application for a second domain name. Describe in a couple of sentences why your company needs another domain name, identifying how they will not be used for the same thing. You should very well consider the use of a subdomain, since it is fast and efficient to use, especially when you need another domain for an office of the same company in another location.

Originally, the EDU domain was designed to be the top-level domain for all educational institutions. However, due to the explosive growth of the Internet, the InterNIC now limits registrations in the EDU domain to 4-year, degree granting colleges and universities. All other educational institutions must register in the US domain. If you intend to register in the EDU domain, you must include a brief sentence in your application affirming your organization is a 4-year college or university.

This top-level domain is reserved for certain Federal Government Agencies and only under specific circumstances. Details regarding these specifications can be found in RFC 2146.

Any department or agency of the US military may register a name in the MIL domain. In your application, be sure to affirm you are a department or agency of the US military.

The NET domain is intended to hold only the computers of network providers. The appropriate entity for a NET domain is an Internet Service Provider or an administrative organization providing Internet support functions (such as the InterNIC).

The InterNIC previously defined the ORG domain for non-profit organizations and other organizations that did not fit anywhere else. Currently, registering in the ORG domain is restricted to only non-profit organizations. Be sure to affirm you are a non-profit organization in your application.

The INT domain is used only for registering organizations established by international treaties between governments or Internet infrastructure databases. Applicants for the International Organization domain must comply with the requirements found in RFC 1591.

This is the top-level country domain for the United States. The US Domain currently registers hosts of businesses, individuals, federal government agencies, state government agencies, K12 schools, community colleges, technical/vocational schools, private schools, libraries, museums, city and county government agencies. Further information can be obtained at:
http://www.nic.us/

This was originally used during the ARPANET's transition from host tables to DNS. All ARPANET hosts originally had host names under "arpa" so they were easy to find. Later, they moved into various subdomains of the organizational top-level domains.