Domain Name System Structure and Delegation
RFC 1591

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Network Working Group                                          J. Postel
Request for Comments: 1591                                           ISI
Category: Informational                                       March 1994

              Domain Name System Structure and Delegation

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

1. Introduction

   This memo provides some information on the structure of the names in
   the Domain Name System (DNS), specifically the top-level domain
   names; and on the administration of domains.  The Internet Assigned
   Numbers Authority (IANA) is the overall authority for the IP
   Addresses, the Domain Names, and many other parameters, used in the
   Internet.  The day-to-day responsibility for the assignment of IP
   Addresses, Autonomous System Numbers, and most top and second level
   Domain Names are handled by the Internet Registry (IR) and regional
   registries.

2.  The Top Level Structure of the Domain Names

   In the Domain Name System (DNS) naming of computers there is a
   hierarchy of names.  The root of system is unnamed.  There are a set
   of what are called "top-level domain names" (TLDs).  These are the
   generic TLDs (EDU, COM, NET, ORG, GOV, MIL, and INT), and the two
   letter country codes from ISO-3166.  It is extremely unlikely that
   any other TLDs will be created.

   Under each TLD may be created a hierarchy of names.  Generally, under
   the generic TLDs the structure is very flat.  That is, many
   organizations are registered directly under the TLD, and any further
   structure is up to the individual organizations.

   In the country TLDs, there is a wide variation in the structure, in
   some countries the structure is very flat, in others there is
   substantial structural organization.  In some country domains the
   second levels are generic categories (such as, AC, CO, GO, and RE),
   in others they are based on political geography, and in still others,
   organization names are listed directly under the country code.  The
   organization for the US country domain is described in RFC 1480 [1].

Postel                                                          [Page 1]
RFC 1591      Domain Name System Structure and Delegation     March 1994

   Each of the generic TLDs was created for a general category of
   organizations.  The country code domains (for example, FR, NL, KR,
   US) are each organized by an administrator for that country.  These
   administrators may further delegate the management of portions of the
   naming tree.  These administrators are performing a public service on
   behalf of the Internet community.  Descriptions of the generic
   domains and the US country domain follow.

   Of these generic domains, five are international in nature, and two
   are restricted to use by entities in the United States.

   World Wide Generic Domains:

   COM - This domain is intended for commercial entities, that is
         companies.  This domain has grown very large and there is
         concern about the administrative load and system performance if
         the current growth pattern is continued.  Consideration is
         being taken to subdivide the COM domain and only allow future
         commercial registrations in the subdomains.

   EDU - This domain was originally intended for all educational
         institutions.  Many Universities, colleges, schools,
         educational service organizations, and educational consortia
         have registered here.  More recently a decision has been taken
         to limit further registrations to 4 year colleges and
         universities.  Schools and 2-year colleges will be registered
         in the country domains (see US Domain, especially K12 and CC,
         below).

   NET - This domain is intended to hold only the computers of network
         providers, that is the NIC and NOC computers, the
         administrative computers, and the network node computers.  The
         customers of the network provider would have domain names of
         their own (not in the NET TLD).

   ORG - This domain is intended as the miscellaneous TLD for
         organizations that didn't fit anywhere else.  Some non-
         government organizations may fit here.

   INT - This domain is for organizations established by international
         treaties, or international databases.

   United States Only Generic Domains:

   GOV - This domain was originally intended for any kind of government
         office or agency.  More recently a decision was taken to
         register only agencies of the US Federal government in this
         domain.  State and local agencies are registered in the country

Postel                                                          [Page 2]
RFC 1591      Domain Name System Structure and Delegation     March 1994