RFC 920
Domain Requirements

Network Working Group
J.Postel, J.Reynolds
October 1984

Status of this Memo

This memo is a policy statement on the requirements of establishing a new domain in the ARPA-Internet and the DARPA research community. This is an official policy statement of the IAB and the DARPA. Distribution of this memo is unlimited.


This memo restates and refines the requirements on establishing a Domain first described in RFC-881 [1]. It adds considerable detail to that discussion, and introduces the limited set of top level domains.

The Purpose of Domains

Domains are administrative entities. The purpose and expected use of domains is to divide the name management required of a central administration and assign it to sub-administrations. There are no geographical, topological, or technological constraints on a domain. The hosts in a domain need not have common hardware or software, nor even common protocols. Most of the requirements and limitations on domains are designed to ensure responsible administration.

The domain system is a tree-structured global name space that has a few top level domains. The top level domains are subdivided into second level domains. The second level domains may be subdivided into third level domains, and so on.

The administration of a domain requires controlling the assignment of names within that domain and providing access to the names and name related information (such as addresses) to users both inside and outside the domain.

General Purpose Domains

While the initial domain name "ARPA" arises from the history of the development of this system and environment, in the future most of the top level names will be very general categories like "government", "education", or "commercial". The motivation is to provide an organization name that is free of undesirable semantics.

After a short period of initial experimentation, all current ARPA-Internet hosts will select some domain other than ARPA for their future use. The use of ARPA as a top level domain will eventually cease.

Initial Set of Top Level Domains

The initial top level domain names are:

Possible Examples of Domains

The following examples are fictions of the authors' creation, any similarity to the real world is coincidental.

General Requirements on a Domain

There are several requirements that must be met to establish a domain. In general, it must be responsibly managed. There must be a responsible person to serve as an authoritative coordinator for domain related questions. There must be a robust domain name lookup service, it must be of at least a minimum size, and the domain must be registered with the central domain administrator (the Network Information Center (NIC) Domain Registrar).

Top Level Domain Requirements

There are very few top level domains, each of these may have many second level domains.

An initial set of top level names has been identified. Each of these has an administrator and an agent.

Note: The NIC is listed as the agent and registrar for all the currently allowed top level domains. If there are other entities that would be more appropriate agents and registrars for some or all of these domains then it would be desirable to reassign the responsibility.

Second Level Domain Requirements

Each top level domain may have many second level domains. Every second level domain must meet the general requirements on a domain specified above, and be registered with a top level domain administrator.

Third through Nth Level Domain Requirements

Each second level domain may have many third level domains, etc. Every third level domain (through Nth level domain) must meet the requirements set by the administrator of the immediately higher level domain. Note that these may be more or less strict than the general requirements. One would expect the minimum size requirements to decrease at each level.

The ARPA Domain

At the time the implementation of the domain concept was begun it was thought that the set of hosts under the administrative authority of DARPA would make up a domain. Thus the initial domain selected was called ARPA. Now it is seen that there is no strong motivation for there to be a top level ARPA domain. The plan is for the current ARPA domain to go out of business as soon as possible. Hosts that are currently members of the ARPA domain should make arrangements to join another domain. It is likely that for experimental purposes there will be a second level domain called ARPA in the ORG domain (i.e., there will probably be an ARPA.ORG domain).

The DDN Hosts

DDN hosts that do not desire to participate in this domain naming system will continue to use the HOSTS.TXT data file maintained by the NIC for name to address translations. This file will be kept up to date for the DDN hosts. However, all DDN hosts will change their names from "host.ARPA" to (for example) "host.DDN.MIL" some time in the future. The schedule for changes required in DDN hosts will be established by the DDN-PMO.

Impact on Hosts

What is a host administrator to do about all this?

The owner of a host may decide which domain to join, and the administrator of a domain may decide which hosts to accept into his domain. Thus the owner of a host and a domain administrator must come to an understanding about the host being in the domain. This is the foundation of responsible administration.

The domain is part of the host name. Thus if USC-ISIA.ARPA changes its domain affiliation to DDN.MIL to become USC-ISIA.DDN.MIL, it has changed its name. This means that any previous references to USC-ISIA.ARPA are now out of date. Such old references may include private host name to address tables, and any recorded information about mailboxes such as mailing lists, the headers of old messages, printed directories, and peoples' memories.

The experience of the DARPA community suggests that changing the name of a host is somewhat painful. It is recommended that careful thought be given to choosing a new name for a host - which includes selecting its place in the domain hierarchy.

The Roles of the Network Information Center

The NIC plays two types of roles in the administration of domains. First, the NIC is the registrar of all top level domains. Second the NIC is the administrator of several top level domains (and the registrar for second level domains in these).


We would like to thank the many people who contributed to this memo, including the participants in the Namedroppers Group, the ICCB, the PCCB, and especially the staff of the Network Information Center, particularly J. Feinler and K. Harrenstien.


  1. Postel, J., "The Domain Names Plan and Schedule", RFC-881, USC Information Sciences Institute, November 1983.
  2. Mockapetris, P., "Domain Names - Concepts and Facilities", RFC-882, USC Information Sciences Institute, November 1983.
  3. Mockapetris, P., "Domain Names - Implementation and Specification", RFC-883, USC Information Sciences Institute, November 1983.
  4. Postel, J., "Domain Name System Implementation Schedule", RFC-897, USC Information Sciences Institute, February 1984.
  5. ISO, "Codes for the Representation of Names of Countries", ISO-3166, International Standards Organization, May 1981.
  6. Postel, J., "Domain Name System Implementation Schedule - Revised", RFC-921, USC Information Sciences Institute, October 1984.
  7. Mockapetris, P., "The Domain Name System", Proceedings of the IFIP 6.5 Working Conference on Computer Message Services, Nottingham, England, May 1984. Also as ISI/RS-84-133, June 1984.
  8. Mockapetris, P., J. Postel, and P. Kirton, "Name Server Design for Distributed Systems", Proceedings of the Seventh International Conference on Computer Communication, October 30 to November 3 1984, Sidney, Australia. Also as ISI/RS-84-132, June 1984.