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IETF RFC 920
Domain requirements
Last modified on Tuesday, January 27th, 1987
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Network Working Group J. Postel
Request for Comments: 920 J. Reynolds
ISI
October 1984
Domain Requirements
 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.
Introduction
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.
Postel & Reynolds PAGE 1 
RFC 920 October 1984
Domain Requirements
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:
Temporary
ARPA = The current ARPA-Internet hosts.
Categories
GOV = Government, any government related domains meeting the
second level requirements.
EDU = Education, any education related domains meeting the
second level requirements.
COM = Commercial, any commercial related domains meeting the
second level requirements.
MIL = Military, any military related domains meeting the
second level requirements.
ORG = Organization, any other domains meeting the second
level requirements.
Countries
The English two letter code (alpha-2) identifying a country
according the the ISO Standard for "Codes for the
Representation of Names of Countries" [5].
Postel & Reynolds PAGE 2
RFC 920 October 1984
Domain Requirements
Multiorganizations
A multiorganization may be a top level domain if it is large,
and is composed of other organizations; particularly if the
multiorganization can not be easily classified into one of the
categories and is international in scope.
Possible Examples of Domains
The following examples are fictions of the authors' creation, any
similarity to the real world is coincidental.
The UC Domain
It might be that a large state wide university with, say, nine
campuses and several laboratories may want to form a domain. Each
campus or major off-campus laboratory might then be a subdomain,
and within each subdomain, each department could be further
distinguished. This university might be a second level domain in
the education category.
One might see domain style names for hosts in this domain like
these:
LOCUS.CS.LA.UC.EDU
CCN.OAC.LA.UC.EDU
ERNIE.CS.CAL.UC.EDU
A.S1.LLNL.UC.EDU
A.LAND.LANL.UC.EDU
NMM.LBL.CAL.UC.EDU
The MIT Domain
Another large university may have many hosts using a variety of
machine types, some even using several families of protocols.
However, the administrators at this university may see no need for
the outside world to be aware of these internal differences. This
university might be a second level domain in the education
category.
One might see domain style names for hosts in this domain like
these:
APIARY-1.MIT.EDU
BABY-BLUE.MIT.EDU
CEZANNE.MIT.EDU
DASH.MIT.EDU
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RFC 920 October 1984
Domain Requirements
MULTICS.MIT.EDU
TAC.MIT.EDU
XX.MIT.EDU
The CSNET Domain
There may be a consortium of universities and industry research
laboratories called, say, "CSNET". This CSNET is not a network
per se, but rather a computer mail exchange using a variety of
protocols and network systems. Therefore, CSNET is not a network
in the sense of the ARPANET, or an Ethernet, or even the
ARPA-Internet, but rather a community. Yet it does, in fact, have
the key property needed to form a domain; it has a responsible
administration. This consortium might be large enough and might
have membership that cuts across the categories in such a way that
it qualifies under the "multiorganization rule" to be a top level
domain.
One might see domain style names for hosts in this domain like
these:
CIC.CSNET
EMORY.CSNET
GATECH.CSNET
HP-LABS.CSNET
SJ.IBM.CSNET
UDEL.CSNET
UWISC.CSNET
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).
Responsible Person:
An individual must be identified who has authority for the
administration of the names within the domain, and who seriously
takes on the responsibility for the behavior of the hosts in the
domain, plus their interactions with hosts outside the domain.
This person must have some technical expertise and the authority
within the domain to see that problems are fixed.
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RFC 920 October 1984
Domain Requirements
If a host in a given domain somehow misbehaves in its interactions
with hosts outside the domain (e.g., consistently violates
protocols), the responsible person for the domain must be
competent and available to receive reports of problems, take
action on the reported problems, and follow through to eliminate
the problems.
Domain Servers:
A robust and reliable domain server must be provided. One way of
meeting this requirement is to provide at least two independent
domain servers for the domain. The database can, of course, be
the same. The database can be prepared and copied to each domain
server. But, the servers should be in separate machines on
independent power supplies, et cetera; basically as physically
independent as can be. They should have no common point of
failure.
Some domains may find that providing a robust domain service can
most easily be done by cooperating with another domain where each
domain provides an additional server for the other.
In other situations, it may be desirable for a domain to arrange
for domain service to be provided by a third party, perhaps on
hosts located outside the domain.
One of the difficult problems in operating a domain server is the
acquisition and maintenance of the data. In this case, the data
are the host names and addresses. In some environments this
information changes fairly rapidly and keeping up-to-date data may
be difficult. This is one motivation for sub-domains. One may
wish to create sub-domains until the rate of change of the data in
a sub-domain domain server database is easily managed.
In the technical language of the domain server implementation the
data is divided into zones. Domains and zones are not necessarily
one-to-one. It may be reasonable for two or more domains to
combine their data in a single zone.
The responsible person or an identified technical assistant must
understand in detail the procedures for operating a domain server,
including the management of master files and zones.
The operation of a domain server should not be taken on lightly.
There are some difficult problems in providing an adequate
service, primarily the problems in keeping the database up to
date, and keeping the service operating.
Postel & Reynolds PAGE 5
RFC 920 October 1984
Domain Requirements
The concepts and implementation details of the domain server are
given in RFC 882 [2] and RFC 883 [3].
Minimum Size:
The domain must be of at least a minimum size. There is no
requirement to form a domain because some set of hosts is above
the minimum size.
Top level domains must be specially authorized. In general, they
will only be authorized for domains expected to have over 500
hosts.
The general guideline for a second level domain is that it have
over 50 hosts. This is a very soft "requirement". It makes sense
that any major organization, such as a university or corporation,
be allowed as a second level domain -- even if it has just a few
hosts.
Registration:
Top level domains must be specially authorized and registered with
the NIC domain registrar.
The administrator of a level N domain must register with the
registrar (or responsible person) of the level N-1 domain. This
upper level authority must be satisfied that the requirements are
met before authorization for the domain is granted.
The registration procedure involves answering specific questions
about the prospective domain. A prototype of what the NIC Domain
Registrar may ask for the registration of a second level domain is
shown below. These questions may change from time to time. It is
the responsibility of domain administrators to keep this
information current.
The administrator of a domain is required to make sure that host
and sub-domain names within that jurisdiction conform to the
standard name conventions and are unique within that domain.
If sub-domains are set up, the administrator may wish to pass
along some of his authority and responsibility to a sub-domain
administrator. Even if sub-domains are established, the
responsible person for the top-level domain is ultimately
responsible for the whole tree of sub-domains and hosts.
This does not mean that a domain administrator has to know the
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RFC 920 October 1984
Domain Requirements
details of all the sub-domains and hosts to the Nth degree, but
simply that if a problem occurs he can get it fixed by calling on
the administrator of the sub-domain containing the problem.
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.
The top level domains:
ARPA = The ARPA-Internet *** TEMPORARY ***
Administrator: DARPA
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
GOV = Government
Administrator: DARPA
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
EDU = Education
Administrator: DARPA
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
COM = Commercial
Administrator: DARPA
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
MIL = Military
Administrator: DDN-PMO
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
Postel & Reynolds PAGE 7
RFC 920 October 1984
Domain Requirements
ORG = Organization
Administrator: DARPA
Agent: The Network Information Center
Mailbox: HOSTMASTER@SRI-NIC.ARPA
Countries
The English two letter code (alpha-2) identifying a country
according the the ISO Standard for "Codes for the
Representation of Names of Countries" [5].
As yet no country domains have been established. As they are
established information about the administrators and agents
will be made public, and will be listed in subsequent editions
of this memo.
Multiorganizations
A multiorganization may be a top level domain if it is large,
and is composed of other organizations; particularly if the
multiorganization can not be easily classified into one of the
categories and is international in scope.
As yet no multiorganization domains have been established. As
they are established information about the administrators and
agents will be made public, and will be listed in subsequent
editions of this memo.
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.
Postel & Reynolds PAGE 8
RFC 920 October 1984
Domain Requirements
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?
For existing hosts already operating in the ARPA-Internet, the
best advice is to sit tight for now. Take a few months to
consider the options, then select a domain to join. Plan
carefully for the impact that changing your host name will have on
both your local users and on their remote correspondents.
For a new host, careful thought should be given (as discussed
below). Some guidance can be obtained by comparing notes on what
other hosts with similar administrative properties have done.
The owner of a host may decide which domain to join, and the
Postel & Reynolds PAGE 9
RFC 920 October 1984
Domain Requirements
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.
For example, a host "XYZ" at MIT might possible be considered as a
candidate for becoming any of XYZ.ARPA.ORG, XYZ.CSNET, or
XYZ.MIT.EDU.
The owner of host XYZ may choose which domain to join,
depending on which domain administrators are willing to have
him.
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).
Top Level Domain Registrar
As the registrar for top level domains, the NIC is the contact
point for investigating the possibility of establishing a new top
level domain.
Top Level Domain Administrator
For the top level domains designated so far, the NIC is the
administrator of each of these domains. This means the NIC is
responsible for the management of these domains and the
registration of the second level domains or hosts (if at the
second level) in these domains.
Postel & Reynolds PAGE 10
RFC 920 October 1984
Domain Requirements
It may be reasonable for the administration of some of these
domains to be taken on by other authorities in the future. It is
certainly not desired that the NIC be the administrator of all top
level domains forever.
Prototypical Questions
To establish a domain, the following information must be provided to
the NIC Domain Registrar (HOSTMASTER@SRI-NIC.ARPA):
Note: The key people must have computer mail mailboxes and
NIC-Idents. If they do not at present, please remedy the
situation at once. A NIC-Ident may be established by contacting
NIC@SRI-NIC.ARPA.
1) The name of the top level domain to join.
For example: EDU
2) The name, title, mailing address, phone number, and organization
of the administrative head of the organization. This is the contact
point for administrative and policy questions about the domain. In
the case of a research project, this should be the Principal
Investigator. The online mailbox and NIC-Ident of this person should
also be included.
For example:
Administrator
Organization USC/Information Sciences Institute
Name Keith Uncapher
Title Executive Director
Mail Address USC/ISI
4676 Admiralty Way, Suite 1001
Marina del Rey, CA. 90292-6695
Phone Number 213-822-1511
Net Mailbox Uncapher@USC-ISIB.ARPA
NIC-Ident KU
3) The name, title, mailing address, phone number, and organization
of the domain technical contact. The online mailbox and NIC-Ident of
the domain technical contact should also be included. This is the
contact point for problems with the domain and for updating
information about the domain. Also, the domain technical contact may
be responsible for hosts in this domain.
Postel & Reynolds PAGE 11
RFC 920 October 1984
Domain Requirements
For example:
Technical Contact
Organization USC/Information Sciences Institute
Name Craig Milo Rogers
Title Researcher
Mail Address USC/ISI
4676 Admiralty Way, Suite 1001
Marina del Rey, CA. 90292-6695
Phone Number 213-822-1511
Net Mailbox Rogers@USC-ISIB.ARPA
NIC-Ident CMR
4) The name, title, mailing address, phone number, and organization
of the zone technical contact. The online mailbox and NIC-Ident of
the zone technical contact should also be included. This is the
contact point for problems with the zone and for updating information
about the zone. In many cases the zone technical contact and the
domain technical contact will be the same person.
For example:
Technical Contact
Organization USC/Information Sciences Institute
Name Craig Milo Rogers
Title Researcher
Mail Address USC/ISI
4676 Admiralty Way, Suite 1001
Marina del Rey, CA. 90292-6695
Phone Number 213-822-1511
Net Mailbox Rogers@USC-ISIB.ARPA
NIC-Ident CMR
5) The name of the domain (up to 12 characters). This is the name
that will be used in tables and lists associating the domain and the
domain server addresses. [While technically domain names can be
quite long (programmers beware), shorter names are easier for people
to cope with.]
For example: ALPHA-BETA
6) A description of the servers that provides the domain service for
translating name to address for hosts in this domain, and the date
they will be operational.
Postel & Reynolds PAGE 12
RFC 920 October 1984
Domain Requirements
A good way to answer this question is to say "Our server is
supplied by person or company X and does whatever their standard
issue server does".
For example: Our server is a copy of the server operated by
the NIC, and will be installed and made operational on
1-November-84.
7) A description of the server machines, including:
(a) hardware and software (using keywords from the Assigned
Numbers)
(b) addresses (what host on what net for each connected net)
For example:
(a) hardware and software
VAX-11/750 and UNIX, or
IBM-PC and MS-DOS, or
DEC-1090 and TOPS-20
(b) address
10.9.0.193 on ARPANET
8) An estimate of the number of hosts that will be in the domain.
(a) initially,
(b) within one year,
(c) two years, and
(d) five years.
For example:
(a) initially = 50
(b) one year = 100
(c) two years = 200
(d) five years = 500
Postel & Reynolds PAGE 13
RFC 920 October 1984
Domain Requirements
Acknowledgment
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.
References
[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.
Postel & Reynolds PAGE 14
Domain requirements
RFC TOTAL SIZE: 27823 bytes
PUBLICATION DATE: Tuesday, January 27th, 1987
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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