INTERNET-DRAFT Thomas Narten
IBM
<draft-iesg-iana-considerations-00.txt> Harald Tveit Alvestrand
UNINETT
October 6, 1997
Guidelines for Writing an IANA Considerations Section in RFCs
<draft-iesg-iana-considerations-00.txt>
Status of this Memo
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Abstract
Many protocols make use of identifiers consisting of constants and
other well-known values. Even after a protocol has been defined and
deployment has begun, new values may need to be assigned (e.g., a new
option type in DHCP). To insure that such quantities have unique
values, their assignment must be administered by a central authority.
In the Internet, that role is provided by the Internet Assigned
Numbers Authority (IANA).
In order for the IANA to manage a given numbering space prudently, it
needs guidelines describing the conditions under which new values can
be assigned. If the IANA is expected to play a role in the management
of a numbering space, the IANA must be given clear and concise
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guidelines describing that role. This document discusses issues that
should be considered in formulating an identifier assignment policy
and provides guidelines to document authors on the specific text that
must be included in documents that place demands on the IANA.
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Contents
Status of this Memo.......................................... 1
1. Introduction............................................. 3
2. Issues To Consider....................................... 4
3. What To Put In Documents................................. 6
4. Security Considerations.................................. 6
5. References............................................... 6
6. Authors' Addresses....................................... 7
1. Introduction
Many protocols make use of fields that contain constants and other
well-known values (e.g., the Protocol field in the IP header [IP] or
MIME types in mail messages [MIME]). Even after a protocol has been
defined and deployment has begun, new values may need to be assigned
(e.g., a new option type in DHCP [DHCP]). To insure that such fields
have unique values, their assignment must be administered by a
central authority. In the Internet, that role is provided by the
Internet Assigned Numbers Authority (IANA).
In order for the IANA to manage a given numbering space prudently, it
needs guidelines describing the conditions under which new values
should be assigned. This document provides guidelines to authors on
what sort of text should be added to their documents, and reviews
issues that should be considered in formulating an appropriate policy
for assigning identifiers.
Not all name spaces require centralized administration. In some
cases, it is possible to delegate a name space in such a way that
further assignments can be made independently and with no further
(central) coordination. In the Domain Name System, for example, the
IANA only deals with assignments at the higher-levels, while
subdomains are administered by the organization to which the space
has been delegated. As another example, Object Identifiers (OIDs) as
defined by the ITU are also delegated [XXX reference]. When a name
space can be delegated, the IANA only deals with assignments at the
top level.
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2. Issues To Consider
The primary issue to consider in managing a numbering space is its
size. If the space is small and limited in size, assignments must be
made carefully to insure that the space doesn't become exhausted. On
the other hand, it may be perfectly reasonable to hand out new values
to anyone that wants one, if the space is essentially unlimited. Even
when the space is essentially unlimited, however, it may be desirable
to have a minimal review to prevent hoarding of the space. For
example, if the space consists of text strings, it may be desirable
to prevent organizations from obtaining large sets of strings that
correspond to the "best" names (e.g., existing company names).
A second consideration is whether it makes sense to delegate the name
space in some manner. This route should be pursued when appropriate,
as it lessens the burden on the IANA for dealing with assignments.
In most cases, some review of prospective allocations is appropriate,
and the first question to answer is who should perform the review.
In some cases, it is reasonable for the IANA to review prospective
assignments. In such cases, the IANA will need specific guidelines
on what types of requests it should grant, and what information must
be provided before a request of an assigned number will be
considered. Note that the IANA will not define such a policy; it
should be given a set of guidelines that allow it to make allocation
decisions with little subjectivity. The following are example
policies, some of which are in use today:
Free For All - For local use only, with the type and purpose
defined by the local site. No attempt is made to prevent
multiple sites from using the same value in different (and
incompatible) ways. There is no need for IANA to review
such assignments and assignments are not generally useful
for interoperability.
Examples: Site-specific options in DHCP [DHCP] have
significance only within a single site.
Hierarchical allocation - Delegated managers can assign
identifiers provided they have been given control over that
part of the identifier space. IANA controls the top levels
of the namespace according to one of the other policies.
Examples: DNS names
First Come First Served - Anyone can obtain an identifier, so long
as they provide a point of contact and a brief description
of what the identifier would be used for. For numbers, the
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exact value is generally assigned by the IANA, with names,
specific names are usually requested.
Examples: MIME types, TCP and UDP port numbers.
Documentation Required - Values and their meaning must be
documented in an RFC or other permanent reference, in
sufficient detail so that interoperability between
independent implementations is possible.
Examples: XXX
IESG Action - IESG must explicitly approve new values.
Examples: XXX
Standards Action - Only identifiers that have been documented in
standards track RFCs approved by the IESG will be
registered.
Examples: XXX
In some cases, it may be appropriate for the IANA to serve as a
point-of-contact for publishing information about numbers that have
been assigned, without actually having it evaluate and grant
requests. For example, it is useful (and sometimes necessary) to
discuss proposed additions on a mailing list dedicated to the purpose
(e.g., the ietf-types@iana.org for media types) or on a mailing list
associated with an IETF Working Group. Since the IANA cannot
participate in all of these mailing lists and cannot determine if or
when such discussion reaches a consensus, the IANA will rely on a
designated subject matter expert to advise it in these matters.
Consequently, the IANA should be directed to forward the requests it
receives to a specific point-of-contact or mailing list (i.e., a
mailing list set up specifically for the purpose of discussing such
requests) and act upon the returned recommendation from the
designated subject matter expert. In all cases, it is the designated
subject matter expert that the IANA relies on for an authoritative
response.
Of course, combinations of the above are also possible. When defining
new DHCP option types [DHCP], for example, the IANA assigns options
to anyone, with the stipulation that the number will be returned to
the IANA should the option fail to gain acceptance.
In some cases, it may make sense to partition the number space into
several categories, with assignments out of each category handled
differently. For example, the DHCP option space [DHCP] is split into
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two parts. Option numbers in the range of 1-127 are globally unique
and assigned according to the Documentation Required policy described
earlier, while options number 128-254 are "site specific", i.e., Free
For All.
3. What To Put In Documents
The previous section presented some issues that should be considered
in formulating a policy for assigning well-known numbers and other
protocol constants. It is the Working Group and/or document author's
job to formulate an appropriate policy and specify it in the
appropriate document. In some cases, having an "IANA Considerations"
section may be appropriate. Such a section should state clearly:
- who reviews an application for an assigned number. If a request
should be reviewed by a designated subject matter expert,
contact information for that person should be provided. If the
request should also be reviewed by a specific mailing list (such
as the ietf-types@iana.org for media types), that mailing
address should be specified.
- if the IANA is expected to review requests itself, sufficient
guidance must be provided so that the requests can be evaluated
with minimal subjectivity.
Finally, it is quite acceptable to pick one of the example policies
cited above and refer to it by name. For example, a document could
say something like:
numbers are allocated as First Come First Served as defined in
[RFC ASSIGN]
XXX: give pointers to 3 or 4 particularly good examples in existing
RFCs? 1) DHCP options seems reasonable. Others?
4. Security Considerations
There are no known security issues raised by this document.
5. References
[DHCP-OPTIONS] S. Alexander, R. Droms, DHCP Options and BOOTP
Vendor Extensions, RFC 2132, March 1997.
[IP] J. Postel, Internet Protocol, RFC 791, September 1, 1981.
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[MIME] N. Freed, J. Klensin & J. Postel, Multipurpose Internet Mail
Extension (MIME) Part Four: Registration Procedures. RFC
2048, November, 1996.
6. Authors' Addresses
Thomas Narten
IBM Corporation
3039 Cornwallis Ave.
PO Box 12195 - BRQA/502
Research Triangle Park, NC 27709-2195
Phone: 919-254-7798
EMail: narten@raleigh.ibm.com
Harald Tveit Alvestrand
UNINETT
P.O.Box 6883 Elgeseter
N-7002 TRONDHEIM
NORWAY
Phone: +47 73 59 70 94
EMail: Harald.T.Alvestrand@uninett.no
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