rfc2434.txt

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Network Working Group                                          T. Narten
Request for Comments: 2434                                           IBM
BCP: 26                                                    H. Alvestrand
Category: Best Current Practice                                  Maxware
                                                            October 1998


     Guidelines for Writing an IANA Considerations Section in RFCs

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

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., for a
   new option type in DHCP, or a new encryption or authentication
   algorithm for IPSec).  To insure that such quantities have consistent
   values and interpretations in different implementations, their
   assignment must be administered by a central authority. For IETF
   protocols, that role is provided by the Internet Assigned Numbers
   Authority (IANA).

   In order for the IANA to manage a given name 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 name space, the IANA must be given clear and concise
   instructions describing that role.  This document discusses issues
   that should be considered in formulating a policy for assigning
   values to a name space 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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Table of Contents

   Status of this Memo..........................................    1
   1.  Introduction.............................................    2
   2.  Issues To Consider.......................................    3
   3.  Registration maintenance.................................    6
   4.  What To Put In Documents.................................    7
   5.  Applicability to Past and Future RFCs....................    8
   6.  Security Considerations..................................    8
   7.  Acknowledgments..........................................    9
   8.  References...............................................    9
   9.  Authors' Addresses.......................................   10
   10. Full Copyright Statement.................................   11

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-REG]). 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] or a new encryption
   or authentication algorithm for IPSec [IPSEC]).  To insure that such
   fields have consistent values and interpretations in different
   implementations, their assignment must be administered by a central
   authority. For IETF protocols, that role is provided by the Internet
   Assigned Numbers Authority (IANA).

   In this document, we call the set of possible values for such a field
   a "name space"; its actual content may be a name, a number or another
   kind of value. The assignment of a specific value to a name space is
   called an assigned number (or assigned value). Each assignment of a
   number in a name space is called a registration.

   In order for the IANA to manage a given name 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 numbers to name spaces.

   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 [ASSIGNED].  When a name space



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   can be delegated, the IANA only deals with assignments at the top
   level.

   This document uses the terms 'MUST', 'SHOULD' and 'MAY', and their
   negatives, in the way described in RFC 2119 [KEYWORDS]. In this case,
   "the specification" as used by RFC 2119 refers to the processing of
   protocols being submitted to the IETF standards process.

2.  Issues To Consider

   The primary issue to consider in managing a name 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. If the
   space is essentially unlimited, on the other hand, it may be
   perfectly reasonable to hand out new values to anyone that wants one.
   Even when the space is essentially unlimited, however, it is usually
   desirable to have a minimal review to prevent the hoarding of or
   unnecessary wasting of a 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 some cases, the name space is essentially unlimited, and assigned
   numbers can safely be given out to anyone. When no subjective review
   is needed, the IANA can make assignments directly, provided that the
   IANA is given specific instructions on what types of requests it
   should grant, and what information must be provided before a request
   for an assigned number will be considered. Note that the IANA will
   not define an assignment policy; it should be given a set of
   guidelines that allow it to make allocation decisions with little
   subjectivity.

   In most cases, some review of prospective allocations is appropriate,
   and the question becomes who should perform the review and how
   rigorous the review needs to be.  In many cases, one might think that
   an IETF Working Group (WG) familiar with the name space at hand
   should be consulted. In practice, however, WGs eventually disband, so
   they cannot be considered a permanent evaluator. It is also possible
   for name spaces to be created through individual submission
   documents, for which no WG is ever formed.

   One way to insure community review of prospective assignments is to
   have the requester submit a document for publication as an RFC. Such
   an action insures that the IESG and relevant WGs review the



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   assignment. This is the preferred way of insuring review, and is
   particularly important if any potential interoperability issues can
   arise. For example, many assignments are not just assignments, but
   also involve an element of protocol specification. A new option may
   define fields that need to be parsed and acted on, which (if
   specified poorly) may not fit cleanly with the architecture of other
   options or the base protocols on which they are built.

   In some cases, however, the burden of publishing an RFC in order to
   get an assignment is excessive. However, it is generally still useful
   (and sometimes necessary) to discuss proposed additions on a mailing
   list dedicated to the purpose (e.g., the [e-mail] for
   media types) or on a more general mailing list (e.g., that of a
   current or former IETF WG).  Such a mailing list provides a way for
   new registrations to be publicly reviewed prior to getting assigned,
   or to give advice for persons who want help in understanding what a
   proper registration should contain.

   While discussion on a mailing list can provide valuable technical
   expertise, opinions may vary and discussions may continue for some
   time without resolution.  In addition, the IANA cannot participate in
   all of these mailing lists and cannot determine if or when such
   discussions reach consensus.  Therefore, the IANA cannot allow
   general mailing lists to fill the role of providing definitive
   recommendations regarding a registration question.  Instead, the IANA
   will use a designated subject matter expert.  The IANA will rely on a
   "designated expert" to advise it in assignment matters.  That is, the
   IANA forwards the requests it receives to a specific point-of-contact
   (one or a small number of individuals) and acts upon the returned
   recommendation from the designated expert. The designated expert can
   initiate and coordinate as wide a review of an assignment request as
   may be necessary to evaluate it properly.

   Designated experts are appointed by the relevant Area Director of the
   IESG. They are typically named at the time a document that creates a
   new numbering space is published as an RFC, but as experts originally
   appointed may later become unavailable, the relevant Area Director
   will appoint replacements if necessary.

   Any decisions made by the designated expert can be appealed using the
   normal IETF appeals process as outlined in Section 6.5 of [IETF-
   PROCESS]. Since the designated experts are appointed by the IESG,
   they may be removed by the IESG.








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   The following are example policies, some of which are in use today:

      Private Use - For private or 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.  "X-foo:" header
           lines in email messages.

      Hierarchical allocation - Delegated managers can assign values
           provided they have been given control over that part of the
           name space.  IANA controls the higher levels of the namespace
           according to one of the other policies.

           Examples: DNS names, Object Identifiers

      First Come First Served - Anyone can obtain an assigned number, so
           long as they provide a point of contact and a brief
           description of what the value would be used for.  For
           numbers, the exact value is generally assigned by the IANA;
           with names, specific names are usually requested.

           Examples: vnd. (vendor assigned) MIME types [MIME-REG], TCP
           and UDP port numbers.

      Expert Review - approval by a Designated Expert is required.

      Specification Required - Values and their meaning must be
           documented in an RFC or other permanent and readily available
           reference, in sufficient detail so that interoperability
           between independent implementations is possible.

           Examples: SCSP [SCSP]

      IESG Approval - New assignments must be approved by the IESG, but
           there is no requirement that the request be documented in an
           RFC (though the IESG has discretion to request documents or
           other supporting materials on a case-by-case basis).









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      IETF Consensus - New values are assigned through the IETF
           consensus process. Specifically, new assignments are made via
           RFCs approved by the IESG. Typically, the IESG will seek
           input on prospective assignments from appropriate persons
           (e.g., a relevant Working Group if one exists).

           Examples: SMTP extensions [SMTP-EXT], BGP Subsequent Address
           Family Identifiers [BGP4-EXT].

      Standards Action - Values are assigned only for Standards Track
           RFCs approved by the IESG.

           Examples: MIME top level types [MIME-REG]

   It should be noted that it often makes sense to partition a name
   space into several categories, with assignments out of each category
   handled differently. For example, the DHCP option space [DHCP] is
   split into two parts. Option numbers in the range of 1-127 are
   globally unique and assigned according to the Specification Required
   policy described above, while options number 128-254 are "site
   specific", i.e., Local Use. Dividing the name space up makes it
   possible to allow some assignments to be made with minimal review,
   while simultaneously reserving some part of the space for future use.