TitleGuidelines for Writing an IANA Considerations Section in RFCs
AuthorT. Narten, H. Alvestrand
DateOctober 1998
Format:TXT, HTML
Updated byRFC3692

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.


   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.

RFC 2434           Guidelines for IANA Considerations       October 1998

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

RFC 2434           Guidelines for IANA Considerations       October 1998

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

   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

   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

RFC 2434           Guidelines for IANA Considerations       October 1998

   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 ietf-types@iana.org 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.

RFC 2434           Guidelines for IANA Considerations       October 1998

   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

           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).

RFC 2434           Guidelines for IANA Considerations       October 1998

      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.

3.  Registration maintenance

   Registrations are a request for an assigned number, including the
   related information needed to evaluate and document the request. Even
   after a number has been assigned, some types of registrations contain
   additional information that may need to be updated over time. For
   example, mime types, character sets, language tags, etc. typically
   include more information than just the registered value itself.
   Example information can include point of contact information,
   security issues, pointers to updates, literature references, etc.  In
   such cases, the document must clearly state who is responsible for
   maintaining and updating a registration. It is appropriate to:

      - Let the author update the registration, subject to the same
        constraints and review as with new registrations.

      - Allow some mechanism to attach comments to the registration, for
        cases where others have significant objections to claims in a
        registration, but the author does not agree to change the

RFC 2434           Guidelines for IANA Considerations       October 1998

      - Designate the IESG or another authority as having the right to
        reassign ownership of a registration. This is mainly to get
        around the problem when some registration owner cannot be
        reached in order to make necessary updates.

4.  What To Put In Documents

   The previous sections 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. Specifically, documents that create an
   name space (or modify the definition of an existing space) and that
   expect the IANA to play a role in maintaining that space (e.g.,
   serving as a repository for registered values) MUST document the
   process through which future assignments are made.  Such a section
   MUST state clearly:

      - whether or not an application for an assigned number needs to be
        reviewed. If review is necessary, the review mechanism MUST be
        specified.  When a Designated Expert is used, documents MUST NOT
        name the Designated Expert in the document itself; instead, the
        name should be relayed to the appropriate IESG Area Director at
        the time the document is sent to the IESG for approval.

      - If the request should also be reviewed on a specific public
        mailing list (such as the ietf-types@iana.org for media types),
        that mailing address should be specified. Note, however, that
        use of a Designated Expert MUST also be specified.

      - if the IANA is expected to make assignments without requiring an
        outside review, sufficient guidance MUST be provided so that the
        requests can be evaluated with minimal subjectivity.

   Authors SHOULD attempt to provide guidelines that allow the IANA to
   assign new values directly without requiring review by a Designated
   Expert. This can be done easily in many cases by designating a range
   of values for direct assignment by the IANA while simultaneously
   reserving a sufficient portion of the name space for future use by
   requiring that assignments from that space be made only after a more
   stringent review.

   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:

RFC 2434           Guidelines for IANA Considerations       October 1998

        Following the policies outlined in [IANA-CONSIDERATIONS],
        numbers in the range 0-63 are allocated as First Come First
        Served, numbers between 64-240 are allocated through an IETF
        Consensus action and values in the range 241-255 are reserved
        for Private Use.

   For examples of documents that provide good and detailed guidance to
   the IANA on the issue of assigning numbers, consult [MIME-REG, MIME-

5.  Applicability to Past and Future RFCs

   For all existing RFCs that either explicitly or implicitly rely on
   the IANA to evaluate assignments without specifying a precise
   evaluation policy, the IANA will continue to decide what policy is
   appropriate. The default policy has been first come, first served.
   Changes to existing policies can always be initiated through the
   normal IETF consensus process.

   All future RFCs that either explicitly or implicitly rely on the IANA
   to register or otherwise manage assignments MUST provide guidelines
   for managing the name space.

6.  Security Considerations

   Information that creates or updates a registration needs to be

   Information concerning possible security vulnerabilities of a
   protocol may change over time. Likewise, security vulnerabilities
   related to how an assigned number is used (e.g., if it identifies a
   protocol) may change as well. As new vulnerabilities are discovered,
   information about such vulnerabilities may need to be attached to
   existing registrations, so that users are not mislead as to the true
   security issues surrounding the use of a registered number.

   An analysis of security issues is required for all parameters (data
   types, operation codes, keywords, etc.) used in IETF protocols or
   registered by the IANA. All descriptions of security issues must be
   as accurate as possible regardless of level of registration.  In
   particular, a statement that there are "no security issues associated
   with this type" must not given when it would be more accurate to
   state that "the security issues associated with this type have not
   been assessed".

RFC 2434           Guidelines for IANA Considerations       October 1998

7.  Acknowledgments

   Jon Postel and Joyce K. Reynolds provided a detailed explanation on
   what the IANA needs in order to manage assignments efficiently, and
   patiently provided comments on multiple versions of this document.
   Brian Carpenter provided helpful comments on earlier versions of the
   document. One paragraph in the Security Considerations section was
   borrowed from [MIME-REG].

8.  References

   [ASSIGNED]            Reynolds, J., and J. Postel, "Assigned
                         Numbers", STD 2, RFC 1700, October 1994.  See
                         also: http://www.iana.org/numbers.html

   [BGP4-EXT]            Bates. T., Chandra, R., Katz, D. and Y.
                         Rekhter, "Multiprotocol Extensions for BGP-4",
                         RFC 2283, February 1998.

   [DHCP-OPTIONS]        Alexander, S. and R. Droms, "DHCP Options and
                         BOOTP Vendor Extensions", RFC 2132, March 1997.

   [IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for
                         Writing an IANA Considerations Section in
                         RFCs", BCP 26, RFC 2434, October 1998.

   [IETF-PROCESS]        Bradner, S., "The Internet Standards Process --
                         Revision 3", BCP 9, RFC 2026, October 1996.

   [IP]                  Postel, J., "Internet Protocol", STD 5, RFC
                         791, September 1981.

   [IPSEC]               Atkinson, R., "Security Architecture for the
                         Internet Protocol", RFC 1825, August 1995.

   [KEYWORDS]            Bradner, S., "Key words for use in RFCs to
                         Indicate Requirement Levels", BCP 14, RFC 2119,
                         March 1997.

   [MIME-LANG]           Freed, N. and K. Moore, "MIME Parameter Value
                         and Encoded Word Extensions: Character Sets,
                         Languages, and Continuations", RFC 2184, August

   [MIME-REG]            Freed, N., Klensin, J. and J. Postel,
                         "Multipurpose Internet Mail Extension (MIME)
                         Part Four: Registration Procedures", RFC 2048,
                         November 1996.

RFC 2434           Guidelines for IANA Considerations       October 1998

   [SCSP]                Luciani, J., Armitage, G. and J. Halpern,
                         "Server Cache Synchronization Protocol (SCSP)",
                         RFC 2334, April 1998.

   [SMTP-EXT]            Klensin, J., Freed, N., Rose, M., Stefferud, E.
                         and D. Crocker, "SMTP Service Extensions", RFC
                         1869, November 1995.

9.  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
   N-7005 Trondheim

   Phone: +47 73 54 57 97
   EMail: Harald@Alvestrand.no

RFC 2434           Guidelines for IANA Considerations       October 1998

10.  Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an