Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


Network Working Group T. Narten Request for Comments: 5226 IBM BCP: 26 H. Alvestrand Obsoletes: 2434 Google Category: Best Current Practice May 2008

   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.


 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
 transform for IPsec).  To ensure that such quantities have consistent
 values and interpretations across all 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 IANA to manage a given namespace prudently, it needs
 guidelines describing the conditions under which new values can be
 assigned or when modifications to existing values can be made.  If
 IANA is expected to play a role in the management of a namespace,
 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 namespace and provides
 guidelines for authors on the specific text that must be included in
 documents that place demands on IANA.
 This document obsoletes RFC 2434.

Narten & Alvestrand Best Current Practice [Page 1] RFC 5226 IANA Considerations Section in RFCs May 2008

Table of Contents

 1. Introduction ....................................................2
 2. Why Management of a Namespace May Be Necessary ..................3
 3. Designated Experts ..............................................4
    3.1. The Motivation for Designated Experts ......................4
    3.2. The Role of the Designated Expert ..........................5
    3.3. Designated Expert Reviews ..................................7
 4. Creating a Registry .............................................8
    4.1. Well-Known IANA Policy Definitions .........................9
    4.2. What to Put in Documents That Create a Registry ...........12
    4.3. Updating IANA Guidelines for Existing Registries ..........15
 5. Registering New Values in an Existing Registry .................15
    5.1. What to Put in Documents When Registering Values ..........15
    5.2. Updating Registrations ....................................17
    5.3. Overriding Registration Procedures ........................17
 6. Miscellaneous Issues ...........................................18
    6.1. When There Are No IANA Actions ............................18
    6.2. Namespaces Lacking Documented Guidance ....................19
    6.3. After-the-Fact Registrations ..............................19
    6.4. Reclaiming Assigned Values ................................19
 7. Appeals ........................................................20
 8. Mailing Lists ..................................................20
 9. Security Considerations ........................................20
 10. Changes Relative to RFC 2434 ..................................21
 11. Acknowledgments ...............................................22
 12. References ....................................................22
    12.1. Normative References .....................................22
    12.2. Informative References ...................................22

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 media types [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-OPTIONS] or a new encryption or
 authentication transform for IPsec [IPSEC]).  To ensure 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) [IANA-MOU].
 In this document, we call the set of possible values for such a field
 a "namespace"; its actual value may be a text string, a number, or
 another kind of value.  The binding or association of a specific
 value with a particular purpose within a namespace is called an
 assigned number (or assigned value, or sometimes a "code point",

Narten & Alvestrand Best Current Practice [Page 2] RFC 5226 IANA Considerations Section in RFCs May 2008

 "protocol constant", or "protocol parameter").  Each assignment of a
 value in a namespace is called a registration.
 In order for IANA to manage a given namespace prudently, it needs
 guidelines describing the conditions under which new values should be
 assigned or when (and how) modifications to existing values can be
 made.  This document provides guidelines to authors on what sort of
 text should be added to their documents in order to provide IANA
 clear guidelines, and it reviews issues that should be considered in
 formulating an appropriate policy for assigning numbers to name
 Not all namespaces require centralized administration.  In some
 cases, it is possible to delegate a namespace in such a way that
 further assignments can be made independently and with no further
 (central) coordination.  In the Domain Name System, for example, 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]; IANA manages the subtree
 rooted at "" ( .  When a namespace is
 delegated, the scope of IANA is limited to the parts of the namespace
 where IANA has authority.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 document are to be interpreted as described in RFC 2119 [KEYWORDS].
 For this document, "the specification" as used by RFC 2119 refers to
 the processing of protocol documents within the IETF standards

2. Why Management of a Namespace May Be Necessary

 One issue to consider in managing a namespace is its size.  If the
 space is small and limited in size, assignments must be made
 carefully to prevent exhaustion of the space.  If the space is
 essentially unlimited, on the other hand, potential exhaustion will
 probably not be a practical concern at all.  Even when the space is
 essentially unlimited, however, it is usually desirable to have at
 least a minimal review prior to assignment in order to:
  1. prevent the hoarding of or unnecessary wasting of values. For

example, if the space consists of text strings, it may be

      desirable to prevent entities from obtaining large sets of
      strings that correspond to desirable names (e.g., existing
      company names).

Narten & Alvestrand Best Current Practice [Page 3] RFC 5226 IANA Considerations Section in RFCs May 2008

  1. provide a sanity check that the request actually makes sense and

is necessary. Experience has shown that some level of minimal

      review from a subject matter expert is useful to prevent
      assignments in cases where the request is malformed or not
      actually needed (i.e., an existing assignment for an essentially
      equivalent service already exists).
 A second consideration is whether it makes sense to delegate the
 namespace in some manner.  This route should be pursued when
 appropriate, as it lessens the burden on IANA for dealing with
 A third, and perhaps most important, consideration concerns potential
 impact on the interoperability of unreviewed extensions.  Proposed
 protocol extensions generally benefit from community review; indeed,
 review is often essential to avoid future interoperability problems
 When the namespace is essentially unlimited and there are no
 potential interoperability issues, assigned numbers can safely be
 given out to anyone without any subjective review.  In such cases,
 IANA can make assignments directly, provided that IANA is given
 specific instructions on what types of requests it should grant, and
 what information must be provided as part of a well-formed request
 for an assigned number.

3. Designated Experts

3.1. The Motivation for Designated Experts

 It should be noted that IANA does not create or define assignment
 policy itself; rather, it carries out policies that have been defined
 by others and published in RFCs.  IANA must be given a set of
 guidelines that allow it to make allocation decisions with minimal
 subjectivity and without requiring any technical expertise with
 respect to the protocols that make use of a registry.
 In many cases, some review of prospective allocations is appropriate,
 and the question becomes who should perform the review and what is
 the purpose of the review.  One might think that an IETF working
 group (WG) familiar with the namespace at hand should be consulted.
 In practice, however, WGs eventually disband, so they cannot be
 considered a permanent evaluator.  It is also possible for namespaces
 to be created through individual submission documents, for which no
 WG is ever formed.

Narten & Alvestrand Best Current Practice [Page 4] RFC 5226 IANA Considerations Section in RFCs May 2008

 One way to ensure community review of prospective assignments is to
 have the requester submit a document for publication as an RFC.  Such
 an action helps ensure that the specification is publicly and
 permanently available, and it allows some review of the specification
 prior to publication and assignment of the requested code points.
 This is the preferred way of ensuring review, and is particularly
 important if any potential interoperability issues can arise.  For
 example, some 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
 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 gives advice to persons wanting help in understanding what a
 proper registration should contain.
 While discussion on a mailing list can provide valuable technical
 feedback, opinions may vary and discussions may continue for some
 time without clear resolution.  In addition, IANA cannot participate
 in all of these mailing lists and cannot determine if or when such
 discussions reach consensus.  Therefore, IANA relies on a "designated
 expert" for advice regarding the specific question of whether an
 assignment should be made.  The designated expert is an individual
 who is responsible for carrying out an appropriate evaluation and
 returning a recommendation to IANA.
 It should be noted that a key motivation for having designated
 experts is for the IETF to provide IANA with a subject matter expert
 to whom the evaluation process can be delegated.  IANA forwards
 requests for an assignment to the expert for evaluation, and the
 expert (after performing the evaluation) informs IANA as to whether
 or not to make the assignment or registration.

3.2. The Role of the Designated Expert

 The designated expert is responsible for initiating and coordinating
 the appropriate review of an assignment request.  The review may be
 wide or narrow, depending on the situation and the judgment of the
 designated expert.  This may involve consultation with a set of
 technology experts, discussion on a public mailing list, consultation
 with a working group (or its mailing list if the working group has

Narten & Alvestrand Best Current Practice [Page 5] RFC 5226 IANA Considerations Section in RFCs May 2008

 disbanded), etc.  Ideally, the designated expert follows specific
 review criteria as documented with the protocol that creates or uses
 the namespace.  (See the IANA Considerations sections of [RFC3748]
 and [RFC3575] for examples that have been done for specific
 Designated experts are expected to be able to defend their decisions
 to the IETF community, and the evaluation process is not intended to
 be secretive or bestow unquestioned power on the expert.  Experts are
 expected to apply applicable documented review or vetting procedures,
 or in the absence of documented criteria, follow generally accepted
 norms, e.g., those in Section 3.3.
 Section 5.2 discusses disputes and appeals in more detail.
 Designated experts are appointed by the IESG (normally upon
 recommendation by the relevant Area Director).  They are typically
 named at the time a document creating or updating a namespace is
 approved by the IESG, but as experts originally appointed may later
 become unavailable, the IESG will appoint replacements if necessary.
 For some registries, it has proven useful to have multiple designated
 experts.  Sometimes those experts work together in evaluating a
 request, while in other cases additional experts serve as backups.
 In cases of disagreement among those experts, it is the
 responsibility of those experts to make a single clear recommendation
 to IANA.  It is not appropriate for IANA to resolve disputes among
 experts.  In extreme situations (e.g., deadlock), the IESG may need
 to step in to resolve the problem.
 In registries where a pool of experts evaluates requests, the pool
 should have a single chair responsible for defining how requests are
 to be assigned to and reviewed by experts.  In some cases, the expert
 pool may consist of a primary and backups, with the backups involved
 only when the primary expert is unavailable.  In other cases, IANA
 might assign requests to individual members in sequential or
 approximate random order.  In the event that IANA finds itself having
 received conflicting advice from its experts, it is the
 responsibility of the pool's chair to resolve the issue and provide
 IANA with clear instructions.
 Since the designated experts are appointed by the IESG, they may be
 removed by the IESG.

Narten & Alvestrand Best Current Practice [Page 6] RFC 5226 IANA Considerations Section in RFCs May 2008

3.3. Designated Expert Reviews

 In the eight years since RFC 2434 was published and has been put to
 use, experience has led to the following observations:
  1. A designated expert must respond in a timely fashion, normally

within a week for simple requests to a few weeks for more

      complex ones.  Unreasonable delays can cause significant
      problems for those needing assignments, such as when products
      need code points to ship.  This is not to say that all reviews
      can be completed under a firm deadline, but they must be
      started, and the requester and IANA should have some
      transparency into the process if an answer cannot be given
  1. If a designated expert does not respond to IANA's requests

within a reasonable period of time, either with a response or

      with a reasonable explanation for the delay (e.g., some requests
      may be particularly complex), and if this is a recurring event,
      IANA must raise the issue with the IESG.  Because of the
      problems caused by delayed evaluations and assignments, the IESG
      should take appropriate actions to ensure that the expert
      understands and accepts his or her responsibilities, or appoint
      a new expert.
  1. The designated expert is not required to personally bear the

burden of evaluating and deciding all requests, but acts as a

      shepherd for the request, enlisting the help of others as
      appropriate.  In the case that a request is denied, and
      rejecting the request is likely to be controversial, the expert
      should have the support of other subject matter experts.  That
      is, the expert must be able to defend a decision to the
      community as a whole.
 In the case where a designated expert is used, but there are no
 specific documented criteria for performing an evaluation, the
 presumption should be that a code point should be granted, unless
 there is a compelling reason to the contrary.  Possible reasons to
 deny a request include:
  1. scarcity of code points, where the finite remaining code points

should be prudently managed, or when a request for a large

      number of code points is made, when a single code point is the
  1. documentation is not of sufficient clarity to evaluate or ensure


Narten & Alvestrand Best Current Practice [Page 7] RFC 5226 IANA Considerations Section in RFCs May 2008

  1. the code point is needed for a protocol extension, but the

extension is not consistent with the documented (or generally

      understood) architecture of the base protocol being extended,
      and would be harmful to the protocol if widely deployed.  It is
      not the intent that "inconsistencies" refer to minor differences
      "of a personal preference nature".  Instead, they refer to
      significant differences such as inconsistencies with the
      underlying security model, implying a change to the semantics of
      an existing message type or operation, requiring unwarranted
      changes in deployed systems (compared with alternate ways of
      achieving a similar result), etc.
  1. the extension would cause problems with existing deployed


  1. the extension would conflict with one under active development

by the IETF, and having both would harm rather than foster


4. Creating a Registry

 Creating a registry involves describing the namespaces to be created,
 an initial set of assignments (if appropriate), and guidelines on how
 future assignments are to be made.
 Once a registry has been created, IANA records assignments that have
 been made.  The following labels describe the status of an individual
 (or range) of assignments:
    Private Use: Private use only (not assigned), as described in
          Section 4.1.
    Experimental: Available for experimental use as described in
          [EXPERIMENTATION].  IANA does not record specific
          assignments for any particular use.
    Unassigned: Unused and available for assignment via documented
    Reserved:  Not to be assigned.  Reserved values are held for
          special uses, such as to extend the namespace when it become
          exhausted.  Reserved values are not available for general

Narten & Alvestrand Best Current Practice [Page 8] RFC 5226 IANA Considerations Section in RFCs May 2008

4.1. Well-Known IANA Policy Definitions

 The following are some defined policies, some of which are in use
 today.  These cover a range of typical policies that have been used
 to date to describe the procedure for assigning new values in a
 namespace.  It is not required that documents use these terms; the
 actual requirement is that the instructions to IANA are clear and
 unambiguous.  However, use of these terms is RECOMMENDED where
 possible, since their meaning is widely understood.
    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 (since IANA does not record
          them) and assignments are not generally useful for broad
          interoperability.  It is the responsibility of the sites
          making use of the Private Use range to ensure that no
          conflicts occur (within the intended scope of use).
          Examples: Site-specific options in DHCP [DHCP-IANA], Fibre
          Channel Port Type Registry [RFC4044], Exchange Types in the
          IKEv2 header [RFC4306].
    Experimental Use - Similar to private or local use only, with the
          purpose being to facilitate experimentation.  See
          [EXPERIMENTATION] for details.
          Example: Experimental Values in IPv4, IPv6, ICMPv4, ICMPv6,
          UDP, and TCP Headers [RFC4727].
    Hierarchical Allocation - Delegated managers can assign values
          provided they have been given control over that part of the
          namespace.  IANA controls the higher levels of the namespace
          according to one of the other policies.
          Examples: DNS names, Object Identifiers, IP addresses.
    First Come First Served - Assignments are made to anyone on a
          first come, first served basis.  There is no substantive
          review of the request, other than to ensure that it is
          well-formed and doesn't duplicate an existing assignment.
          However, requests must include a minimal amount of clerical
          information, such as a point of contact (including an email
          address) and a brief description of how the value will be
          used.  Additional information specific to the type of value
          requested may also need to be provided, as defined by the
          namespace.  For numbers, the exact value is generally

Narten & Alvestrand Best Current Practice [Page 9] RFC 5226 IANA Considerations Section in RFCs May 2008

          assigned by IANA; with names, specific text strings can
          usually be requested.
          Examples: SASL mechanism names [RFC4422], LDAP Protocol
          Mechanisms, and LDAP Syntax [RFC4520].
    Expert Review (or Designated Expert) - approval by a Designated
          Expert is required.  The required documentation and review
          criteria for use by the Designated Expert should be provided
          when defining the registry.  For example, see Sections 6 and
          7.2 in [RFC3748].
          Examples: EAP Method Types [RFC3748], HTTP Digest AKA
          algorithm versions [RFC4169], URI schemes [RFC4395], GEOPRIV
          Location Types [RFC4589].
    Specification Required - Values and their meanings must be
          documented in a permanent and readily available public
          specification, in sufficient detail so that interoperability
          between independent implementations is possible.  When used,
          Specification Required also implies use of a Designated
          Expert, who will review the public specification and
          evaluate whether it is sufficiently clear to allow
          interoperable implementations.  The intention behind
          "permanent and readily available" is that a document can
          reasonably be expected to be findable and retrievable long
          after IANA assignment of the requested value.  Publication
          of an RFC is an ideal means of achieving this requirement,
          but Specification Required is intended to also cover the
          case of a document published outside of the RFC path.  For
          RFC publication, the normal RFC review process is expected
          to provide the necessary review for interoperability, though
          the Designated Expert may be a particularly well-qualified
          person to perform such a review.
          Examples: Diffserv-aware TE Bandwidth Constraints Model
          Identifiers [RFC4124], TLS ClientCertificateType Identifiers
          [RFC4346], ROHC Profile Identifiers [RFC4995].
    RFC Required - RFC publication (either as an IETF submission or as
          an RFC Editor Independent submission [RFC3932]) suffices.
          Unless otherwise specified, any type of RFC is sufficient
          (e.g., Informational, Experimental, Standards Track, etc.).

Narten & Alvestrand Best Current Practice [Page 10] RFC 5226 IANA Considerations Section in RFCs May 2008

    IETF Review - (Formerly called "IETF Consensus" in
          [IANA-CONSIDERATIONS]) New values are assigned only through
          RFCs that have been shepherded through the IESG as AD-
          Sponsored or IETF WG Documents [RFC3932] [RFC3978].  The
          intention is that the document and proposed assignment will
          be reviewed by the IESG and appropriate IETF WGs (or
          experts, if suitable working groups no longer exist) to
          ensure that the proposed assignment will not negatively
          impact interoperability or otherwise extend IETF protocols
          in an inappropriate or damaging manner.
          To ensure adequate community review, such documents are
          shepherded through the IESG as AD-sponsored (or WG)
          documents with an IETF Last Call.
          Examples: IPSECKEY Algorithm Types [RFC4025],
          Accounting-Auth-Method AVP values in DIAMETER [RFC4005], TLS
          Handshake Hello Extensions [RFC4366].
    Standards Action - Values are assigned only for Standards Track
          RFCs approved by the IESG.
          Examples: BGP message types [RFC4271], Mobile Node
          Identifier option types [RFC4283], DCCP Packet Types
    IESG Approval - New assignments may be approved by the IESG.
          Although there is no requirement that the request be
          documented in an RFC, the IESG has discretion to request
          documents or other supporting materials on a case-by-case
          IESG Approval is not intended to be used often or as a
          "common case"; indeed, it has seldom been used in practice
          during the period RFC 2434 was in effect.  Rather, it is
          intended to be available in conjunction with other policies
          as a fall-back mechanism in the case where one of the other
          allowable approval mechanisms cannot be employed in a timely
          fashion or for some other compelling reason.  IESG Approval
          is not intended to circumvent the public review processes
          implied by other policies that could have been employed for
          a particular assignment.  IESG Approval would be
          appropriate, however, in cases where expediency is desired
          and there is strong consensus for making the assignment
          (e.g., WG consensus).

Narten & Alvestrand Best Current Practice [Page 11] RFC 5226 IANA Considerations Section in RFCs May 2008

          The following guidelines are suggested for any evaluation
          under IESG Approval:
  1. The IESG can (and should) reject a request if another path

for registration is available that is more appropriate and

            there is no compelling reason to use that path.
  1. Before approving a request, the community should be

consulted, via a "call for comments" that provides as much

            information as is reasonably possible about the request.
          Examples: IPv4 Multicast address assignments [RFC3171], IPv4
          IGMP Type and Code values [RFC3228], Mobile IPv6 Mobility
          Header Type and Option values [RFC3775].
 It should be noted that it often makes sense to partition a namespace
 into multiple categories, with assignments within each category
 handled differently.  For example, many protocols now partition
 namespaces into two (or even more) parts, where one range is reserved
 for Private or Experimental Use, while other ranges are reserved for
 globally unique assignments assigned following some review process.
 Dividing a namespace into ranges makes it possible to have different
 policies in place for different ranges.
 Examples:  LDAP [RFC4520], Pseudowire Edge to Edge Emulation (PWE3)

4.2. What to Put in Documents That Create a Registry

 The previous sections presented some issues that should be considered
 in formulating a policy for assigning values in namespaces.  It is
 the working group and/or document author's job to formulate an
 appropriate policy and specify it in the appropriate document.  In
 almost all cases, having an explicit "IANA Considerations" section is
 appropriate.  The following and later sections define what is needed
 for the different types of IANA actions.
 Documents that create a new namespace (or modify the definition of an
 existing space) and that expect IANA to play a role in maintaining
 that space (e.g., serving as a repository for registered values) MUST
 provide clear instructions on details of the namespace.  In
 particular, instructions MUST include:
    1) The name of the registry (or sub-registry) being created and/or
       maintained.  The name will appear on the IANA web page and will
       be referred to in future documents that need to allocate a
       value from the new space.  The full name (and abbreviation, if
       appropriate) should be provided.  It is highly desirable that

Narten & Alvestrand Best Current Practice [Page 12] RFC 5226 IANA Considerations Section in RFCs May 2008

       the chosen name not be easily confusable with the name of
       another registry.  When creating a sub-registry, the registry
       that it is a part of should be clearly identified.  When
       referring to an already existing registry, providing a URL to
       precisely identify the registry is helpful.  All such URLs,
       however, will be removed from the RFC prior to final
       publication.  For example, documents could contain: [TO BE
       REMOVED: This registration should take place at the following
    2) What information must be provided as part of a request in order
       to assign a new value.  This information may include the need
       to document relevant security considerations, if any.
    3) The review process that will apply to all future requests for a
       value from the namespace.
       Note: 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 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 for media types),
       that mailing address should be specified.  Note, however, that
       when mailing lists are specified, the requirement for a
       Designated Expert MUST also be specified (see Section 3).
       If 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.
    4) The size, format, and syntax of registry entries.  When
       creating a new name/number space, authors must describe any
       technical requirements on registry (and sub-registry) values
       (e.g., valid ranges for integers, length limitations on
       strings, etc.) as well as the exact format in which registry
       values should be displayed.  For number assignments, one should
       specify whether values are to be recorded in decimal,
       hexadecimal, or some other format.  For strings, the encoding
       format should be specified (e.g., ASCII, UTF8, etc.).  Authors
       should also clearly specify what fields to record in the
    5) Initial assignments and reservations.  Clear instructions
       should be provided to identify any initial assignments or
       registrations.  In addition, any ranges that are to be reserved

Narten & Alvestrand Best Current Practice [Page 13] RFC 5226 IANA Considerations Section in RFCs May 2008

       for "Private Use", "Reserved", "Unassigned", etc. should be
       clearly indicated.
 When specifying the process for making future assignments, it is
 quite acceptable to pick one (or more) of the example policies listed
 in Section 4.1 and refer to it by name.  Indeed, this is the
 preferred mechanism in those cases where the sample policies provide
 the desired level of review.  It is also acceptable to cite one of
 the above policies and include additional guidelines for what kind of
 considerations should be taken into account by the review process.
 For example, RADIUS [RFC3575] specifies the use of a Designated
 Expert, but includes specific additional criteria the Designated
 Expert should follow.
 For example, a document could say something like:
    This document defines a new DHCP option, entitled "FooBar" (see
    Section y), assigned a value of TBD1 from the DHCP Option space
    [to be removed upon publication:]
          Tag     Name            Length      Meaning
          ----    ----            ------      -------
          TBD1    FooBar          N           FooBar server
    The FooBar option also defines an 8-bit FooType field, for which
    IANA is to create and maintain a new sub-registry entitled
    "FooType values" under the FooBar option.  Initial values for the
    DHCP FooBar FooType registry are given below; future assignments
    are to be made through Expert Review [IANA-CONSIDERATIONS].
    Assignments consist of a DHCP FooBar FooType name and its
    associated value.
          Value    DHCP FooBar FooType Name        Definition
          ----     ------------------------        ----------
          0        Reserved
          1        Frobnitz                        See Section y.1
          2        NitzFrob                        See Section y.2
          3-254    Unassigned
          255      Reserved
    For examples of documents that provide detailed guidance to IANA
    on the issue of assigning numbers, consult [RFC2929], [RFC3575],
    [RFC3968], and [RFC4520].

Narten & Alvestrand Best Current Practice [Page 14] RFC 5226 IANA Considerations Section in RFCs May 2008

4.3. Updating IANA Guidelines for Existing Registries

 Updating the registration process for an already existing (i.e.,
 previously created) namespace (whether created explicitly or
 implicitly) follows a process similar to that used when creating a
 new namespace.  That is, a document is produced that makes reference
 to the existing namespace and then provides detailed guidelines for
 handling assignments in each individual namespace.  Such documents
 are normally processed as Best Current Practices (BCPs)
 Example documents that updated the guidelines for managing (then)
 pre-existing registries include: [RFC2929], [RFC3228], and [RFC3575].

5. Registering New Values in an Existing Registry

5.1. What to Put in Documents When Registering Values

 Often, documents request an assignment from an already existing
 namespace (i.e., one created by a previously published RFC).  In such
  1. Documents should clearly identify the namespace in which each

value is to be registered. If the registration goes into a

      sub-registry, the author should clearly describe where the
      assignment or registration should go.  It is helpful to use the
      exact namespace name as listed on the IANA web page (and
      defining RFC), and cite the RFC where the namespace is defined.
      Note 1: There is no need to mention what the assignment policy
      for new assignments is, as that should be clear from the
      Note 2: When referring to an existing registry, providing a URL
      to precisely identify the registry is helpful.  Such URLs,
      however, should usually be removed from the RFC prior to final
      publication, since IANA URLs are not guaranteed to be stable in
      the future.  In cases where it is important to include a URL in
      the document, IANA should concur on its inclusion.
      As an example, documents could contain: [TO BE REMOVED: This
      registration should take place at the following location:]
  1. Each value requested should be given a unique reference. When

the value is numeric, use the notation: TBD1, TBD2, etc.

      Throughout the document where an actual IANA-assigned value
      should be filled in, use the "TBDx" notation.  This helps ensure

Narten & Alvestrand Best Current Practice [Page 15] RFC 5226 IANA Considerations Section in RFCs May 2008

      that the final RFC has the correct assigned values inserted in
      all of the relevant places where the value is expected to appear
      in the final document.  For values that are text strings, a
      specific name can be suggested.  IANA will normally assign the
      name, unless it conflicts with a name already in use.
  1. Normally, the values to be used are chosen by IANA and documents

should specify values of "TBD". However, in some cases, a value

      may have been used for testing or in early implementations.  In
      such cases, it is acceptable to include text suggesting what
      specific value should be used (together with the reason for the
      choice).  For example, one might include the text "the value XXX
      is suggested as it is used in implementations".  However, it
      should be noted that suggested values are just that; IANA will
      attempt to assign them, but may find that impossible, if the
      proposed number has already been assigned for some other use.
      For some registries, IANA has a long-standing policy prohibiting
      assignment of names or codes on a vanity or organization name
      basis, e.g., codes are always assigned sequentially unless there
      is a strong reason for making an exception.  Nothing in this
      document is intended to change those policies or prevent their
      future application.
  1. The IANA Considerations section should summarize all of the IANA

actions, with pointers to the relevant sections elsewhere in the

      document as appropriate.  When multiple values are requested, it
      is generally helpful to include a summary table.  It is also
      helpful for this table to be in the same format as it should
      appear on the IANA web site.  For example:
          Value     Description          Reference
          --------  -------------------  ---------
          TBD1      Foobar               [RFCXXXX]
    Note: In cases where authors feel that including the full table is
    too verbose or repetitive, authors should still include the table,
    but may include a note asking that the table be removed prior to
    publication of the final RFC.
 As an example, the following text could be used to request assignment
 of a DHCPv6 option number:
    IANA has assigned an option code value of TBD1 to the DNS
    Recursive Name Server option and an option code value of TBD2 to
    the Domain Search List option from the DHCP option code space
    defined in Section 24.3 of RFC 3315.

Narten & Alvestrand Best Current Practice [Page 16] RFC 5226 IANA Considerations Section in RFCs May 2008

5.2. Updating Registrations

 Registrations are a request to assign a new value, 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 media types, character sets, and 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 defining the namespace
 must clearly state who is responsible for maintaining and updating a
 registration.  In different cases, it may be appropriate to specify
 one or more of the following:
  1. Let the author update the registration, subject to the same

constraints and review as with new registrations.

  1. 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
  1. Designate the IESG, a Designated Expert, or another entity as

having the right to change the registrant associated with a

      registration and any requirements or conditions on doing so.
      This is mainly to get around the problem when a registrant
      cannot be reached in order to make necessary updates.

5.3. Overriding Registration Procedures

 Since RFC 2434 was published, experience has shown that the
 documented IANA considerations for individual protocols do not always
 adequately cover the reality after the protocol is deployed.  For
 example, many older routing protocols do not have documented,
 detailed IANA considerations.  In addition, documented IANA
 considerations are sometimes found to be too stringent to allow even
 working group documents (for which there is strong consensus) to
 obtain code points from IANA in advance of actual RFC publication.
 In other cases, the documented procedures are unclear or neglected to
 cover all the cases.  In order to allow assignments in individual
 cases where there is strong IETF consensus that an allocation should
 go forward, but the documented procedures do not support such an
 assignment, the IESG is granted authority to approve assignments in
 such cases.  The intention is not to overrule properly documented
 procedures, or to obviate the need for protocols to properly document
 their IANA considerations.  Instead, the intention is to permit
 assignments in individual cases where it is obvious that the

Narten & Alvestrand Best Current Practice [Page 17] RFC 5226 IANA Considerations Section in RFCs May 2008

 assignment should just be made, but updating the IANA process just to
 assign a particular code point is viewed as too heavy a burden.
 In general, the IETF would like to see deficient IANA registration
 procedures for a namespace revised through the IETF standards
 process, but not at the cost of unreasonable delay for needed
 assignments.  If the IESG has had to take the action in this section,
 it is a strong indicator that the IANA registration procedures should
 be updated, possibly in parallel with ongoing protocol work.

6. Miscellaneous Issues

6.1. When There Are No IANA Actions

 Before an Internet-Draft can be published as an RFC, IANA needs to
 know what actions (if any) it needs to perform.  Experience has shown
 that it is not always immediately obvious whether a document has no
 IANA actions, without reviewing the document in some detail.  In
 order to make it clear to IANA that it has no actions to perform (and
 that the author has consciously made such a determination), such
 documents should include an IANA Considerations section that states:
    This document has no IANA actions.
 This statement, or an equivalent, must only be inserted after the WG
 or individual submitter has carefully verified it to be true.  Using
 such wording as a matter of "boilerplate" or without careful
 consideration can lead to incomplete or incorrect IANA actions being
 If a specification makes use of values from a namespace that is not
 managed by IANA, it may be useful to note this fact, e.g., with
 wording such as:
    The values of the Foobar parameter are assigned by the Barfoo
    registry on behalf of the Rabfoo Forum.  Therefore, this document
    has no IANA actions.
 In some cases, the absence of IANA-assigned values may be considered
 valuable information for future readers; in other cases, it may be
 considered of no value once the document has been approved, and may
 be removed before archival publication.  This choice should be made
 clear in the draft, for example, by including a sentence such as
    [RFC Editor: please remove this section prior to publication.]

Narten & Alvestrand Best Current Practice [Page 18] RFC 5226 IANA Considerations Section in RFCs May 2008

    [RFC Editor: please do not remove this section.]

6.2. Namespaces Lacking Documented Guidance

 For all existing RFCs that either explicitly or implicitly rely on
 IANA to evaluate assignments without specifying a precise evaluation
 policy, IANA (in consultation with the IESG) will continue to decide
 what policy is appropriate.  Changes to existing policies can always
 be initiated through the normal IETF consensus process.
 All future RFCs that either explicitly or implicitly rely on IANA to
 register or otherwise manage namespace assignments MUST provide
 guidelines for managing the namespace.

6.3. After-the-Fact Registrations

 Occasionally, IANA becomes aware that an unassigned value from a
 managed namespace is in use on the Internet or that an assigned value
 is being used for a different purpose than originally registered.
 IANA will not condone such misuse; i.e., procedures of the type
 described in this document MUST be applied to such cases.  In the
 absence of specifications to the contrary, values may only be
 reassigned for a different purpose with the consent of the original
 assignee (when possible) and with due consideration of the impact of
 such a reassignment.  In cases of likely controversy, consultation
 with the IESG is advised.

6.4. Reclaiming Assigned Values

 Reclaiming previously assigned values for reuse is tricky, because
 doing so can lead to interoperability problems with deployed systems
 still using the assigned values.  Moreover, it can be extremely
 difficult to determine the extent of deployment of systems making use
 of a particular value.  However, in cases where the namespace is
 running out of unassigned values and additional ones are needed, it
 may be desirable to attempt to reclaim unused values.  When
 reclaiming unused values, the following (at a minimum) should be
  1. Attempts should be made to contact the original party to which a

value is assigned, to determine if the value was ever used, and

      if so, the extent of deployment.  (In some cases, products were
      never shipped or have long ceased being used.  In other cases,
      it may be known that a value was never actually used at all.)

Narten & Alvestrand Best Current Practice [Page 19] RFC 5226 IANA Considerations Section in RFCs May 2008

  1. Reassignments should not normally be made without the

concurrence of the original requester. Reclamation under such

      conditions should only take place where there is strong evidence
      that a value is not widely used, and the need to reclaim the
      value outweighs the cost of a hostile reclamation.  In any case,
      IESG Approval is needed in this case.
  1. It may be appropriate to write up the proposed action and

solicit comments from relevant user communities. In some cases,

      it may be appropriate to write an RFC that goes through a formal
      IETF process (including IETF Last Call) as was done when DHCP
      reclaimed some of its "Private Use" options [RFC3942].

7. Appeals

 Appeals of registration decisions made by IANA can be made using the
 normal IETF appeals process as described in Section 6.5 of
 [IETF-PROCESS].  Specifically, appeals should be directed to the
 IESG, followed (if necessary) by an appeal to the IAB, etc.

8. Mailing Lists

 All IETF mailing lists associated with evaluating or discussing
 assignment requests as described in this document are subject to
 whatever rules of conduct and methods of list management are
 currently defined by Best Current Practices or by IESG decision.

9. Security Considerations

 Information that creates or updates a registration needs to be
 authenticated and authorized.  IANA updates registries according to
 instructions in published RFCs and from the IESG.  It also may accept
 clarifications from document authors, relevant WG chairs, Designated
 Experts, and mail list participants, too.
 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 misled as to the true
 security issues surrounding the use of a registered number.
 An analysis of security issues is generally required for all
 protocols that make use of parameters (data types, operation codes,
 keywords, etc.) used in IETF protocols or registered by IANA.  Such
 security considerations are usually included in the protocol document
 [RFC3552].  It is the responsibility of the IANA considerations

Narten & Alvestrand Best Current Practice [Page 20] RFC 5226 IANA Considerations Section in RFCs May 2008

 associated with a particular registry to specify what (if any)
 security considerations must be provided when assigning new values,
 and the process for reviewing such claims.

10. Changes Relative to RFC 2434

 Changes include:
  1. Major reordering of text to expand descriptions and to better

group topics such as "updating registries" vs. "creating new

      registries", in order to make it easier for authors to find the
      text most applicable to their needs.
  1. Numerous editorial changes to improve readability.
  1. Changed the term "IETF Consensus" to "IETF Review" and added

more clarifications. History has shown that people see the

      words "IETF Consensus" (without consulting the actual
      definition) and are quick to make incorrect assumptions about
      what the term means in the context of IANA Considerations.
  1. Added "RFC Required" to list of defined policies.
  1. Much more explicit directions and examples of "what to put in


  1. "Specification Required" now implies use of a Designated Expert

to evaluate specs for sufficient clarity.

  1. Significantly changed the wording in Section 3. Main purpose is

to make clear that Expert Reviewers are accountable to the

      community, and to provide some guidance for review criteria in
      the default case.
  1. Changed wording to remove any special appeals path. The normal

RFC 2026 appeals path is used.

  1. Added a section about reclaiming unused value.
  1. Added a section on after-the-fact registrations.
  1. Added a section indicating that mailing lists used to evaluate

possible assignments (e.g., by a Designated Expert) are subject

      to normal IETF rules.

Narten & Alvestrand Best Current Practice [Page 21] RFC 5226 IANA Considerations Section in RFCs May 2008

11. Acknowledgments

 This document has benefited from specific feedback from Jari Arkko,
 Marcelo Bagnulo Braun, Brian Carpenter, Michelle Cotton, Spencer
 Dawkins, Barbara Denny, Miguel Garcia, Paul Hoffman, Russ Housley,
 John Klensin, Allison Mankin, Blake Ramsdell, Mark Townsley, Magnus
 Westerlund, and Bert Wijnen.
 The original acknowledgments section in RFC 2434 was:
 Jon Postel and Joyce Reynolds provided a detailed explanation on what
 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].

12. References

12.1. Normative References

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

12.2. Informative References

 [ASSIGNED]            Reynolds, J., Ed., "Assigned Numbers: RFC 1700
                       is Replaced by an On-line Database", RFC 3232,
                       January 2002.
 [DHCP-OPTIONS]        Alexander, S. and R. Droms, "DHCP Options and
                       BOOTP Vendor Extensions", RFC 2132, March 1997.
 [DHCP-IANA]           Droms, R., "Procedures and IANA Guidelines for
                       Definition of New DHCP Options and Message
                       Types", BCP 43, RFC 2939, September 2000.
 [EXPERIMENTATION]     Narten, T., "Assigning Experimental and Testing
                       Numbers Considered Useful", BCP 82, RFC 3692,
                       January 2004.
 [IANA-CONSIDERATIONS] Narten, T. and H. Alvestrand, "Guidelines for
                       Writing an IANA Considerations Section in
                       RFCs", BCP 26, RFC 2434, October 1998.

Narten & Alvestrand Best Current Practice [Page 22] RFC 5226 IANA Considerations Section in RFCs May 2008

 [IANA-MOU]            Carpenter, B., Baker, F., and M. Roberts,
                       "Memorandum of Understanding Concerning the
                       Technical Work of the Internet Assigned Numbers
                       Authority", RFC 2860, June 2000.
 [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]               Kent, S. and K. Seo, "Security Architecture for
                       the Internet Protocol", RFC 4301, December
 [MIME-REG]            Freed, N. and J. Klensin, "Media Type
                       Specifications and Registration Procedures",
                       BCP 13, RFC 4288, December 2005.
 [PROTOCOL-EXT]        Carpenter, B. and B. Aboba, "Design
                       Considerations for Protocol Extensions", Work
                       in Progress, December 2007.
 [RFC2929]             Eastlake 3rd, D., Brunner-Williams, E., and B.
                       Manning, "Domain Name System (DNS) IANA
                       Considerations", BCP 42, RFC 2929, September
 [RFC3171]             Albanna, Z., Almeroth, K., Meyer, D., and M.
                       Schipper, "IANA Guidelines for IPv4 Multicast
                       Address Assignments", BCP 51, RFC 3171, August
 [RFC3228]             Fenner, B., "IANA Considerations for IPv4
                       Internet Group Management Protocol (IGMP)", BCP
                       57, RFC 3228, February 2002.
 [RFC3552]             Rescorla, E. and B. Korver, "Guidelines for
                       Writing RFC Text on Security Considerations",
                       BCP 72, RFC 3552, July 2003.
 [RFC3575]             Aboba, B., "IANA Considerations for RADIUS
                       (Remote Authentication Dial In User Service)",
                       RFC 3575, July 2003.

Narten & Alvestrand Best Current Practice [Page 23] RFC 5226 IANA Considerations Section in RFCs May 2008

 [RFC3748]             Aboba, B., Blunk, L., Vollbrecht, J., Carlson,
                       J., and H. Levkowetz, Ed., "Extensible
                       Authentication Protocol (EAP)", RFC 3748, June
 [RFC3775]             Johnson, D., Perkins, C., and J. Arkko,
                       "Mobility Support in IPv6", RFC 3775, June
 [RFC3932]             Alvestrand, H., "The IESG and RFC Editor
                       Documents: Procedures", BCP 92, RFC 3932,
                       October 2004.
 [RFC3942]             Volz, B., "Reclassifying Dynamic Host
                       Configuration Protocol version 4 (DHCPv4)
                       Options", RFC 3942, November 2004.
 [RFC3968]             Camarillo, G., "The Internet Assigned Number
                       Authority (IANA) Header Field Parameter
                       Registry for the Session Initiation Protocol
                       (SIP)", BCP 98, RFC 3968, December 2004.
 [RFC3978]             Bradner, S., Ed., "IETF Rights in
                       Contributions", BCP 78, RFC 3978, March 2005.
 [RFC4005]             Calhoun, P., Zorn, G., Spence, D., and D.
                       Mitton, "Diameter Network Access Server
                       Application", RFC 4005, August 2005.
 [RFC4025]             Richardson, M., "A Method for Storing IPsec
                       Keying Material in DNS", RFC 4025, March 2005.
 [RFC4044]             McCloghrie, K., "Fibre Channel Management MIB",
                       RFC 4044, May 2005.
 [RFC4124]             Le Faucheur, F., Ed., "Protocol Extensions for
                       Support of Diffserv-aware MPLS Traffic
                       Engineering", RFC 4124, June 2005.
 [RFC4169]             Torvinen, V., Arkko, J., and M. Naslund,
                       "Hypertext Transfer Protocol (HTTP) Digest
                       Authentication Using Authentication and Key
                       Agreement (AKA) Version-2", RFC 4169, November
 [RFC4271]             Rekhter, Y., Ed., Li, T., Ed., and S. Hares,
                       Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC
                       4271, January 2006.

Narten & Alvestrand Best Current Practice [Page 24] RFC 5226 IANA Considerations Section in RFCs May 2008

 [RFC4283]             Patel, A., Leung, K., Khalil, M., Akhtar, H.,
                       and K. Chowdhury, "Mobile Node Identifier
                       Option for Mobile IPv6 (MIPv6)", RFC 4283,
                       November 2005.
 [RFC4306]             Kaufman, C., Ed., "Internet Key Exchange
                       (IKEv2) Protocol", RFC 4306, December 2005.
 [RFC4340]             Kohler, E., Handley, M., and S. Floyd,
                       "Datagram Congestion Control Protocol (DCCP)",
                       RFC 4340, March 2006.
 [RFC4346]             Dierks, T. and E. Rescorla, "The Transport
                       Layer Security (TLS) Protocol Version 1.1", RFC
                       4346, April 2006.
 [RFC4366]             Blake-Wilson, S., Nystrom, M., Hopwood, D.,
                       Mikkelsen, J., and T. Wright, "Transport Layer
                       Security (TLS) Extensions", RFC 4366, April
 [RFC4395]             Hansen, T., Hardie, T., and L. Masinter,
                       "Guidelines and Registration Procedures for New
                       URI Schemes", BCP 115, RFC 4395, February 2006.
 [RFC4422]             Melnikov, A., Ed., and K. Zeilenga, Ed.,
                       "Simple Authentication and Security Layer
                       (SASL)", RFC 4422, June 2006.
 [RFC4446]             Martini, L., "IANA Allocations for Pseudowire
                       Edge to Edge Emulation (PWE3)", BCP 116, RFC
                       4446, April 2006.
 [RFC4520]             Zeilenga, K., "Internet Assigned Numbers
                       Authority (IANA) Considerations for the
                       Lightweight Directory Access Protocol (LDAP)",
                       BCP 64, RFC 4520, June 2006.
 [RFC4589]             Schulzrinne, H. and H. Tschofenig, "Location
                       Types Registry", RFC 4589, July 2006.
 [RFC4727]             Fenner, B., "Experimental Values In IPv4, IPv6,
                       ICMPv4, ICMPv6, UDP, and TCP Headers", RFC
                       4727, November 2006.
 [RFC4995]             Jonsson, L-E., Pelletier, G., and K. Sandlund,
                       "The RObust Header Compression (ROHC)
                       Framework", RFC 4995, July 2007.

Narten & Alvestrand Best Current Practice [Page 25] RFC 5226 IANA Considerations Section in RFCs May 2008

Authors' Addresses

 Thomas Narten
 IBM Corporation
 3039 Cornwallis Ave.
 PO Box 12195 - BRQA/502
 Research Triangle Park, NC 27709-2195
 Phone: 919-254-7798
 Harald Tveit Alvestrand
 Beddingen 10
 Trondheim,   7014

Narten & Alvestrand Best Current Practice [Page 26] RFC 5226 IANA Considerations Section in RFCs May 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at

Narten & Alvestrand Best Current Practice [Page 27]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5226.txt · Last modified: 2008/05/16 23:46 by

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki