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Procedures for Standards Track Documents to Refer Normatively to Documents at a Lower Level

Document Type Active Internet-Draft (individual)
Author Murray Kucherawy
Last updated 2022-01-20 (Latest revision 2021-10-17)
Stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
Stream WG state (None)
Document shepherd Erik Kline
IESG IESG state Publication Requested
Action Holder
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Erik Kline
IESG note AD-sponsored update to BCP97 documents.
Send notices to (None)
Network Working Group                                  M. Kucherawy, Ed.
Internet-Draft                                           17 October 2021
Obsoletes: 3967, 4897, 8067 (if approved)                               
Intended status: Best Current Practice                                  
Expires: 20 April 2022

    Procedures for Standards Track Documents to Refer Normatively to
                       Documents at a Lower Level


   IETF procedures generally require that a standards track RFC may not
   have a normative reference to another standards track document at a
   lower maturity level or to a non standards track specification (other
   than specifications from other standards bodies).  For example, a
   standards track document may not have a normative reference to an
   informational RFC.  Exceptions to this rule are sometimes needed as
   the IETF uses informational RFCs to describe non-IETF standards or
   IETF-specific modes of use of such standards.  This document defines
   the procedure used in these circumstances.

   This document merges and updates, and thus obsoletes, RFC 3967, RFC
   4897, and RFC 8067.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 20 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
   2.  The Need for Downward References  . . . . . . . . . . . . . .   4
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Authors and Editors . . . . . . . . . . . . . . . . . . .   5
     4.2.  The IESG  . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IETF Target Documents . . . . . . . . . . . . . . . . . . . .   7
   6.  Non-IETF Target Documents . . . . . . . . . . . . . . . . . .   7
   7.  Downref Registry  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Changes  . . . . . . . . . . . . . . . . . . . . . .   9
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Internet Standards Process [RFC2026] (BCP 9) Section 4.2.4
   specifies the following:

     Standards track specifications normally must not depend on other
     standards track specifications which are at a lower maturity level
     or on non standards track specifications other than referenced
     specifications from other standards bodies.

   One intent is to avoid creating a perception that a standard is more
   mature than it actually is.

   It should also be noted that Best Current Practice documents (BCPs;
   see [RFC2026]) have generally been considered similar to Standards
   Track documents in terms of what they can reference.  For example, a
   normative reference from a BCP to an Experimental RFC has been
   considered an improper reference.

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   This document describes a process for allowing normative references
   to documents at lower maturity levels ("downrefs"), after due notice
   and consideration as the document progresses toward publication.  The
   original process was defined in [RFC3967] and later amended by
   [RFC4897] and [RFC8067].  This document consolidates those, and
   presents further guidance regarding normative references to non-IETF

1.1.  Normative References

   Within an RFC, references to other documents fall into two general
   categories: "normative" and "informative".  Broadly speaking, a
   normative reference specifies a document that must be read to fully
   understand or implement the subject matter in the RFC, or whose
   contents are effectively part of the RFC, as its omission would leave
   the RFC incompletely specified.  An informative reference is not
   normative; rather, it provides only additional background

   An exact and precise definition of what is (and is not) a normative
   reference has proven challenging in practice, as the details and
   implications can be subtle.  Moreover, whether a reference needs to
   be normative can depend on the context in which a particular RFC is
   being published in the first place.  For example, in the context of
   an IETF Standard, it is important that all dependent pieces be
   clearly specified and available in an archival form so that there is
   no disagreement over what constitutes a standard.  This is not always
   the case for other documents.

   The rest of this section provides guidance on what might (and might
   not) be considered normative in the context of the IETF standards

   In the IETF, it is a basic assumption that implementers must have a
   clear understanding of what they need to implement in order to be
   fully compliant with a standard and to be able to interoperate with
   other implementations of that standard.  For documents that are
   referenced, any document that includes key information an implementer
   needs would be normative.  For example, if one needs to understand a
   packet format defined in another document in order to fully implement
   a specification, the reference to that format would be normative.
   Likewise, if a reference to a required algorithm is made, the
   reference would be normative.

   Some specific examples:

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   *  If a protocol relies on IPsec to provide security, one cannot
      fully implement the protocol unless the specification for IPsec is
      available; hence, the reference would be normative.  The
      referenced specification would likely include details about
      specific key management requirements, which transforms are
      required and which are optional, etc.

   *  In MIB documents, an IMPORTS clause by definition is a normative

   *  When a reference to an example is made, such a reference need not
      be normative.  For example, text such as "an algorithm such as the
      one specified in [RFCxxxx] would be acceptable" indicates an
      informative reference, since that cited algorithm is just one of
      several possible algorithms that could be used.

2.  The Need for Downward References

   There are a number of circumstances in which an IETF document may
   need to make a normative reference to a document at a lower maturity
   level, but such a reference conflicts with Section 4.2.4 of
   [RFC2026].  For example:

   *  A standards track document may need to refer to a protocol or
      algorithm developed by an external body but modified, adapted, or
      profiled by an IETF informational RFC, for example, MD5 [RFC1321]
      and HMAC [RFC2104].  Note that this does not override the IETF's
      duty to see that the specification is indeed sufficiently clear to
      enable creation of interoperable implementations.

   *  A standards document may need to refer to a proprietary protocol,
      and the IETF normally documents proprietary protocols using
      informational RFCs.

   *  A migration or co-existence document may need to define a
      standards track mechanism for migration from, and/or co-existence
      with, an historic protocol, a proprietary protocol, or possibly a
      non-standards track protocol.

   *  There are exceptional procedural or legal reasons that force the
      target of the normative reference to be an informational or
      historical RFC or to be at a lower standards level than the
      referring document.

   *  A BCP document may want to describe best current practices for
      experimental or informational specifications.

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3.  Definitions

   A reference involves two documents, the one in which the reference is
   embedded and the document referenced.  Where needed for clarity,
   these documents are referred to as the "source document" and "target
   document", respectively.

   The term "Standards-Track document", as used in this specification,
   is assumed to include only Standards-Track documents at any maturity
   level, plus BCPs, but not documents with any other status.

4.  Procedure

   The following sections describe the procedures to be used by authors/
   editors and the IESG when handling downrefs.

4.1.  Authors and Editors

   When a Standards-Track or BCP document requires a normative reference
   to a document of lower maturity, the authors/editors should apply the
   following very simple procedure:

   *  The reference text (i.e., in the "Normative References" section of
      the source document) is written as usual.

   *  A note is included in the reference text that indicates that the
      reference is to a target document of a lower maturity level, that
      some caution should be used since it may be less stable than the
      document from which it is being referenced, and, optionally,
      explaining why the downref is appropriate.

   The Internet Engineering Steering Group (IESG) may, at its
   discretion, specify the exact text to be used, establish procedures
   regarding the text to use, or give guidance on this text.  When
   establishing procedures, the IESG should seek appropriate community

   These annotations are part of the source document.  If members of the
   community consider either the downref or the annotation text to be
   inappropriate, those issues can be raised at any time during the
   document life cycle, just as with any other text in the document.
   There is no separate review of these references.  For example, when
   the downref is to a document of a lower maturity level that is
   understood to be stable, the annotation can be omitted.  Such
   decisions should be noted in the document shepherd writeup [RFC4858]
   so the IESG is aware at the time of its review why the annotation is

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   At the option of the author/editor, similar notes may be attached to
   non-normative references.

4.2.  The IESG

   With appropriate community review, the IESG may establish procedures
   for when normative downref should delay a document and when downrefs
   should be noted.  Absent specific guidance, authors and reviewers
   should use their best judgment.  It is assumed that, in a significant
   majority of cases, noting a downref is preferable to delaying

   When a document is presented to the IESG for publication that
   contains a downref not called out by the author/editor(s) as
   described in the previous section, it is strongly recommended that
   the normal IETF Last Call procedure will be issued, with the need for
   the downref explicitly documented in the Last Call itself.  Any
   community comments on the appropriateness of downrefs will be
   considered by the IESG as part of its deliberations.

   If, by oversight, the Last Call does not identify the downref, the
   IESG may choose to repeat the Last Call with the downref properly
   identified.  If it elects not to do so, then any future downref to
   the same target document is subject again to the procedures described
   in this document.  In making this decision, the IESG should take into
   account the general discussion in Section 2.

   Once a specific downref to a particular document has been accepted by
   the community (e.g., has been mentioned in one or more Last Calls),
   an Area Director may waive subsequent notices in the Last Call of
   downrefs to it.  This should only occur when the same document (and
   version) are being referenced and when the Area Director believes
   that the document's use is an accepted part of the community's
   understanding of the relevant technical area.  For example, the use
   of MD5 [RFC1321] and HMAC [RFC2104] is well known among
   cryptographers.  Such documents are added to the "Downref Registry".

   In the case of a downref approved in this manner, the annotations
   described above should be added to the reference unless the IESG,
   after consideration of Last Call input, concludes it is

   This procedure is not to be used if the proper step is to move the
   document to which the reference is being made into the appropriate
   category.  It is not intended as an easy way out of normal process.
   Rather, the procedure is intended for dealing with specific cases
   where putting particular documents into the required category is
   problematic and unlikely ever to happen.

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5.  IETF Target Documents

   The "downward reference by annotation" model specified here is
   applicable only to published Standards-Track RFCs at lower maturity

   Obviously, such downward references are part of the relevant source
   document at IETF Last Call and subject to comments from the

   Advancing documents, when appropriate, is still strongly preferred to
   the use of either this procedure or the one specified in Section 4.2.
   This specification does not impose a specific test or requirement to
   determine appropriateness.  This is partially because it would be
   impossible to do so for the general case, but more so because the
   intention is to permit the IESG and the community to balance the
   importance of getting a source document published against the time
   and difficulty associated with upgrading a target document.  That
   requirement is intended to be less stringent than the one of
   Section 4.2.

6.  Non-IETF Target Documents

   A reference to a non-IETF document provides a few challenges relative
   to the RFC series:

   *  its development may not have been as rigorous as the Standards-
      Track document referencing it;

   *  the actual reference to it (e.g., a web link) may have dubious

   *  it may be subject to unexpected revision in situ; or

   *  it may not be freely available.

   The IESG may, at its discretion, establish policies regarding
   external documents referenced normatively by Standards-Track RFCs in
   light of these challenges.  Such policies are to be developed with
   solicitation of community input.

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   At a minimum, authors/editors of source documents need to secure
   freely available copies of the target documents for use by all
   anticipated reviewers during the source document's life cycle, which
   includes working group participants, any member of the community that
   chooses to participate in Last Call discussions, area review teams,
   IANA expert reviewers, and members of the IESG.  The mechanism for
   acquiring access to those documents is to be be specified in the
   shepherd writeup.

7.  Downref Registry

   The IETF has previously established a registry of downrefs to RFCs
   that have been previously waived by the IESG in the manner described
   in Section 4.2.  The registry includes the name of the referenced RFC
   and the Internet-Draft whose publication resulted it its addition to
   the registry.  The IESG is responsible for the maintenance of this
   registry, adding new entries to it as appropriate.

   Going forward, new registry entries should also record the reason the
   registry addition was made, and the name of the Area Director making
   the new entry.

   Note that there is currently no registry of downrefs to non-IETF

8.  Security Considerations

   This document is not known to create any new vulnerabilities for the
   Internet.  On the other hand, inappropriate or excessive use of these
   processes might be considered a downgrade attack on the quality of
   IETF standards or, worse, on the rigorous review of security aspects
   of standards.

9.  References

9.1.  Normative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,

   [RFC3967]  Bush, R. and T. Narten, "Clarifying when Standards Track
              Documents may Refer Normatively to Documents at a Lower
              Level", BCP 97, RFC 3967, DOI 10.17487/RFC3967, December
              2004, <>.

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   [RFC4897]  Klensin, J. and S. Hartman, "Handling Normative References
              to Standards-Track Documents", BCP 97, RFC 4897,
              DOI 10.17487/RFC4897, June 2007,

9.2.  Informative References

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,

   [RFC4858]  Levkowetz, H., Meyer, D., Eggert, L., and A. Mankin,
              "Document Shepherding from Working Group Last Call to
              Publication", RFC 4858, DOI 10.17487/RFC4858, May 2007,

   [RFC8067]  Leiba, B., "Updating When Standards Track Documents May
              Refer Normatively to Documents at a Lower Level", BCP 97,
              RFC 8067, DOI 10.17487/RFC8067, January 2017,

Appendix A.  Changes

   The following are the changes in this document relative to the
   current state of BCP 97:

   *  Apply erratum #2793.

   *  Remove references to RFC 1818, which is historic.

   *  Describe the downref registry's format and ownership.

   *  Discuss restricted-access documents.

   *  Allow for skipping downref annotations when the target document is
      understood to be stable.

   *  Stronger language against using this process when advancing the
      target document is The Right Thing To Do.

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Appendix B.  Acknowledgments

   This editor offers a salute to the authors of and contributors to RFC
   3967, RFC 4897, and RFC 8067: Randy Bush, Thomas Narten, John
   Klensin, Sam Hartman, and Barry Leiba.

   This revision benefited from contributions by Scott Bradner, Brian
   Campbell, Russ Housley, John Klensin, Michael Richardson, and Rich

Author's Address

   Murray Kucherawy (editor)


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