Network Working Group                                            R. Bush
Request for Comments: 3967                                           IIJ
BCP: 97                                                        T. Narten
Category: Best Current Practice                          IBM Corporation
                                                           December 2004

          Clarifying when Standards Track Documents may Refer
               Normatively to Documents at a Lower Level

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 (2004).


   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
   clarifies and updates the procedure used in these circumstances.

1.  Introduction

   The Internet Standards Process [RFC2026] Section 4.2.4 specifies the

      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.

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   It should also be noted that Best Current Practice documents
   [RFC1818] have generally been considered similar to Standards Track
   documents in terms of what they can reference.  For example, a
   normative reference to an Experimental RFC has been considered an
   improper reference per [RFC2026].

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 new RFC, or whose
   contents are effectively part of the new RFC, as its omission would
   leave the new 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 implementors 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:

   -  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.

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      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:

   o  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.

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

   o  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.

   o  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.

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

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3.  The Procedure to Be Used

   For Standards Track or BCP documents requiring normative reference to
   documents of lower maturity, the normal IETF Last Call procedure will
   be issued, with the need for the downward reference explicitly
   documented in the Last Call itself.  Any community comments on the
   appropriateness of downward references will be considered by the IESG
   as part of its deliberations.

   Once a specific down reference to a particular document has been
   accepted by the community (e.g., has been mentioned in several Last
   Calls), an Area Director may waive subsequent notices in the Last
   Call of down references to it.  This should only occur when the same
   document (and version) are being referenced and when the AD 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

   This procedure should not 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.

4.  Security Considerations

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

5.  Acknowledgments

   This document is the result of discussion within the IESG, with
   particular contribution by Harald Alvestrand, Steve Bellovin, Scott
   Bradner, Ned Freed, Allison Mankin, Jeff Schiller, and Bert Wijnen.

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6.  References

6.1.  Normative References

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

6.2.  Informative References

   [RFC1818]  Postel, J., Li, T., and Y. Rekhter, "Best Current
              Practices", BCP 1, RFC 1818, August 1995.

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

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

7.  Authors' Addresses

   Randy Bush
   5147 Crystal Springs
   Bainbridge Island, WA  98110

   Phone: +1 206 780 0431

   Thomas Narten
   IBM Corporation
   P.O. Box 12195
   Research Triangle Park, NC  27709-2195

   Phone: +1 919 254 7798

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8.  Full Copyright Statement

   Copyright (C) The Internet Society (2004).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and at, 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
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   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 ISOC's procedures with respect to rights in ISOC 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
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   this standard.  Please address the information to the IETF at ietf-


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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