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Versions: 00 01 02 03 rfc3967                      Best Current Practice
Network Working Group                                            R. Bush
Internet-Draft                                                       IIJ
Updates: 2026 (if approved)                                    T. Narten
Expires: January 2005                                    IBM Corporation
                                                           July 19, 2004

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

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.


   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.  There are needs for exceptions to this rule,
   often caused by the IETF using informational RFCs to describe non-

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   IETF standards, or IETF-specific modes of use of such standards. This
   document clarifies and updates the procedure used in these

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1. Normative References Expected to be to Equal or Higher Level

   The Internet Standards Process [RFC2026] Section 4.2.4 specifies:

      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
   [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 in the sense that its
   omission would leave the new RFC incompletely specified.  An
   informative reference is not normative; rather, it provides only
   additional, background information.

   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. Morever, 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 an IETF
   Standard's context, 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

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   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 without the specification for IPsec
        also being 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 the case of MIB documents, an IMPORTS clause by definition is
        a normative reference.

      - 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 [RFCxxx] 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 where an IETF document may need
   to make a normative reference to a document at a lower maturity
   level, but such a reference is in conflict 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 which force the
      target of the normative reference to be an informational or
      historical RFC, or for it to be at a lower standards level than
      the referring document.

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

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 when the appropriate step to take
   is to move the document to which the reference is being made into the
   appropriate category. I.e., this is not intended as an easy way out
   of normal process. Rather, it is intended for dealing with specific
   cases where putting particular documents into the required category
   is problematical and unlikely to ever 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 down-grade attack on the quality of
   IETF standards, or worse, on the rigorous review of security aspects
   of standards.

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.

Normative References

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

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Informative References

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

   [2223bis]  "Instructions to Request for Comments (RFC) Authors",

   [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

   [RFC2362] Protocol Independent Multicast-Sparse Mode (PIM-SM):
              Protocol Specification. D. Estrin, D. Farinacci, A. Helmy,
              D. Thaler, S.  Deering, M. Handley, V. Jacobson, C. Liu,
              P. Sharma, L. Wei. June 1998.

Authors' Addresses

   Randy Bush
   5147 Crystal Springs
   Bainbridge Island, WA  98110

   Phone: +1 206 780 0431
   EMail: randy@psg.com
   URI:   http://psg.com/~randy/

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

   Phone: +1 919 254 7798
   EMail: narten@us.ibm.com

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