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rfc:rfc3967

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).

Abstract

 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
 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.

Bush & Narten Best Current Practice [Page 1] RFC 3967 Document Down-Ref Clarifications December 2004

 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
 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.  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
 process.
 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:
  1. 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.

Bush & Narten Best Current Practice [Page 2] RFC 3967 Document Down-Ref Clarifications December 2004

    The referenced specification would likely include details about
    specific key management requirements, which transforms are
    required and which are optional, etc.
  1. In MIB documents, an IMPORTS clause by definition is a normative

reference.

  1. 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.

Bush & Narten Best Current Practice [Page 3] RFC 3967 Document Down-Ref Clarifications December 2004

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
 cryptographers.
 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
 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.

Bush & Narten Best Current Practice [Page 4] RFC 3967 Document Down-Ref Clarifications December 2004

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
 IIJ
 5147 Crystal Springs
 Bainbridge Island, WA  98110
 US
 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
 US
 Phone: +1 919 254 7798
 EMail: narten@us.ibm.com

Bush & Narten Best Current Practice [Page 5] RFC 3967 Document Down-Ref Clarifications December 2004

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 www.rfc-editor.org, and except as set
 forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 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
 http://www.ietf.org/ipr.
 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 ietf-
 ipr@ietf.org.

Acknowledgement

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

Bush & Narten Best Current Practice [Page 6]

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