Network Working Group B. Carpenter (ed)
Internet-Draft IBM
Expires: December 18, 2006 June 16, 2006
Procedures for protocol extensions
draft-carpenter-protocol-extensions-00
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Abstract
This document discusses issues related to the extensibility of IETF
protocols, including when it is reasonable to extend IETF protocols
with little or no review, and when extensions need to be reviewed by
the larger IETF community. Experience with IETF protocols has shown
that extensibility of protocols without IETF review can cause
problems. The document also recommends that major extensions to IETF
protocols only take place through normal IETF processes or in
coordination with the IETF.
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This draft replaces draft-iesg-vendor-extensions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. General Considerations . . . . . . . . . . . . . . . . . . . . 4
2.1. Interoperability as a Goal . . . . . . . . . . . . . . . . 4
2.2. Quality and Consistency . . . . . . . . . . . . . . . . . 4
2.3. Registered Values and the Importance of IANA
Assignments . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Major versus Minor Extensions . . . . . . . . . . . . . . 5
3. Procedure for Review of Extensions . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
7. Change log [RFC Editor: please remove this section] . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
For the origins of this draft, please see the Acknowledgements
section. It is posted as a personal draft although the material was
historically developed in the IESG.
BCP 9 [RFC2026] is the current definition of the IETF standards
track. It is implicitly presumed that this process will apply not
only to the initial definition of a protocol, but also to any
subsequent updates, such that continued interoperability can be
guaranteed. However, it is not always clear whether extensions to a
protocol fall within this presumption, especially when they originate
outside the IETF community. This document lays down procedures for
such extensions.
When developing protocols, IETF working groups typically include
mechanisms whereby these protocols can be extended in the future.
Vendors, standards development organizations and technology fora have
used those facilities. Sometimes the result is a poorly designed
mechanism and non-interoperability.
It is of course a good principle to design extensiblity into
protocols; one common definition of a successful protocol is one that
becomes widely used in ways not originally anticipated. Well-
designed extensibility mechanisms facilitate the evolution of
protocols and help make it easier to roll-out incremental changes in
an interoperable fashion. At the same time, experience has shown
that extensibility features should be limited to what is clearly
necessary when the protocol is developed and any later extensions
should be done carefully and with a full understanding of the base
protocol, existing implementations, and current operational practice.
However, it is not the purpose of this document to describe the
architectural principles of sound extensibility design.
When extensions to IETF protocols are made within the IETF, the
normal IETF process is followed, including the normal process for
review and approval by the IESG. It is presumed that this will
ensure that extensions developed in this way will respect all
applicable architectural principles and technical criteria.
When extensions to IETF protocols are made outside the IETF,
experience has shown that documentation of these extensions can be
hard to obtain, short-sighted design choices are sometimes made,
basic underlying architectural principals of the protocol are
sometimes violated, assessing the quality of the specification is
hard and achieving interoperability can be hard. Also, there is a
risk that mutually incompatible extensions may be developed
independently. Simply put, the peer review that occurs within the
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IETF process is lacking.
This document is focussed on appropriate process and practices to
ensure that extensions developed outside the IETF will not fall into
this trap and therefore become useless or, worse, damaging to the
Internet. However, some general considerations are listed first.
2. General Considerations
2.1. Interoperability as a Goal
An extension is of little value if it is not interoperable with the
unextended protocol, i.e. the extended protocol correctly supports
all mandatory and optional features of the unextended protocol, and
implementations of the base protocol operate correctly in the
presence of the extensions. This places requirements on both the
base protocol (design for extensibility) and on the extension. These
architectural considerations are outside the scope of the present
draft.
2.2. Quality and Consistency
In order to be adequately reviewed by relevant experts, a proposed
extension must be documented in a clear and well-written
specification, which must be sufficiently consistent in terminology
and content with the unextended specification that these experts can
readily identify the technical changes proposed.
2.3. Registered Values and the Importance of IANA Assignments
An extension is often likely to make use of additional values added
to an existing IANA registry (in many cases, simply by adding a new
"TLV" (type-length-value) field). It is essential that such new
values are properly registered by the applicable procedures,
including expert review where applicable (see BCP 26, [RFC2434]).
Extensions may even need to create new IANA registries in some cases.
Experience shows that the importance of this is often underestimated
during extension design; designers sometimes assume that a new
codepoint is theirs for the asking, or even simply for the taking.
However, in many cases IANA assignment requests trigger a thorough
technical review of the proposal by a designated IETF expert
reviewer. Requests are sometimes refused after such a review. Thus,
extension designers must pay particular attention to any needed IANA
assignments and to the applicable criteria.
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2.4. Major versus Minor Extensions
Some extensions may be considered minor (e.g. adding a
straightforward new TLV to an application protocol, which will only
impact a subset of hosts) and some may be considered major (e.g.
adding a new IP option type, which will potentially impact every node
on the Internet). This is essentially a matter of judgement. It
could be argued that anything requiring at most Expert Review in
[RFC2434] is probably minor, and anything beyond that is major.
However, even an apparently minor extension may have unforeseen
consequences on interoperability. Thus, the distinction between
major and minor is less important than ensuring that the right amount
of technical review takes place in either case.
For example, RADIUS [RFC2865] is designed to carry attributes and
allow definition of new attributes. But it is important that
discussion of new attributes involve the IETF community of experts
knowledgeable about the protocol's architecture and existing usage in
order to fully understand the implications of a proposed extension.
Adding new attributes without such discussion creates a high risk of
interoperability failure. For this reason among others, the IETF has
an active RADIUS Extensions working group at the time of writing.
Thus the only safe rule is that, even if an extension appears minor
to the person proposing it, review by subject matter experts is
always advisable. The proper forum for such review is the IETF,
either in the relevant Working Group, or by individual IETF experts
if no such WG exists.
3. Procedure for Review of Extensions
Extensions to IETF protocols developed within the IETF will be
subject to the normal IETF process, exactly like new designs.
Extensions to IETF protocols discussed in an IRTF Research Group may
well be the prelude to regular IETF discussion. However, a Research
Group may desire to specify an experimental extension before the work
is mature enough for IETF processing. In this case, the Research
Group is required to involve appropriate IETF or IANA experts in
their process to avoid oversights.
Extensions to IETF protocols described in Independent Submissions to
the RFC Editor are subject to IESG review as described in BCP 92
[RFC3932]. A possible outcome is that the IESG advises the RFC
Editor that full IETF processing is needed, or that relevant IANA
procedures have not been followed.
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Where vendors or other Standards Development Organisations (SDOs) see
a requirement for extending an IETF protocol, their first step should
be to select the most appropriate of the above three routes. Regular
IETF process is most likely to be suitable, assuming sufficient
interest can be found in the IETF community. IRTF process is
unlikely to be suitable unless there is a genuine research context
for the proposed extension.
In the case of an SDO that identifies a requirement for a
standardised extension, a standards development process within the
IETF (while maintaining appropriate liaison) is strongly recommended
in preference to publishing a non-IETF standard. Otherwise, the
implementor community will be faced with a standard split into two or
more parts in different styles, obtained from different sources, with
no unitary control over quality, compatibility, interoperability, and
intellectual property conditions. Note that, since participation in
the IETF is open, there is no formality or restriction for
particpants in other SDOs choosing to work in the IETF as well.
Vendors that identify a requirement for an extension are strongly
recommended to start informal discussion in the IETF and to publish a
preliminary Internet Draft. This will allow the vendor, and the
community, to evaluate whether there is community interest and
whether there are any major or fundamental issues. However, in the
case of a vendor that identifies a requirement for a proprietary
extension that does not generate interest in the IETF (or IRTF)
communities, an Independent Submission to the RFC Editor is strongly
recommended in preference to publishing a proprietary document. Not
only does this bring the draft to the attention of the community; it
also ensures a minimum of community review [RFC3932], and (if
published) makes the proprietary extension available to the whole
community.
If, despite these strong recommendations, a vendor or SDO does choose
to publish its own specification for an extension to an IETF
protocol, the following guidance applies:
o Extensions to IETF protocols should be well, and publicly,
documented, and reviewed by the IETF community to be sure that the
extension does not undermine basic assumptions and safeguards
designed into the protocol, such as security functions, or
undermine its architectural integrity.
o Therefore, vendors and other SDOs are formally requested to submit
any such proposed publications for IETF review, by an established
liaison channel if it exists, or by direct communication with the
IESG.
o In the case of simple, minor extensions involving routine IANA
parameter assignments, this request is satsified as long as the
IANA Considerations of the underlying IETF specification are
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satisfied (see [RFC2434]). Anything beyond this requires an
explicit protocol review process.
o Note that, like IETF specifications, such proposed publications
must include an IANA considerations section to ensure that
protocol parameter assignments that are needed to deploy
extensions are not made until after a proposed extension has
received adequate review, and then to ensure that IANA has precise
guidance on how to make those assignments.
4. Security Considerations
An extension must not introduce new security risks without also
providing an adequate counter-measure, and in particular it must not
inadvertently defeat security measures in the unextended protocol.
This aspect must always be considered during IETF review.
5. IANA Considerations
The IESG requests IANA to pay attention to the requirements of this
document when requested to make protocol parameter assignments for
vendors or other SDOs, i.e. to respect the IANA Considerations of all
RFCs that contain them, and the general considerations of BCP 26
[RFC2434].
6. Acknowledgements
This document is heavily based on an earlier draft under a different
title by Scott Bradner and Thomas Narten. Final authorship
attributions remain to be determined.
That earlier draft stated: The initial version of this document was
put together by the IESG in 2002. Since then, it has been reworked
in response to feedback from John Loughney, Henrik Levkowetz, Mark
Townsley, Randy Bush, Bernard Aboba and others.
Ted Hardie and Thomas Narten made valuable comments on this version.
This document was produced using the xml2rfc tool[RFC2629].
7. Change log [RFC Editor: please remove this section]
draft-carpenter-protocol-extensions-00: original version, 2006-06-16.
Derived from draft-iesg-vendor-extensions-02.txt dated 2004-06-04 by
focussing on procedural issues; the more architectural issues in that
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draft are left to the IAB.
8. References
8.1. Normative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC3932] Alvestrand, H., "The IESG and RFC Editor Documents:
Procedures", BCP 92, RFC 3932, October 2004.
8.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
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Author's Address
Brian Carpenter (ed)
IBM
8 Chemin de Blandonnet
1214 Vernier,
Switzerland
Email: brc@zurich.ibm.com
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