Network Working Group S. Bradner
Internet-Draft Harvard
Intended status: Best Current B. Carpenter (ed)
Practice IBM
Expires: February 5, 2007 August 4, 2006
Procedures for protocol extensions and variations
draft-carpenter-protocol-extensions-01
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Abstract
This document discusses procedural 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
or variations need to be reviewed by the larger IETF community.
Experience with IETF protocols has shown that extensibility of
protocols without early IETF review can cause problems. The document
also recommends that major extensions to or variations of IETF
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protocols only take place through normal IETF processes or in
coordination with the IETF.
This draft replaces draft-iesg-vendor-extensions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. General Considerations . . . . . . . . . . . . . . . . . . . . 4
2.1. Quality and Consistency . . . . . . . . . . . . . . . . . 4
2.2. Registered Values and the Importance of IANA
Assignments . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. All extensions require technical review . . . . . . . . . 5
3. Procedure for Review of Extensions . . . . . . . . . . . . . . 5
4. Some Specific Issues . . . . . . . . . . . . . . . . . . . . . 7
5. Intellectual Property . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. Change log [RFC Editor: please remove this section] . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
For the origins of this draft, please see the Acknowledgements
section.
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. In
addition to the IETF itself, vendors, standards development
organizations and technology fora have used those facilities.
Although the results are often good, there is a real risk of poorly
designed mechanisms and of 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
IETF-wide 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 they may not be done with the full
understanding of why the existing protocol was designed the way that
it is - e.g., what ideas were brought up during the original
development and rejected because of some problem with them. Also
such extensions could, because of a lack of understanding, negate
some key function of the existing protocol (such as security or
congestion control). Generally, short-sighted design choices are
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sometimes made, and basic underlying architectural principles of the
protocol are sometimes violated.
Additionally, documentation of non-IETF extensions can be hard to
obtain, so 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 early peer review that occurs within the IETF process
may be lacking.
All that can be said about extensions applies with equal or greater
force to variations - in fact, by definition, protocol variations
damage interoperability. They must therefore be intensely
scrutinized. Throughout this document, what is said about extensions
also applies to variations.
This document is focussed on appropriate process and practices to
ensure that extensions developed outside the IETF will not fall into
these traps and therefore become useless or, worse, damaging to
interoperability. Architectural considerations are documented
elsewhere.
2. General Considerations
2.1. 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 published as an Internet Draft, which must be
sufficiently consistent in terminology and content with the
unextended specification that these experts can readily identify the
technical changes proposed at an early stage.
2.2. 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.
This is hazardous; it is far too likely that someone just taking a
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protocol value will find that the same value will later be formally
assigned to another function, thus guaranteeing an interoperability
problem.
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.
2.3. All extensions require technical review
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 or functionality 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, early 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
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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, currently 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.
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. In
some cases (e.g., [RFC3427], [I-D.andersson-rtg-gmpls-change]) the
IETF has well defined procedures for this in place.
Naturally, SDOs can and do develop scenarios, requirements and
architectures based on IETF specifications. It is only actual
protocol changes that need to go through the IETF process. Other
SDOs are encouraged to communicate informally or formally with the
IETF as early as possible, to avoid false starts. Early technical
review in a collaborative spirit is of great value. Each SDO can
"own" its ideas and discuss them in its own fora, but should start
talking to the IETF experts about those ideas the moment the spark
hits.
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 describing the requirements. 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
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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, unless preliminary IETF discussion has
already revealed serious flaws in the proposal. 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 at an early stage 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. This should be done at an early stage, before a large
investment of effort has taken place, in case basic prroblems are
revealed.
o In the case of simple, minor extensions involving routine IANA
parameter assignments, this request is satisfied as long as the
IANA Considerations of the underlying IETF specification are
satisfied (see [RFC2434]). Anything beyond this requires an
explicit protocol review by experts within the IETF.
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. Some Specific Issues
It is relatively common for MIBs, which are all in effect extensions
of the SMI data model, to be defined or extended outside the IETF.
BCP 111 [RFC4181] offers detailed guidance for authors and reviewers.
A number of protocols have foreseen experimental values for certain
IANA parameters, so that experimental usages and extensions may be
tested without need for a special parameter assignment. It must be
stressed that such values are not intended for production use or as a
way to evade the type of technical review described in this document.
See [I-D.fenner-iana-exp-2780].
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There are certain documents that specify a change process for
specific IETF protocols:
The SIP change process [RFC3427]
The (G)MPLS change process [I-D.andersson-rtg-gmpls-change]
5. Intellectual Property
All IETF documents fall under the IETF's intellectual property rules,
BCP 78 [RFC3978] and BCP 79 [RFC3979], as amended. In particular,
there are restrictions on the production of derivative works, and
there are rights that remain with the original authors. Anybody
outside the IETF considering an extension based on an IETF document
must bear these restrictions and rights in mind.
6. 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.
7. IANA Considerations
The IETF 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].
8. Acknowledgements
This document is heavily based on an earlier draft under a different
title by Scott Bradner and Thomas Narten.
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, Scott Brim, Dan Romascanu, Jari Arkko, Loa Andersson,...
also made valuable comments on this document.
This document was produced using the xml2rfc tool [RFC2629].
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9. Change log [RFC Editor: please remove this section]
draft-carpenter-protocol-extensions-01: 2006-08-04. Removed
additional architectural material, added material on MIBs,
experimental values and IPR, reflected other comments. Extended
scope to cover variations as well as extensions. Updated authorship.
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
draft are left to a separate document.
10. References
10.1. Normative References
[I-D.fenner-iana-exp-2780]
Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP and TCP Headers",
draft-fenner-iana-exp-2780-05 (work in progress),
June 2006.
[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.
[RFC3427] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J.,
and B. Rosen, "Change Process for the Session Initiation
Protocol (SIP)", BCP 67, RFC 3427, December 2002.
[RFC3932] Alvestrand, H., "The IESG and RFC Editor Documents:
Procedures", BCP 92, RFC 3932, October 2004.
[RFC3978] Bradner, S., "IETF Rights in Contributions", BCP 78,
RFC 3978, March 2005.
[RFC3979] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3979, March 2005.
[RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB
Documents", BCP 111, RFC 4181, September 2005.
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10.2. Informative References
[I-D.andersson-rtg-gmpls-change]
Andersson, L., "MPLS and GMPLS Change Process",
draft-andersson-rtg-gmpls-change-02 (work in progress),
December 2005.
[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.
Authors' Addresses
Scott Bradner
Harvard University
29 Oxford St.
Cambridge, MA 02138
US
Email: sob@harvard.edu
Brian Carpenter (ed)
IBM
8 Chemin de Blandonnet
1214 Vernier,
CH
Email: brc@zurich.ibm.com
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