Network Working Group S. Bradner
Internet-Draft Harvard
Intended status: Best Current B. Carpenter (ed)
Practice T. Narten
Expires: March 12, 2007 IBM
September 8, 2006
Procedures for protocol extensions and variations
draft-carpenter-protocol-extensions-02
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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
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also recommends that major extensions to or variations of IETF
protocols only take place through normal IETF processes or in
coordination with the IETF.
This document is directed principally at other Standards Development
Organizations (SDOs) and vendors considering requirements for
extensions to IETF protocols. It does not modify formal IETF
processes.
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 . . . . . . . . . . . . . . 6
4. Some Specific Issues . . . . . . . . . . . . . . . . . . . . . 8
5. Intellectual Property . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. Change log [RFC Editor: please remove this section] . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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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, protocol extensions can also
result in poorly designed mechanisms and in non-interoperability.
It is of course a good principle to design extensibility 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 and
without consulting 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). Short-sighted design
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choices are sometimes made, and basic underlying architectural
principles of the protocol are sometimes violated. Of course, the
IETF itself is not immune to such mistakes, suggesting a need for
working groups to document their design decisions (including paths
rejected) and some rationale for those decisions, for the benefit of
both those within IETF and those outside of IETF.
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 by experienced subject matter
experts that occurs within the IETF process may be lacking,
regardless of the competence or efficiency of the outside
developers..
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. This document is directed principally at other Standards
Development Organizations (SDOs) and vendors considering requirements
for extensions to IETF protocols. It does not modify formal IETF
processes.
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 normally 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
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"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
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. The expertise for
such review for IETF protocols lies within the IETF.
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
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if no such WG exists.
There may sometimes be doubt whether a particular proposal is or is
not truly a protocol extension. When in doubt, it is preferable to
err on the side of additional review. However, it should be noted
that if an 'extension' only consists of registering a new value with
IANA in a First Come First Served registry [RFC2434], this document
is not intended to require formal IETF review. Informal review by
experts may nevertheless be valuable.
3. Procedure for Review of Extensions
In some cases, explicit provision is made in the relevant RFCs for
extending individual IETF protocols. Nothing in this document
overrides such procedures. Some such cases are mentioned in
Section 4.
There are several ways in which an extension to an IETF protocol can
be considered for publication as an RFC:
1. Extensions to IETF protocols developed within the IETF will be
subject to the normal IETF process, exactly like new designs. It
is not suggested that this is a panacea; appropriate cross-
working-group and cross-Area review is needed within the IETF to
avoid oversights and mistakes.
2. 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.
3. Extensions to IETF protocols described in Independent Submissions
to the RFC Editor are subject to IESG review, currently described
in BCP 92 [RFC3932]. If appropriate, the IESG advises the RFC
Editor that full IETF processing is needed, or that relevant IANA
procedures need to be followed before publication can proceed.
Note that Independent Submissions cannot be placed on the IETF
Standards Track; they would need to enter full IETF processing.
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
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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
participants in other SDOs choosing to work in the IETF as well. In
some cases (see Section 4) 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 extensions and changes that need to go through the IETF
process. However, there is still a large potential for harm if
significant investment is made in planning stages for use of IETF
technology without early review and feedback from the IETF. 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 idea is
well formulated. It is understood that close collaboration may be
needed in order that the IETF experts correctly understand the
systems architecture envisaged by the other SDO. This is much
preferable to a situation where another SDO presents the IANA and the
IETF with a 'fait accompli.'
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
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:
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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 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 relevant
working group or with the IESG. This should be done at an early
stage, before a large investment of effort has taken place, in
case basic problems are revealed. When there is a formal liaison
in place between the other SDO and the IETF, the liaison channel
should be used to ensure that review takes place, both by relevant
experts and by established review teams or Directorates within the
IETF. If there is no formal liaison, the other SDO or vendor
should ask the IESG (or a relevant Area Director) to obtain such
reviews. Note that general aspects such as security,
internationalization and management may need review, as well as
the protocol as such.
o In the case of extensions involving only routine IANA parameter
assignments, for which there is an underlying IETF specification
containing clear IANA Considerations, this request is satisfied as
long as those considerations 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 MIB modules, 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 [RFC3692] and [I-D.fenner-iana-exp-2780].
There are certain documents that specify a change process for
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specific IETF protocols, such as:
The SIP change process [RFC3427]
The (G)MPLS change process [I-D.andersson-rtg-gmpls-change]
This document does not override such specific change processes.
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 legal 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,
Adrian Farrel, Roy Fielding, Keith Moore, Bernard Aboba, Elwyn
Davies, Stephen Trowbridge, and Ted Ts'o also made valuable comments
on this document.
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This document was produced using the xml2rfc tool [RFC2629].
9. Change log [RFC Editor: please remove this section]
This draft replaces draft-iesg-vendor-extensions.
draft-carpenter-protocol-extensions-02: 2006-09-08. Clarifications
in response to IETF Last Call comments. Most significantly,
clarified that this document does not override change processes that
have been documented for specific protocols. Updated authorship.
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.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC3932] Alvestrand, H., "The IESG and RFC Editor Documents:
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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.
10.2. Informative References
[I-D.andersson-rtg-gmpls-change]
Andersson, L. and A. Farrel, "Change Process for
Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS) Protocols and Procedures",
draft-andersson-rtg-gmpls-change-03 (work in progress),
August 2006.
[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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Thomas Narten
IBM
3039 Cornwallis Ave.
PO Box 12195 - BRQA/502
Research Triangle Park, NC 27709-2195
US
Email: narten@us.ibm.com
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