Out With the Old and In With the New: Planning for Protocol Transitions
draft-iab-protocol-transitions-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8170.
|
|
|---|---|---|---|
| Author | Dave Thaler | ||
| Last updated | 2016-09-12 | ||
| Replaces | draft-thaler-transition-principles | ||
| RFC stream | Internet Architecture Board (IAB) | ||
| Formats | |||
| Additional resources | |||
| Stream | IAB state | (None) | |
| Consensus boilerplate | Unknown | ||
| IAB shepherd | (None) |
draft-iab-protocol-transitions-03
Internet Architecture Board D. Thaler, Ed.
Internet-Draft Microsoft
Intended status: Informational September 12, 2016
Expires: March 16, 2017
Out With the Old and In With the New: Planning for Protocol Transitions
draft-iab-protocol-transitions-03.txt
Abstract
Over the many years since the introduction of the Internet Protocol,
we have seen a number of transitions from one protocol or technology
to another, throughout the protocol stack. Many protocols and
technologies were not designed to enable smooth transition to
alternatives or to easily deploy extensions, and thus some
transitions, such as the introduction of IPv6, have been difficult.
This document attempts to summarize some basic principles to enable
future transitions, and also summarizes what makes for a good
transition plan.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 16, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Transition vs. Co-existence . . . . . . . . . . . . . . . . . 4
3. Translation/Adaptation Location . . . . . . . . . . . . . . . 5
4. Translation Plans . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. IAB Members at the Time of This Writing . . . . . . . . . . . 6
8. Informative References . . . . . . . . . . . . . . . . . . . 6
Appendix A. Case Studies . . . . . . . . . . . . . . . . . . . . 9
A.1. Explicit Congestion Notification . . . . . . . . . . . . 10
A.2. Classless Inter-Domain Routing (CIDR) . . . . . . . . . . 10
A.3. Internationalized Domain Names . . . . . . . . . . . . . 11
A.4. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
A.5. HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.5.1. Bundling of Features with New Versions . . . . . . . 13
A.5.2. Planning for Replacement . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
A "transition" is "the process or period of changing from one state
or condition to another". There are several types of such
transitions, including both technical transitions (e.g., changing
protocols or deploying an extension) and organizational transitions
(e.g., changing what organization manages the IETF web site, or the
RFC production center). This document focuses solely on technical
transitions, although some principles might apply to other types as
well.
There have been many IETF and IAB RFCs and IAB statements discussing
transitions of various sorts. Most are protocol-specific documents
about specific transitions. For example, some relevant ones in which
the IAB has been involved include:
o IAB RFC 3424 [RFC3424] recommended that any technology for so-
called "unilateral self-address fixing (UNSAF)" across NATs
include an exit strategy to transition away from such a mechanism.
Since the IESG, not the IAB, approves IETF documents, the IESG
thus became the body to enforce (or not) such a requirement.
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o IAB RFC 4690 [RFC4690] gave recommendations around
internationalized domain names. It discussed issues around the
process of transitioning to new versions of Unicode, and this
resulted in the creation of the IETF Precis WG to address this
problem.
o The IAB statement on "Follow-up-work on NAT-PT"
[IabIpv6TransitionStatement] pointed out gaps at the time in
transitioning to IPv6, and this resulted in the rechartering of
the IETF Behave WG to solve this problem.
More recently, the IAB has done work on more generally applicable
principles, including two RFCs.
IAB RFC 5218 [RFC5218] on "What Makes for a Successful Protocol?"
studied specifically what factors contribute to, and detract from,
the success of a protocol and it made a number of recommendations.
It discussed two types of transitions: "initial success" (the
transition to the technology) and extensibility (the transition to
updated versions of it). The principles and recommendations in that
document are generally applicable to all technical transitions. Some
important principles included:
1. Incentive: Transition is easiest when the benefits come to those
bearing the costs. That is, the benefits should outweigh the
costs at *each* entity. Some successful cases did this by
providing incentives (e.g., tax breaks), or by reducing costs
(e.g., freely available source), or by imposing costs of not
transitioning (e.g., regulation), or even by narrowing the
scenarios of applicability to just the cases where benefits do
outweigh costs at all relevant entities.
2. Incremental Deployability: Backwards compatibility makes
transition easier. Furthermore, transition is easiest when
changing only one entity still benefits that entity. In the
easiest case, the benefit immediately outweighs the cost and so
entities are naturally incented to transition. More commonly,
the benefits only outweigh the costs once a significant number of
other entities also transition. Unfortunately, in such cases,
the natural incentive is often to delay transitioning.
3. Total Cost: Don't underestimate the cost of things other than the
hardware/software itself. For example, operational tools and
processes, personnel training, business model (accounting/
billing) dependencies, and legal (regulation, patents, etc.)
costs all add up.
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4. Extensibility: Design for extensibility so that things can be
fixed up later.
IAB RFC 7305 [RFC7305] reported on a IAB workshop on Internet
Technology Adoption and Transition (ITAT). Like RFC 5218, this
workshop also discussed economic aspects of transition, not just
technical aspects. Some important observations included:
1. Early-Adopter Incentives: Part of Bitcoin's strategy was extra
incentives for early adopters compared to late adopters. That
is, providing a long-term advantage to early adopters can help
stimulate transition even when the initial costs outweigh the
initial benefit.
2. Policy Partners: Policy-making organizations of various sorts
(RIRs, ICANN, etc.) can be important partners in enabling and
facilitating transition.
The remainder of this document continues the discussion started in
those two RFCs and provides some additional thoughts on the topic of
transition strategies and plans.
2. Transition vs. Co-existence
There is an important distinction between a strict "flag-day" style
transition where an old mechanism is immediately replaced with a new
mechanism, vs. a looser co-existence based approach where transition
proceeds in stages where a new mechanism is first added alongside an
existing one for some overlap period, and then the old mechanism is
removed at a later stage.
When a new mechanism is backwards compatible with an existing
mechanism, transition is easiest, and the difference between the two
types of transition is not particularly significant. However, when
no backwards compatibility exists (such as in the IPv4 to IPv6
transition), a transition plan must choose either a "flag day" or a
period of co-existence. When a large number of entities are
involved, a flag day becomes impractical. Coexistence, on the other
hand, involves additional costs of maintaining two separate
mechanisms during the overlap period which could be quite long.
Furthermore, the longer the overlap period, the more the old
mechanism might get further deployment and thus increase the overall
pain of transition.
Often the decision between a "flag day" and a sustained co-existence
period may be difficult, such as in the case of IDNA2008 [RFC5891]
[RFC5895] and Unicode TR46 [TR46].
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3. Translation/Adaptation Location
A translation or adaptation mechanism is often required if the old
and new mechanisms are not interoperable. Care must be taken when
determining where such a translator is best placed.
Requiring a translator in the middle of the path can hamper end-to-
end security and reliability. For example, see the discussion of
network-based filtering in [RFC7754].
On the other hand, requiring a translation layer within an endpoint
can be a resource issue in some cases, such as if the endpoint could
be a constrained node [RFC7228].
Any transition strategy for a non-backward-compatible mechanism
should include a discussion of where it is placed and a rationale.
4. Translation Plans
The case studies described in Appendix A suggest that a good
transition plan includes at least the following components:
1. An explanation of incentives for each entity involved
2. A description of transition phases. For example, there might be
pilot, co-existence, deprecation, and removal phases for a
transition from one technology to another incompatible one.
3. A proposed timeline
4. A way to measure whether the transition is succeeding
5. A contingency plan, in case something goes wrong as a result of
the transition
6. A way to effectively communicate the proposed plan to the
entities affected, and incorporate their feedback
We recommend that such criteria be considered when evaluating
proposals to transition to new or updated protocols.
5. Security Considerations
This document discusses attributes of protocol transitions. Some
types of transition can adversely affect security or privacy. For
example, requiring a translator in the middle of the path may hamper
end-to-end security and privacy, since it creates an attractive
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target. For further discussion of some of these issues, see
Section 5 of [RFC7754].
6. IANA Considerations
This document requires no actions by the IANA.
7. IAB Members at the Time of This Writing
Jari Arkko
Ralph Droms
Ted Hardie
Joe Hildebrand
Russ Housley
Lee Howard
Erik Nordmark
Robert Sparks
Andrew Sullivan
Dave Thaler
Martin Thomson
Brian Trammell
Suzanne Woolf
8. Informative References
[HTTP0.9] Tim Berners-Lee, "The Original HTTP as defined in 1991",
1991, <https://www.w3.org/Protocols/HTTP/
AsImplemented.html>.
[IabIpv6TransitionStatement]
IAB, "Follow-up work on NAT-PT", October 2007,
<https://www.iab.org/documents/correspondence-reports-
documents/docs2007/follow-up-work-on-nat-pt//>.
[IPv6Survey2011]
Botterman, M., "IPv6 Deployment Survey", 2011,
<https://www.nro.net/wp-content/uploads/
ipv6_deployment_survey.pdf>.
[IPv6Survey2015]
British Telecommunications, "IPv6 Industry Survey Report",
August 2015, <http://www.globalservices.bt.com/static/asse
ts/pdf/products/diamond_ip/IPv6-Survey-Report-2015.pdf>.
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[PAM2015] Trammell, B., Kuehlewind, M., Boppart, D., Learmonth, I.,
Fairhurst, G., and R. Scheffenegger, "Enabling Internet-
Wide Deployment of Explicit Congestion Notification",
Proceedings of PAM 2015, 2015, <target:
http://ecn.ethz.ch/ecn-pam15.pdf>.
[RFC1883] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 1883, DOI 10.17487/RFC1883,
December 1995, <http://www.rfc-editor.org/info/rfc1883>.
[RFC1933] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 1933, DOI 10.17487/RFC1933,
April 1996, <http://www.rfc-editor.org/info/rfc1933>.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
<http://www.rfc-editor.org/info/rfc1945>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999,
<http://www.rfc-editor.org/info/rfc2616>.
[RFC2893] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, DOI 10.17487/RFC2893,
August 2000, <http://www.rfc-editor.org/info/rfc2893>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC3424] Daigle, L., Ed. and IAB, "IAB Considerations for
UNilateral Self-Address Fixing (UNSAF) Across Network
Address Translation", RFC 3424, DOI 10.17487/RFC3424,
November 2002, <http://www.rfc-editor.org/info/rfc3424>.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<http://www.rfc-editor.org/info/rfc4380>.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
2006, <http://www.rfc-editor.org/info/rfc4632>.
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[RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
Recommendations for Internationalized Domain Names
(IDNs)", RFC 4690, DOI 10.17487/RFC4690, September 2006,
<http://www.rfc-editor.org/info/rfc4690>.
[RFC5218] Thaler, D. and B. Aboba, "What Makes For a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<http://www.rfc-editor.org/info/rfc5218>.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<http://www.rfc-editor.org/info/rfc5891>.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, DOI 10.17487/RFC5895, September 2010,
<http://www.rfc-editor.org/info/rfc5895>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <http://www.rfc-editor.org/info/rfc6146>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<http://www.rfc-editor.org/info/rfc6269>.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<http://www.rfc-editor.org/info/rfc6455>.
[RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
DOI 10.17487/RFC6709, September 2012,
<http://www.rfc-editor.org/info/rfc6709>.
[RFC7021] Donley, C., Ed., Howard, L., Kuarsingh, V., Berg, J., and
J. Doshi, "Assessing the Impact of Carrier-Grade NAT on
Network Applications", RFC 7021, DOI 10.17487/RFC7021,
September 2013, <http://www.rfc-editor.org/info/rfc7021>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <http://www.rfc-editor.org/info/rfc7301>.
[RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet
Technology Adoption and Transition (ITAT)", RFC 7305,
DOI 10.17487/RFC7305, July 2014,
<http://www.rfc-editor.org/info/rfc7305>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<http://www.rfc-editor.org/info/rfc7541>.
[RFC7754] Barnes, R., Cooper, A., Kolkman, O., Thaler, D., and E.
Nordmark, "Technical Considerations for Internet Service
Blocking and Filtering", RFC 7754, DOI 10.17487/RFC7754,
March 2016, <http://www.rfc-editor.org/info/rfc7754>.
[TR46] Unicode Consortium, "Unicode IDNA Compatibility
Processing", June 2015,
<http://www.unicode.org/reports/tr46/>.
[TSV2007] Sridharan, M., Bansal, D., and D. Thaler, "Implementation
Report on Experiences with Various TCP RFCs", Proceedings
of IETF 68, March 2007,
<http://www.ietf.org/proceedings/68/slides/tsvarea-3/
sld1.htm>.
Appendix A. Case Studies
Appendix A of [RFC5218] describes a number of case studies that are
relevant to this document and highlight various transition problems
and strategies (see for instance the Inter-Domain Multicast case
study in Section A.4 of [RFC5218]). We now include several
additional case studies that focus on transition problems and
strategies. Many other equally good case studies could have been
included, but, in the interests of brevity, only a sampling is
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included here that is sufficient to justify the conclusions in the
body of this document.
A.1. Explicit Congestion Notification
Explicit Congestion Notification (ECN) is a mechanism to replace loss
as the only signal for the detection of congestion, with an explicit
signal sent from a router to the recipient of a packet, then
reflected back to the sender. It was standardized in 2000 in
[RFC3168], and the mechanism consists of two parts: congestion
detection in the IP layer, reusing two bits of the old IP Type of
Service (TOS) field, and congestion feedback in the transport layer.
Feedback in TCP uses two TCP flags, ECN Echo and Congestion Window
Reduced. Together with a suitably configured active queue management
(AQM), ECN can improve TCP performance on congested links.
The deployment of ECN is a case study in failed transition followed
by possible redemption. Initial deployment of ECN in the early and
mid 2000s led to severe problems with some network equipment,
including home router crashes and reboots when packets with ECN IP or
TCP flags was received [TSV2007]. This led to firewalls stripping
ECN IP and TCP flags, or even dropping packets with these flags set.
This stalled deployment. The need for both endpoints (to negotiate
and support ECN) and on-path devices (to mark traffic when congestion
occurs) to cooperate in order to see any benefits from ECN deployment
was a further issue. The deployment of ECN across the Interent had
failed.
In the late 2000s, Linux and Windows servers began defaulting to
"passive ECN support", meaning they would negotiate ECN if asked by
the client, but would not ask to negotiate ECN by default. This
decision was regarded as without risk: only if a client were
explicitly configured to negotiate ECN would any possible
connectivity problems surface. Gradually, this has increased server
support in the Internet from near zero in 2008, to 11% of the top
million Alexa webservers in 2011, to 30% in 2012, to 65% in late
2014. In the meantime, the risk to connectivity of ECN negotiation
has reduced dramatically [PAM2015], leading to ongoing work to make
Windows, Apple iOS, OSX, and Linux clients negotiate ECN by default.
It is hoped that a critical mass of clients and servers negotiating
ECN will provide an incentive to mark congestion on ECN-enabled
traffic, thus breaking the logjam.
A.2. Classless Inter-Domain Routing (CIDR)
TODO To be filled in... [RFC4632]
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A.3. Internationalized Domain Names
TODO To be filled in...
A.4. IPv6
Twenty-one years after publication of [RFC1883], the transition to
IPv6 is still in progress. The first document to describe a
transition plan ([RFC1933], later obsoleted by [RFC2893]) was
published less than a year after the protocol itself. It recommended
co-existence (dual-stack or tunneling technology) with the
expectation that over time, all hosts would have IPv6, and IPv4 could
be quietly retired.
In the early stages, deployment was limited to peer-to-peer uses,
tunneled over IPv4 networks. For example, Teredo [RFC4380] aligned
the cost of fixing the problem with the benefit, and allowed for
incremental benefits to those who used it.
Operating System vendors had incentives because with such tunneling
protocols, they could get peer-to-peer apps working without depending
on any infrastructure changes. That resulted in the main apps using
IPv6 being in the peer-to-peer category (BitTorrent, XBox gaming,
etc.).
Router vendors had some incentive because IPv6 could be used within
an intra-domain network more efficiently than tunneling, once the OS
vendors already had IPv6 support and some special-purpose apps
existed.
For content providers and ISPs, on the other hand, there was little
incentive for deployment: there was no incremental benefit to
deploying locally. Since everyone already had IPv4, there was no
network effect benefit to deploying IPv6. Even as proponents argued
that workarounds to extend the life of IPv4--such as CIDR, NAT, and
stingy allocations--made it more complex, IPv4 continued to work well
enough for most applications.
Workarounds to NAT problems documented in [RFC6269] and [RFC7021]
included ICE, STUN, and TURN, technologies that allowed those
experiencing the problems to deploy technologies to resolve them. As
with end-to-end IPv6 tunneling (e.g., Teredo), the incentives there
aligned the cost of fixing the problem with the benefit, and allowed
for incremental benefits to those who used them. The IAB discussed
NAT technology proposals [RFC3424] and recommended they be considered
short-term fixes, and said that proposals must include an exit plan,
such that they would decline over time. In particular, the IAB
warned against generalizing NAT solutions, which would lead to
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greater dependence on them. In some ways, these solutions, along
with other IPv4 development (e.g., the workarounds above, and
retrofitting IPsec into IPv4) continued to reduce the incentive to
deploy IPv6.
Indeed, not until a few years after IPv4 runout in various Regional
Address Registry (RIR) regions did IPv6 deployment significantly
increase. The RIRs and others conducted surveys of different
industries and industry segments to learn why people did not deploy
IPv6 [IPv6Survey2011] [IPv6Survey2015], which commonly listed lack of
a business case, lack of training, and lack of vendor support as
primary hurdles. Arguably forward-looking companies collaborated
with ISOC on World IPv6 Day and World IPv6 Launch to jump start
global IPv6 deployment, and arguably their work gave vendors
incentives to support IPv6 well. Key aspects of World IPv6 Day and
World IPv6 Launch that contributed to their successes were the
communication mechanism, and the measurement metrics and contingency
plans that were announced in advance.
Several efforts have been made to mitigate the lack of a business
case. Some governments (South Korea, Japan) provided tax incentives
to include IPv6. Other governments (Belgium, Singapore) mandated
IPv6 support by private companies. Few of these had enough value to
drive significant IPv6 deployment.
The concern about lack of training is often a common issue in
transitions. Because IPv4 is so ubiquitous, its use is routine and
simplified with common tools, and it is taught in network training
everywhere. While IPv6 deployment was low, ignorance of it was no
obstacle to being hired as a network administrator or developer.
Organizations with the greatest incentives to deploy IPv6 are those
which continue to grow quickly, even after IPv4 free pool exhaustion.
Thus, ISPs have had varying levels of commitment, based on the growth
of their user base, services being added (especially video over IP),
and the number of IPv4 addresses they had available. Cloud-based
providers, including CDN and hosting companies, have been major
buyers of IPv4 addresses, and several have been strong deployers and
advocates of IPv6.
Different organizations will use different transition models for
their networks, based on their needs. Some are electing to use
IPv6-only hosts in the network with IPv6-IPv4 translation at the
edge. Others are using dual-stack hosts with IPv6-only routers in
the core of the network, and IPv4 tunneled or translated through them
to dual-stack edge routers. Still others are using native dual-stack
throughout the network, but that generally persists as an interim
measure: adoption of two technologies is not the same as
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transitioning from one technology to another. Finally, some walled
gardens or isolated networks, such as management networks, use
IPv6-only end-to-end.
It is impossible to predict with certainty the path IPv6 deployment
will have taken when it is complete. Lessons learned so far include
aligning costs and benefits (incentive), and ensuring incremental
benefit (network effect, or backward compatibility).
A.5. HTTP/2
HTTP/2 [RFC7540] is a new version of the popular HTTP protocol
[RFC7230]. The original versions of HTTP (0.9 [HTTP0.9], 1.0
[RFC1945], and 1.1 [RFC2616]) have only small differences; each
iteration made small improvements over the previous version without
making major changes.
The changes in HTTP/2 are largely aimed at improving performance.
The primary improvement is request multiplexing, which is supported
by request prioritization and flow control. HTTP/2 includes
efficiency improvements with header compression [RFC7541] and binary
framing.
A.5.1. Bundling of Features with New Versions
The bundling of additional constraints on a new version of a protocol
could affect adoption by making the transition more costly. However,
the transition to a new version also represents an opportunity to
improve multiple aspects of a protocol at the same time.
The HTTP working group decided that a new version of the protocol
represented an opportunity to improve security posture. HTTP/2 is
much stricter about its use of TLS. In particular, a long list of
TLS cipher suites are prohibited, constraints are placed on the key
exchange method, and renegotiation is prohibited. These changes did
cause deployment problems. Though most were minor and transitory,
disabling renegotiation caused problems for deployments that relied
on the feature to authenticate clients and prompted new work to
replace the feature.
A number of other features or characteristics of HTTP were identified
as potentially undesirable. Several such features were considered
for removal during the design process. This included trailers, the
1xx series of responses, certain modes of request forms, and the
unsecured (http://) variant of the protocol. For each of these, the
risk to the successful deployment of the new version was considered
to be too great to justify removing the feature. However, deployment
of the unsecured variant of HTTP/2 remains extremely limited.
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Internet-Draft Planning for Transition September 2016
A.5.2. Planning for Replacement
HTTP/1.1 provides a mechanism, Upgrade, to transition to an entirely
different protocol. That same facility was little used other than to
enable the use of WebSockets [RFC6455]. However, with performance
being a primary motivation for HTTP/2, a new mechanism was needed to
avoid spending an additional round trip on this negotiation. A new
mechanism was added to TLS to permit the negotiation of the new
version of HTTP: Application Layer Protocol Negotiation (ALPN)
[RFC7301]. Upgrade was used only for the unsecured variant of the
protocol.
ALPN was identified as the way in which future protocol versions
would be negotiated. The mechanism was well-tested during
development of the specification, which proved that new versions
could be deployed safely and easily using ALPN. Several draft
versions of the protocol were successfully deployed during protocol
development, and version negotiation was never shown to be an issue.
Confidence that new versions would be easy to deploy if necessary
lead to a particular design stance that might be considered unusual
in light of the advice in RFC 5218 [RFC5218], though is completely
consistent with RFC 6709 [RFC6709]: many of the ways in which the
protocol might be extended were removed unless an immediate need was
understood. This decision was made on the basis that it would be
easier to revise the entire protocol than it would be to ensure that
an extension point was correctly specified and implemented such that
it would be available when needed.
Author's Address
Dave Thaler (editor)
Microsoft
One Microsoft Way
Redmond, WA 98052
US
Email: dthaler@microsoft.com
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