Internet Architecture Board (IAB)                         D. Thaler, Ed.
Request for Comments: 8170                                      May 2017
Category: Informational
ISSN: 2070-1721
Internet Architecture Board (IAB)                         D. Thaler, Ed.
Request for Comments: 8170                                      May 2017
Category: Informational
ISSN: 2070-1721

Planning for Protocol Adoption and Subsequent Transitions




Over the many years since the introduction of the Internet Protocol, we have seen a number of transitions throughout the protocol stack, such as deploying a new protocol, or updating or replacing an existing protocol. Many protocols and technologies were not designed to enable smooth transition to alternatives or to easily deploy extensions; 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 it also summarizes what makes for a good transition plan.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


This document is a product of the Internet Architecture Board (IAB) and represents information that the IAB has deemed valuable to provide for permanent record. It represents the consensus of the Internet Architecture Board (IAB). Documents approved for publication by the IAB are not a candidate for any level of Internet Standard; see Section 2 of RFC 7841.

本文件是互联网体系结构委员会(IAB)的产品,代表IAB认为有价值提供永久记录的信息。它代表了互联网体系结构委员会(IAB)的共识。IAB批准发布的文件不适用于任何级别的互联网标准;见RFC 7841第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2017 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。

Table of Contents


   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extensibility . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Transition vs. Coexistence  . . . . . . . . . . . . . . . . .   5
   4.  Translation/Adaptation Location . . . . . . . . . . . . . . .   6
   5.  Transition Plans  . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Understanding of Existing Deployment  . . . . . . . . . .   7
     5.2.  Explanation of Incentives . . . . . . . . . . . . . . . .   7
     5.3.  Description of Phases and Proposed Criteria . . . . . . .   8
     5.4.  Measurement of Success  . . . . . . . . . . . . . . . . .   8
     5.5.  Contingency Planning  . . . . . . . . . . . . . . . . . .   8
     5.6.  Communicating the Plan  . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Case Studies . . . . . . . . . . . . . . . . . . . .  14
     A.1.  Explicit Congestion Notification  . . . . . . . . . . . .  14
     A.2.  Internationalized Domain Names  . . . . . . . . . . . . .  15
     A.3.  IPv6  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     A.4.  HTTP  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
       A.4.1.  Protocol Versioning, Extensions, and 'Grease' . . . .  20
       A.4.2.  Limits on Changes in Major Versions . . . . . . . . .  20
       A.4.3.  Planning for Replacement  . . . . . . . . . . . . . .  21
   IAB Members at the Time of Approval . . . . . . . . . . . . . . .  22
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  22
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22
   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extensibility . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Transition vs. Coexistence  . . . . . . . . . . . . . . . . .   5
   4.  Translation/Adaptation Location . . . . . . . . . . . . . . .   6
   5.  Transition Plans  . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Understanding of Existing Deployment  . . . . . . . . . .   7
     5.2.  Explanation of Incentives . . . . . . . . . . . . . . . .   7
     5.3.  Description of Phases and Proposed Criteria . . . . . . .   8
     5.4.  Measurement of Success  . . . . . . . . . . . . . . . . .   8
     5.5.  Contingency Planning  . . . . . . . . . . . . . . . . . .   8
     5.6.  Communicating the Plan  . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Case Studies . . . . . . . . . . . . . . . . . . . .  14
     A.1.  Explicit Congestion Notification  . . . . . . . . . . . .  14
     A.2.  Internationalized Domain Names  . . . . . . . . . . . . .  15
     A.3.  IPv6  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     A.4.  HTTP  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
       A.4.1.  Protocol Versioning, Extensions, and 'Grease' . . . .  20
       A.4.2.  Limits on Changes in Major Versions . . . . . . . . .  20
       A.4.3.  Planning for Replacement  . . . . . . . . . . . . . .  21
   IAB Members at the Time of Approval . . . . . . . . . . . . . . .  22
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  22
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22
1. Introduction
1. 介绍

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 a web site). This document focuses solely on technical transitions, although some principles might apply to other types as well.


In this document, we use the term "transition" generically to apply to any of:


o adoption of a new protocol where none existed before,

o 通过一项以前不存在的新议定书,

o deployment of a new protocol that obsoletes a previous protocol,

o 部署淘汰以前协议的新协议,

o deployment of an updated version of an existing protocol, or

o 部署现有协议的更新版本,或

o decommissioning of an obsolete protocol.

o 废弃协议的退役。

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:

已经有许多IETF和IAB RFC以及IAB声明讨论了各种类型的转换。大多数是关于特定转换的协议特定文档。例如,IAB参与的一些相关项目包括:

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.

o IAB RFC 3424[RFC3424]建议,任何跨NAT的所谓“单边自定址(UNSAF)”技术都应包括一种退出策略,以摆脱这种机制。由于IESG而非IAB批准IETF文件,因此IESG成为执行(或不执行)此类要求的机构。

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 Working Group (WG) to address this problem.

o IAB RFC 4690[RFC4690]给出了关于国际化域名的建议。它讨论了向Unicode新版本过渡过程中的问题,并由此成立了IETF Precis工作组(WG)来解决这个问题。

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.

o IAB关于“NAT-PT的后续工作”[IabIpv6TransitionStatement]的声明指出了过渡到IPv6时的差距,这导致IETF Behave WG重新调整以解决此问题。

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:

IAB RFC 5218[RFC5218]关于“什么促成了一个成功的方案?”专门研究了哪些因素有助于和有损于一个方案的成功,并提出了一些建议。它讨论了两种类型的转换:“初始成功”(向技术的转换)和可扩展性(向更新版本的转换)。该文件中的原则和建议通常适用于所有技术过渡。一些重要原则包括:

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.

1. 激励措施:当利益降临到承担成本的人身上时,转型是最容易的。也就是说,每个实体的收益应该大于成本。一些成功案例通过提供激励(如税收减免)或通过降低成本(如免费提供来源),或通过施加不过渡的成本(如监管),甚至通过将适用场景缩小到所有相关实体的收益确实大于成本的情况来实现这一点。

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, 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.

2. 增量部署能力:向后兼容性使转换更容易。此外,当仅更改一个实体仍使该实体受益时,转换是最容易的。在最简单的情况下,收益立即超过成本,因此实体自然会被激励进行转型。更常见的情况是,一旦大量其他实体也进行了转型,收益才会超过成本。不幸的是,在这种情况下,自然的动机往往是推迟过渡。

3. Total Cost: It is important to consider costs that go beyond the core hardware and software, such as operational tools and processes, personnel training, business model (accounting/ billing) dependencies, and legal (regulation, patents, etc.) costs.

3. 总成本:重要的是考虑超出核心硬件和软件的成本,如操作工具和过程、人员培训、业务模型(计费/计费)依赖和法律(法规、专利等)成本。

4. Extensibility: Design for extensibility [RFC6709] so that things can be fixed up later.

4. 可扩展性:针对可扩展性[RFC6709]进行设计,以便以后可以解决问题。

IAB RFC 7305 [RFC7305] reported on an 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:

IAB RFC 7305[RFC7305]报告了IAB关于互联网技术采用和过渡(ITAT)的研讨会。与RFC 5218一样,本次研讨会也讨论了转型的经济方面,而不仅仅是技术方面。一些重要的意见包括:

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.

1. 早期采用者激励:比特币战略的一部分是与后期采用者相比,对早期采用者的额外激励。也就是说,为早期采用者提供长期优势有助于刺激转型,即使初始成本超过初始收益。

2. Policy Partners: Policy-making organizations of various sorts (Regional Internet Registries (RIRs), ICANN, etc.) can be important partners in enabling and facilitating transition.

2. 政策伙伴:各种政策制定组织(区域互联网注册中心(RIR)、ICANN等)可以成为促成和促进转型的重要伙伴。

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. Extensibility
2. 扩展性

Many protocols are designed to be extensible, using mechanisms such as options, version negotiation, etc., to ease the transition to new features. However, implementations often succumb to commercial pressures to ignore this flexibility in favor of performance or economy, and as a result such extension mechanisms (e.g., IPv6 Hop-by-Hop Options) often experience problems in practice once they begin to be used. In other cases, a mechanism might be put into a protocol for future use without having an adequate sense of how it will be used, which causes problems later (e.g., SNMP's original 'security'


field, or the IPv6 Flow Label). Thus, designers need to consider whether it would be easier to transition to a new protocol than it would be to ensure that an extension point is correctly specified and implemented such that it would be available when needed.


A protocol that plans for its own eventual replacement during its design makes later transitions easier. Developing and testing a design for the technical mechanisms needed to signal or negotiate a replacement is essential in such a plan.


When there is interest in translation between a new mechanism and an old one, complexity of such translation must also be considered. The major challenge in translation is for semantic differences. Often, syntactic differences can be translated seamlessly; semantic ones almost never. Hence, when designing for translatability, syntactic and semantic differences should be clearly documented.


See RFC 3692 [RFC3692] and RFC 6709 [RFC6709] for more discussion of design considerations for protocol extensions.

有关协议扩展设计注意事项的更多讨论,请参见RFC 3692[RFC3692]和RFC 6709[RFC6709]。

3. Transition vs. Coexistence
3. 过渡与共存

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 coexistence-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 because different parties can transition at different times. 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 coexistence. When a large number of entities are involved, a flag day becomes impractical or even impossible. 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 coexistence period may be complicated when differing incentives are involved (e.g., see the case studies in the Appendix).


Some new protocols or protocol versions are developed with the intent of never retiring the protocol they intend to replace. Such a


protocol might only aim to address a subset of the use cases for which an original is used. For these protocols, coexistence is the end state.


Indefinite coexistence as an approach could be viable if removal of the existing protocol is not an urgent goal. It might also be necessary for "wildly successful" protocols that have more disparate uses than can reasonably be considered during the design of a replacement. For example, HTTP/2 does not aspire to cause the eventual decommissioning of HTTP/1.1 for these reasons.


4. Translation/Adaptation Location
4. 翻译/改编地点

A translation or adaptation mechanism is often required if the old and new mechanisms are not interoperable. Care must be taken when determining whether one will work and where such a translator is best placed.


A translation mechanism may not work for every use case. For example, if translation from one protocol (or protocol version) to another produces indeterminate results, translation will not work reliably. In addition, if translation always produces a downgraded protocol result, the incentive considerations in Section 5.2 will be relevant.


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].


In addition, when a translator is within an endpoint, it can attempt to hide the difference between an older protocol and a newer protocol, either by exposing one of the two sets of behavior to applications and internally mapping it to the other set of behavior, or by exposing a higher level of abstraction that is then alternatively mapped to either one depending on detecting which is needed. In contrast, when a translator is in the middle of the path, typically only the first approach can be done since the middle of the path is typically unable to provide a higher level of abstraction.


Any transition strategy for a non-backward-compatible mechanism should include a discussion of where the incompatible mechanism is placed and a rationale. The transition plan should also consider the transition away from the use of translation and adaptation technologies.


5. Transition Plans
5. 过渡计划

A review of the case studies described in Appendix A suggests that a good transition plan include at least the following components: an understanding of what is already deployed and in use, an explanation of incentives for each entity involved, a description of the phases of the transition along with a proposed criteria for each phase, a method for measuring the transition's success, a contingency plan for failure of the transition, and an effective method for communicating the plan to the entities involved and incorporating their feedback thereon. We recommend that such criteria be considered when evaluating proposals to transition to new or updated protocols. Each of these components is discussed in the subsections below.


5.1. Understanding of Existing Deployment
5.1. 对现有部署的理解

Often an existing mechanism has variations in implementations and operational deployments. For example, a specification might include optional behaviors that may or may not be implemented or deployed. In addition, there may also be implementations or deployments that deviate from, or include vendor-specific extensions to, various aspects of a specification. It is important when considering a transition to understand what variations one is intending to transition from or coexist with, since the technical and non-technical issues may vary greatly as a result.


5.2. Explanation of Incentives
5.2. 对激励措施的解释

A transition plan should explain the incentives to each involved entity to support the transition. Note here that many entities other than the endpoint applications and their users may be affected, and the barriers to transition may be non-technical as well as technical. When considering these incentives, also consider network operations tools, practices and processes, personnel training, accounting and billing dependencies, and legal and regulatory incentives.


If there is opposition to a particular new protocol (e.g., from another standards organization, or a government, or some other affected entity), various non-technical issues arise that should be part of what is planned and dealt with. Similarly, if there are significant costs or other disincentives, the plan needs to consider how to overcome them.


It's worth noting that an analysis of incentives can be difficult and at times led astray by wishful thinking, as opposed to adequately considering economic realities. Thus, honestly considering any barriers to transition, and justifying one's conclusions about others' incentives, are key to a successful analysis.


5.3. Description of Phases and Proposed Criteria
5.3. 阶段和拟议标准的说明

Transition phases might include pilot/experimental deployment, coexistence, deprecation, and removal phases for a transition from one technology to another incompatible one.


Timelines are notoriously difficult to predict and impossible to impose on uncoordinated transitions at the scale of the Internet, but rough estimates can sometimes help all involved entities to understand the intended duration of each phase. More often, it is useful to provide criteria that must be met in order to move to the next phase. For example, is removal scheduled for a particular date (e.g., Federal Communications Commission (FCC) regulation to discontinue analog TV broadcasts in the U.S. by June 12, 2009), or is removal to be based on the use of the old mechanism falling below a specified level, or some other criteria?


As one example, RFC 5211 [RFC5211] proposed a transition plan for IPv6 that included a proposed timeline and criteria specific to each phase. While the timeline was not accurately followed, the phases and timeline did serve as inputs to the World IPv6 Day and World IPv6 Launch events.

例如,RFC 5211[RFC5211]提出了IPv6的过渡计划,其中包括针对每个阶段提出的时间表和标准。虽然没有准确遵循时间线,但阶段和时间线确实作为世界IPv6日和世界IPv6发布活动的输入。

5.4. Measurement of Success
5.4. 成功的衡量

The degree of deployment of a given protocol or feature at a given phase in its transition can be measured differently, depending on its design. For example, server-side protocols and options that identify themselves through a versioning or negotiation mechanism can be discovered through active Internet measurement studies.


5.5. Contingency Planning
5.5. 应急计划

A contingency plan can be as simple as providing for indefinite coexistence between an old and new protocol, or for reverting to the old protocol until an updated version of the new protocol is available. Such a plan is useful in the event that unforeseen problems are discovered during deployment, so that such problems can be quickly mitigated.


For example, World IPv6 Day included a contingency plan that was to revert to the original state at the end of the day. After discovering no issues, some participants found that this contingency plan was unnecessary and kept the new state.


5.6. Communicating the Plan
5.6. 传达计划

Many of the entities involved in a protocol transition may not be aware of the IETF or the RFC series, so dissemination through other channels is key for sufficiently broad communication of the transition plan. While flag days are impractical at Internet scale, coordinated "events" such as World IPv6 Launch may improve general awareness of an ongoing transition.


Also, there is often a need for an entity facilitating the transition through advocacy and focus. Such an entity, independent of the IETF, can be key in communicating the plan and its progress.


Some transitions have a risk of breaking backwards compatibility for some fraction of users. In such a case, when a transition affects competing entities facing the risk of losing customers to each other, there is an economic disincentive to transition. Thus, one role for a facilitating entity is to get competitors to transition during the same timeframe, so as to mitigate this fear. For example, the success of World IPv6 Launch was largely due to ISOC playing this role.


6. Security Considerations
6. 安全考虑

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 target. For further discussion of some of these issues, see Section 5 of [RFC7754].


In addition, coexistence of two protocols in general increases risk in the sense that it doubles the attack surface. It allows exploiters to choose the weaker of two protocols when both are available, or to force use of the weaker when negotiating between the protocols by claiming not to understand the stronger one.


7. IANA Considerations
7. IANA考虑

This document does not require any IANA actions.


8. Conclusion
8. 结论

This document summarized the set of issues that should be considered by protocol designers and deployers to facilitate transition and provides pointers to previous work (e.g., [RFC3692] and [RFC6709]) that provided detailed design guidelines. This document also covered what makes for a good transition plan and includes several case studies that provide examples. As more experience is gained over time on how to successfully apply these principles and design effective transition plans, we encourage the community to share such learnings with the IETF community and on the mailing list so that any future document on this topic can leverage such experience.


9. Informative References
9. 资料性引用

[GREASE] Benjamin, D., "Applying GREASE to TLS Extensibility", Work in Progress, draft-ietf-tls-grease-00, January 2017.


[HTTP0.9] Tim Berners-Lee, "The Original HTTP as defined in 1991", 1991, < AsImplemented.html>.

[HTTP0.9]Tim Berners Lee,“1991年定义的原始HTTP”,1991年< AsImplemented.html>。

[IabIpv6TransitionStatement] IAB, "Follow-up work on NAT-PT", October 2007, <>.


[IPv6Survey2011] Botterman, M., "IPv6 Deployment Survey", 2011, < ipv6_deployment_survey.pdf>.

[IPv6Survey2011]Botterman,M.,“IPv6部署调查”,2011年< ipv6\u部署\u调查.pdf>。

[IPv6Survey2015] British Telecommunications, "IPv6 Industry Survey Report", August 2015, < ts/pdf/products/diamond_ip/IPv6-Survey-Report-2015.pdf>.

[IPv6Survey2015]英国电信,“IPv6行业调查报告”,2015年8月< ts/pdf/products/diamond_ip/IPv6-Survey-Report-2015.pdf>。

[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, DOI 10.1007/978-3-319-15509-8_15, 2015, <>.

[PAM2015]Trammell,B.,Kuehlewind,M.,Boppart,D.,Learmonth,I.,Fairhurst,G.,和R.Scheffenegger,“在互联网范围内部署明确的拥塞通知”,PAM 2015会议录,DOI 10.1007/978-3-319-15509-8,2015<>.

[RFC1883] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 1883, DOI 10.17487/RFC1883, December 1995, <>.

[RFC1883]Deering,S.和R.Hinden,“互联网协议,第6版(IPv6)规范”,RFC 1883,DOI 10.17487/RFC1883,1995年12月<>.

[RFC1933] Gilligan, R. and E. Nordmark, "Transition Mechanisms for IPv6 Hosts and Routers", RFC 1933, DOI 10.17487/RFC1933, April 1996, <>.

[RFC1933]Gilligan,R.和E.Nordmark,“IPv6主机和路由器的过渡机制”,RFC 1933,DOI 10.17487/RFC1933,1996年4月<>.

[RFC1945] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945, DOI 10.17487/RFC1945, May 1996, <>.

[RFC1945]Berners Lee,T.,Fielding,R.,和H.Frystyk,“超文本传输协议——HTTP/1.0”,RFC 1945,DOI 10.17487/RFC1945,1996年5月<>.

[RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, DOI 10.17487/RFC2068, January 1997, <>.

[RFC2068]菲尔丁,R.,盖蒂斯,J.,莫卧儿,J.,弗莱斯蒂克,H.,和T.伯纳斯李,“超文本传输协议——HTTP/1.1”,RFC 2068,DOI 10.17487/RFC2068,1997年1月<>.

[RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Frystyk, "Use and Interpretation of HTTP Version Numbers", RFC 2145, DOI 10.17487/RFC2145, May 1997, <>.

[RFC2145]Mogul,J.,Fielding,R.,Gettys,J.,和H.Frystyk,“HTTP版本号的使用和解释”,RFC 2145,DOI 10.17487/RFC2145,1997年5月<>.

[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, <>.

[RFC3168]Ramakrishnan,K.,Floyd,S.,和D.Black,“向IP添加显式拥塞通知(ECN)”,RFC 3168,DOI 10.17487/RFC3168,2001年9月<>.

[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, <>.

[RFC3424]Daigle,L.,Ed.和IAB,“网络地址转换中单边自地址固定(UNSAF)的IAB考虑”,RFC 3424DOI 10.17487/RFC3424,2002年11月<>.

[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, DOI 10.17487/RFC3692, January 2004, <>.

[RFC3692]Narten,T.,“分配被认为有用的实验和测试数字”,BCP 82,RFC 3692,DOI 10.17487/RFC3692,2004年1月<>.

[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)", RFC 4380, DOI 10.17487/RFC4380, February 2006, <>.

[RFC4380]Huitema,C.,“Teredo:通过网络地址转换(NAT)通过UDP传输IPv6”,RFC 4380,DOI 10.17487/RFC4380,2006年2月<>.

[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, <>.

[RFC4632]Fuller,V.和T.Li,“无类域间路由(CIDR):互联网地址分配和聚合计划”,BCP 122,RFC 4632,DOI 10.17487/RFC4632,2006年8月<>.

[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, <>.

[RFC4690]Klensin,J.,Faltstrom,P.,Karp,C.,和IAB,“国际化域名(IDN)的审查和建议”,RFC 4690,DOI 10.17487/RFC4690,2006年9月<>.

[RFC5211] Curran, J., "An Internet Transition Plan", RFC 5211, DOI 10.17487/RFC5211, July 2008, <>.

[RFC5211]Curran,J.,“互联网转型计划”,RFC 5211DOI 10.17487/RFC5211,2008年7月<>.

[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008, <>.

[RFC5218]Thaler,D.和B.Aboba,“什么是成功的方案?”RFC 5218,DOI 10.17487/RFC5218,2008年7月<>.

[RFC5894] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010, <>.

[RFC5894]Klensin,J.,“应用程序的国际化域名(IDNA):背景、解释和理由”,RFC 5894,DOI 10.17487/RFC5894,2010年8月<>.

[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008", RFC 5895, DOI 10.17487/RFC5895, September 2010, <>.

[RFC5895]Resnick,P.和P.Hoffman,“应用程序中国际化域名的映射字符(IDNA)2008”,RFC 5895,DOI 10.17487/RFC5895,2010年9月<>.

[RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on Encodings for Internationalized Domain Names", RFC 6055, DOI 10.17487/RFC6055, February 2011, <>.

[RFC6055]Thaler,D.,Klensin,J.,和S.Cheshire,“IAB对国际化域名编码的思考”,RFC 6055,DOI 10.17487/RFC6055,2011年2月<>.

[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, <>.

[RFC6269]福特,M.,Ed.,Boucadair,M.,Durand,A.,Levis,P.,和P.Roberts,“IP地址共享问题”,RFC 6269,DOI 10.17487/RFC62692011年6月<>.

[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC 6455, DOI 10.17487/RFC6455, December 2011, <>.

[RFC6455]Fette,I.和A.Melnikov,“WebSocket协议”,RFC 6455,DOI 10.17487/RFC6455,2011年12月<>.

[RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design Considerations for Protocol Extensions", RFC 6709, DOI 10.17487/RFC6709, September 2012, <>.

[RFC6709]Carpenter,B.,Aboba,B.,Ed.,和S.Cheshire,“协议扩展的设计考虑”,RFC 6709,DOI 10.17487/RFC6709,2012年9月<>.

[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, <>.

[RFC7021]Donley,C.,Ed.,Howard,L.,Kuarsingh,V.,Berg,J.,和J.Doshi,“评估运营商级NAT对网络应用的影响”,RFC 7021,DOI 10.17487/RFC70212013年9月<>.

[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, <>.

[RFC7228]Bormann,C.,Ersue,M.和A.Keranen,“受限节点网络的术语”,RFC 7228,DOI 10.17487/RFC7228,2014年5月<>.

[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, <>.

[RFC7230]Fielding,R.,Ed.和J.Reschke,Ed.,“超文本传输协议(HTTP/1.1):消息语法和路由”,RFC 7230,DOI 10.17487/RFC7230,2014年6月<>.

[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, <>.

[RFC7301]Friedl,S.,Popov,A.,Langley,A.,和E.Stephan,“传输层安全(TLS)应用层协议协商扩展”,RFC 7301,DOI 10.17487/RFC7301,2014年7月<>.

[RFC7305] Lear, E., Ed., "Report from the IAB Workshop on Internet Technology Adoption and Transition (ITAT)", RFC 7305, DOI 10.17487/RFC7305, July 2014, <>.

[RFC7305]李尔,E.,编辑,“IAB互联网技术采用和转型研讨会(ITAT)的报告”,RFC 7305,DOI 10.17487/RFC7305,2014年7月<>.

[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, <>.

[RFC7540]Belshe,M.,Paon,R.,和M.Thomson,编辑,“超文本传输协议版本2(HTTP/2)”,RFC 7540,DOI 10.17487/RFC7540,2015年5月<>.

[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, <>.

[RFC7541]Paun,R.和H.Ruellan,“HPACK:HTTP/2的报头压缩”,RFC 7541,DOI 10.17487/RFC7541,2015年5月<>.

[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, <>.

[RFC7754]Barnes,R.,Cooper,A.,Kolkman,O.,Thaler,D.,和E.Nordmark,“互联网服务阻塞和过滤的技术考虑”,RFC 7754,DOI 10.17487/RFC7754,2016年3月<>.

[TR46] The Unicode Consortium, "Unicode IDNA Compatibility Processing", Version 9.0.0, June 2016, <>.

[TR46]Unicode联盟,“Unicode IDNA兼容性处理”,9.0.0版,2016年6月<>.

[TSV2007] Sridharan, M., Bansal, D., and D. Thaler, "Implementation Report on Experiences with Various TCP RFCs", Proceedings of IETF 68, March 2007, < 68/slides/tsvarea-3/sld1.htm>.

[TSV2007]Sridharan,M.,Bansal,D.,和D.Thaler,“关于各种TCP RFC经验的实施报告”,IETF 68会议记录,2007年3月< 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 Appendix 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 included here that is sufficient to justify the conclusions in the body of this document.


A.1. Explicit Congestion Notification
A.1. 显式拥塞通知

Explicit Congestion Notification (ECN) is a mechanism to replace loss as the only signal for the detection of congestion. It does this with an explicit signal first sent from a router to a recipient of a packet, which is then reflected back to the sender. It was standardized in 2001 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.

显式拥塞通知(ECN)是一种替代丢失作为拥塞检测唯一信号的机制。它通过一个明确的信号来实现这一点,该信号首先从路由器发送到数据包的接收者,然后反射回发送者。该机制于2001年在[RFC3168]中进行了标准化,该机制由两部分组成:IP层中的拥塞检测、重用旧IP服务类型(TOS)字段的两位以及传输层中的拥塞反馈。TCP中的反馈使用两个TCP标志,ECN Echo和拥塞窗口缩减。与适当配置的主动队列管理(AQM)一起,ECN可以提高拥塞链路上的TCP性能。

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 were 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 Internet had failed.

ECN的部署是一个失败的过渡以及可能的赎回的案例研究。在2000年代早期和中期首次部署ECN导致一些网络设备出现严重问题,包括当接收到带有ECN IP或TCP标志的数据包时家庭路由器崩溃和重新启动[TSV2007]。这导致防火墙剥离ECN IP和TCP标志,甚至丢弃设置了这些标志的数据包。这使部署陷入僵局。需要两个端点(协商并支持ECN)和路径设备(在发生拥塞时标记流量)进行合作,以便从ECN部署中看到任何好处,这是一个进一步的问题。在Internet上部署ECN失败。

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 was 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, and 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

在21世纪末,Linux和Windows服务器开始默认为“被动ECN支持”,这意味着如果客户端要求,它们将协商ECN,但默认情况下不会要求协商ECN。这个决定被认为是没有风险的:只有当客户端被明确配置为协商ECN时,任何可能的连接问题才会出现。逐渐地,这增加了互联网上的服务器支持,从2008年的接近零,到2011年Alexa Web服务器总数的11%,到2012年的30%,到2014年底的65%。同时,ECN协商的连通性风险已大幅降低[PAM2015],导致正在进行的工作需要进一步改进

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.

默认情况下,Windows、Apple iOS、OSX和Linux客户端协商ECN。希望通过协商ECN的大量客户机和服务器将提供一种激励,在启用ECN的流量上标记拥塞,从而打破僵局。

A.2. Internationalized Domain Names
A.2. 国际化域名

The deployment of Internationalized Domain Names (IDNs) has a long and complicated history. This should not be surprising, since internationalization deals with language and cultural issues regarding differing expectations of users around the world, thus making it inherently difficult to agree on common rules.


Furthermore, because human languages evolve and change over time, even if common rules can be established, there is likely to be a need to review and update them regularly.


There have been multiple technical transitions related to IDNs, including the introduction of non-ASCII in DNS, the transition to each new version of Unicode, and the transition from IDNA 2003 to IDNA 2008. A brief history of the introduction of non-ASCII in DNS and the various complications that arose therein, can be found in Section 3 of [RFC6055]. While IDNA 2003 was limited to Unicode version 3.2 only, one of the IDNA 2008 changes was to decouple its rules from any particular version of Unicode (see [RFC5894], especially Section 1.4, for more discussion of this point, and see [RFC4690] for a list of other issues with IDNA 2003 that motivated IDNA 2008). However, the transition from IDNA 2003 to IDNA 2008 itself presented a problem since IDNA 2008 did not preserve backwards compatibility with IDNA 2003 for a couple of codepoints. Investigations and discussions with affected parties led to the IETF ultimately choosing IDNA 2008 because the overall gain by moving to IDNA 2008 to fix the problems with IDNA 2003 was seen to be much greater than the problems due to the few incompatibilities at the time of the change, as not many IDNs were in use and even fewer that might see incompatibilities.

与IDN相关的技术转换有多个,包括在DNS中引入非ASCII,转换到每个新版本的Unicode,以及从IDNA 2003转换到IDNA 2008。[RFC6055]第3节简要介绍了DNS中引入非ASCII码的历史以及由此产生的各种复杂情况。虽然IDNA 2003仅限于Unicode版本3.2,但IDNA 2008的一个变化是将其规则与任何特定的Unicode版本分离(有关这一点的更多讨论,请参阅[RFC5894],特别是第1.4节,并参阅[RFC4690]以了解IDNA 2003引发IDNA 2008的其他问题列表)。然而,从IDNA 2003到IDNA 2008的过渡本身就带来了一个问题,因为IDNA 2008没有为几个代码点保留与IDNA 2003的向后兼容性。通过与受影响方的调查和讨论,IETF最终选择了IDNA 2008,因为通过转移到IDNA 2008解决IDNA 2003的问题,总体收益被视为远远大于因变更时少数不兼容而产生的问题,由于使用的IDN不多,甚至更少,因此可能会出现不兼容。

A couple of browser vendors in particular were concerned about the differences between IDNA 2003 and IDNA 2008, and the fact that if a browser stopped being able to get to some site, or unknowingly sent a user to a different (e.g., phishing) site instead, the browser would be blamed. As such, any user-perceivable change from IDNA 2003 behavior would be painful to the vendor to deal with; hence, they could not depend on solutions that would need action by other entities.

一些浏览器供应商特别关注IDNA 2003和IDNA 2008之间的差异,如果浏览器无法访问某个站点,或者在不知情的情况下将用户发送到另一个(如钓鱼)站点,那么浏览器将受到指责。因此,用户从IDNA 2003行为中感知到的任何变化都会让供应商感到痛苦;因此,它们不能依赖需要其他实体采取行动的解决办法。

Thus, to deal with issues like such incompatibilities, some applications and client-side frameworks wanted to map one string into another (namely, a string that would give the same result as when IDNA 2003 was used) before invoking DNS.

因此,为了处理此类不兼容问题,一些应用程序和客户端框架希望在调用DNS之前将一个字符串映射到另一个字符串(即,一个与使用IDNA 2003时产生相同结果的字符串)。

To provide such mapping (and some other functionality), the Unicode Consortium published [TR46], which continued down the path of IDNA 2003 with a code point by code point selection mechanism. This was implemented by some, but never adopted by the IETF.

为了提供这样的映射(以及一些其他功能),Unicode联盟发布了[TR46],它通过一种逐码点选择机制沿着IDNA 2003的道路继续前进。这是由一些人实现的,但IETF从未采用过。

Meanwhile, the IETF did not publish any mapping mechanism, but [RFC5895] was published on the Independent Submission stream. In discussions around mapping, one of the key topics was about how long the transition should last. At one end of the duration spectrum is a flag day where some entities would be broken initially but the change would happen before IDN usage became even more ubiquitous. At the other end of the spectrum is the need to maintain mappings indefinitely. Local incentives at each entity who needed to change, however, meant that a short timeframe was impractical.


There are many affected types of entities with very different incentives. For example, the incentives affecting browser vendors, registries, domain name marketers and applicants, app developers, and protocol designers are each quite different, and the various solutions require changes by multiple types of entities, where the benefits do not always align with the costs. If there is some group (or even an individual) that is opposed to a change/transition and able to put significant resources behind their opposition, transitions get a lot harder.


Finally, there are multiple naming contexts, and the protocol behavior (including how internationalized domain names are handled) within each naming context can be different. Hence, applications and frameworks often encounter a variety of behaviors and may or may not be designed to deal with them. See Sections 2 and 3 of [RFC6055] for more discussion.


In summary, all this diversity can cause problems for each affected entity, especially if a competitor does not have such a problem, e.g., for browser vendors if competing browsers do not have the same problems, or for an email server provider if competing server providers do not have the same problems.


A.3. IPv6
A.3. 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]) was published less than a year after the protocol itself. It recommended coexistence (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 Classless Inter-Domain Routing (CIDR) [RFC4632] , 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 Interactive Connectivity Establishment (ICE), Session Traversal Utilities for NAT (STUN), and Traversal Using Relays around NAT (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 that 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 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.


Some early advocates overstated the benefits of IPv6, suggesting that it had better security (because IPsec was required) or that NAT was worse than it often appeared to be or that IPv4 exhaustion would happen years sooner than it actually did. Some people pushed back on these exaggerations, and decided that the protocol itself somehow lacked credibility.


Not until a few years after IPv4 addresses were exhausted in various RIR regions did IPv6 deployment significantly increase. The RIRs had been advocating in their communities for IPv6 for some time, reducing fees for IPv6, and in some cases providing training; there is little to suggest that these had a significant effect. 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. By including multiple competitors, World IPv6 Day reduced the risk that any of them would lose customers if a user's IPv6 implementation was broken. World IPv6 Launch then set a goal for content providers to permanently enable IPv6, and for large ISPs to enable IPv6 for at least 1% of end users. These large, visible deployments gave vendors specific features and target dates to support IPv6 well. Key aspects of World IPv6 Day and World IPv6 Launch that contributed to their successes (measured as increased deployment of IPv6) were the communication through ISOC, and that measurement metrics and contingency plans were announced in advance.

可以说,具有前瞻性的公司在世界IPv6日和世界IPv6发布日与ISOC合作,以启动全球IPv6部署。通过将多个竞争对手包括在内,世界IPv6日降低了如果用户的IPv6实施被破坏,其中任何一家都会失去客户的风险。然后,World IPv6 Launch为内容提供商设定了永久启用IPv6的目标,并为大型ISP设定了至少1%的最终用户启用IPv6的目标。这些大型、可见的部署为供应商提供了特定的功能和目标日期,以更好地支持IPv6。世界IPv6日和世界IPv6发布的关键方面(衡量为IPv6部署的增加)是通过ISOC进行的通信,并且提前宣布了度量指标和应急计划,这两个方面为其成功做出了贡献。

Several efforts have been made to mitigate the lack of a business case. Some governments (South Korea and Japan) provided tax incentives to include IPv6. Other governments (Belgium and 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 that 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 Content Delivery Network (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 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.4. 超文本传输协议

HTTP has been through several transitions as a protocol.


The first version [HTTP0.9] was extremely simple, with no headers, status codes, or explicit versioning. HTTP/1.0 [RFC1945] introduced these and a number of other concepts; it succeeded mostly because deployment of HTTP was still relatively new, with a small pool of implementers and (comparatively) small set of deployments and users.


HTTP/1.1 [RFC7230] (first defined in [RFC2068]) was an attempt to make the protocol suitable for the massive scale it was being deployed upon and to introduce some new features.


HTTP/2 [RFC7540] was largely aimed at improving performance. The primary improvement was the introduction of request multiplexing, which is supported by request prioritization and flow control. It also introduced header compression [RFC7541] and binary framing; this made it completely backwards incompatible on the wire, but still semantically compatible with previous versions of the protocol.


A.4.1. Protocol Versioning, Extensions, and 'Grease'
A.4.1. 协议版本控制、扩展和“润滑脂”

During the development of HTTP/1.1, there was a fair amount of confusion regarding the semantics of HTTP version numbers, resulting in [RFC2145]. Later, it was felt that minor versioning in the protocol caused more confusion than it was worth, so HTTP/2.0 became HTTP/2.


This decision was informed by the observation that many implementations ignored the major version number of the protocol or misinterpreted it. As is the case with many protocol extension points, HTTP versioning had failed to be "greased" by use often enough, and so had become "rusted" so that only a limited range of values could interoperate.


This phenomenon has been observed in other protocols, such as TLS (as exemplified by [GREASE]), and there are active efforts to identify extension points that are in need of such "grease" and making it appear as if they are in use.


Besides the protocol version, HTTP's extension points that are well-greased include header fields, status codes, media types, and cache-control extensions; HTTP methods, content-encodings, and chunk-extensions enjoy less flexibility, and need to be extended more cautiously.


A.4.2. Limits on Changes in Major Versions
A.4.2. 主要版本中的更改限制

Each update to the "major" version of HTTP has been accompanied by changes that weren't compatible with previous versions. This was not uniformly successful given the diversity and scale of deployment and implementations.


HTTP/1.1 introduced pipelining to improve protocol efficiency. Although it did enjoy implementation, interoperability did not follow.


This was partially because many existing implementations had chosen architectures that did not lend themselves to supporting it; pipelining was not uniformly implemented and where it was, support was sometimes incorrect or incomplete. Since support for pipelining was indicated by the protocol version number itself, interop was difficult to achieve, and furthermore its inability to completely address head-of-line blocking issues made pipelining unattractive.


Likewise, HTTP/1.1's Expect/Continue mechanism relied on wide support for the new semantics it introduced and did not have an adequate fallback strategy for previous versions of the protocol. As a


result, interoperability and deployment suffered and is still considered a "problem area" for the protocol.


More recently, the HTTP working group decided that HTTP/2 represented an opportunity to improve security, making the protocol much stricter than previous versions about the use of TLS. To this end, a long list of TLS cipher suites were prohibited, constraints were placed on the key exchange method, and renegotiation was prohibited.


This 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 as part of the HTTP/2 process and considered for removal. 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.


A.4.3. Planning for Replacement
A.4.3. 更换计划

HTTP/1.1 provided the Upgrade header field to enable transitioning a connection to an entirely different protocol. So far, this has been little-used, other than to enable the use of WebSockets [RFC6455].

HTTP/1.1提供了Upgrade header字段,以允许将连接转换为完全不同的协议。到目前为止,除了支持WebSocket的使用[RFC6455]之外,很少使用它。

With performance being a primary motivation for HTTP/2, a new mechanism was needed to avoid spending an additional round trip on protocol 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 primary way in which future protocol versions would be negotiated. The mechanism was well-tested during development of the specification, proving that new versions could be deployed safely and easily. Several draft versions of the protocol were successfully deployed during 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 [RFC5218], though is completely consistent


with [RFC6709]: few extension points were added, 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.


IAB Members at the Time of Approval


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




This document is a product of the IAB Stack Evolution Program, with input from many others. In particular, Mark Nottingham, Dave Crocker, Eliot Lear, Joe Touch, Cameron Byrne, John Klensin, Patrik Faltstrom, the IETF Applications Area WG, and others provided helpful input on this document.


Author's Address


Dave Thaler (editor) One Microsoft Way Redmond, WA 98052 United States of America

Dave Thaler(编辑)One Microsoft Way Redmond,WA 98052美利坚合众国