Network Working Group                                                IAB
Request for Comments: 3177                                          IESG
Category: Informational                                   September 2001
Network Working Group                                                IAB
Request for Comments: 3177                                          IESG
Category: Informational                                   September 2001

IAB/IESG Recommendations on IPv6 Address Allocations to Sites


Status of this Memo


This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.


Copyright Notice


Copyright (C) The Internet Society (2001). All Rights Reserved.




This document provides recommendations to the addressing registries (APNIC, ARIN and RIPE-NCC) on policies for assigning IPv6 address blocks to end sites. In particular, it recommends the assignment of /48 in the general case, /64 when it is known that one and only one subnet is needed and /128 when it is absolutely known that one and only one device is connecting.


The original recommendations were made in an IAB/IESG statement mailed to the registries on September 1, 2000. This document refines the original recommendation and documents it for the historical record.


1. Introduction
1. 介绍

There have been many discussions between IETF and RIR experts on the topic of IPv6 address allocation policy. This memo addresses the issue of the boundary in between the public and the private topology in the Internet, that is, how much address space should an ISP allocate to homes, small and large enterprises, mobile networks and transient customers.


This document does not address the issue of the other boundaries in the public topology, that is, between the RIRs and the LIRs.


This document was developed by the IPv6 Directorate, IAB and IESG, and is a recommendation from the IAB and IESG to the RIRs.


2. Background
2. 出身背景

The technical principles that apply to address allocation seek to balance healthy conservation practices and wisdom with a certain ease of access. On one hand, when managing a potentially limited resource, one must conserve wisely to prevent exhaustion within an expected lifetime. On the other hand, the IPv6 address space is in no sense as limited a resource as the IPv4 address space, and unwarranted conservatism acts as a disincentive in a marketplace already dampened by other factors. So from a market development perspective, we would like to see it be very easy for a user or an ISP to obtain as many IPv6 addresses as they really need without a prospect of immediate renumbering or of scaling inefficiencies.


The IETF makes no comment on business issues or relationships. However, in general, we observe that technical delegation policy can have strong business impacts. A strong requirement of the address delegation plan is that it not be predicated on or unduly bias business relationships or models.


The IPv6 address, as currently defined, consists of 64 bits of "network number" and 64 bits of "host number". The technical reasons for this are several. The requirements for IPv6 agreed to in 1993 included a plan to be able to address approximately 2^40 networks and 2^50 hosts; the 64/64 split effectively accomplishes this. Procedures used in host address assignment, such as the router advertisement of a network's prefix to hosts [RFC2462], which in turn place a locally unique number in the host portion, depend on this split. Subnet numbers must be assumed to come from the network part. This is not to preclude routing protocols such as IS-IS level 1 (intra-area) routing, which routes individual host addresses, but says that it may not be depended upon in the world outside that zone. The 64-bit host field can also be used with EUI-64 for a flat, uniquely allocated space, and therefore it may not be globally treated as a subnetting resource. Those concerned with privacy issues linked to the presence of a globally unique identifier may note that 64 bits makes a large enough field to maintain excellent random-number-draw properties for self-configured End System Designators. That alternative construction of this 64-bit host part of an IPv6 address is documented in [RFC3041].


While the IETF has also gone to a great deal of effort to minimize the impacts of network renumbering, renumbering of IPv6 networks is neither invisible nor completely painless. Therefore, renumbering should be considered a tolerable event, but to be avoided if reasonably feasible.


In [RFC2374] and [RFC2450], the IETF's IPNG working group has recommended that the address block given to a single edge network which may be recursively subnetted be a 48-bit prefix. This gives each such network 2^16 subnet numbers to use in routing, and a very large number of unique host numbers within each network. This is deemed to be large enough for most enterprises, and to leave plenty of room for delegation of address blocks to aggregating entities.


It is not obvious, however, that all edge networks are likely to be recursively subnetted; a single PC in a home or a telephone in a mobile cellular network, for example, may or may not interface to a subnetted local network. When a network number is delegated to a place that will not require subnetting, therefore, it might be acceptable for an ISP to give a single 64-bit prefix - perhaps shared among the dial-in connections to the same ISP router. However this decision may be taken in the knowledge that there is objectively no shortage of /48s, and the expectation that personal, home networks will become the norm. Indeed, it is widely expected that all IPv6 subscribers, whether domestic (homes), mobile (vehicles or individuals), or enterprises of any size, will eventually possess multiple always-on hosts, at least one subnet with the potential for additional subnetting, and therefore some internal routing capability. In other words the subscriber allocation unit is not always a host; it is always potentially a site. The question this memo is addressing is how much address space should be delegated to such sites.


3. Address Delegation Recommendations
3. 处理代表团的建议

The IESG and the IAB recommend the allocations for the boundary between the public and the private topology to follow those general rules:


- /48 in the general case, except for very large subscribers. - /64 when it is known that one and only one subnet is needed by design. - /128 when it is absolutely known that one and only one device is connecting.

- /48在一般情况下,除了非常大的订户/64当已知设计只需要一个子网时。-/128当完全知道只有一个设备正在连接时。

In particular, we recommend:


- Home network subscribers, connecting through on-demand or always-on connections should receive a /48. - Small and large enterprises should receive a /48. - Very large subscribers could receive a /47 or slightly shorter prefix, or multiple /48's.

- 家庭网络用户,通过按需或常开连接连接,应收到a/48。-小型和大型企业应获得a/48非常大的订户可以收到一个/47或略短的前缀,或多个/48。

- Mobile networks, such as vehicles or mobile phones with an additional network interface (such as bluetooth or 802.11b) should receive a static /64 prefix to allow the connection of multiple devices through one subnet. - A single PC, with no additional need to subnet, dialing-up from a hotel room may receive its /128 IPv6 address for a PPP style connection as part of a /64 prefix.

- 移动网络,如带有附加网络接口(如蓝牙或802.11b)的车辆或移动电话,应接收静态/64前缀,以允许通过一个子网连接多个设备。-从酒店房间拨号的一台PC(无需附加子网)可能会收到其作为/64前缀的一部分的PPP式连接的/128 IPv6地址。

Note that there seems to be little benefit in not giving a /48 if future growth is anticipated. In the following, we give the arguments for a uniform use of /48 and then demonstrate that it is entirely compatible with responsible stewardship of the total IPv6 address space.


The arguments for the fixed boundary are:


- That only by having a provider-independent boundary can we guarantee that a change of ISP will not require a costly internal restructuring or consolidation of subnets.

- 只有拥有一个独立于提供商的边界,我们才能保证ISP的变更不需要昂贵的内部重组或子网整合。

- That during straightforward site renumbering from one prefix to another the whole process, including parallel running of the two prefixes, would be greatly complicated if the prefixes had different lengths (depending of course on the size and complexity of the site).

- 在直接将站点从一个前缀重新编号到另一个前缀的过程中,如果前缀的长度不同(当然取决于站点的大小和复杂性),整个过程(包括两个前缀的并行运行)将非常复杂。

- There are various possible approaches to multihoming for IPv6 sites, including the techniques already used for IPv4 multihoming. The main open issue is finding solutions that scale massively without unduly damaging route aggregation and/or optimal route selection. Much more work remains to be done in this area, but it seems likely that several approaches will be deployed in practice, each with their own advantages and disadvantages. Some (but not all) will work better with a fixed prefix boundary. (Multihoming is discussed in more detail below.)

- IPv6站点的多宿主有多种可能的方法,包括已用于IPv4多宿主的技术。主要的公开问题是找到大规模扩展的解决方案,而不会过度破坏路线聚合和/或最佳路线选择。在这方面还有许多工作要做,但似乎有可能在实践中采用几种方法,每种方法各有优缺点。有些(但不是全部)在使用固定前缀边界时效果更好。(下文将更详细地讨论多重归宿。)

- To allow easy growth of the subscribers' networks without need to go back to ISPs for more space (except for that relatively small number of subscribers for which a /48 is not enough).

- 允许用户网络的轻松增长,而无需回到ISP获得更多空间(除了数量相对较少的用户,a/48还不够)。

- To remove the burden from the ISPs and registries of judging sites' needs for address space, unless the site requests more space than a /48. This carries several advantages:

- 消除ISP和注册中心判断站点地址空间需求的负担,除非站点请求的空间超过a/48。这有几个好处:

- It may become less critical for ISPs to be able to maintain detailed knowledge of their customers' network architecture and growth plans,

- ISP能够保持对其客户网络架构和增长计划的详细了解可能变得不那么重要,

- ISPs and registries may reduce the effort spent on assessing rates of address consumption, with address space ample for long-term growth plans, - Registry operations may be made more efficient or more focused, by reducing the urgency of tracking and assessment. - Address space will no longer be a precious resource for customers, removing the major incentive for subscribers to install v6/v6 NATs, which would defeat the IPv6 restoration of address transparency.

- ISP和注册中心可能会减少在评估地址消耗率上所花费的精力,因为地址空间对于长期增长计划来说是充足的,-通过减少跟踪和评估的紧迫性,注册中心的运营可能会更加高效或更加集中。-地址空间将不再是客户的宝贵资源,从而消除了订阅者安装v6/v6 NAT的主要动机,这将破坏IPv6地址透明性恢复。

- To allow the site to maintain a single reverse-DNS zone covering all prefixes.

- 允许站点维护覆盖所有前缀的单个反向DNS区域。

- If and only if a site can use the same subnetting structure under each of its prefixes, then it can use the same zone file for the address-to-name mapping of all of them. And, using the conventions of [RFC2874], it can roll the reverse mapping data into the "forward" (name-keyed) zone.

- 如果且仅当一个站点可以在其每个前缀下使用相同的子网结构,则它可以使用相同的区域文件作为所有前缀的地址到名称映射。并且,使用[RFC2874]的约定,它可以将反向映射数据滚动到“前进”(名称键控)区域。

Specific advantages of the fixed boundary being at /48 include


- To leave open the technical option of retro-fitting the GSE (Global, Site and End-System Designator, a.k.a., "8+8") proposal for separating locators and identifiers, which assumes a fixed boundary between global and site addressing at /48. Although the GSE technique was deferred a couple of years ago, it still has strong proponents. Also, the IRTF Namespace Research Group is actively looking into topics closely related to GSE. It is still possible that GSE or a derivative of GSE will be used with IPv6 in the future.

- 保留对GSE(全球、现场和终端系统指示器,也称“8+8”)进行重新装配的技术选项,用于分离定位器和标识符,假设全球和现场地址在/48之间存在固定边界。虽然GSE技术在几年前被推迟,但它仍然有强烈的支持者。此外,IRTF名称空间研究小组正在积极研究与GSE密切相关的主题。GSE或GSE的衍生物将来仍有可能与IPv6一起使用。

- Since the site-local prefix is fec0::/48, global site prefixes of /48 will allow sites to easily maintain a trivial (identity) mapping between the global topology and the site-local topology in the SLA field.

- 由于站点本地前缀为fec0::/48,全局站点前缀为/48将允许站点在SLA字段中轻松维护全局拓扑和站点本地拓扑之间的简单(标识)映射。

- Similarly, if the 6to4 proposal is widely deployed, migration from a 6to4 prefix, which is /48 by construction, to a native IPv6 prefix will be simplified if the native prefix is /48.

- 类似地,如果6to4方案得到广泛部署,则如果本机前缀为/48,则从6to4前缀(构造为/48)到本机IPv6前缀的迁移将简化。

4. Conservation of Address Space
4. 地址空间守恒

The question naturally arises whether giving a /48 to every subscriber represents a profligate waste of address space. Objective analysis shows that this is not the case. A /48 prefix under the 001 Global Unicast Address prefix contains 45 variable bits. That is, the number of available prefixes is 2 to the power 45 or about 35 trillion (35,184,372,088,832).


More precisely,


- [RFC1715] defines an "H ratio" based on experience in address space assignment in various networks. The H ratio varies between 0 and 0.3, with larger values denoting denser, more efficient assignment. Experience shows that problems start to occur when the H ratio becomes greater than 0.25. At an H ratio of 0.25, a 45 bit address space would have 178 billion (178 thousand million) identifiers.

- [RFC1715]根据各种网络中地址空间分配的经验定义了“H比率”。H比率在0和0.3之间变化,较大的值表示更密集、更有效的分配。经验表明,当H比大于0.25时,问题开始出现。在H比率为0.25时,45位地址空间将有1780亿(178亿)标识符。

            H = log10(178*10^9) / 45 = 0.25
            H = log10(178*10^9) / 45 = 0.25

This means that we feel comfortable about the prospect of allocating 178 billions /48 prefixes under that scheme before problems start to appear. To understand how big that number is, one has to compare 178 billion to 10 billion, which is the projected population on earth in year 2050 (see These numbers give no grounds for concern provided that the ISPs, under the guidance of the RIRs, allocate /48's prudently, and that the IETF refrains from new recommendations that further reduce the remaining 45 variable bits, unless a compelling requirement emerges.

这意味着,在问题开始出现之前,我们对在该方案下分配1780亿/48个前缀的前景感到放心。要了解这个数字有多大,我们必须将1780亿到100亿进行比较,这是2050年地球上的预计人口(参见 如果ISP在RIRs的指导下谨慎分配/48,并且IETF不提出进一步减少剩余45个可变位的新建议,则这些数字没有理由令人担忧,除非出现强制要求。

- We are highly confident in the validity of this analysis, based on experience with IPv4 and several other address spaces, and on extremely ambitious scaling goals for the Internet amounting to an 80 bit address space *per person*. Even so, being acutely aware of the history of under-estimating demand, the IETF has reserved more than 85% of the address space (i.e., the bulk of the space not under the 001 Global Unicast Address prefix). Therefore, if the analysis does one day turn out to be wrong, our successors will still have the option of imposing much more restrictive allocation policies on the remaining 85%. However, we must stress that vendors should not encode any of the boundaries discussed here either in software nor hardware. Under that assumption, should we ever have to use the remaining 85% of the address space, such a migration may not be devoid of pain, but it should be far less disruptive than deployment of a new version of IP.

- 基于IPv4和其他几个地址空间的经验,以及互联网达到每人80位地址空间*的雄心勃勃的扩展目标,我们对该分析的有效性充满信心。即便如此,IETF敏锐地意识到低估需求的历史,保留了85%以上的地址空间(即,大部分空间不在001全局单播地址前缀下)。因此,如果有一天分析结果是错误的,我们的继任者仍然可以选择对剩下的85%实施更严格的分配政策。但是,我们必须强调,供应商不应在软件或硬件中对此处讨论的任何边界进行编码。在这种假设下,如果我们不得不使用剩余的85%的地址空间,这样的迁移可能并非毫无痛苦,但它应该比部署新版本的IP具有更少的破坏性。

To summarize, we argue that although careful stewardship of IPv6 address space is essential, this is completely compatible with the convenience and simplicity of a uniform prefix size for IPv6 sites of any size. The numbers are such that there seems to be no objective risk of running out of space, giving an unfair amount of space to early customers, or of getting back into the over-constrained IPv4


situation where address conservation and route aggregation damage each other.


5. Multihoming Issues
5. 多宿主问题

In the realm of multi-homed networks, the techniques used in IPv4 can all be applied, but they have known scaling problems. Specifically, if the same prefix is advertised by multiple ISPs, the routing information will grow as a function of the number of multihomed sites. To go beyond this for IPv6, we only have initial proposals on the table at this time, and active work is under way in the IETF IPNG and Multi6 working groups. Until current or new proposals become more fully developed, existing techniques known to work in IPv4 will continue to be used in IPv6.


Key characteristics of an ideal multi-homing proposal include (at minimum) that it provides routing connectivity to any multi-homed network globally, conserves address space, produces high quality routes via any of the network's providers, enables a multi-homed network to connect to multiple ISPs, does not unintentionally bias routing to use any proper subset of those networks, does not damage route aggregation, and scales to very large numbers of multi-homed networks.


One class of solutions being considered amounts to permanent parallel running of two (or more) prefixes per site. In the absence of a fixed prefix boundary, such a site might be required to have multiple different internal subnet numbering strategies, (one for each prefix length) or, if it only wanted one, be forced to use the most restrictive one as defined by the longest prefix it received from any of its ISPs. In this approach, a multi-homed network would have an address block from each of its upstream providers. Each host would either have exactly one address picked from the set of upstream providers, or one address per host from each of the upstream providers. The first case is essentially a variant on [RFC2260], with known scaling limits.


In the second case (multiple addresses per host), if two multi-homed networks communicate, having respectively M and N upstream providers, then the one initiating the connection will select one address pair from the N*M potential address pairs to connect between, and in so doing will select the providers, and therefore the applicable route, for the life of the connection. Given that each path will have a different available bit rate, loss rate, and delay, if neither host is in possession of any routing or metric information, the initiating host has only a 1/(M*N) probability of selecting the optimal address pair. Work on better-than-random address selection is in progress in the IETF, but is incomplete.


The existing IPv4 Internet shows us that a network prefix which is independent of, and globally advertised to, all upstream providers permits the routing system to select a reasonably good path within the applicable policy. Present-day routing policies are not QoS policies but reachability policies, which means that they will not necessarily select the optimal delay, bit rate, or loss rate, but the route will be the best within the metrics that are in use. One may therefore conclude that this would work correctly for IPv6 networks as well, apart from scaling issues.


6. Security Considerations
6. 安全考虑

This document does not have any security implications.


7. Acknowledgments
7. 致谢

This document originated from the IETF IPv6 directorate, with much input from the IAB and IESG. The original text forming the basis of this document was contributed by Fred Baker and Brian Carpenter. Allison Mankin and Thomas Narten merged the original contributions into a single document, and Alain Durand edited the document through its final stages.

本文件来源于IETF IPv6理事会,IAB和IESG提供了大量信息。构成本文件基础的原始文本由Fred Baker和Brian Carpenter提供。Allison Mankin和Thomas Narten将原始贡献合并到一个文档中,Alain Durand在文档的最后阶段对其进行了编辑。

8. References
8. 工具书类

[RFC1715] Huitema, C., "The H Ratio for Address Assignment Efficiency", RFC 1715, November 1994.


[RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996.

[RFC2026]Bradner,S.,“互联网标准过程——第3版”,BCP 9,RFC 2026,1996年10月。

[RFC2260] Bates, T. and Y. Rekhter, "Scalable Support for Multi-homed Multi-provider Connectivity", RFC 2260, January 1998.

[RFC2260]Bates,T.和Y.Rekhter,“多宿多提供商连接的可扩展支持”,RFC 2260,1998年1月。

[RFC2374] Hinden, R., O'Dell, M. and S. Deering, "An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, July 1998.

[RFC2374]Hinden,R.,O'Dell,M.和S.Deering,“一种IPv6可聚合全球单播地址格式”,RFC 2374,1998年7月。

[RFC2450] Hinden, R., "Proposed TLA and NLA Assignment Rule", RFC 2450, December 1998.

[RFC2450]Hinden,R.,“拟议的TLA和NLA分配规则”,RFC 2450,1998年12月。

[RFC2462] Thompson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998.


[RFC2874] Crawford, M. and C. Huitema, "DNS Extensions to Support IPv6 Address Aggregation and Renumbering", RFC 2874, July 2000.

[RFC2874]Crawford,M.和C.Huitema,“支持IPv6地址聚合和重新编号的DNS扩展”,RFC 28742000年7月。

[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.

[RFC3041]Narten,T.和R.Draves,“IPv6中无状态地址自动配置的隐私扩展”,RFC 3041,2001年1月。

[MobIPv6] Johnson, D. and C. Perkins, "Mobility Support in IPv6", Work in Progress.


9. Authors Address
9. 作者地址

Internet Architecture Board



Internet Engineering Steering Group


10. Full Copyright Statement
10. 完整版权声明

Copyright (C) The Internet Society (2001). All Rights Reserved.


This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.


The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.






Funding for the RFC Editor function is currently provided by the Internet Society.