Network Working Group                                        E. Nordmark
Request for Comments: 4213                        Sun Microsystems, Inc.
Obsoletes: 2893                                              R. Gilligan
Category: Standards Track                                 Intransa, Inc.
                                                            October 2005
Network Working Group                                        E. Nordmark
Request for Comments: 4213                        Sun Microsystems, Inc.
Obsoletes: 2893                                              R. Gilligan
Category: Standards Track                                 Intransa, Inc.
                                                            October 2005

Basic Transition Mechanisms for IPv6 Hosts and Routers


Status of This Memo


This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

本文件规定了互联网社区的互联网标准跟踪协议,并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态,请参考当前版本的“互联网官方协议标准”(STD 1)。本备忘录的分发不受限制。

Copyright Notice


Copyright (C) The Internet Society (2005).




This document specifies IPv4 compatibility mechanisms that can be implemented by IPv6 hosts and routers. Two mechanisms are specified, dual stack and configured tunneling. Dual stack implies providing complete implementations of both versions of the Internet Protocol (IPv4 and IPv6), and configured tunneling provides a means to carry IPv6 packets over unmodified IPv4 routing infrastructures.


This document obsoletes RFC 2893.

本文件淘汰了RFC 2893。

Table of Contents


   1. Introduction ....................................................2
      1.1. Terminology ................................................3
   2. Dual IP Layer Operation .........................................4
      2.1. Address Configuration ......................................5
      2.2. DNS ........................................................5
   3. Configured Tunneling Mechanisms .................................6
      3.1. Encapsulation ..............................................7
      3.2. Tunnel MTU and Fragmentation ...............................8
           3.2.1. Static Tunnel MTU ...................................9
           3.2.2. Dynamic Tunnel MTU ..................................9
      3.3. Hop Limit .................................................11
      3.4. Handling ICMPv4 Errors ....................................11
      3.5. IPv4 Header Construction ..................................13
      3.6. Decapsulation .............................................14
      3.7. Link-Local Addresses ......................................17
      3.8. Neighbor Discovery over Tunnels ...........................18
   4. Threat Related to Source Address Spoofing ......................18
   5. Security Considerations ........................................19
   6. Acknowledgements ...............................................21
   7. References .....................................................21
      7.1. Normative References ......................................21
      7.2. Informative References ....................................21
   8. Changes from RFC 2893 ..........................................23
   1. Introduction ....................................................2
      1.1. Terminology ................................................3
   2. Dual IP Layer Operation .........................................4
      2.1. Address Configuration ......................................5
      2.2. DNS ........................................................5
   3. Configured Tunneling Mechanisms .................................6
      3.1. Encapsulation ..............................................7
      3.2. Tunnel MTU and Fragmentation ...............................8
           3.2.1. Static Tunnel MTU ...................................9
           3.2.2. Dynamic Tunnel MTU ..................................9
      3.3. Hop Limit .................................................11
      3.4. Handling ICMPv4 Errors ....................................11
      3.5. IPv4 Header Construction ..................................13
      3.6. Decapsulation .............................................14
      3.7. Link-Local Addresses ......................................17
      3.8. Neighbor Discovery over Tunnels ...........................18
   4. Threat Related to Source Address Spoofing ......................18
   5. Security Considerations ........................................19
   6. Acknowledgements ...............................................21
   7. References .....................................................21
      7.1. Normative References ......................................21
      7.2. Informative References ....................................21
   8. Changes from RFC 2893 ..........................................23
1. Introduction
1. 介绍

The key to a successful IPv6 transition is compatibility with the large installed base of IPv4 hosts and routers. Maintaining compatibility with IPv4 while deploying IPv6 will streamline the task of transitioning the Internet to IPv6. This specification defines two mechanisms that IPv6 hosts and routers may implement in order to be compatible with IPv4 hosts and routers.


The mechanisms in this document are designed to be employed by IPv6 hosts and routers that need to interoperate with IPv4 hosts and utilize IPv4 routing infrastructures. We expect that most nodes in the Internet will need such compatibility for a long time to come, and perhaps even indefinitely.


The mechanisms specified here are:


- Dual IP layer (also known as dual stack): A technique for providing complete support for both Internet protocols -- IPv4 and IPv6 -- in hosts and routers.

- 双IP层(也称为双堆栈):一种在主机和路由器中为Internet协议(IPv4和IPv6)提供完全支持的技术。

- Configured tunneling of IPv6 over IPv4: A technique for establishing point-to-point tunnels by encapsulating IPv6 packets within IPv4 headers to carry them over IPv4 routing infrastructures.

- IPv4上配置的IPv6隧道:一种通过将IPv6数据包封装在IPv4报头中以在IPv4路由基础设施上传输来建立点对点隧道的技术。

The mechanisms defined here are intended to be the core of a "transition toolbox" -- a growing collection of techniques that implementations and users may employ to ease the transition. The tools may be used as needed. Implementations and sites decide which techniques are appropriate to their specific needs.


This document defines the basic set of transition mechanisms, but these are not the only tools available. Additional transition and compatibility mechanisms are specified in other documents.


1.1. Terminology
1.1. 术语

The following terms are used in this document:


Types of Nodes


IPv4-only node:


A host or router that implements only IPv4. An IPv4-only node does not understand IPv6. The installed base of IPv4 hosts and routers existing before the transition begins are IPv4-only nodes.


IPv6/IPv4 node:


A host or router that implements both IPv4 and IPv6.


IPv6-only node:


A host or router that implements IPv6 and does not implement IPv4. The operation of IPv6-only nodes is not addressed in this memo.


IPv6 node:


Any host or router that implements IPv6. IPv6/IPv4 and IPv6- only nodes are both IPv6 nodes.


IPv4 node:


Any host or router that implements IPv4. IPv6/IPv4 and IPv4- only nodes are both IPv4 nodes.


Techniques Used in the Transition


IPv6-over-IPv4 tunneling:


The technique of encapsulating IPv6 packets within IPv4 so that they can be carried across IPv4 routing infrastructures.


Configured tunneling:


IPv6-over-IPv4 tunneling where the IPv4 tunnel endpoint address(es) are determined by configuration information on tunnel endpoints. All tunnels are assumed to be bidirectional. The tunnel provides a (virtual) point-to-point link to the IPv6 layer, using the configured IPv4 addresses as the lower-layer endpoint addresses.


Other transition mechanisms, including other tunneling mechanisms, are outside the scope of this document.


The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119].


2. Dual IP Layer Operation
2. 双IP层操作

The most straightforward way for IPv6 nodes to remain compatible with IPv4-only nodes is by providing a complete IPv4 implementation. IPv6 nodes that provide complete IPv4 and IPv6 implementations are called "IPv6/IPv4 nodes". IPv6/IPv4 nodes have the ability to send and receive both IPv4 and IPv6 packets. They can directly interoperate with IPv4 nodes using IPv4 packets, and also directly interoperate with IPv6 nodes using IPv6 packets.


Even though a node may be equipped to support both protocols, one or the other stack may be disabled for operational reasons. Here we use a rather loose notion of "stack". A stack being enabled has IP addresses assigned, but whether or not any particular application is available on the stacks is explicitly not defined. Thus, IPv6/IPv4 nodes may be operated in one of three modes:


- With their IPv4 stack enabled and their IPv6 stack disabled.

- 其IPv4堆栈已启用,IPv6堆栈已禁用。

- With their IPv6 stack enabled and their IPv4 stack disabled.

- 其IPv6堆栈已启用,IPv4堆栈已禁用。

- With both stacks enabled.

- 启用两个堆栈时。

IPv6/IPv4 nodes with their IPv6 stack disabled will operate like IPv4-only nodes. Similarly, IPv6/IPv4 nodes with their IPv4 stacks


disabled will operate like IPv6-only nodes. IPv6/IPv4 nodes MAY provide a configuration switch to disable either their IPv4 or IPv6 stack.


The configured tunneling technique, which is described in Section 3, may or may not be used in addition to the dual IP layer operation.


2.1. Address Configuration
2.1. 地址配置

Because the nodes support both protocols, IPv6/IPv4 nodes may be configured with both IPv4 and IPv6 addresses. IPv6/IPv4 nodes use IPv4 mechanisms (e.g., DHCP) to acquire their IPv4 addresses, and IPv6 protocol mechanisms (e.g., stateless address autoconfiguration [RFC2462] and/or DHCPv6) to acquire their IPv6 addresses.


2.2. DNS
2.2. 域名服务器

The Domain Naming System (DNS) is used in both IPv4 and IPv6 to map between hostnames and IP addresses. A new resource record type named "AAAA" has been defined for IPv6 addresses [RFC3596]. Since IPv6/IPv4 nodes must be able to interoperate directly with both IPv4 and IPv6 nodes, they must provide resolver libraries capable of dealing with IPv4 "A" records as well as IPv6 "AAAA" records. Note that the lookup of A versus AAAA records is independent of whether the DNS packets are carried in IPv4 or IPv6 packets and that there is no assumption that the DNS servers know the IPv4/IPv6 capabilities of the requesting node.


The issues and operational guidelines for using IPv6 with DNS are described at more length in other documents, e.g., [DNSOPV6].


DNS resolver libraries on IPv6/IPv4 nodes MUST be capable of handling both AAAA and A records. However, when a query locates an AAAA record holding an IPv6 address, and an A record holding an IPv4 address, the resolver library MAY order the results returned to the application in order to influence the version of IP packets used to communicate with that specific node -- IPv6 first, or IPv4 first.


The applications SHOULD be able to specify whether they want IPv4, IPv6, or both records [RFC3493]. That defines which address families the resolver looks up. If there is not an application choice, or if the application has requested both, the resolver library MUST NOT filter out any records.


Since most applications try the addresses in the order they are returned by the resolver, this can affect the IP version "preference" of applications.


The actual ordering mechanisms are out of scope of this memo. Address selection is described at more length in [RFC3484].


3. Configured Tunneling Mechanisms
3. 配置隧道机制

In most deployment scenarios, the IPv6 routing infrastructure will be built up over time. While the IPv6 infrastructure is being deployed, the existing IPv4 routing infrastructure can remain functional and can be used to carry IPv6 traffic. Tunneling provides a way to utilize an existing IPv4 routing infrastructure to carry IPv6 traffic.


IPv6/IPv4 hosts and routers can tunnel IPv6 datagrams over regions of IPv4 routing topology by encapsulating them within IPv4 packets. Tunneling can be used in a variety of ways:


- Router-to-Router. IPv6/IPv4 routers interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans one segment of the end-to-end path that the IPv6 packet takes.

- 路由器对路由器。由IPv4基础设施互连的IPv6/IPv4路由器可以在它们之间通过隧道传输IPv6数据包。在这种情况下,隧道跨越IPv6数据包所采用的端到端路径的一段。

- Host-to-Router. IPv6/IPv4 hosts can tunnel IPv6 packets to an intermediary IPv6/IPv4 router that is reachable via an IPv4 infrastructure. This type of tunnel spans the first segment of the packet's end-to-end path.

- 主机到路由器。IPv6/IPv4主机可以通过隧道将IPv6数据包传输到可通过IPv4基础结构访问的中间IPv6/IPv4路由器。这种类型的隧道跨越数据包端到端路径的第一段。

- Host-to-Host. IPv6/IPv4 hosts that are interconnected by an IPv4 infrastructure can tunnel IPv6 packets between themselves. In this case, the tunnel spans the entire end-to-end path that the packet takes.

- 主机对主机。由IPv4基础结构互连的IPv6/IPv4主机可以在它们之间通过隧道传输IPv6数据包。在这种情况下,隧道跨越数据包所采用的整个端到端路径。

- Router-to-Host. IPv6/IPv4 routers can tunnel IPv6 packets to their final destination IPv6/IPv4 host. This tunnel spans only the last segment of the end-to-end path.

- 路由器到主机。IPv6/IPv4路由器可以通过隧道将IPv6数据包传输到其最终目标IPv6/IPv4主机。此隧道仅跨越端到端路径的最后一段。

Configured tunneling can be used in all of the above cases, but it is most likely to be used router-to-router due to the need to explicitly configure the tunneling endpoints.


The underlying mechanisms for tunneling are:


- The entry node of the tunnel (the encapsulator) creates an encapsulating IPv4 header and transmits the encapsulated packet.

- 隧道的入口节点(封装器)创建封装的IPv4报头并传输封装的数据包。

- The exit node of the tunnel (the decapsulator) receives the encapsulated packet, reassembles the packet if needed, removes the IPv4 header, and processes the received IPv6 packet.

- 隧道的出口节点(解封装器)接收封装的数据包,根据需要重新组装数据包,删除IPv4报头,并处理接收到的IPv6数据包。

- The encapsulator may need to maintain soft-state information for each tunnel recording such parameters as the MTU of the tunnel in order to process IPv6 packets forwarded into the tunnel.

- 封装器可能需要为记录诸如隧道的MTU之类的参数的每个隧道维护软状态信息,以便处理转发到隧道中的IPv6分组。

In configured tunneling, the tunnel endpoint addresses are determined in the encapsulator from configuration information stored for each tunnel. When an IPv6 packet is transmitted over a tunnel, the destination and source addresses for the encapsulating IPv4 header are set as described in Section 3.5.


The determination of which packets to tunnel is usually made by routing information on the encapsulator. This is usually done via a routing table, which directs packets based on their destination address using the prefix mask and match technique.


The decapsulator matches the received protocol-41 packets to the tunnels it has configured, and allows only the packets in which IPv4 source addresses match the tunnels configured on the decapsulator. Therefore, the operator must ensure that the tunnel's IPv4 address configuration is the same both at the encapsulator and the decapsulator.


3.1. Encapsulation
3.1. 封装

The encapsulation of an IPv6 datagram in IPv4 is shown below:


                                             |    IPv4     |
                                             |   Header    |
             +-------------+                 +-------------+
             |    IPv6     |                 |    IPv6     |
             |   Header    |                 |   Header    |
             +-------------+                 +-------------+
             |  Transport  |                 |  Transport  |
             |   Layer     |      ===>       |   Layer     |
             |   Header    |                 |   Header    |
             +-------------+                 +-------------+
             |             |                 |             |
             ~    Data     ~                 ~    Data     ~
             |             |                 |             |
             +-------------+                 +-------------+
                                             |    IPv4     |
                                             |   Header    |
             +-------------+                 +-------------+
             |    IPv6     |                 |    IPv6     |
             |   Header    |                 |   Header    |
             +-------------+                 +-------------+
             |  Transport  |                 |  Transport  |
             |   Layer     |      ===>       |   Layer     |
             |   Header    |                 |   Header    |
             +-------------+                 +-------------+
             |             |                 |             |
             ~    Data     ~                 ~    Data     ~
             |             |                 |             |
             +-------------+                 +-------------+

Encapsulating IPv6 in IPv4


In addition to adding an IPv4 header, the encapsulator also has to handle some more complex issues:


- Determine when to fragment and when to report an ICMPv6 "packet too big" error back to the source.

- 确定何时对ICMPv6“数据包太大”错误进行分段以及何时向源报告。

- How to reflect ICMPv4 errors from routers along the tunnel path back to the source as ICMPv6 errors.

- 如何将路由器沿隧道路径返回到源的ICMPv4错误反映为ICMPv6错误。

Those issues are discussed in the following sections.


3.2. Tunnel MTU and Fragmentation
3.2. 隧道MTU与破碎

Naively, the encapsulator could view encapsulation as IPv6 using IPv4 as a link layer with a very large MTU (65535-20 bytes at most; 20 bytes "extra" are needed for the encapsulating IPv4 header). The encapsulator would only need to report ICMPv6 "packet too big" errors back to the source for packets that exceed this MTU. However, such a scheme would be inefficient or non-interoperable for three reasons and therefore MUST NOT be used:


1) It would result in more fragmentation than needed. IPv4 layer fragmentation should be avoided due to the performance problems caused by the loss unit being smaller than the retransmission unit [KM97].

1) 这将导致比需要更多的碎片。由于丢失单元小于重传单元[KM97]导致的性能问题,应避免IPv4层碎片。

2) Any IPv4 fragmentation occurring inside the tunnel, i.e., between the encapsulator and the decapsulator, would have to be reassembled at the tunnel endpoint. For tunnels that terminate at a router, this would require additional memory and other resources to reassemble the IPv4 fragments into a complete IPv6 packet before that packet could be forwarded.

2) 隧道内发生的任何IPv4碎片,即封装器和解封装器之间的碎片,都必须在隧道端点重新组装。对于在路由器上终止的隧道,这将需要额外的内存和其他资源来将IPv4片段重新组装成完整的IPv6数据包,然后才能转发该数据包。

3) The encapsulator has no way of knowing that the decapsulator is able to defragment such IPv4 packets (see Section 3.6 for details), and has no way of knowing that the decapsulator is able to handle such a large IPv6 Maximum Receive Unit (MRU).

3) 封装器无法知道解封装器是否能够对此类IPv4数据包进行碎片整理(有关详细信息,请参阅第3.6节),也无法知道解封装器是否能够处理如此大的IPv6最大接收单元(MRU)。

Hence, the encapsulator MUST NOT treat the tunnel as an interface with an MTU of 64 kilobytes, but instead either use the fixed static MTU or OPTIONAL dynamic MTU determination based on the IPv4 path MTU to the tunnel endpoint.

因此,封装器不得将隧道视为具有64 KB MTU的接口,而是使用固定静态MTU或基于到隧道端点的IPv4路径MTU的可选动态MTU确定。

If both the mechanisms are implemented, the decision of which to use SHOULD be configurable on a per-tunnel endpoint basis.


3.2.1. Static Tunnel MTU
3.2.1. 静态隧道MTU

A node using static tunnel MTU treats the tunnel interface as having a fixed-interface MTU. By default, the MTU MUST be between 1280 and 1480 bytes (inclusive), but it SHOULD be 1280 bytes. If the default is not 1280 bytes, the implementation MUST have a configuration knob that can be used to change the MTU value.


A node must be able to accept a fragmented IPv6 packet that, after reassembly, is as large as 1500 octets [RFC2460]. This memo also includes requirements (see Section 3.6) for the amount of IPv4 reassembly and IPv6 MRU that MUST be supported by all the decapsulators. These ensure correct interoperability with any fixed MTUs between 1280 and 1480 bytes.

节点必须能够接受碎片化的IPv6数据包,在重新组装后,该数据包的大小可达1500个八位字节[RFC2460]。本备忘录还包括所有去封装器必须支持的IPv4重新组装和IPv6 MRU数量要求(见第3.6节)。这些可确保与1280和1480字节之间的任何固定MTU的正确互操作性。

A larger fixed MTU than supported by these requirements must not be configured unless it has been administratively ensured that the decapsulator can reassemble or receive packets of that size.


The selection of a good tunnel MTU depends on many factors, at least:


- Whether the IPv4 protocol-41 packets will be transported over media that may have a lower path MTU (e.g., IPv4 Virtual Private Networks); then picking too high a value might lead to IPv4 fragmentation.

- IPv4协议-41数据包是否将通过可能具有较低路径MTU的媒体(例如,IPv4虚拟专用网络)传输;然后选择太高的值可能会导致IPv4碎片。

- Whether the tunnel is used to transport IPv6 tunneled packets (e.g., a mobile node with an IPv6-in-IPv4 configured tunnel, and an IPv6-in-IPv6 tunnel interface); then picking too low a value might lead to IPv6 fragmentation.

- 隧道是否用于传输IPv6隧道包(例如,具有IPv6-in-IPv4配置隧道和IPv6-in-IPv6隧道接口的移动节点);然后选择太低的值可能会导致IPv6碎片。

If layered encapsulation is believed to be present, it may be prudent to consider supporting dynamic MTU determination instead as it is able to minimize fragmentation and optimize packet sizes.


When using the static tunnel MTU, the Don't Fragment bit MUST NOT be set in the encapsulating IPv4 header. As a result, the encapsulator should not receive any ICMPv4 "packet too big" messages as a result of the packets it has encapsulated.


3.2.2. Dynamic Tunnel MTU
3.2.2. 动态隧道MTU

The dynamic MTU determination is OPTIONAL. However, if it is implemented, it SHOULD have the behavior described in this document.


The fragmentation inside the tunnel can be reduced to a minimum by having the encapsulator track the IPv4 path MTU across the tunnel, using the IPv4 Path MTU Discovery Protocol [RFC1191] and recording


the resulting path MTU. The IPv6 layer in the encapsulator can then view a tunnel as a link layer with an MTU equal to the IPv4 path MTU, minus the size of the encapsulating IPv4 header.


Note that this does not eliminate IPv4 fragmentation in the case when the IPv4 path MTU would result in an IPv6 MTU less than 1280 bytes. (Any link layer used by IPv6 has to have an MTU of at least 1280 bytes [RFC2460].) In this case, the IPv6 layer has to "see" a link layer with an MTU of 1280 bytes and the encapsulator has to use IPv4 fragmentation in order to forward the 1280 byte IPv6 packets.

请注意,当IPv4路径MTU将导致IPv6 MTU小于1280字节时,这不会消除IPv4碎片。(IPv6使用的任何链路层必须具有至少1280字节的MTU[RFC2460])在这种情况下,IPv6层必须“查看”MTU为1280字节的链路层,并且封装器必须使用IPv4分段以转发1280字节的IPv6数据包。

The encapsulator SHOULD employ the following algorithm to determine when to forward an IPv6 packet that is larger than the tunnel's path MTU using IPv4 fragmentation, and when to return an ICMPv6 "packet too big" message per [RFC1981]:


         if (IPv4 path MTU - 20) is less than 1280
                 if packet is larger than 1280 bytes
                         Send ICMPv6 "packet too big" with MTU = 1280.
                         Drop packet.
                         Encapsulate but do not set the Don't Fragment
                         flag in the IPv4 header.  The resulting IPv4
                         packet might be fragmented by the IPv4 layer
                         on the encapsulator or by some router along
                         the IPv4 path.
                 if packet is larger than (IPv4 path MTU - 20)
                         Send ICMPv6 "packet too big" with
                         MTU = (IPv4 path MTU - 20).
                         Drop packet.
                         Encapsulate and set the Don't Fragment flag
                         in the IPv4 header.
         if (IPv4 path MTU - 20) is less than 1280
                 if packet is larger than 1280 bytes
                         Send ICMPv6 "packet too big" with MTU = 1280.
                         Drop packet.
                         Encapsulate but do not set the Don't Fragment
                         flag in the IPv4 header.  The resulting IPv4
                         packet might be fragmented by the IPv4 layer
                         on the encapsulator or by some router along
                         the IPv4 path.
                 if packet is larger than (IPv4 path MTU - 20)
                         Send ICMPv6 "packet too big" with
                         MTU = (IPv4 path MTU - 20).
                         Drop packet.
                         Encapsulate and set the Don't Fragment flag
                         in the IPv4 header.

Encapsulators that have a large number of tunnels may choose between dynamic versus static tunnel MTUs on a per-tunnel endpoint basis. In cases where the number of tunnels that any one node is using is large, it is helpful to observe that this state information can be cached and discarded when not in use.


Note that using dynamic tunnel MTU is subject to IPv4 path MTU blackholes should the ICMPv4 "packet too big" messages be dropped by firewalls or not generated by the routers [RFC1435, RFC2923].


3.3. Hop Limit
3.3. 跳数限制

IPv6-over-IPv4 tunnels are modeled as "single-hop" from the IPv6 perspective. The tunnel is opaque to users of the network, and it is not detectable by network diagnostic tools such as traceroute.


The single-hop model is implemented by having the encapsulators and decapsulators process the IPv6 hop limit field as they would if they were forwarding a packet on to any other datalink. That is, they decrement the hop limit by 1 when forwarding an IPv6 packet. (The originating node and final destination do not decrement the hop limit.)


The TTL of the encapsulating IPv4 header is selected in an implementation-dependent manner. The current suggested value is published in the "Assigned Numbers" RFC [RFC3232][ASSIGNED]. Implementations MAY provide a mechanism to allow the administrator to configure the IPv4 TTL as the IP Tunnel MIB [RFC4087].

封装IPv4报头的TTL是以依赖于实现的方式选择的。当前建议值发布在“指定编号”RFC[RFC3232][Assigned]中。实现可能提供一种机制,允许管理员将IPv4 TTL配置为IP隧道MIB[RFC4087]。

3.4. Handling ICMPv4 Errors
3.4. 处理ICMPv4错误

In response to encapsulated packets it has sent into the tunnel, the encapsulator might receive ICMPv4 error messages from IPv4 routers inside the tunnel. These packets are addressed to the encapsulator because it is the IPv4 source of the encapsulated packet.


ICMPv4 error handling is only applicable to dynamic MTU determination, even though the functions could be used with static MTU tunnels as well.


The ICMPv4 "packet too big" error messages are handled according to IPv4 Path MTU Discovery [RFC1191] and the resulting path MTU is recorded in the IPv4 layer. The recorded path MTU is used by IPv6 to determine if an ICMPv6 "packet too big" error has to be generated as described in Section 3.2.2.


The handling of other types of ICMPv4 error messages depends on how much information is available from the encapsulated packet that caused the error.


Many older IPv4 routers return only 8 bytes of data beyond the IPv4 header of the packet in error, which is not enough to include the address fields of the IPv6 header. More modern IPv4 routers are likely to return enough data beyond the IPv4 header to include the entire IPv6 header and possibly even the data beyond that. See [RFC1812].


If sufficient data bytes from the offending packet are available, the encapsulator MAY extract the encapsulated IPv6 packet and use it to generate an ICMPv6 message directed back to the originating IPv6 node, as shown below:


                         | IPv4 Header  |
                         | dst = encaps |
                         |       node   |
                         |    ICMPv4    |
                         |    Header    |
                  - -    +--------------+
                         | IPv4 Header  |
                         | src = encaps |
                 IPv4    |       node   |
                         +--------------+   - -
                 Packet  |    IPv6      |
                         |    Header    |   Original IPv6
                  in     +--------------+   Packet -
                         |  Transport   |   Can be used to
                 Error   |    Header    |   generate an
                         +--------------+   ICMPv6
                         |              |   error message
                         ~     Data     ~   back to the source.
                         |              |
                  - -    +--------------+   - -
                         | IPv4 Header  |
                         | dst = encaps |
                         |       node   |
                         |    ICMPv4    |
                         |    Header    |
                  - -    +--------------+
                         | IPv4 Header  |
                         | src = encaps |
                 IPv4    |       node   |
                         +--------------+   - -
                 Packet  |    IPv6      |
                         |    Header    |   Original IPv6
                  in     +--------------+   Packet -
                         |  Transport   |   Can be used to
                 Error   |    Header    |   generate an
                         +--------------+   ICMPv6
                         |              |   error message
                         ~     Data     ~   back to the source.
                         |              |
                  - -    +--------------+   - -

ICMPv4 Error Message Returned to Encapsulating Node


When receiving ICMPv4 errors as above and the errors are not "packet too big", it would be useful to log the error as an error related to the tunnel. Also, if sufficient headers are available, then the originating node MAY send an ICMPv6 error of type "unreachable" with code "address unreachable" to the IPv6 source. (The "address unreachable" code is appropriate since, from the perspective of IPv6, the tunnel is a link and that code is used for link-specific errors [RFC2463]).


Note that when the IPv4 path MTU is exceeded, and sufficient bytes of payload associated with the ICMPv4 errors are not available, or ICMPv4 errors do not cause the generation of ICMPv6 errors in case there is enough payload, there will be at least two packet drops instead of at least one (the case of a single layer of MTU discovery). Consider a case where an IPv6 host is connected to an IPv4/IPv6 router, which is connected to a network where an ICMPv4 error about too big packet size is generated. First, the router needs to learn the tunnel (IPv4) MTU that causes at least one packet


loss, and then the host needs to learn the (IPv6) MTU from the router that causes at least one packet loss. Still, in all cases there can be more than one packet loss if there are multiple large packets in flight at the same time.


3.5. IPv4 Header Construction
3.5. IPv4报头构造

When encapsulating an IPv6 packet in an IPv4 datagram, the IPv4 header fields are set as follows:






IP Header Length in 32-bit words:


5 (There are no IPv4 options in the encapsulating header.)


Type of Service:


0 unless otherwise specified. (See [RFC2983] and [RFC3168] Section 9.1 for issues relating to the Type-of-Service byte and tunneling.)


Total Length:


Payload length from IPv6 header plus length of IPv6 and IPv4 headers (i.e., IPv6 payload length plus a constant 60 bytes).




Generated uniquely as for any IPv4 packet transmitted by the system.




Set the Don't Fragment (DF) flag as specified in Section 3.2. Set the More Fragments (MF) bit as necessary if fragmenting.


Fragment Offset:


Set as necessary if fragmenting.


Time to Live:


Set in an implementation-specific manner, as described in Section 3.3.




41 (Assigned payload type number for IPv6).


Header Checksum:


Calculate the checksum of the IPv4 header [RFC791].


Source Address:


An IPv4 address of the encapsulator: either configured by the administrator or an address of the outgoing interface.


Destination Address:


IPv4 address of the tunnel endpoint.


When encapsulating the packets, the node must ensure that it will use the correct source address so that the packets are acceptable to the decapsulator as described in Section 3.6. Configuring the source address is appropriate particularly in cases in which automatic selection of source address may produce different results in a certain period of time. This is often the case with multiple addresses, and multiple interfaces, or when routes may change frequently. Therefore, it SHOULD be possible to administratively specify the source address of a tunnel.


3.6. Decapsulation
3.6. 脱封

When an IPv6/IPv4 host or a router receives an IPv4 datagram that is addressed to one of its own IPv4 addresses or a joined multicast group address, and the value of the protocol field is 41, the packet is potentially a tunnel packet and needs to be verified to belong to one of the configured tunnel interfaces (by checking source/destination addresses), reassembled (if fragmented at the IPv4 level), and have the IPv4 header removed and the resulting IPv6 datagram be submitted to the IPv6 layer code on the node.


The decapsulator MUST verify that the tunnel source address is correct before further processing packets, to mitigate the problems with address spoofing (see Section 4). This check also applies to packets that are delivered to transport protocols on the decapsulator. This is done by verifying that the source address is the IPv4 address of the encapsulator, as configured on the decapsulator. Packets for which the IPv4 source address does not match MUST be discarded and an ICMP message SHOULD NOT be generated;


however, if the implementation normally sends an ICMP message when receiving an unknown protocol packet, such an error message MAY be sent (e.g., ICMPv4 Protocol 41 Unreachable).


A side effect of this address verification is that the node will silently discard packets with a wrong source address and packets that were received by the node but not directly addressed to it (e.g., broadcast addresses).


Independent of any other forms of IPv4 ingress filtering the administrator of the node may have configured, the implementation MAY perform ingress filtering, i.e., check that the packet is arriving from the interface in the direction of the route toward the tunnel end-point, similar to a Strict Reverse Path Forwarding (RPF) check [RFC3704]. As this may cause problems on tunnels that are routed through multiple links, it is RECOMMENDED that this check, if done, is disabled by default. The packets caught by this check SHOULD be discarded; an ICMP message SHOULD NOT be generated by default.


The decapsulator MUST be capable of having, on the tunnel interfaces, an IPv6 MRU of at least the maximum of 1500 bytes and the largest (IPv6) interface MTU on the decapsulator.

解封装器必须能够在隧道接口上具有至少最大1500字节的IPv6 MRU和解封装器上最大(IPv6)接口MTU。

The decapsulator MUST be capable of reassembling an IPv4 packet that is (after the reassembly) the maximum of 1500 bytes and the largest (IPv4) interface MTU on the decapsulator. The 1500-byte number is a result of encapsulators that use the static MTU scheme in Section 3.2.1, while encapsulators that use the dynamic scheme in Section 3.2.2 can cause up to the largest interface MTU on the decapsulator to be received. (Note that it is strictly the interface MTU on the last IPv4 router *before* the decapsulator that matters, but for most links the MTU is the same between all neighbors.)


This reassembly limit allows dynamic tunnel MTU determination by the encapsulator to take advantage of larger IPv4 path MTUs. An implementation MAY have a configuration knob that can be used to set a larger value of the tunnel reassembly buffers than the above number, but it MUST NOT be set below the above number.


The decapsulation is shown below:


            |    IPv4     |
            |   Header    |
            +-------------+                 +-------------+
            |    IPv6     |                 |    IPv6     |
            |   Header    |                 |   Header    |
            +-------------+                 +-------------+
            |  Transport  |                 |  Transport  |
            |   Layer     |      ===>       |   Layer     |
            |   Header    |                 |   Header    |
            +-------------+                 +-------------+
            |             |                 |             |
            ~    Data     ~                 ~    Data     ~
            |             |                 |             |
            +-------------+                 +-------------+
            |    IPv4     |
            |   Header    |
            +-------------+                 +-------------+
            |    IPv6     |                 |    IPv6     |
            |   Header    |                 |   Header    |
            +-------------+                 +-------------+
            |  Transport  |                 |  Transport  |
            |   Layer     |      ===>       |   Layer     |
            |   Header    |                 |   Header    |
            +-------------+                 +-------------+
            |             |                 |             |
            ~    Data     ~                 ~    Data     ~
            |             |                 |             |
            +-------------+                 +-------------+

Decapsulating IPv6 from IPv4


The decapsulator performs IPv4 reassembly before decapsulating the IPv6 packet.


When decapsulating the packet, the IPv6 header is not modified. (However, see [RFC2983] and [RFC3168] section 9.1 for issues relating to the Type of Service byte and tunneling.) If the packet is subsequently forwarded, its hop limit is decremented by one.


The encapsulating IPv4 header is discarded, and the resulting packet is checked for validity when submitted to the IPv6 layer. When reconstructing the IPv6 packet, the length MUST be determined from the IPv6 payload length since the IPv4 packet might be padded (thus have a length that is larger than the IPv6 packet plus the IPv4 header being removed).


After the decapsulation, the node MUST silently discard a packet with an invalid IPv6 source address. The list of invalid source addresses SHOULD include at least:


- all multicast addresses (FF00::/8)

- 所有多播地址(FF00::/8)

- the loopback address (::1)

- 环回地址(::1)

- all the IPv4-compatible IPv6 addresses [RFC3513] (::/96), excluding the unspecified address for Duplicate Address Detection (::/128)

- 所有与IPv4兼容的IPv6地址[RFC3513](::/96),不包括用于重复地址检测的未指定地址(::/128)

- all the IPv4-mapped IPv6 addresses (::ffff:0:0/96)

- 所有IPv4映射的IPv6地址(::ffff:0:0/96)

In addition, the node should be configured to perform ingress filtering [RFC2827][RFC3704] on the IPv6 source address, similar to on any of its interfaces, e.g.:


1) if the tunnel is toward the Internet, the node should be configured to check that the site's IPv6 prefixes are not used as the source addresses, or

1) 如果隧道朝向Internet,则应将节点配置为检查站点的IPv6前缀是否未用作源地址,或

2) if the tunnel is toward an edge network, the node should be configured to check that the source address belongs to that edge network.

2) 如果隧道朝向边缘网络,则应将节点配置为检查源地址是否属于该边缘网络。

The prefix lists in the former typically need to be manually configured; the latter could be verified automatically, e.g., by using a strict unicast RPF check, as long as an interface can be designated to be toward an edge.


It is RECOMMENDED that the implementations provide a single knob to make it easier to for the administrators to enable strict ingress filtering toward edge networks.


3.7. Link-Local Addresses
3.7. 链接本地地址

The configured tunnels are IPv6 interfaces (over the IPv4 "link layer") and thus MUST have link-local addresses. The link-local addresses are used by, e.g., routing protocols operating over the tunnels.


The interface identifier [RFC3513] for such an interface may be based on the 32-bit IPv4 address of an underlying interface, or formed using some other means, as long as it is unique from the other tunnel endpoint with a reasonably high probability.


Note that it may be desirable to form the link-local address in a fashion that minimizes the probability and the effect of having to renumber the link-local address in the event of a topology or hardware change.


If an IPv4 address is used for forming the IPv6 link-local address, the interface identifier is the IPv4 address, prepended by zeros. Note that the "Universal/Local" bit is zero, indicating that the interface identifier is not globally unique. The link-local address is formed by appending the interface identifier to the prefix FE80::/64.


When the host has more than one IPv4 address in use on the physical interface concerned, a choice of one of these IPv4 addresses is made


by the administrator or the implementation when forming the link-local address.


      |  FE      80      00      00      00      00      00     00  |
      |  00      00      00      00   |        IPv4 Address         |
      |  FE      80      00      00      00      00      00     00  |
      |  00      00      00      00   |        IPv4 Address         |
3.8. Neighbor Discovery over Tunnels
3.8. 隧道上的邻居发现

Configured tunnel implementations MUST at least accept and respond to the probe packets used by Neighbor Unreachability Detection (NUD) [RFC2461]. The implementations SHOULD also send NUD probe packets to detect when the configured tunnel fails at which point the implementation can use an alternate path to reach the destination. Note that Neighbor Discovery allows that the sending of NUD probes be omitted for router-to-router links if the routing protocol tracks bidirectional reachability.


For the purposes of Neighbor Discovery, the configured tunnels specified in this document are assumed to NOT have a link-layer address, even though the link-layer (IPv4) does have an address. This means that:


- the sender of Neighbor Discovery packets SHOULD NOT include Source Link Layer Address options or Target Link Layer Address options on the tunnel link.

- 邻居发现数据包的发送方不应在隧道链路上包含源链路层地址选项或目标链路层地址选项。

- the receiver MUST, while otherwise processing the Neighbor Discovery packet, silently ignore the content of any Source Link Layer Address options or Target Link Layer Address options received on the tunnel link.

- 在以其他方式处理邻居发现数据包时,接收器必须静默地忽略在隧道链路上接收到的任何源链路层地址选项或目标链路层地址选项的内容。

Not using link-layer address options is consistent with how Neighbor Discovery is used on other point-to-point links.


4. Threat Related to Source Address Spoofing
4. 与源地址欺骗相关的威胁

The specification above contains rules that apply tunnel source address verification in particular and ingress filtering [RFC2827][RFC3704] in general to packets before they are decapsulated. When IP-in-IP tunneling (independent of IP versions) is used, it is important that this not be used to bypass any ingress filtering in use for non-tunneled packets. Thus, the rules in this document are derived based on should ingress filtering be used for IPv4 and IPv6, the use of tunneling should not provide an easy way to circumvent the filtering.


In this case, without specific ingress filtering checks in the decapsulator, it would be possible for an attacker to inject a packet with:


- Outer IPv4 source: real IPv4 address of attacker

- 外部IPv4源:攻击者的真实IPv4地址

- Outer IPv4 destination: IPv4 address of decapsulator

- 外部IPv4目标:解封装器的IPv4地址

- Inner IPv6 source: Alice, which is either the decapsulator or a node close to it

- 内部IPv6源:Alice,它是解封装器或其附近的节点

- Inner IPv6 destination: Bob

- 内部IPv6目标:Bob

Even if all IPv4 routers between the attacker and the decapsulator implement IPv4 ingress filtering, and all IPv6 routers between the decapsulator and Bob implement IPv6 ingress filtering, the above spoofed packets will not be filtered out. As a result, Bob will receive a packet that looks like it was sent from Alice even though the sender was some unrelated node.


The solution to this is to have the decapsulator accept only encapsulated packets from the explicitly configured source address (i.e., the other end of the tunnel) as specified in Section 3.6. While this does not provide complete protection in the case ingress filtering has not been deployed, it does provide a significant increase in security. The issue and the remainder threats are discussed at more length in Security Considerations.


5. Security Considerations
5. 安全考虑

Generic security considerations of using IPv6 are discussed in a separate document [V6SEC].


An implementation of tunneling needs to be aware that although a tunnel is a link (as defined in [RFC2460]), the threat model for a tunnel might be rather different than for other links, since the tunnel potentially includes all of the Internet.


Several mechanisms (e.g., Neighbor Discovery) depend on Hop Count being 255 and/or the addresses being link local for ensuring that a packet originated on-link, in a semi-trusted environment. Tunnels are more vulnerable to a breach of this assumption than physical links, as an attacker anywhere in the Internet can send an IPv6-in-IPv4 packet to the tunnel decapsulator, causing injection of an encapsulted IPv6 packet to the configured tunnel interface unless the decapsulation checks are able to discard packets injected in such a manner.


Therefore, this memo specifies that the decapsulators make these steps (as described in Section 3.6) to mitigate this threat:


- IPv4 source address of the packet MUST be the same as configured for the tunnel end-point;

- 数据包的IPv4源地址必须与为隧道端点配置的相同;

- Independent of any IPv4 ingress filtering the administrator may have configured, the implementation MAY perform IPv4 ingress filtering to check that the IPv4 packets are received from an expected interface (but as this may cause some problems, it may be disabled by default);

- 独立于管理员可能配置的任何IPv4入口过滤,实现可以执行IPv4入口过滤,以检查是否从预期接口接收到IPv4数据包(但由于这可能会导致一些问题,默认情况下可能会禁用);

- IPv6 packets with several, obviously invalid IPv6 source addresses received from the tunnel MUST be discarded (see Section 3.6 for details); and

- 必须丢弃从隧道接收到的带有多个明显无效IPv6源地址的IPv6数据包(详见第3.6节);和

- IPv6 ingress filtering should be performed (typically requiring configuration from the operator), to check that the tunneled IPv6 packets are received from an expected interface.

- 应执行IPv6入口过滤(通常需要运营商进行配置),以检查隧道IPv6数据包是否从预期接口接收。

Especially the first verification is vital: to avoid this check, the attacker must be able to know the source of the tunnel (ranging from difficult to predictable) and be able to spoof it (easier).


If the remainder threats of tunnel source verification are considered to be significant, a tunneling scheme with authentication should be used instead, e.g., IPsec [RFC2401] (preferable) or Generic Routing Encapsulation with a pre-configured secret key [RFC2890]. As the configured tunnels are set up more or less manually, setting up the keying material is probably not a problem. However, setting up secure IPsec IPv6-in-IPv4 tunnels is described in another document [V64IPSEC].

如果隧道源验证的其余威胁被认为是重大的,则应使用具有身份验证的隧道方案,例如,IPsec[RFC2401](优选)或具有预配置密钥的通用路由封装[RFC2890]。由于配置的隧道或多或少是手动设置的,因此设置键控材质可能不是问题。但是,在另一个文档[V64IPSEC]中描述了如何设置安全的IPsec IPv6-in-IPv4隧道。

If the tunneling is done inside an administrative domain, proper ingress filtering at the edge of the domain can also eliminate the threat from outside of the domain. Therefore, shorter tunnels are preferable to longer ones, possibly spanning the whole Internet.


In addition, an implementation MUST treat interfaces to different links as separate, e.g., to ensure that Neighbor Discovery packets arriving on one link do not affect other links. This is especially important for tunnel links.


When dropping packets due to failing to match the allowed IPv4 source addresses for a tunnel the node should not "acknowledge" the existence of a tunnel, otherwise this could be used to probe the acceptable tunnel endpoint addresses. For that reason, the specification says that such packets MUST be discarded, and an ICMP


error message SHOULD NOT be generated, unless the implementation normally sends ICMP destination unreachable messages for unknown protocols; in such a case, the same code MAY be sent. As should be obvious, not returning the same ICMP code if an error is returned for other protocols may hint that the IPv6 stack (or the protocol 41 tunneling processing) has been enabled -- the behaviour should be consistent on how the implementation otherwise behaves to be transparent to probing.


6. Acknowledgements
6. 致谢

We would like to thank the members of the IPv6 working group, the Next Generation Transition (ngtrans) working group, and the v6ops working group for their many contributions and extensive review of this document. Special thanks are due to (in alphabetical order) Jim Bound, Ross Callon, Tim Chown, Alex Conta, Bob Hinden, Bill Manning, John Moy, Mohan Parthasarathy, Chirayu Patel, Pekka Savola, and Fred Templin for many helpful suggestions. Pekka Savola helped in editing the final revisions of the specification.

我们要感谢IPv6工作组、下一代过渡(ngtrans)工作组和v6ops工作组的成员,感谢他们对本文件的大量贡献和广泛审查。特别感谢(按字母顺序排列)吉姆·邦德、罗斯·卡隆、蒂姆·乔恩、亚历克斯·康塔、鲍勃·欣登、比尔·曼宁、约翰·莫伊、莫汉·帕塔萨拉西、奇拉尤·帕特尔、佩卡·萨沃拉和弗雷德·坦普林提出的许多有益建议。Pekka Savola帮助编辑了规范的最终修订版。

7. References
7. 工具书类
7.1. Normative References
7.1. 规范性引用文件

[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.


[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, November 1990.


[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996.

[RFC1981]McCann,J.,Deering,S.,和J.Mogul,“IP版本6的路径MTU发现”,RFC 1981,1996年8月。

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,1997年3月。

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.

[RFC2460]Deering,S.和R.Hinden,“互联网协议,第6版(IPv6)规范”,RFC 2460,1998年12月。

[RFC2463] Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998.


7.2. Informative References
7.2. 资料性引用
   [ASSIGNED] IANA, "Assigned numbers online database",
   [ASSIGNED] IANA, "Assigned numbers online database",

[DNSOPV6] Durand, A., Ihren, J., and Savola P., "Operational Considerations and Issues with IPv6 DNS", Work in Progress, October 2004.

[DNSOPV6]Durand,A.,Ihren,J.,和Savola P.,“IPv6 DNS的操作注意事项和问题”,正在进行的工作,2004年10月。

[KM97] Kent, C., and J. Mogul, "Fragmentation Considered Harmful". In Proc. SIGCOMM '87 Workshop on Frontiers in Computer Communications Technology. August 1987.


[V6SEC] Savola, P., "IPv6 Transition/Co-existence Security Considerations", Work in Progress, October 2004.


[V64IPSEC] Graveman, R., et al., "Using IPsec to Secure IPv6-over-IPv4 Tunnels", Work in Progress, December 2004.


[RFC1435] Knowles, S., "IESG Advice from Experience with Path MTU Discovery", RFC 1435, March 1993.

[RFC1435]Knowles,S.,“来自Path MTU发现经验的IESG建议”,RFC 1435,1993年3月。

[RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995.


[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998.

[RFC2401]Kent,S.和R.Atkinson,“互联网协议的安全架构”,RFC 2401,1998年11月。

[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.


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


[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000.

[RFC2827]Ferguson,P.和D.Senie,“网络入口过滤:击败利用IP源地址欺骗的拒绝服务攻击”,BCP 38,RFC 2827,2000年5月。

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", RFC 2890, September 2000.

[RFC2890]Dommety,G.“GRE的密钥和序列号扩展”,RFC 28902000年9月。

[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2923, September 2000.

[RFC2923]Lahey,K.,“路径MTU发现的TCP问题”,RFC 29232000年9月。

[RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2983, October 2000.

[RFC2983]Black,D.,“差异化服务和隧道”,RFC 29832000年10月。

[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001.

[RFC3056]Carpenter,B.和K.Moore,“通过IPv4云连接IPv6域”,RFC 3056,2001年2月。

[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001.

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

[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-line Database", RFC 3232, January 2002.

[RFC3232]Reynolds,J.,“分配号码:RFC 1700被在线数据库取代”,RFC 3232,2002年1月。

[RFC3484] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003.

[RFC3484]Draves,R.,“互联网协议版本6(IPv6)的默认地址选择”,RFC 3484,2003年2月。

[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, February 2003.

[RFC3493]Gilligan,R.,Thomson,S.,Bound,J.,McCann,J.,和W.Stevens,“IPv6的基本套接字接口扩展”,RFC 3493,2003年2月。

[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003.

[RFC3513]Hinden,R.和S.Deering,“互联网协议版本6(IPv6)寻址体系结构”,RFC 3513,2003年4月。

[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6", RFC 3596, October 2003.

[RFC3596]Thomson,S.,Huitema,C.,Ksinant,V.,和M.Souissi,“支持IP版本6的DNS扩展”,RFC 3596,2003年10月。

[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004.

[RFC3704]Baker,F.和P.Savola,“多宿网络的入口过滤”,BCP 84,RFC 37042004年3月。

[RFC4087] Thaler, D., "IP Tunnel MIB", RFC 4087, June 2005.

[RFC4087]Thaler,D.,“IP隧道MIB”,RFC 4087,2005年6月。

8. Changes from RFC 2893
8. RFC 2893的变更

The motivation for the bulk of these changes are to simplify the document to only contain the mechanisms of wide-spread use.


RFC 2893 contains a mechanism called automatic tunneling. But a much more general mechanism is specified in RFC 3056 [RFC3056] which gives each node with a (global) IPv4 address a /48 IPv6 prefix i.e., enough for a whole site.

RFC2893包含一种称为自动隧道的机制。但RFC 3056[RFC3056]中规定了一种更为通用的机制,该机制为每个节点提供一个(全局)IPv4地址和一个/48 IPv6前缀,即足以容纳整个站点。

The following changes have been performed since RFC 2893:

自RFC 2893以来,已执行了以下更改:

- Removed references to A6 and retained AAAA.

- 删除对A6的引用并保留AAAA。

- Removed automatic tunneling and use of IPv4-compatible addresses.

- 删除了自动隧道和IPv4兼容地址的使用。

- Removed default Configured Tunnel using IPv4 "Anycast Address"

- 已删除使用IPv4“选播地址”的默认配置隧道

- Removed Source Address Selection section since this is now covered by another document ([RFC3484]).

- 删除了“源地址选择”部分,因为另一个文档([RFC3484])已涵盖该部分。

- Removed brief mention of 6over4.

- 删除了6以上4的简短提及。

- Split into normative and non-normative references and other reference cleanup.

- 分为规范性引用和非规范性引用以及其他引用。

- Dropped "or equal" in if (IPv4 path MTU - 20) is less than or equal to 1280.

- 如果(IPv4路径MTU-20)小于或等于1280,则丢弃的“或等于”。

- Dropped this: However, IPv6 may be used in some environments where interoperability with IPv4 is not required. IPv6 nodes that are designed to be used in such environments need not use or even implement these mechanisms.

- 删除此选项:但是,在某些不需要与IPv4互操作性的环境中,可能会使用IPv6。设计用于此类环境的IPv6节点不需要使用甚至实现这些机制。

- Described Static MTU and Dynamic MTU cases separately; clarified that the dynamic path MTU mechanism is OPTIONAL but if it is implemented it should follow the rules in section 3.2.2.

- 分别描述了静态MTU和动态MTU情况;阐明动态路径MTU机制是可选的,但如果实施,则应遵循第3.2.2节中的规则。

- Specified Static MTU to default to a MTU of 1280 to 1480 bytes, and that this may be configurable. Discussed the issues with using Static MTU at more length.

- 指定的静态MTU默认为1280到1480字节的MTU,并且这可能是可配置的。更详细地讨论了使用静态MTU的问题。

- Specified minimal rules for IPv4 reassembly and IPv6 MRU to enhance interoperability and to minimize blacholes.

- 为IPv4重组和IPv6 MRU指定了最低限度的规则,以增强互操作性并最大限度地减少Blachole。

- Restated the "currently underway" language about Type-of-Service, and loosely point at [RFC2983] and [RFC3168].

- 重申了关于服务类型的“当前正在进行的”语言,并松散地指向[RFC2983]和[RFC3168]。

- Fixed reference to Assigned Numbers to be to online version (with proper pointer to "Assigned Numbers is obsolete" RFC).

- 修正了在线版本中对指定号码的引用(正确指向“指定号码已过时”RFC)。

- Clarified text about ingress filtering e.g., that it applies to packet delivered to transport protocols on the decapsulator as well as packets being forwarded by the decapsulator, and how the decapsulator's checks help when IPv4 and IPv6 ingress filtering is in place.

- 澄清了关于入口过滤的文本,例如,它适用于发送到解封装器上的传输协议的数据包以及由解封装器转发的数据包,以及在IPv4和IPv6入口过滤到位时解封装器的检查如何帮助。

- Removed unidirectional tunneling; assume all tunnels are bidirectional, between endpoint addresses (not nodes).

- 移除单向隧道;假设所有隧道都是双向的,在端点地址(不是节点)之间。

- Removed the guidelines for advertising addresses in DNS as slightly out of scope, referring to another document for the details.

- 删除了DNS中广告地址的指导原则,因为它稍微超出了范围,请参阅另一个文档了解详细信息。

- Removed the SHOULD requirement that the link-local addresses should be formed based on IPv4 addresses.

- 删除了应基于IPv4地址形成链路本地地址的要求。

- Added a SHOULD for implementing a knob to be able to set the source address of the tunnel, and add discussion why this is useful.

- 添加了一个应该用于实现一个旋钮,以便能够设置隧道的源地址,并添加了为什么这是有用的讨论。

- Added stronger wording for source address checks: both IPv4 and IPv6 source addresses MUST be checked, and RPF-like ingress filtering is optional.

- 为源地址检查添加了更强的措辞:必须检查IPv4和IPv6源地址,并且类似RPF的入口过滤是可选的。

- Rewrote security considerations to be more precise about the threats of tunneling.

- 重写安全注意事项,以便更准确地了解隧道的威胁。

- Added a note about considering using TTL=255 when encapsulating.

- 添加了关于在封装时考虑使用TTL=255的说明。

- Added more discussion in Section 3.2 why using an "infinite" IPv6 MTU leads to likely interoperability problems.

- 在第3.2节中添加了更多讨论,为什么使用“无限”IPv6 MTU会导致可能的互操作性问题。

- Added an explicit requirement that if both MTU determination methods are used, choosing one should be possible on a per-tunnel basis.

- 增加了一项明确要求,即如果同时使用两种MTU测定方法,则应在每个隧道的基础上选择一种。

- Clarified that ICMPv4 error handling is only applicable to dynamic MTU determination.

- 阐明ICMPv4错误处理仅适用于动态MTU确定。

- Removed/clarified DNS record filtering; an API is a SHOULD and if it does not exist, MUST NOT filter anything. Decree ordering out of scope, but refer to RFC3484.

- 删除/澄清DNS记录过滤;API是应该的,如果它不存在,就不能过滤任何内容。订单超出范围,但请参考RFC3484。

- Add a note that the destination IPv4 address could also be a multicast address.

- 请注意,目标IPv4地址也可以是多播地址。

- Make it RECOMMENDED to provide a toggle to perform strict ingress filtering on an interface.

- 建议提供一个切换,以便在接口上执行严格的入口过滤。

- Generalize the text on the data in ICMPv4 messages.

- 概括ICMPv4消息中数据上的文本。

- Made a lot of miscellaneous editorial cleanups.

- 进行了大量的杂项编辑清理。

Authors' Addresses


Erik Nordmark Sun Microsystems 17 Network Circle Menlo Park, CA 94025 USA

Erik Nordmark Sun Microsystems 17 Network Circle Menlo Park,加利福尼亚州94025

   Phone: +1 650 786 2921
   Phone: +1 650 786 2921

Robert E. Gilligan Intransa, Inc. 2870 Zanker Rd., Suite 100 San Jose, CA 95134 USA

Robert E.Gilligan Intransa,Inc.美国加利福尼亚州圣何塞市赞克路2870号100室,邮编95134

   Phone : +1 408 678 8600
   Fax :   +1 408 678 8800
   Phone : +1 408 678 8600
   Fax :   +1 408 678 8800

Full Copyright Statement


Copyright (C) The Internet Society (2005).


This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

本文件受BCP 78中包含的权利、许可和限制的约束,除其中规定外,作者保留其所有权利。



Intellectual Property


The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.

IETF对可能声称与本文件所述技术的实施或使用有关的任何知识产权或其他权利的有效性或范围,或此类权利下的任何许可可能或可能不可用的程度,不采取任何立场;它也不表示它已作出任何独立努力来确定任何此类权利。有关RFC文件中权利的程序信息,请参见BCP 78和BCP 79。

Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at


The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at




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