Internet Engineering Task Force (IETF) Y. Cai
Request for Comments: 6420 H. Ou
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 November 2011
Internet Engineering Task Force (IETF) Y. Cai
Request for Comments: 6420 H. Ou
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 November 2011
PIM Multi-Topology ID (MT-ID) Join Attribute
PIM多拓扑ID（MT-ID）连接属性
Abstract
摘要
This document introduces a new type of PIM Join Attribute that extends PIM signaling to identify a topology that should be used when constructing a particular multicast distribution tree.
本文档介绍了一种新类型的PIM连接属性，该属性扩展了PIM信令，以标识在构建特定多播分发树时应使用的拓扑。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6420.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6420.
Copyright Notice
版权公告
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2011 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)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。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Functional Overview .............................................4
3.1. PIM RPF Topology ...........................................4
3.2. PIM MT-ID ..................................................6
3.3. Applicability ..............................................7
4. Protocol Specification of PIM MT-ID .............................7
4.1. PIM MT-ID Hello Option .....................................7
4.2. PIM MT-ID Join Attribute ...................................7
4.2.1. Sending PIM MT-ID Join Attribute ....................7
4.2.2. Receiving PIM MT-ID Join Attribute ..................8
4.2.3. Validating PIM MT-ID Join Attribute .................8
4.2.4. Conflict Resolution .................................9
4.2.4.1. Conflict Resolution Rules for
Upstream Routers ..........................10
4.2.4.2. Conflict Resolution Rules for
Downstream Routers ........................10
5. Packet Format ..................................................10
5.1. PIM MT-ID Hello Option ....................................11
5.2. PIM MT-ID Join Attribute TLV Format .......................11
6. IANA Considerations ............................................11
6.1. PIM MT-ID Hello Option ....................................11
6.2. PIM MT-ID Join Attribute Type .............................12
7. Security Considerations ........................................12
8. Acknowledgments ................................................12
9. References .....................................................12
9.1. Normative References ......................................12
9.2. Informative References ....................................13
1. Introduction ....................................................2
2. Terminology .....................................................3
3. Functional Overview .............................................4
3.1. PIM RPF Topology ...........................................4
3.2. PIM MT-ID ..................................................6
3.3. Applicability ..............................................7
4. Protocol Specification of PIM MT-ID .............................7
4.1. PIM MT-ID Hello Option .....................................7
4.2. PIM MT-ID Join Attribute ...................................7
4.2.1. Sending PIM MT-ID Join Attribute ....................7
4.2.2. Receiving PIM MT-ID Join Attribute ..................8
4.2.3. Validating PIM MT-ID Join Attribute .................8
4.2.4. Conflict Resolution .................................9
4.2.4.1. Conflict Resolution Rules for
Upstream Routers ..........................10
4.2.4.2. Conflict Resolution Rules for
Downstream Routers ........................10
5. Packet Format ..................................................10
5.1. PIM MT-ID Hello Option ....................................11
5.2. PIM MT-ID Join Attribute TLV Format .......................11
6. IANA Considerations ............................................11
6.1. PIM MT-ID Hello Option ....................................11
6.2. PIM MT-ID Join Attribute Type .............................12
7. Security Considerations ........................................12
8. Acknowledgments ................................................12
9. References .....................................................12
9.1. Normative References ......................................12
9.2. Informative References ....................................13
Some unicast protocols, such as OSPF and IS-IS, allow a single network to be viewed as multiple topologies [RFC4915] [RFC5120]. Deploying multi-topology (MT) routing allows different paths through the network to be selected to support different traffic or to offer protection paths in the event of failures.
一些单播协议，如OSPF和IS-IS，允许将单个网络视为多个拓扑[RFC4915][RFC5120]。部署多拓扑（MT）路由允许选择通过网络的不同路径，以支持不同的通信量，或在发生故障时提供保护路径。
PIM [RFC4601] employs a technique known as Reverse Path Forwarding (RPF) to construct forwarding trees between multicast sources and receivers. The procedure of RPF uses topology information provided by routing protocols, such as OSPF and IS-IS. Using the PIM MT-ID Join Attribute specified in this document enables PIM to access the multiple topologies created by the routing protocols and construct multicast forwarding trees using separate network paths even when the roots of the trees are the same.
PIM[RFC4601]采用一种称为反向路径转发（RPF）的技术在多播源和接收器之间构建转发树。RPF过程使用路由协议（如OSPF和IS-IS）提供的拓扑信息。使用本文档中指定的PIM MT-ID Join属性，PIM可以访问路由协议创建的多个拓扑，并使用单独的网络路径构建多播转发树，即使树的根相同。
This capability would allow for an improvement to the resilience of multicast applications. For instance, a multicast stream can be duplicated and transported using two source trees, (S1, G1) and (S1, G2), simultaneously. By using MT-capable unicast routing protocols and procedures described in this document, it is possible to construct two source trees for (S1, G1) and (S1, G2) in such a way that they do not share any transit network segment. As a result, a single network failure will not cause any loss to the stream.
此功能将允许提高多播应用程序的恢复能力。例如，可以同时使用两个源树（S1，G1）和（S1，G2）复制和传输多播流。通过使用本文档中描述的支持MT的单播路由协议和过程，可以为（S1，G1）和（S1，G2）构建两个源树，使它们不共享任何传输网段。因此，单个网络故障不会对流造成任何损失。
This document introduces a new type of PIM Join Attribute [RFC5384], named "MT-ID Join Attribute". It is used to encode the numerical identity of the topology PIM uses when performing RPF for the forwarding tree that is being joined. This document also specifies procedures and rules to process the attribute and resolve conflicts arising from mismatches in capabilities to support the attribute or the value of the attribute.
本文档介绍了一种新类型的PIM连接属性[RFC5384]，名为“MT-ID连接属性”。它用于对PIM在对正在加入的转发树执行RPF时使用的拓扑的数字标识进行编码。本文档还指定了处理属性和解决因支持属性或属性值的功能不匹配而产生的冲突的过程和规则。
This document does not introduce any change to the RPF check procedure used to verify the incoming interface when a packet is forwarded as defined in [RFC4601]. For example, to use the capability described by this document, an application can choose to use group addresses, and/or source addresses, to identify a unique multicast stream. It might further need to perform the functions of splitting and merging. However, the detailed processing is beyond the scope of the document.
本文件未对RPF检查程序进行任何更改，RPF检查程序用于在[RFC4601]中定义的数据包转发时验证传入接口。例如，要使用本文档描述的功能，应用程序可以选择使用组地址和/或源地址来标识唯一的多播流。它可能还需要执行拆分和合并功能。但是，详细处理超出了本文件的范围。
In the rest of the document, the MT-ID Join Attribute will be referred to as "MT-ID".
在文档的其余部分中，MT-ID连接属性将被称为“MT-ID”。
The following acronyms are frequently used in the document.
本文件中经常使用以下首字母缩略词。
- RPF: RPF stands for "Reverse Path Forwarding". A PIM router performs RPF for two purposes. When building a forwarding tree, a PIM router identifies an interface (the RPF interface) and an upstream PIM neighbor (the RPF neighbor) to which to send PIM Joins. Upon receiving a data packet, a PIM router verifies if the packet arrives from the expected incoming interface (aka RPF check) before deciding whether or not to replicate the packets.
- RPF:RPF代表“反向路径转发”。PIM路由器执行RPF有两个目的。在构建转发树时，PIM路由器识别要向其发送PIM加入的接口（RPF接口）和上游PIM邻居（RPF邻居）。收到数据包后，PIM路由器在决定是否复制数据包之前，验证数据包是否来自预期的传入接口（也称为RPF检查）。
- RPF Topology: An RPF topology is a collection of routes that a PIM router uses for RPF. One or more RPF topologies may be created on a PIM router.
- RPF拓扑：RPF拓扑是PIM路由器用于RPF的路由集合。可以在PIM路由器上创建一个或多个RPF拓扑。
- MT: MT stands for "Multi-Topology" in this document. Sometimes it is also referred to as "multi-topology routing". In the context of PIM, MT refers to the capability of building and maintaining multiple RPF topologies.
- MT:MT在本文档中代表“多拓扑”。有时也称为“多拓扑路由”。在PIM的上下文中，MT指的是构建和维护多个RPF拓扑的能力。
- PIM MT-ID: An MT-ID is a numerical identifier associated with an RPF topology.
- PIM MT-ID：MT-ID是与RPF拓扑相关联的数字标识符。
- PIM MT-ID Join Attribute: This is a new type of Join Attribute that is introduced by this document in order to specify RPF topology in the PIM Join messages.
- PIM MT-ID连接属性：这是本文档引入的一种新类型的连接属性，用于在PIM连接消息中指定RPF拓扑。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“建议”、“不建议”、“可”和“可选”应按照[RFC2119]中的说明进行解释。
PIM relies on routes learned from routing protocols for the purpose of RPF. These routes form one or more topologies. This section describes the function of multi-topology routing for PIM and its applicability.
为了实现RPF，PIM依赖于从路由协议中学习的路由。这些路由形成一个或多个拓扑。本节介绍PIM的多拓扑路由功能及其适用性。
PIM RPF topology is a collection of routes used by PIM to perform the RPF operation when building shared or source trees. The routes in the topology may be contributed by different protocols. In the rest of the document, PIM RPF topology may be simply referred to as "topology" when there is no ambiguity.
PIM RPF拓扑是PIM在构建共享树或源树时用于执行RPF操作的路由集合。拓扑中的路由可能由不同的协议提供。在本文档的其余部分中，如果没有歧义，PIM RPF拓扑可以简单地称为“拓扑”。
In a multi-topology environment, multiple RPF topologies can be created in the same network. A particular source may be reachable in only one of the topologies or in several of them via different paths.
在多拓扑环境中，可以在同一网络中创建多个RPF拓扑。一个特定的源可以仅在一个拓扑中或通过不同的路径在多个拓扑中可到达。
To help explain the relationship between an MT-capable unicast routing protocol and MT-capable RPF topologies, consider the following example described by Figure 1.
为了帮助解释MT单播路由协议与MT能力的RPF拓扑之间的关系，考虑图1所描述的以下示例。
+++ A +++ B +++
+ +
S -- R1 R2 -- receivers
* *
*** C *** D ***
+++ A +++ B +++
+ +
S -- R1 R2 -- receivers
* *
*** C *** D ***
Figure 1. A simple topology for multicast
图1。一种简单的组播拓扑
- The traffic source is S. S is announced by R1 using Multiprotocol BGP (MBGP) to every router. This route is installed in every topology.
- 流量源是S。R1使用多协议BGP（MBGP）向每个路由器宣布S。此路由安装在每个拓扑中。
- Two topologies are created in the unicast IGP, let us call them OSPF 1000 and OSPF 2000. OSPF 1000 includes A, B, and interfaces in R1 and R2 that are configured to be part of OSPF 1000. OSPF 2000 includes C, D, and interfaces on R1 and R2 that are configured to be part of OSPF 2000.
- 单播IGP中创建了两种拓扑，我们称之为OSPF 1000和OSPF 2000。OSPF 1000包括配置为OSPF 1000一部分的R1和R2中的A、B和接口。OSPF 2000包括配置为OSPF 2000一部分的R1和R2上的C、D和接口。
- Two PIM RPF topologies are created, let us call them PIM 500 and PIM 600.
- 创建了两种PIM RPF拓扑，我们称之为PIM 500和PIM 600。
PIM 500 comprises the following routes: S announced by MBGP and those learned via OSPF 1000.
PIM 500包括以下路线：MBGP宣布的路线和通过OSPF 1000学习的路线。
PIM 600 comprises the following routes: S announced by MBGP and those learned via OSPF 2000
PIM 600包括以下路线：MBGP宣布的路线和通过OSPF 2000学习的路线
The above example illustrates that the naming spaces of MT-ID are not required to be the same between PIM and IGPs. Furthermore, a unicast IGP topology and the PIM RPF topology to which the IGP topology contributes routes are not required to have the same set of routes. In the above example, the prefix covering S does not exist in either OSPF 1000 or OSPF 2000, but since it exists in PIM 500 and PIM 600, R2 is able to join to it via either path.
上述示例说明，在PIM和IGP之间，MT-ID的命名空间不需要相同。此外，单播IGP拓扑和IGP拓扑贡献路由的PIM-RPF拓扑不需要具有相同的路由集。在上面的示例中，前缀覆盖S不存在于OSPF 1000或OSPF 2000中，但是由于它存在于PIM 500和PIM 600中，因此R2能够通过任一路径加入到它。
There are two methods to select the RPF topology for a particular multicast distribution tree, via configuration or via PIM.
有两种方法可以通过配置或PIM为特定的多播分发树选择RPF拓扑。
When it is done via configuration, a network administrator configures a policy that maps a group range to a topology and/or maps a source prefix range to a topology. Using the same example, the policy can say that to build a forwarding tree for G1 only routes in PIM 500 are to be used, and to build a forward tree for G2 only routes in PIM 600 are used. The result is that packets for (S, G1) will follow the path of S-R1-A-B-R2 and packets for (S, G2) will follow the path of S-R1-C-D-R2.
通过配置完成后，网络管理员将配置一个策略，将组范围映射到拓扑和/或将源前缀范围映射到拓扑。使用相同的示例，策略可以说要使用PIM 500中的仅G1路由建立转发树，并且要使用PIM 600中的仅G2路由建立转发树。结果是，（S，G1）的数据包将遵循S-R1-A-B-R2的路径，而（S，G2）的数据包将遵循S-R1-C-D-R2的路径。
An alternative to static configuration is to include the RPF topology information as a new PIM Join Attribute in the PIM Join packets sent by downstream routers.
静态配置的替代方法是将RPF拓扑信息作为新的PIM连接属性包含在下游路由器发送的PIM连接数据包中。
Both methods can be used at the same time. The details of the first method are implementation specific and are not discussed in this document. The specification to support the second method is included in this document.
这两种方法可以同时使用。第一种方法的细节是特定于实现的，本文档中不讨论。支持第二种方法的规范包含在本文件中。
For each PIM RPF topology created, a unique numerical ID is assigned per PIM domain. This ID is called the PIM MT-ID. The PIM MT-ID has the following properties.
对于创建的每个PIM RPF拓扑，将为每个PIM域分配一个唯一的数字ID。此ID称为PIM MT-ID。PIM MT-ID具有以下属性。
- It is the path identifier that is used by the PIM control plane, but it does not function in the forwarding state for a specific topology. The differentiation for topologies on the forwarding plane is made by different group addresses and/or source addresses instead.
- 它是PIM控制平面使用的路径标识符，但在特定拓扑的转发状态下不起作用。转发平面上拓扑的区分由不同的组地址和/或源地址代替。
- As shown earlier, this value is not required to be the same as the MT-ID used by the unicast routing protocols that contribute routes to the topology. In practice, when only one unicast routing protocol (such as OSPF or IS-IS) is used, the PIM MT-ID is RECOMMENDED to be assigned using the same value as the IGP topology identifier. Using the same example presented earlier, if every route in PIM 500 is contributed by OSPF 1000, it is RECOMMENDED to name this RPF topology as PIM 1000 instead of PIM 500. This is for the purpose of reducing management overhead and simplifying troubleshooting.
- 如前所示，此值不需要与为拓扑提供路由的单播路由协议使用的MT-ID相同。在实践中，当仅使用一个单播路由协议（例如OSPF或IS-IS）时，建议使用与IGP拓扑标识符相同的值来分配PIM MT-ID。使用前面介绍的相同示例，如果PIM 500中的每个路由都由OSPF 1000提供，建议将此RPF拓扑命名为PIM 1000，而不是PIM 500。这是为了减少管理开销和简化故障排除。
- This value MUST be unique and consistent within the network for the same topology. For example, PIM 500 MUST refer to the same topology on routers R1, C, D, and R2. For actual deployment, one should have a means to detect inconsistency of the PIM MT-ID configuration, but the detail of such mechanism is beyond the scope of this document.
- 对于同一拓扑，此值在网络中必须唯一且一致。例如，PIM 500必须引用路由器R1、C、D和R2上的相同拓扑。对于实际部署，应该有一种方法来检测PIM MT-ID配置的不一致性，但是这种机制的细节超出了本文档的范围。
- 0 is reserved as the default, and it MUST NOT be included in the Join Attribute encoding.
- 0保留为默认值，不能包含在联接属性编码中。
- How to assign a PIM MT-ID to a topology is decided by the network administrator and is outside the scope of this document.
- 如何将PIM MT-ID分配给拓扑由网络管理员决定，不在本文档范围内。
The PIM MT-ID Join Attribute described in this document applies to PIM Join/Assert packets used by PIM SM/SSM/Bidir (Sparse Mode/Source-Specific Mode/Bidirectional). It is not used in any other PIM packets. As such, it can only be used to build shared or source trees for PIM SM/SSM and PIM-Bidir downstream.
本文档中描述的PIM MT-ID连接属性适用于PIM SM/SSM/Bidir（稀疏模式/源特定模式/双向）使用的PIM连接/断言数据包。它不用于任何其他PIM数据包。因此，它只能用于为PIM SM/SSM和PIM Bidir下游构建共享树或源树。
When this attribute is used in combination with RPF vectors defined in [RFC5496] and [MVPN], the vectors are processed against the topology identified by the PIM MT-ID attribute.
当此属性与[RFC5496]和[MVPN]中定义的RPF向量结合使用时，将根据PIM MT-ID属性标识的拓扑处理向量。
The change to the PIM protocol includes two pieces: the PIM MT-ID Hello Option and the PIM MT-ID Join Attribute.
对PIM协议的更改包括两部分：PIM MT-ID Hello选项和PIM MT-ID Join属性。
The PIM MT-ID Hello Option is used by a router to indicate if it supports the functionality described by this document. If it does, it MUST include the PIM Hello Option in its PIM Hello packets and MUST include both the Join Attribute Option [RFC5384] and the new PIM MT-ID Option (see Section 5.1 of this document for packet format).
路由器使用PIM MT-ID Hello选项指示其是否支持本文档所述的功能。如果是，则必须在其PIM Hello数据包中包含PIM Hello选项，并且必须同时包含连接属性选项[RFC5384]和新的PIM MT-ID选项（数据包格式见本文档第5.1节）。
When a PIM router originates a PIM Join/Assert packet, it may choose to encode the PIM MT-ID of the topology in which RPF lookup is to take place for the corresponding (*,G) or (S,G) entry. The PIM MT-ID identifies the topology chosen by local policy/configuration or is the value received from downstream routers after MT-ID conflict resolution procedures have been applied (See Section 4.2.4 for further detail).
当PIM路由器发起PIM连接/断言数据包时，它可以选择为相应（*，G）或（S，G）条目对RPF查找将在其中发生的拓扑的PIM MT-ID进行编码。PIM MT-ID标识本地策略/配置选择的拓扑，或者是应用MT-ID冲突解决程序后从下游路由器接收的值（更多详细信息，请参阅第4.2.4节）。
The following are the exceptions:
以下是例外情况：
- A router SHOULD NOT include the attribute if PIM MT-ID is 0. The value of 0 is ignored on reception.
- 如果PIM MT-ID为0，则路由器不应包含该属性。接收时忽略0的值。
- A router SHOULD NOT include the PIM MT-ID in its Join/Assert packets if the upstream router, or any of the routers on the LAN, does not include the "PIM Join Attribute" or "PIM MT-ID" option in its Hello packets.
- 如果上游路由器或LAN上的任何路由器在其Hello数据包中未包含“PIM连接属性”或“PIM MT-ID”选项，则路由器不应在其连接/断言数据包中包含PIM MT-ID。
- A router SHOULD NOT attach PIM MT-ID for pruned sources. PIM MT-ID MUST be ignored for a pruned source by a router processing the Prune message.
- 路由器不应为删减的源附加PIM MT-ID。处理删减消息的路由器必须忽略删减源的PIM MT-ID。
When a PIM router receives a PIM MT-ID Join Attribute in a Join/Assert packet, it MUST perform the following:
当PIM路由器在连接/断言数据包中接收到PIM MT-ID连接属性时，它必须执行以下操作：
- Validate the attribute encoding. The detail is described in the next section.
- 验证属性编码。细节将在下一节中描述。
- If the Join Attribute is valid, use the rules described in the section "Conflict Resolution" to determine a PIM MT-ID to use.
- 如果连接属性有效，请使用“冲突解决”一节中描述的规则确定要使用的PIM MT-ID。
- Use the topology identified by the selected PIM MT-ID to perform RPF lookup for the (*,G)/(S,G) entry unless a different topology is specified by a local configuration. The local configuration always takes precedence.
- 使用所选PIM MT-ID标识的拓扑对（*，G）/（S，G）条目执行RPF查找，除非本地配置指定了不同的拓扑。本地配置始终优先。
While it is an exception case, it is worthwhile to describe what will happen if a router receives PIM MT-ID Join Attribute but doesn't support the functionality described in [RFC5384] or this document. If the router supports [RFC5384] but not this document, it is able to skip the PIM MT-ID Join Attribute and move on to the next Join Attribute, if one is present. The RPF decision will not be altered because the router doesn't understand the meaning of the PIM MT-ID Join Attribute. The router will use the procedures described by [RFC5384] to perform conflict resolution.
虽然这是一个例外情况，但值得描述的是，如果路由器接收到PIM MT-ID连接属性，但不支持[RFC5384]或本文档中描述的功能，将会发生什么情况。如果路由器支持[RFC5384]，但不支持本文档，则可以跳过PIM MT-ID连接属性，并转到下一个连接属性（如果存在）。RPF决定不会被更改，因为路由器不理解PIM MT-ID Join属性的含义。路由器将使用[RFC5384]描述的程序执行冲突解决。
If a router doesn't support [RFC5384], it will ignore the Join/Assert message because it is not able to parse the encoded sources.
如果路由器不支持[RFC5384]，它将忽略Join/Assert消息，因为它无法解析编码的源。
If a router does support both [RFC5384] and this document, but chooses not to send either the PIM MT-ID or the PIM Join Attribute Option in its Hello packets (likely due to administrative reasons), it SHOULD ignore the Join/Assert message when it receives a PIM Join/Assert packet with the PIM MT-ID Join Attribute.
如果路由器确实支持[RFC5384]和本文档，但选择不在其Hello数据包中发送PIM MT-ID或PIM Join属性选项（可能是由于管理原因），则当它接收到具有PIM MT-ID Join属性的PIM Join/Assert数据包时，应忽略Join/Assert消息。
An upstream router MUST be known to support this document in order for a downstream router to include the PIM MT-ID attribute in its Join packets. However, an upstream router doesn't need to know whether or not a downstream router supports this document when deciding whether to accept the attribute. Hence, if the Join packet sender doesn't include the "PIM Join Attribute" or "PIM MT-ID"
必须知道上游路由器支持本文档，以便下游路由器在其连接数据包中包含PIM MT-ID属性。但是，在决定是否接受该属性时，上游路由器不需要知道下游路由器是否支持该文档。因此，如果连接数据包发送方不包括“PIM连接属性”或“PIM MT-ID”
options in its Hello packets, the PIM MT-ID attribute in the Join may still be considered valid. This is also in accordance with the "Robustness Principle" outlined in [RFC793].
在其Hello数据包中的选项中，联接中的PIM MT-ID属性可能仍然有效。这也符合[RFC793]中概述的“稳健性原则”。
The following text specifies the detail of the validity check.
以下文本指定了有效性检查的详细信息。
- There is at most 1 PIM MT-ID attribute encoded. If there are multiple PIM MT-ID Join Attributes included (possibly due to an error in the implementation), only the last one is accepted for this particular source. Processing of the rest of the Join message continues.
- 最多有1个PIM MT-ID属性已编码。如果包含多个PIM MT-ID连接属性（可能是由于实现中的错误），则此特定源只接受最后一个属性。继续处理联接消息的其余部分。
- The Length field must be 2. If the Length field is not 2, the rest of the Join message, including the current (S,G) or (*,G) entry, MUST be ignored. The group, source, and Rendezvous Point (RP) in the Join message that have already been processed SHOULD still be considered valid.
- 长度字段必须为2。如果长度字段不是2，则必须忽略连接消息的其余部分，包括当前（S，G）或（*，G）条目。联接消息中已处理的组、源和集合点（RP）仍应视为有效。
- The value MUST NOT be 0. If it is 0, the PIM MT-ID attribute is ignored. Processing of the rest of the Join message, including the current (S,G) or (*,G) entry, continues as if the particular PIM MT-ID attribute weren't present in the packet.
- 该值不能为0。如果为0，则忽略PIM MT-ID属性。连接消息的其余部分（包括当前（S，G）或（*，G）条目）的处理将继续进行，就像特定的PIM MT-ID属性不在数据包中一样。
The definition of "PIM MT-ID conflict" varies depending on whether it is on an upstream or a downstream router.
“PIM MT-ID冲突”的定义取决于它是在上游路由器上还是在下游路由器上。
PIM MT-ID conflicts arises on an upstream router when the router doesn't have a local topology selection policy and receives Join packets from downstream routers and/or Assert packets from other forwarding routers on the LAN and those packets contain different PIM MT-IDs.
当上游路由器没有本地拓扑选择策略，并且从下游路由器接收连接数据包和/或从LAN上的其他转发路由器接收断言数据包，并且这些数据包包含不同的PIM MT ID时，PIM MT-ID冲突在上游路由器上产生。
However, if an upstream router has a local configuration that specifies PIM MT-IDs to identify RPF topologies, and those MT-IDs do not match the MT-ID on a received Join or Assert packet, this is not considered to be a conflict and the resolution procedures are not applied. This includes the case where there are local PIM MT-IDs, but there is no PIM MT-ID encoded in the incoming packet.
但是，如果上游路由器具有指定PIM MT ID以识别RPF拓扑的本地配置，并且这些MT ID与接收到的Join或Assert数据包上的MT-ID不匹配，则不认为这是冲突，也不应用解决过程。这包括存在本地PIM MT ID，但传入分组中没有编码的PIM MT-ID的情况。
On the other hand, when a downstream router sees a different PIM MT-ID attribute from other routers on the LAN, it applies rules to resolve the conflicts regardless of whether or not the router has local topology selection policy.
另一方面，当下游路由器看到与LAN上其他路由器不同的PIM MT-ID属性时，它应用规则来解决冲突，而不管路由器是否具有本地拓扑选择策略。
When two PIM MT-IDs are compared, only the 12-bit Value field (see Section 5.2) is compared. Other fields of the PIM MT-ID Join Attribute TLV Format (including the four reserved bits) MUST NOT be used in the comparison.
比较两个PIM MT ID时，仅比较12位值字段（见第5.2节）。不得在比较中使用PIM MT-ID连接属性TLV格式的其他字段（包括四个保留位）。
- If an upstream router receives different PIM MT-ID attributes from PIM Join packets, it MUST follow the rules specified in [RFC5384] to select one. The PIM MT-ID chosen will be the one encoded for its upstream neighbor.
- 如果上游路由器从PIM连接数据包接收到不同的PIM MT-ID属性，它必须遵循[RFC5384]中指定的规则来选择一个。选择的PIM MT-ID将是为其上游邻居编码的。
In order to minimize the chances of potential transient forwarding loops, an upstream router MAY choose to ignore the incoming PIM Join packets altogether if it sees a conflict in PIM MT-ID attributes. This action may also be taken by an upstream router that has locally configured topology selection policy, as an exception to the rules described above.
为了最大限度地减少潜在的瞬时转发循环，如果上游路由器发现PIM MT-ID属性中存在冲突，则可以选择完全忽略传入的PIM连接数据包。作为上述规则的例外，具有本地配置的拓扑选择策略的上游路由器也可以采取此操作。
- If an upstream router receives a different PIM MT-ID attribute in an Assert packet, it MUST use the tiebreaker rules as specified in [RFC4601] to determine an Assert winner. PIM MT-ID is not considered in deciding a winner from Assert process.
- 如果上游路由器在断言数据包中接收到不同的PIM MT-ID属性，则它必须使用[RFC4601]中指定的分层规则来确定断言获胜者。在从断言过程中决定胜利者时，不考虑PIM MT-ID。
- If a downstream router sees different PIM MT-ID attributes from PIM Join packets, it MUST follow the specification of [RFC4601] as if the attribute did not exist. For example, the router suppresses its own Join packet if a Join for the same (S,G) is seen.
- 如果下游路由器从PIM连接数据包中看到不同的PIM MT-ID属性，则它必须遵循[RFC4601]的规范，就像该属性不存在一样。例如，如果看到相同（S，G）的连接，路由器将抑制其自己的连接数据包。
The router MUST NOT use the rules specified in [RFC5384] to select a PIM MT-ID from Join packets sent by other downstream routers.
路由器不得使用[RFC5384]中指定的规则从其他下游路由器发送的连接数据包中选择PIM MT-ID。
- If a downstream router sees its preferred upstream router loses in the Assert process, and the Assert winner uses a different PIM MT-ID, the downstream router SHOULD still choose the Assert winner as the RPF neighbour, but it MUST NOT encode PIM MT-ID when sending Join packets to it.
- 如果下游路由器发现其首选的上游路由器在断言过程中丢失，并且断言赢家使用不同的PIM MT-ID，则下游路由器仍应选择断言赢家作为RPF邻居，但在向其发送加入数据包时不得对PIM MT-ID进行编码。
This section describes the format of new PIM messages introduced by this document. The messages follow the same transmission order as the messages defined in [RFC4601].
本节介绍本文档引入的新PIM消息的格式。这些消息遵循与[RFC4601]中定义的消息相同的传输顺序。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType = 30 | OptionLength = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType = 30 | OptionLength = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- OptionType: 30.
- 选项类型：30。
- OptionLength: 0.
- 选项长度：0。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type | Length |R R R R| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Attr Type | Length |R R R R| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- F bit: 0 Non-transitive Attribute.
- F位：0非传递属性。
- E bit: As specified by [RFC5384].
- E位：按照[RFC5384]的规定。
- Attr Type: 2
- 属性类型：2
- Length: 2.
- 长度：2。
- R: Reserved bits, 4 in total. Set to zero on transmission. Ignored upon receipt.
- R：保留位，共4位。在变速器上设置为零。收到时忽略。
- Value: PIM MT-ID, 1 to 4095.
- 值：PIM MT-ID，1至4095。
IANA maintains a registry of "Protocol Independent Multicast (PIM) Parameters" with a sub-registry called "PIM-Hello Options".
IANA使用一个名为“PIM Hello Options”的子注册表维护“协议独立多播（PIM）参数”注册表。
The IANA has assigned the PIM Hello Option type value 30 for the PIM MT-ID Hello Option according to the First Come First Served allocation policy.
IANA根据先到先得的分配策略为PIM MT-ID Hello选项分配了PIM Hello选项类型值30。
The IANA has assigned a Length value of 0.
IANA已指定长度值0。
The IANA maintains a registry of "Protocol Independent Multicast (PIM) Parameters" with a sub-registry called "PIM Join Attribute Types".
IANA使用一个名为“PIM连接属性类型”的子注册表维护“协议独立多播（PIM）参数”注册表。
The IANA has assigned a value of 2 for the PIM MT-ID Join Attribute defined in Section 5.2 of this document.
IANA已为本文件第5.2节中定义的PIM MT-ID连接属性分配了一个值2。
As described in [RFC5384], the security of the Join Attribute is only guaranteed by the security of the PIM packet that carries it. Similarly, the security of the Hello Option is only guaranteed by securing the whole Hello Packet.
如[RFC5384]所述，连接属性的安全性仅由携带该属性的PIM数据包的安全性来保证。类似地，Hello选项的安全性仅通过保护整个Hello数据包来保证。
In view of the fact that malicious alteration of the PIM MT-ID Hello Option or the PIM MT-ID carried in a packet might cause the PIM resiliency goals to be violated, the security considerations of [RFC4601] apply to the extensions described in this document.
鉴于恶意更改数据包中的PIM MT-ID Hello选项或PIM MT-ID可能导致违反PIM弹性目标，因此[RFC4601]的安全注意事项适用于本文档中描述的扩展。
As a type of PIM Join Attribute, the security considerations described in [RFC5384] apply here. Specifically, malicious alteration of PIM MT-ID may cause the resiliency goals to be violated.
作为PIM连接属性的一种类型，[RFC5384]中描述的安全注意事项适用于此处。具体而言，恶意更改PIM MT-ID可能会违反恢复性目标。
The authors would like to thank Eric Rosen, Ice Wijnands, Dino Farinacci, Colby Barth, Les Ginsberg, Dimitri Papadimitriou, Thomas Morin, and Hui Liu for their input.
作者要感谢Eric Rosen、Ice Wijnands、Dino Farinaci、Colby Barth、Les Ginsberg、Dimitri Papadimitriou、Thomas Morin和Hui Liu的投入。
The authors would also like to thank Adrian Farrel for his detailed and constructive comments during the AD review.
作者还想感谢阿德里安·法雷尔在广告评论期间的详细和建设性评论。
[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。
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4601]Fenner，B.，Handley，M.，Holbrook，H.，和I.Kouvelas，“协议独立多播-稀疏模式（PIM-SM）：协议规范（修订版）”，RFC 46012006年8月。
[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol Independent Multicast (PIM) Join Attribute Format", RFC 5384, November 2008.
[RFC5384]Boers，A.，Wijnands，I.，和E.Rosen，“协议独立多播（PIM）连接属性格式”，RFC 5384，2008年11月。
[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981.
[RFC793]Postel，J.，“传输控制协议”，标准7，RFC 793，1981年9月。
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, June 2007.
[RFC4915]Psenak，P.，Mirtorabi，S.，Roy，A.，Nguyen，L.，和P.Pillay Esnault，“OSPF中的多拓扑（MT）路由”，RFC 4915，2007年6月。
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5120]Przygienda，T.，Shen，N.，和N.Sheth，“M-ISIS：中间系统到中间系统（IS-ISs）的多拓扑（MT）路由”，RFC 5120，2008年2月。
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path Forwarding (RPF) Vector TLV", RFC 5496, March 2009.
[RFC5496]Wijnands，IJ.，Boers，A.，和E.Rosen，“反向路径转发（RPF）向量TLV”，RFC 54962009年3月。
[MVPN] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP VPNs", Work in Progress, January 2010.
[MVPN]Rosen，E.和R.Aggarwal，“MPLS/BGP IP VPN中的多播”，正在进行的工作，2010年1月。
Authors' Addresses
作者地址
Yiqun Cai Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134
伊群蔡思科系统有限公司，加利福尼亚州圣何塞市西塔斯曼大道170号，邮编95134
EMail: ycai@cisco.com
EMail: ycai@cisco.com
Heidi Ou Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134
Heidi Ou Cisco Systems，Inc.加利福尼亚州圣何塞西塔斯曼大道170号，邮编95134
EMail: hou@cisco.com
EMail: hou@cisco.com