Internet Engineering Task Force (IETF) W. Cheng
Request for Comments: 8184 L. Wang
Category: Informational H. Li
ISSN: 2070-1721 China Mobile
S. Davari
Broadcom Corporation
J. Dong
Huawei Technologies
June 2017
Internet Engineering Task Force (IETF) W. Cheng
Request for Comments: 8184 L. Wang
Category: Informational H. Li
ISSN: 2070-1721 China Mobile
S. Davari
Broadcom Corporation
J. Dong
Huawei Technologies
June 2017
Dual-Homing Protection for MPLS and the MPLS Transport Profile (MPLS-TP) Pseudowires
MPLS和MPLS传输配置文件（MPLS-TP）伪线的双重归巢保护
Abstract
摘要
This document describes a framework and several scenarios for a pseudowire (PW) dual-homing local protection mechanism that avoids unnecessary switchovers and does not depend on whether a control plane is used. A Dual-Node Interconnection (DNI) PW is used to carry traffic between the dual-homing Provider Edge (PE) nodes when a failure occurs in one of the Attachment Circuits (AC) or PWs. This PW dual-homing local protection mechanism is complementary to existing PW protection mechanisms.
本文档描述了伪线（PW）双归巢局部保护机制的框架和几种场景，该机制避免了不必要的切换，并且不依赖于是否使用控制平面。当其中一个连接电路（AC）或PW发生故障时，双节点互连（DNI）PW用于在双归属提供商边缘（PE）节点之间承载通信量。这种PW双归巢局部保护机制是对现有PW保护机制的补充。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 7841.
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。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 7841第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8184.
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/rfc8184.
Copyright Notice
版权公告
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2017 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents
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) 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.
(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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Reference Models of Dual-Homing Local Protection . . . . . . 4
2.1. PE Architecture . . . . . . . . . . . . . . . . . . . . . 4
2.2. Dual-Homing Local Protection Reference Scenarios . . . . 5
2.2.1. One-Side Dual-Homing Protection . . . . . . . . . . . 5
2.2.2. Two-Side Dual-Homing Protection . . . . . . . . . . . 6
3. Generic Dual-Homing PW Protection Mechanism . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Reference Models of Dual-Homing Local Protection . . . . . . 4
2.1. PE Architecture . . . . . . . . . . . . . . . . . . . . . 4
2.2. Dual-Homing Local Protection Reference Scenarios . . . . 5
2.2.1. One-Side Dual-Homing Protection . . . . . . . . . . . 5
2.2.2. Two-Side Dual-Homing Protection . . . . . . . . . . . 6
3. Generic Dual-Homing PW Protection Mechanism . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
[RFC6372] and [RFC6378] describe the framework and mechanism of MPLS Transport Profile (MPLS-TP) linear protection, which can provide protection for the MPLS Label Switched Path (LSP) or pseudowire (PW) between the edge nodes. This mechanism does not protect against failure of the Attachment Circuit (AC) or the Provider Edge (PE) node. [RFC6718] and [RFC6870] describe the framework and mechanism for PW redundancy to provide protection against AC or PE node failure. The PW redundancy mechanism is based on the signaling of the Label Distribution Protocol (LDP), which is applicable to PWs with a dynamic control plane. [RFC8104] describes a fast local repair mechanism for PW egress endpoint failures, which is based on PW redundancy, upstream label assignment, and context-specific label switching. The mechanism defined in [RFC8104] is only applicable to PWs with a dynamic control plane.
[RFC6372]和[RFC6378]描述了MPLS传输配置文件（MPLS-TP）线性保护的框架和机制，它可以为边缘节点之间的MPLS标签交换路径（LSP）或伪线（PW）提供保护。此机制不能防止连接电路（AC）或提供程序边缘（PE）节点出现故障。[RFC6718]和[RFC6870]描述了PW冗余的框架和机制，以提供针对AC或PE节点故障的保护。PW冗余机制基于标签分发协议（LDP）的信令，适用于具有动态控制平面的PWs。[RFC8104]描述了PW出口端点故障的快速本地修复机制，该机制基于PW冗余、上游标签分配和上下文特定的标签切换。[RFC8104]中定义的机构仅适用于具有动态控制平面的PWs。
There is a need to support a dual-homing local protection mechanism that avoids unnecessary switches of the AC or PW and can be used regardless of whether a control plane is used. In some scenarios, such as mobile backhauling, the MPLS PWs are provisioned with dual-homing topology in which at least the Customer Edge (CE) node on one side is dual-homed to two PEs. If some fault occurs in the primary AC, operators usually prefer to have the switchover only on the dual-homing PE side and keep the working pseudowires unchanged if possible. This is to avoid massive PW switchover in the mobile backhaul network due to AC failure in the mobile core site; such massive PW switchover may in turn lead to congestion caused by migrating traffic away from the preferred paths of network planners. Similarly, as multiple PWs share the physical AC in the mobile core site, it is preferable to keep using the working AC when one working PW fails in the Packet Switched Network (PSN) to potentially avoid unnecessary switchover for other PWs. To meet the above requirements, a fast dual-homing local PW protection mechanism is needed to protect against the failures of an AC, the PE node, and the PSN.
需要支持双归位本地保护机制，避免不必要的AC或PW开关，并且无论是否使用控制平面都可以使用。在一些场景中，例如移动回程，MPLS pw被配置为双归宿拓扑，其中至少一侧的客户边缘（CE）节点被双归宿到两个PEs。如果一次交流发生故障，操作员通常倾向于仅在双回零PE侧进行切换，并尽可能保持工作假线不变。这是为了避免移动回程网络中由于移动核心站点的交流故障而发生大规模PW切换；如此大规模的PW切换可能反过来导致拥塞，这是由于将流量从网络规划者的首选路径迁移而造成的。类似地，由于多个PW共享移动核心站点中的物理AC，因此当一个工作PW在分组交换网络（PSN）中失败时，最好保持使用该工作AC，以潜在地避免其他PW的不必要切换。为了满足上述要求，需要一种快速双归宿本地PW保护机制来防止AC、PE节点和PSN的故障。
This document describes the framework and several typical scenarios of PW dual-homing local protection. A Dual-Node Interconnection (DNI) PW is used between the dual-homing PE nodes to carry traffic when a failure occurs in the AC or PW side. In order for the dual-homing PE nodes to determine the forwarding state of AC, PW, and DNI-PW, necessary state exchange and coordination between the dual-homing PEs is needed. The necessary mechanisms and protocol extensions are defined in [RFC8185].
本文件描述了PW双归宿局部保护的框架和几个典型场景。当AC或PW侧发生故障时，双归宿PE节点之间使用双节点互连（DNI）PW来承载流量。为了让双归属PE节点确定AC、PW和DNI-PW的转发状态，需要在双归属PE之间进行必要的状态交换和协调。[RFC8185]中定义了必要的机制和协议扩展。
This section shows the reference architecture of the dual-homing PW local protection and the usage of the architecture in different scenarios.
本节介绍了双归位PW局部保护的参考体系结构以及该体系结构在不同场景中的使用。
Figure 1 shows the PE architecture for dual-homing local protection. This is based on the architecture in Figure 4a of [RFC3985]. In addition to the AC and the service PW between the local and remote PEs, a DNI-PW is used to connect the forwarders of the dual-homing PEs. It can be used to forward traffic between the dual-homing PEs when a failure occurs in the AC or service PW side. As [RFC3985] specifies: "any required switching functionality is the responsibility of a forwarder function". In this case, the forwarder is responsible for switching the payloads between three entities: the AC, the service PW, and the DNI-PW.
图1显示了双归宿本地保护的PE体系结构。这是基于[RFC3985]图4a中的架构。除了本地和远程PEs之间的AC和服务PW外，还使用DNI-PW连接双归宿PEs的转发器。当交流侧或维修PW侧发生故障时，它可用于转发双归巢PEs之间的通信量。正如[RFC3985]所规定的：“任何所需的交换功能均由转发器功能负责”。在这种情况下，货运代理负责在三个实体之间切换有效载荷：AC、服务PW和DNI-PW。
+----------------------------------------+
| Dual-Homing PE Device |
+----------------------------------------+
AC | | | Service PW
<------>o Forwarder + Service X<===========>
| | PW |
+--------+--------+ |
| DNI-PW | |
+--------X--------+----------------------+
^
| DNI-PW
|
V
+--------X--------+----------------------+
| DNI-PW | |
+--------+--------+ | Service PW
AC | | Service X<===========>
<------>o Forwarder + PW |
| | |
+----------------------------------------+
| Dual-Homing PE Device |
+----------------------------------------+
+----------------------------------------+
| Dual-Homing PE Device |
+----------------------------------------+
AC | | | Service PW
<------>o Forwarder + Service X<===========>
| | PW |
+--------+--------+ |
| DNI-PW | |
+--------X--------+----------------------+
^
| DNI-PW
|
V
+--------X--------+----------------------+
| DNI-PW | |
+--------+--------+ | Service PW
AC | | Service X<===========>
<------>o Forwarder + PW |
| | |
+----------------------------------------+
| Dual-Homing PE Device |
+----------------------------------------+
Figure 1: PE Architecture for Dual-Homing Protection
图1：双归巢保护的PE体系结构
Figure 2 illustrates the network scenario of dual-homing PW local protection where only one of the CEs is dual-homed to two PE nodes. CE1 is dual-homed to PE1 and PE2, while CE2 is single-homed to PE3. A DNI-PW is established between the dual-homing PEs, which is used to bridge traffic when a failure occurs in the PSN or the AC side. A dual-homing control mechanism enables the PEs and CE to determine which AC should be used to carry traffic between CE1 and the PSN. The necessary control mechanisms and protocol extensions are defined in [RFC8185].
图2说明了双归宿PW本地保护的网络场景，其中只有一个CE双归宿到两个PE节点。CE1是PE1和PE2的双宿位，而CE2是PE3的单宿位。在双归宿PEs之间建立DNI-PW，用于在PSN或交流侧发生故障时桥接通信量。双归巢控制机制使PEs和CE能够确定应使用哪个AC在CE1和PSN之间传输流量。[RFC8185]中定义了必要的控制机制和协议扩展。
This scenario can protect against node failure of PE1 or PE2 or failure of one of the ACs between CE1 and the dual-homing PEs. In addition, dual-homing PW protection can protect against failure occurring in the PSN that impacts the working PW; thus, it can be an alternative solution of PSN tunnel protection mechanisms. This topology can be used in mobile backhauling application scenarios. For example, CE2 might be an equipment cell site such as a NodeB, while CE1 is the shared Radio Network Controller (RNC). PE3 functions as an access-side MPLS device, while PE1 and PE2 function as core-side MPLS devices.
该场景可以防止PE1或PE2的节点故障，或CE1和双归宿PEs之间的一个ACs故障。此外，双归位PW保护可防止PSN中发生影响工作PW的故障；因此，它可以作为PSN隧道保护机制的替代解决方案。此拓扑可用于移动回程应用场景。例如，CE2可能是设备小区站点，如NodeB，而CE1是共享无线网络控制器（RNC）。PE3用作接入端MPLS设备，而PE1和PE2用作核心端MPLS设备。
|<--------------- Emulated Service --------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ V
+-----+ | | PE1| | | +-----+
| |----------|........PW1.(working).......| | |
| | | | | | | |
| | +-+--+ | | AC3 | |
| | | | | | | |
| CE1 | DNI-PW | |PE3 |----------| CE2 |
| | | | | | |
| | +-+--+ | | | |
| | | | | | | |
| |----------|......PW2.(protection)......| | |
+-----+ | | PE2| | | +-----+
AC2 +----+ +----+
|<--------------- Emulated Service --------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ V
+-----+ | | PE1| | | +-----+
| |----------|........PW1.(working).......| | |
| | | | | | | |
| | +-+--+ | | AC3 | |
| | | | | | | |
| CE1 | DNI-PW | |PE3 |----------| CE2 |
| | | | | | |
| | +-+--+ | | | |
| | | | | | | |
| |----------|......PW2.(protection)......| | |
+-----+ | | PE2| | | +-----+
AC2 +----+ +----+
Figure 2: One-Side Dual-Homing PW Protection
图2：单侧双归位PW保护
Consider the example where in normal state AC1 from CE1 to PE1 is initially active and AC2 from CE1 to PE2 is initially standby. PW1 is configured as the working PW and PW2 is configured as the protection PW.
考虑在正常状态下AC1从CE1到PE1最初激活的情况，AC2从CE1到PE2最初是备用的。PW1配置为工作PW，PW2配置为保护PW。
When a failure occurs in AC1, then the state of AC2 changes to active based on the AC dual-homing control mechanism. In order to keep the switchover local and continue using PW1 for traffic forwarding as preferred according to traffic planning, the forwarder on PE2 needs to connect AC2 to the DNI-PW, and the forwarder on PE1 needs to connect the DNI-PW to PW1. In this way, the failure in AC1 will not impact the forwarding of the service PWs across the network. After the switchover, traffic will go through the bidirectional path: CE1-(AC2)-PE2-(DNI-PW)-PE1-(PW1)-PE3-(AC3)-CE2.
当AC1发生故障时，AC2的状态将根据AC双归位控制机制变为激活状态。为了保持本地切换，并根据交通规划继续优先使用PW1进行交通转发，PE2上的转发器需要将AC2连接到DNI-PW，PE1上的转发器需要将DNI-PW连接到PW1。这样，AC1中的故障将不会影响网络中服务PW的转发。切换后，流量将通过双向路径：CE1-（AC2）-PE2-（DNI-PW）-PE1-（PW1）-PE3-（AC3）-CE2。
When a failure in the PSN affects the working PW (PW1), according to PW protection mechanisms [RFC6378], traffic is switched onto the protection PW (PW2) while the state of AC1 remains active. Then, the forwarder on PE1 needs to connect AC1 to the DNI-PW, and the forwarder on PE2 needs to connect the DNI-PW to PW2. In this way, the failure in the PSN will not impact the state of the ACs. After the switchover, traffic will go through the bidirectional path: CE1-(AC1)-PE1-(DNI-PW)-PE2-(PW2)-PE3-(AC3)-CE2.
当PSN中的故障影响工作PW（PW1）时，根据PW保护机制[RFC6378]，当AC1的状态保持激活时，通信量切换到保护PW（PW2）。然后，PE1上的转发器需要将AC1连接到DNI-PW，PE2上的转发器需要将DNI-PW连接到PW2。这样，PSN中的故障将不会影响ACs的状态。切换后，流量将通过双向路径：CE1-（AC1）-PE1-（DNI-PW）-PE2-（PW2）-PE3-（AC3）-CE2。
When a failure occurs in the working PE (PE1), it is equivalent to a failure of the working AC, the working PW, and the DNI-PW. The state of AC2 changes to active based on the AC dual-homing control mechanism. In addition, according to the PW protection mechanism, traffic is switched on to the protection PW "PW2". In this case, the forwarder on PE2 needs to connect AC2 to PW2. After the switchover, traffic will go through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE3-(AC3)-CE2.
当工作PE（PE1）发生故障时，相当于工作AC、工作PW和DNI-PW的故障。AC2的状态根据交流双归位控制机制变为激活状态。此外，根据PW保护机制，通信量被切换到保护PW“PW2”。在这种情况下，PE2上的转发器需要将AC2连接到PW2。切换后，交通将通过双向路径：CE1-（AC2）-PE2-（PW2）-PE3-（AC3）-CE2。
Figure 3 illustrates the network scenario of dual-homing PW protection where the CEs in both sides are dual-homed. CE1 is dual-homed to PE1 and PE2, and CE2 is dual-homed to PE3 and PE4. A dual-homing control mechanism enables the PEs and CEs to determine which AC should be used to carry traffic between the CE and the PSN. DNI-PWs are used between the dual-homing PEs on both sides. One service PW is established between PE1 and PE3, and another service PW is established between PE2 and PE4. The role of working and protection PWs can be determined by either configuration or existing signaling mechanisms.
图3说明了双归宿PW保护的网络场景，其中两侧的CE均为双归宿。CE1是PE1和PE2的双宿位，CE2是PE3和PE4的双宿位。双归巢控制机制使PEs和CEs能够确定应使用哪个AC在CE和PSN之间传输流量。DNI PWs用于两侧的双归位PEs之间。一个维修PW建立在PE1和PE3之间，另一个维修PW建立在PE2和PE4之间。工作和保护PW的作用可通过配置或现有信号机制确定。
This scenario can protect against node failure on one of the dual-homing PEs or failure on one of the ACs between the CEs and their dual-homing PEs. Also, dual-homing PW protection can protect against the occurrence of failure in the PSN that impacts one of the PWs; thus, it can be used as an alternative solution of PSN tunnel protection mechanisms. Note, this scenario is mainly used for services requiring high availability as it requires redundancy of the PEs and network utilization. In this case, CE1 and CE2 can be regarded as service access points.
此场景可以防止其中一个双归属PE上的节点故障或CEs与其双归属PE之间的一个ACs上的故障。此外，双归巢PW保护可防止PSN中发生影响其中一个PW的故障；因此，它可以作为PSN隧道保护机制的替代解决方案。注意，此场景主要用于需要高可用性的服务，因为它需要PEs冗余和网络利用率。在这种情况下，CE1和CE2可以被视为服务接入点。
|<---------------- Emulated Service -------------->|
| |
| |<-------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ AC3 V
+-----+ | | ...|...PW1.(working)..|... | | +-----+
| |----------| PE1| | PE3|----------| |
| | +----+ +----+ | |
| | | | | |
| CE1 | DNI-PW1 | | DNI-PW2 | CE2 |
| | | | | |
| | +----+ +----+ | |
| | | | | | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | | ...|.PW2.(protection).|... | | +-----+
AC2 +----+ +----+ AC4
|<---------------- Emulated Service -------------->|
| |
| |<-------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC1 +----+ +----+ AC3 V
+-----+ | | ...|...PW1.(working)..|... | | +-----+
| |----------| PE1| | PE3|----------| |
| | +----+ +----+ | |
| | | | | |
| CE1 | DNI-PW1 | | DNI-PW2 | CE2 |
| | | | | |
| | +----+ +----+ | |
| | | | | | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | | ...|.PW2.(protection).|... | | +-----+
AC2 +----+ +----+ AC4
Figure 3: Two-Side Dual-Homing PW Protection
图3：两侧双归位PW保护
Consider the example where in normal state AC1 between CE1 and PE1 is initially active, AC2 between CE1 and PE2 is initially standby, AC3 between CE2 and PE3 is initially active and AC4 from CE2 to PE4 is initially standby. PW1 is configured as the working PW and PW2 is configured as the protection PW.
考虑在CE1和PE1之间的正常状态AC1初始活性的例子中，CE1和PE2之间的AC2最初是备用的，在Ce2和PE3之间的AC3最初是活性的，而AC4从CE2到PE4最初是备用的。PW1配置为工作PW，PW2配置为保护PW。
When a failure occurs in AC1, the state of AC2 changes to active based on the AC dual-homing control mechanism. In order to keep the switchover local and continue using PW1 for traffic forwarding, the forwarder on PE2 needs to connect AC2 to the DNI-PW1, and the forwarder on PE1 needs to connect DNI-PW1 with PW1. In this way, failures in the AC side will not impact the forwarding of the service PWs across the network. After the switchover, traffic will go through the bidirectional path: CE1-(AC2)-PE2-(DNI-PW1)-PE1-(PW1)-PE3-(AC3)-CE2.
当AC1发生故障时，AC2的状态将根据交流双归位控制机制变为激活状态。为了保持本地切换并继续使用PW1进行流量转发，PE2上的转发器需要将AC2连接到DNI-PW1，PE1上的转发器需要将DNI-PW1连接到PW1。这样，交流侧的故障将不会影响服务PW在网络上的转发。切换后，流量将通过双向路径：CE1-（AC2）-PE2-（DNI-PW1）-PE1-（PW1）-PE3-（AC3）-CE2。
When a failure occurs in the working PW (PW1), according to the PW protection mechanism [RFC6378], traffic needs to be switched onto the protection PW "PW2". In order to keep the state of AC1 and AC3 unchanged, the forwarder on PE1 needs to connect AC1 to DNI-PW1, and the forwarder on PE2 needs to connect DNI-PW1 to PW2. On the other side, the forwarder of PE3 needs to connect AC3 to DNI-PW2, and the forwarder on PE4 needs to connect PW2 to DNI-PW2. In this way, the state of the ACs will not be impacted by the failure in the PSN. After the switchover, traffic will go through the bidirectional path: CE1-(AC1)-PE1-(DNI-PW1)-PE2-(PW2)-PE4-(DNI-PW2)-PE3-(AC3)-CE2.
当工作PW（PW1）发生故障时，根据PW保护机制[RFC6378]，需要将通信量切换到保护PW“PW2”。为了保持AC1和AC3的状态不变，PE1上的转发器需要将AC1连接到DNI-PW1，PE2上的转发器需要将DNI-PW1连接到PW2。另一方面，PE3的转发器需要将AC3连接到DNI-PW2，PE4的转发器需要将PW2连接到DNI-PW2。这样，ACs的状态将不会受到PSN故障的影响。切换后，通信量将通过双向路径：CE1-（AC1）-PE1-（DNI-PW1）-PE2-（PW2）-PE4-（DNI-PW2）-PE3-（AC3）-CE2。
When a failure occurs in the working PE (PE1), it is equivalent to the failures of the working AC, the working PW, and the DNI-PW. The state of AC2 changes to active based on the AC dual-homing control mechanism. In addition, according to the PW protection mechanism, traffic is switched on to the protection PW "PW2". In this case, the forwarder on PE2 needs to connect AC2 to PW2, and the forwarder on PE4 needs to connect PW2 to DNI-PW2. After the switchover, traffic will go through the bidirectional path: CE1-(AC2)-PE2-(PW2)-PE4-(DNI-PW2)-PE3-(AC3)-CE2.
当工作PE（PE1）发生故障时，相当于工作AC、工作PW和DNI-PW的故障。AC2的状态根据交流双归位控制机制变为激活状态。此外，根据PW保护机制，通信量被切换到保护PW“PW2”。在这种情况下，PE2上的转发器需要将AC2连接到PW2，PE4上的转发器需要将PW2连接到DNI-PW2。切换后，流量将通过双向路径：CE1-（AC2）-PE2-（PW2）-PE4-（DNI-PW2）-PE3-（AC3）-CE2。
As shown in the above scenarios, with the described dual-homing PW protection, failures in the AC side will not impact the forwarding behavior of the PWs in the PSN, and vice-versa.
如上述场景所示，使用所述的双归巢PW保护，AC侧的故障不会影响PSN中PWs的转发行为，反之亦然。
In order for the dual-homing PEs to coordinate traffic forwarding during failures, synchronization of the status information of the involved entities and coordination of switchover between the dual-homing PEs are needed. For PWs with a dynamic control plane, such synchronization and coordination information can be achieved with a dynamic protocol, such as that described in [RFC7275], possibly with some extensions. For PWs that are manually configured without a control plane, a new mechanism is needed to exchange the status information and coordinate switchover between the dual-homing PEs, e.g., over an embedded PW control channel. This is described in [RFC8185].
为了使双归属PEs在故障期间协调业务转发，需要同步相关实体的状态信息并协调双归属PEs之间的切换。对于具有动态控制平面的PWs，可以通过动态协议（如[RFC7275]中所述）实现此类同步和协调信息，可能需要一些扩展。对于在没有控制平面的情况下手动配置的PW，需要一种新的机制来交换状态信息并协调双归位PEs之间的切换，例如通过嵌入式PW控制通道。这在[RFC8185]中有描述。
This document does not require any IANA action.
本文件不要求IANA采取任何行动。
The scenarios defined in this document do not affect the security model as defined in [RFC3985].
本文档中定义的场景不影响[RFC3985]中定义的安全模型。
With the proposed protection mechanism, the disruption of a dual-homed AC, a component that is outside the core network, would have a reduced impact on the traffic flows in the core network. This could also avoid unnecessary congestion in the core network.
在建议的保护机制下，双宿AC（核心网络外部的组件）的中断将减少对核心网络中流量的影响。这还可以避免核心网络中不必要的拥塞。
The security consideration of the DNI-PW is the same as for service PWs in the data plane [RFC3985]. Security considerations for the coordination/control mechanism will be addressed in the companion document, RFC 8185, which defines the mechanism.
DNI-PW的安全考虑与数据平面中服务PW的安全考虑相同[RFC3985]。协调/控制机制的安全注意事项将在配套文件RFC 8185中讨论，该文件定义了该机制。
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/RFC3985, March 2005, <http://www.rfc-editor.org/info/rfc3985>.
[RFC3985]Bryant，S.，Ed.和P.Pate，Ed.，“伪线仿真边到边（PWE3）架构”，RFC 3985，DOI 10.17487/RFC3985，2005年3月<http://www.rfc-editor.org/info/rfc3985>.
[RFC8185] Cheng, W., Wang, L., Li, H., Dong, J., and A. D'Alessandro, "Dual-Homing Coordination for MPLS Transport Profile (MPLS-TP) Pseudowires Protection", RFC 8185, DOI 10.17487/RFC8185, June 2017.
[RFC8185]Cheng，W.，Wang，L.，Li，H.，Dong，J.，和A.D'Alessandro，“MPLS传输配置文件（MPLS-TP）伪线保护的双归宿协调”，RFC 8185，DOI 10.17487/RFC8185，2017年6月。
[RFC6372] Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport Profile (MPLS-TP) Survivability Framework", RFC 6372, DOI 10.17487/RFC6372, September 2011, <http://www.rfc-editor.org/info/rfc6372>.
[RFC6372]Sprecher，N.，Ed.和A.Farrel，Ed.，“MPLS传输配置文件（MPLS-TP）生存能力框架”，RFC 6372，DOI 10.17487/RFC6372，2011年9月<http://www.rfc-editor.org/info/rfc6372>.
[RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378, October 2011, <http://www.rfc-editor.org/info/rfc6378>.
[RFC6378]Y.Weingarten，Ed.，Bryant，S.，Osborne，E.，Sprecher，N.，和A.Fulignoli，Ed.，“MPLS传输模式（MPLS-TP）线性保护”，RFC 6378，DOI 10.17487/RFC6378，2011年10月<http://www.rfc-editor.org/info/rfc6378>.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire Redundancy", RFC 6718, DOI 10.17487/RFC6718, August 2012, <http://www.rfc-editor.org/info/rfc6718>.
[RFC6718]Muley，P.，Aissaoui，M.和M.Bocci，“伪线冗余”，RFC 6718，DOI 10.17487/RFC6718，2012年8月<http://www.rfc-editor.org/info/rfc6718>.
[RFC6870] Muley, P., Ed. and M. Aissaoui, Ed., "Pseudowire Preferential Forwarding Status Bit", RFC 6870, DOI 10.17487/RFC6870, February 2013, <http://www.rfc-editor.org/info/rfc6870>.
[RFC6870]Muley，P.，Ed.和M.Aissaoui，Ed.，“伪线优先转发状态位”，RFC 6870，DOI 10.17487/RFC6870，2013年2月<http://www.rfc-editor.org/info/rfc6870>.
[RFC7275] Martini, L., Salam, S., Sajassi, A., Bocci, M., Matsushima, S., and T. Nadeau, "Inter-Chassis Communication Protocol for Layer 2 Virtual Private Network (L2VPN) Provider Edge (PE) Redundancy", RFC 7275, DOI 10.17487/RFC7275, June 2014, <http://www.rfc-editor.org/info/rfc7275>.
[RFC7275]Martini，L.，Salam，S.，Sajassi，A.，Bocci，M.，Matsushima，S.，和T.Nadeau，“第2层虚拟专用网络（L2VPN）提供商边缘（PE）冗余的机箱间通信协议”，RFC 7275，DOI 10.17487/RFC72752014年6月<http://www.rfc-editor.org/info/rfc7275>.
[RFC8104] Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang, "Pseudowire (PW) Endpoint Fast Failure Protection", RFC 8104, DOI 10.17487/RFC8104, March 2017, <http://www.rfc-editor.org/info/rfc8104>.
[RFC8104]Shen，Y.，Aggarwal，R.，Henderickx，W.，和Y.Jiang，“伪线（PW）端点快速故障保护”，RFC 8104，DOI 10.17487/RFC8104，2017年3月<http://www.rfc-editor.org/info/rfc8104>.
Contributors
贡献者
The following individuals substantially contributed to the content of this document:
以下个人对本文件的内容做出了重大贡献：
Kai Liu Huawei Technologies Email: alex.liukai@huawei.com
刘凯华为技术电子邮件：alex。liukai@huawei.com
Alessandro D'Alessandro Telecom Italia Email: alessandro.dalessandro@telecomitalia.it
Alessandro D'Alessandro Telecom Italia电子邮件：Alessandro。dalessandro@telecomitalia.it
Authors' Addresses
作者地址
Weiqiang Cheng China Mobile No.32 Xuanwumen West Street Beijing 100053 China
中国移动北京宣武门西街32号威强城100053
Email: chengweiqiang@chinamobile.com
Email: chengweiqiang@chinamobile.com
Lei Wang China Mobile No.32 Xuanwumen West Street Beijing 100053 China
雷王中国移动北京宣武门西街32号100053
Email: Wangleiyj@chinamobile.com
Email: Wangleiyj@chinamobile.com
Han Li China Mobile No.32 Xuanwumen West Street Beijing 100053 China
中国移动北京宣武门西街32号汉力100053
Email: Lihan@chinamobile.com
Email: Lihan@chinamobile.com
Shahram Davari Broadcom Corporation 3151 Zanker Road San Jose 95134-1933 United States of America
美国圣何塞赞克路3151号Shahram Davari Broadcom Corporation 95134-1933
Email: davari@broadcom.com
Email: davari@broadcom.com
Jie Dong Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China
中国北京市北青路156号华为校园华为技术有限公司，邮编：100095
Email: jie.dong@huawei.com
Email: jie.dong@huawei.com