Internet Engineering Task Force (IETF) P. Muley, Ed.
Request for Comments: 6870 M. Aissaoui, Ed.
Updates: 4447 Alcatel-Lucent
Category: Standards Track February 2013
ISSN: 2070-1721
Internet Engineering Task Force (IETF) P. Muley, Ed.
Request for Comments: 6870 M. Aissaoui, Ed.
Updates: 4447 Alcatel-Lucent
Category: Standards Track February 2013
ISSN: 2070-1721
Pseudowire Preferential Forwarding Status Bit
伪线优先转发状态位
Abstract
摘要
This document describes a mechanism for signaling the active and standby status of redundant Pseudowires (PWs) between their termination points. A set of Redundant PWs is configured between Provider Edge (PE) nodes in single-segment pseudowire (SS-PW) applications or between Terminating Provider Edge (T-PE) nodes in Multi-Segment Pseudowire (MS-PW) applications.
本文档描述了一种在其端点之间用信号发送冗余伪线（PW）的活动和备用状态的机制。在单段伪线（SS-PW）应用程序中的提供者边缘（PE）节点之间或在多段伪线（MS-PW）应用程序中的终端提供者边缘（T-PE）节点之间配置一组冗余PW。
In order for the PE/T-PE nodes to indicate the preferred PW to use for forwarding PW packets to one another, a new status bit is defined. This bit indicates a Preferential Forwarding status with a value of active or standby for each PW in a redundant set.
为了使PE/T-PE节点指示用于彼此转发PW分组的优选PW，定义了新的状态位。该位表示优先转发状态，冗余集中每个PW的值为active或standby。
In addition, a second status bit is defined to allow peer PE nodes to coordinate a switchover operation of the PW.
此外，定义第二状态位以允许对等PE节点协调PW的切换操作。
Finally, this document updates RFC 4447 by adding details to the handling of the PW status code bits in the PW Status TLV.
最后，本文档通过在PW状态TLV中添加PW状态代码位的处理细节来更新RFC 4447。
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/rfc6870.
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/rfc6870.
Copyright Notice
版权公告
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2013 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 ....................................................4
1.1. Requirements Language ......................................4
2. Motivation and Scope ............................................4
3. Terminology .....................................................7
4. PE Architecture .................................................9
5. Modes of Operation ..............................................9
5.1. Independent Mode ...........................................9
5.2. Master/Slave Mode .........................................12
6. PW State Transition Signaling Procedures .......................14
6.1. PW Standby Notification Procedures in Independent Mode ....14
6.2. PW Standby Notification Procedures in Master/Slave Mode ...15
6.2.1. PW State Machine ...................................16
6.3. Coordination of PW Switchover .............................17
6.3.1. Procedures at the Requesting Endpoint ..............18
6.3.2. Procedures at the Receiving Endpoint ...............20
7. Status Mapping .................................................20
7.1. AC Defect State Entry/Exit ................................21
7.2. PW Defect State Entry/Exit ................................21
8. Applicability and Backward Compatibility .......................21
9. Security Considerations ........................................22
10. MIB Considerations ............................................22
11. IANA Considerations ...........................................22
11.1. Status Code for PW Preferential Forwarding Status ........22
11.2. Status Code for PW Request Switchover Status .............23
12. Contributors ..................................................23
13. Acknowledgments ...............................................24
14. References ....................................................24
14.1. Normative References .....................................24
14.2. Informative References ...................................24
Appendix A. Applications of PW Redundancy Procedures .............26
A.1. One Multi-Homed CE with Single SS-PW Redundancy ...........26
A.2. Multiple Multi-Homed CEs with SS-PW Redundancy ............28
A.3. Multi-Homed CE with MS-PW Redundancy ......................30
A.4. Multi-Homed CE with MS-PW Redundancy and S-PE Protection ..31
A.5. Single-Homed CE with MS-PW Redundancy .....................32
A.6. PW Redundancy between H-VPLS MTU-s and PE-rs ..............33
1. Introduction ....................................................4
1.1. Requirements Language ......................................4
2. Motivation and Scope ............................................4
3. Terminology .....................................................7
4. PE Architecture .................................................9
5. Modes of Operation ..............................................9
5.1. Independent Mode ...........................................9
5.2. Master/Slave Mode .........................................12
6. PW State Transition Signaling Procedures .......................14
6.1. PW Standby Notification Procedures in Independent Mode ....14
6.2. PW Standby Notification Procedures in Master/Slave Mode ...15
6.2.1. PW State Machine ...................................16
6.3. Coordination of PW Switchover .............................17
6.3.1. Procedures at the Requesting Endpoint ..............18
6.3.2. Procedures at the Receiving Endpoint ...............20
7. Status Mapping .................................................20
7.1. AC Defect State Entry/Exit ................................21
7.2. PW Defect State Entry/Exit ................................21
8. Applicability and Backward Compatibility .......................21
9. Security Considerations ........................................22
10. MIB Considerations ............................................22
11. IANA Considerations ...........................................22
11.1. Status Code for PW Preferential Forwarding Status ........22
11.2. Status Code for PW Request Switchover Status .............23
12. Contributors ..................................................23
13. Acknowledgments ...............................................24
14. References ....................................................24
14.1. Normative References .....................................24
14.2. Informative References ...................................24
Appendix A. Applications of PW Redundancy Procedures .............26
A.1. One Multi-Homed CE with Single SS-PW Redundancy ...........26
A.2. Multiple Multi-Homed CEs with SS-PW Redundancy ............28
A.3. Multi-Homed CE with MS-PW Redundancy ......................30
A.4. Multi-Homed CE with MS-PW Redundancy and S-PE Protection ..31
A.5. Single-Homed CE with MS-PW Redundancy .....................32
A.6. PW Redundancy between H-VPLS MTU-s and PE-rs ..............33
This document provides the extensions to the Pseudowire (PW) control plane to support the protection schemes of the PW redundancy applications described in RFC 6718, "Pseudowire (PW) Redundancy" [8].
本文件提供了伪线（PW）控制平面的扩展，以支持RFC 6718“伪线（PW）冗余”[8]中描述的PW冗余应用的保护方案。
It specifies a new PW status bit as well as the procedures Provider Edge (PE) nodes follow to notify one another of the Preferential Forwarding state of each PW in the redundant set, i.e., active or standby. This status bit is different from the PW status bits already defined in RFC 4447, the pseudowire setup and maintenance protocol [2]. In addition, this document specifies a second status bit to allow peer PE nodes to coordinate a switchover operation of the PW from active to standby, or vice versa.
它指定一个新的PW状态位以及提供者边缘（PE）节点遵循的程序，以相互通知冗余集中每个PW的优先转发状态，即活动或备用。该状态位不同于RFC 4447（伪线设置和维护协议[2]）中已定义的PW状态位。此外，本文档还指定了第二个状态位，以允许对等PE节点协调PW从活动到备用的切换操作，反之亦然。
As a result of the introduction of these new status bits, this document updates RFC 4447 by clarifying the rules for processing status bits not originally defined in RFC 4447. It also updates RFC 4447 by defining that a status bit can indicate a status other than a fault or can indicate an instruction to the peer PE. See more details in Section 8.
由于引入了这些新的状态位，本文档通过澄清处理RFC 4447中未最初定义的状态位的规则来更新RFC 4447。它还通过定义状态位可以指示故障以外的状态，或者可以向对等PE指示指令来更新RFC 4447。详见第8节。
Section 15 shows in detail how the mechanisms described in this document are used to achieve the desired protection schemes of the applications described in [8].
第15节详细说明了如何使用本文件中所述的机制实现[8]中所述应用的预期保护方案。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[1]中所述进行解释。
The PW setup and maintenance protocol defines the following status codes in the PW Status TLV to indicate the state for an attachment circuit (AC) and a PW [7]:
PW设置和维护协议在PW状态TLV中定义以下状态代码，以指示连接电路（AC）和PW的状态[7]：
0x00000000 - Pseudowire forwarding (clear all failures)
0x00000000-伪线转发（清除所有故障）
0x00000001 - Pseudowire Not Forwarding
0x00000001-伪线未转发
0x00000002 - Local Attachment Circuit (ingress) Receive Fault
0x00000002-本地连接电路（入口）接收故障
0x00000004 - Local Attachment Circuit (egress) Transmit Fault
0x00000004-本地连接电路（出口）传输故障
0x00000008 - Local PSN-facing PW (ingress) Receive Fault
0x00000008-面向PW（入口）的本地PSN接收故障
0x00000010 - Local PSN-facing PW (egress) Transmit Fault
0x00000010-本地PSN面对PW（出口）传输故障
The applications defined in [8] allow the provisioning of a primary PW and one or many secondary backup PWs in the same Virtual Private Wire Service (VPWS) or Virtual Private LAN Service (VPLS). The objective of PW redundancy is to maintain end-to-end connectivity for the emulated service by activating the correct PW whenever an AC, a PE, or a PW fails. The correct PW means the one that provides the end-to-end connectivity from Customer Edge (CE) to CE such that packets continue to flow.
[8]中定义的应用程序允许在同一虚拟专用线路服务（VPWS）或虚拟专用局域网服务（VPLS）中提供一个主PW和一个或多个辅助备份PW。PW冗余的目标是通过在AC、PE或PW出现故障时激活正确的PW来维持模拟服务的端到端连接。正确的PW是指提供从客户边缘（CE）到CE的端到端连接以使数据包继续流动的PW。
A PE node makes a selection of which PW to activate at any given time for the purpose of forwarding user packets. This selection takes into account the local state of the PW and AC, as well as the remote state of the PW and AC as indicated in the PW status bits it received from the peer PE node.
为了转发用户分组，PE节点选择在任何给定时间激活哪个PW。此选择考虑PW和AC的本地状态，以及从对等PE节点接收的PW状态位中指示的PW和AC的远程状态。
In the absence of faults, all PWs are up both locally and remotely, and a PE node needs to select a single PW to which to forward user packets. This is referred to as the active PW. All other PWs will be in standby and must not be used to forward user packets.
在没有故障的情况下，所有PW都在本地和远程启动，PE节点需要选择一个PW将用户数据包转发到该PW。这被称为活动PW。所有其他PW将处于备用状态，不得用于转发用户数据包。
In order for both ends of the service to select the same PW for forwarding user packets, this document defines a new status bit: the Preferential Forwarding status bit. It also defines the procedures the PE nodes follow to indicate the Preferential Forwarding state of a PW to its peer PE node.
为了让服务的两端选择相同的PW转发用户数据包，本文档定义了一个新的状态位：优先转发状态位。它还定义了PE节点遵循的程序，以指示PW向对等PE节点的优先转发状态。
In addition, a second status bit is defined to allow peer PE nodes to coordinate a switchover operation of the PW if required by the application. This is known as the Request Switchover status bit.
此外，定义第二状态位以允许对等PE节点在应用程序需要时协调PW的切换操作。这称为请求切换状态位。
Together, the mechanisms described in this document achieve the following protection capabilities defined in [8]:
本文件中描述的机制共同实现了[8]中定义的以下保护功能：
a. A 1:1 protection in which a specific subset of a path for an emulated service, consisting of a standby PW and/or AC, protects another specific subset of a path for the emulated service, consisting of an active PW and/or AC. An active PW can forward data traffic and control plane traffic, such as Operations, Administration, and Maintenance (OAM) packets. A standby PW does not carry data traffic.
a. 一种1:1保护，其中由备用PW和/或AC组成的模拟服务路径的特定子集保护由活动PW和/或AC组成的模拟服务路径的另一特定子集。活动PW可以转发数据流量和控制平面流量，如操作、管理和维护（OAM）小包。备用PW不承载数据通信量。
b. An N:1 protection scheme in which N specific subsets of a path for an emulated service, consisting each of a standby PW and/or AC, protect a specific subset of a path for the emulated service, consisting of an active PW and/or AC.
b. 一种N:1保护方案，其中模拟服务路径的N个特定子集（包括备用PW和/或AC）保护模拟服务路径的特定子集（包括活动PW和/或AC）。
c. A mechanism to allow PW endpoints to coordinate the switchover to a given PW by using an explicit request/acknowledgment switchover procedure. This mechanism is complementary to the independent mode of operation and is described in Section 6.3. 6.3. This mechanism can be invoked manually by the user, effectively providing a manual switchover capability. It can also be invoked automatically to resolve a situation where the PW endpoints could not match the two directions of the PW.
c. 通过使用显式请求/确认切换过程，允许PW端点协调切换到给定PW的机制。该机制是对独立运行模式的补充，并在第6.3节中描述。6.3. 该机制可由用户手动调用，有效地提供手动切换功能。它还可以自动调用，以解决PW端点无法匹配PW两个方向的情况。
d. A locally configured precedence to govern the selection of a PW when more than one PW qualifies for the active state, as defined in Sections 5.1. and 5.2. The PW with the lowest precedence value has the highest priority. Precedence may be configured via, for example, a local configuration parameter at the PW endpoint.
d. 当一个以上的PW符合激活状态时，本地配置的优先级控制PW的选择，如第5.1节所定义。和5.2。优先级值最低的PW具有最高优先级。可通过例如PW端点处的本地配置参数来配置优先级。
e. By configuration, implementations can designate one PW in the 1:1 or N:1 protection as a primary PW and the remaining as secondary PWs. If more than one PW qualifies for the active state, as defined in Sections 5.1 and 5.2, a PE node selects the primary PW in preference to a secondary PW. In other words, the primary PW has implicitly the lowest precedence value. Furthermore, a PE node reverts to the primary PW immediately after it comes back up or after the expiration of a delay effectively achieving revertive protection switching.
e. 通过配置，实现可以将1:1或N:1保护中的一个PW指定为主PW，其余PW指定为辅助PW。如第5.1节和第5.2节所述，如果超过一个PW符合激活状态，则PE节点优先选择主PW而非辅助PW。换句话说，主PW隐式地具有最低优先级值。此外，PE节点在其返回后或在有效地实现恢复保护切换的延迟期满后立即恢复到主PW。
1+1 protection (in which one specific subset of a path for an emulated service, consisting of a standby PW and/or AC, protects another specific subset of a path for the emulated service and in which traffic is permanently duplicated at the ingress node on both the currently active and standby subsets of the paths) is not supported.
不支持1+1保护（其中，由备用PW和/或AC组成的模拟服务路径的一个特定子集保护模拟服务路径的另一个特定子集，并且在其中，流量在入口节点的当前活动和备用路径子集上永久复制）。
The above protection schemes are provided using the following operational modes:
使用以下操作模式提供上述保护方案：
1. An independent mode of operation in which each PW endpoint node uses its own local rule to select which PW it intends to activate at any given time, and advertises that PW to the remote endpoints. Only a PW that is up and that indicated active status bit locally and remotely is in the active state and can be used to forward data packets. This is described in Section 5.1.
1. 一种独立的操作模式，其中每个PW端点节点使用其自己的本地规则来选择在任何给定时间要激活的PW，并向远程端点播发该PW。只有启动且在本地和远程指示活动状态位的PW处于活动状态，并且可用于转发数据包。第5.1节对此进行了说明。
2. A master/slave mode in which one PW endpoint, the master endpoint, selects and dictates to the other endpoint(s), the slave endpoint(s), which PW to activate. This is described in Section 5.2.
2. 一种主/从模式，其中一个PW端点（主端点）选择并向另一个端点（从端点）指示要激活的PW。第5.2节对此进行了说明。
Note that this document specifies the mechanisms to support PW redundancy where a set of redundant PWs terminate on either a PE, in the case of an SS-PW, or on a T-PE, in the case of an MS-PW. PW redundancy scenarios where the redundant set of PW segments terminates on a Switching Provider Edge (S-PE) are for further study.
注意，本文件规定了支持PW冗余的机制，在SS-PW的情况下，一组冗余PW在PE上终止，在MS-PW的情况下，在T-PE上终止。PW冗余场景，其中PW段的冗余集终止于交换提供商边缘（S-PE），供进一步研究。
Pseudowire (PW): A mechanism that carries the essential elements of an emulated service from one PE to one or more other PEs over a Public Service Network (PSN) [9].
伪线（PW）：一种机制，通过公共服务网络（PSN）将模拟服务的基本元素从一个PE传输到一个或多个其他PE[9]。
Single-Segment Pseudowire (SS-PW): A PW set up directly between two T-PE devices. The PW label is unchanged between the originating and terminating PEs [6].
单段伪线（SS-PW）：直接设置在两个T-PE设备之间的PW。PW标签在始发和终止PEs之间保持不变[6]。
Multi-Segment Pseudowire (MS-PW): A static or dynamically configured set of two or more contiguous PW segments that behave and function as a single point-to-point PW. Each end of an MS-PW, by definition, terminates on a T-PE [6].
多段伪线（MS-PW）：一组静态或动态配置的两个或多个连续PW段，作为单点对点PW运行。根据定义，MS-PW的每一端终止于T-PE[6]。
Up PW: A PW that has been configured (label mapping exchanged between PEs) and is not showing any of the PW or AC status bits specified in [7]. Such a PW is available for forwarding traffic [8].
Up PW：已配置（PEs之间交换的标签映射）且未显示[7]中规定的任何PW或AC状态位的PW。这种PW可用于转发流量[8]。
Down PW: A PW that either has not been fully configured or has been configured and is showing any of the PW or AC status bits specified in [7]; such a PW is not available for forwarding traffic [8].
Down PW：未完全配置或已配置的PW，显示[7]中规定的任何PW或AC状态位；这种PW不可用于转发流量[8]。
Active PW: An up PW used for forwarding user, OAM, and control plane traffic [8].
主动PW：用于转发用户、OAM和控制平面流量的上行PW[8]。
Standby PW: An up PW that is not used for forwarding user traffic but may forward OAM and specific control plane traffic [8].
备用PW：一种up PW，不用于转发用户流量，但可以转发OAM和特定控制平面流量[8]。
Primary PW: The PW that a PW endpoint activates in preference to any other PW when more than one PW qualifies for active state. When the primary PW comes back up after a failure and qualifies for active state, the PW endpoint always reverts to it. The designation of primary is performed by local configuration for the PW at the PE and is only required when revertive protection switching is used [8].
主PW：当超过一个PW符合激活状态时，PW端点优先于任何其他PW激活的PW。当主PW在发生故障后恢复并符合激活状态时，PW端点始终恢复到该状态。一次电源的指定由PE处PW的本地配置执行，仅在使用反向保护开关时才需要[8]。
Secondary PW: When it qualifies for active state, a secondary PW is only selected if no primary PW is configured or if the configured primary PW does not qualify for active state (e.g.,
次级PW：当次级PW符合激活状态时，仅当未配置初级PW或配置的初级PW不符合激活状态（例如。，
is down). By default, a PW in a redundancy PW set is considered secondary. There is no revertive mechanism among secondary PWs [8].
（已关闭）。默认情况下，冗余PW集中的PW被视为次要PW。次级PWs之间没有回复机制[8]。
PW Precedence: This is a configuration local to the PE that dictates the order in which a forwarder chooses to use a PW when multiple PWs all qualify for the active state. Note that a PW that has been configured as primary has, implicitly, the lowest precedence value.
PW优先级：这是PE的本地配置，指示当多个PW都符合活动状态时，转发器选择使用PW的顺序。请注意，已配置为主要的PW隐式地具有最低优先级值。
PW Endpoint: A PE where a PW terminates on a point where Native Service Processing is performed, e.g., an SS-PW PE, an MS-PW T-PE, a Hierarchical VPLS (H-VPLS) MTU-s, or PE-rs [8].
PW端点：PW终止于执行本机服务处理的点的PE，例如SS-PW PE、MS-PW T-PE、分级VPLS（H-VPLS）MTU-s或PE rs[8]。
Provider Edge (PE): A device that provides PWE3 to a CE [9].
提供者边缘（PE）：向CE提供PWE3的设备[9]。
PW Terminating Provider Edge (T-PE): A PE where the customer-facing ACs are bound to a PW forwarder. A terminating PE is present in the first and last segments of an MS-PW. This incorporates the functionality of a PE as defined in RFC 3985 [6].
PW端接提供商边缘（T-PE）：面向客户的ACs绑定到PW转发器的PE。终端PE出现在MS-PW的第一段和最后一段中。这包括RFC 3985[6]中定义的PE功能。
PW Switching Provider Edge (S-PE): A PE capable of switching the control and data planes of the preceding and succeeding PW segments in an MS-PW. The S-PE terminates the PSN tunnels of the preceding and succeeding segments of the MS-PW. Therefore, it includes a PW switching point for an MS-PW. A PW switching point is never the S-PE and the T-PE for the same MS-PW. A PW switching point runs necessary protocols to set up and manage PW segments with other PW switching points and terminating PEs. An S-PE can exist anywhere a PW must be processed or policy applied. Therefore, it is not limited to the edge of a provider network [6].
PW交换提供程序边缘（S-PE）：能够在MS-PW中交换前面和后面PW段的控制和数据平面的PE。S-PE终止MS-PW之前和后续段的PSN隧道。因此，它包括MS-PW的PW开关点。PW切换点绝不是同一MS-PW的S-PE和T-PE。PW交换点运行必要的协议，以设置和管理与其他PW交换点和终端PE的PW段。S-PE可以存在于必须处理PW或应用策略的任何位置。因此，它不限于提供商网络的边缘[6]。
MTU-s: A hierarchical virtual private LAN service Multi-Tenant Unit switch, as defined in RFC 4762 [3].
MTU-s：分层虚拟专用LAN服务多租户单元交换机，如RFC 4762[3]中所定义。
PE-rs: A routing and bridging capable PE as defined in RFC 4762 [3].
PE rs：RFC 4762[3]中定义的具有路由和桥接功能的PE。
FEC: Forwarding Equivalence Class.
FEC：转发等价类。
OAM: Operations, Administration, and Maintenance.
OAM：运营、管理和维护。
VCCV: Virtual Connection Connectivity Verification.
虚拟连接连接验证。
This document uses the term 'PE' to be synonymous with both PEs as per RFC 3985 [9] and T-PEs as per RFC 5659 [6].
本文件使用术语“PE”作为RFC 3985[9]中PEs和RFC 5659[6]中T-PEs的同义词。
This document uses the term 'PW' to be synonymous with both PWs as per RFC 3985 [9] and SS-PWs, MS-PWs, and PW segments as per RFC 5659 [6].
本文件使用术语“PW”作为RFC 3985[9]规定的PW和RFC 5659[6]规定的SS PWs、MS PWs和PW段的同义词。
Figure 1 shows the PE architecture for PW redundancy, when more than one PW in a redundant set is associated with a single AC. This is based on the architecture in Figure 4b of RFC 3985 [9]. The forwarder selects which of the redundant PWs to use based on the criteria described in this document.
图1显示了当冗余集中的多个PW与单个AC关联时，PW冗余的PE架构。这基于RFC 3985[9]图4b中的架构。转运商根据本文件中所述的标准选择要使用的冗余PW。
+----------------------------------------+
| PE Device |
+----------------------------------------+
Single | | Single | PW Instance
AC | + PW Instance X<===========>
| | |
| |----------------------|
<------>o | Single | PW Instance
| Forwarder + PW Instance X<===========>
| | |
| |----------------------|
| | Single | PW Instance
| + PW Instance X<===========>
| | |
+----------------------------------------+
+----------------------------------------+
| PE Device |
+----------------------------------------+
Single | | Single | PW Instance
AC | + PW Instance X<===========>
| | |
| |----------------------|
<------>o | Single | PW Instance
| Forwarder + PW Instance X<===========>
| | |
| |----------------------|
| | Single | PW Instance
| + PW Instance X<===========>
| | |
+----------------------------------------+
Figure 1. PE Architecture for PW Redundancy
图1。PW冗余的PE体系结构
There are two modes of operation for the use of the PW Preferential Forwarding status bits:
PW优先转发状态位的使用有两种操作模式：
o independent mode
o 独立模式
o master/slave mode
o 主/从模式
PW endpoint nodes independently select which PWs are eligible to become active and which are not. They advertise the corresponding active or standby Preferential Forwarding status for each PW. Each PW endpoint compares local and remote status bits and uses the PW
PW端点节点独立选择哪些PW符合激活条件，哪些不符合激活条件。它们为每个PW通告相应的活动或备用优先转发状态。每个PW端点比较本地和远程状态位并使用PW
that is up at both endpoints and that advertised active Preferential Forwarding status at both the local and remote endpoints.
这在两个端点上都已启动，并且在本地和远程端点上都已公布活动优先转发状态。
In this mode of operation, the Preferential Forwarding status indicates the preferred forwarding state of each endpoint but the actual forwarding state of the PW is the result of the comparison of the local and remote forwarding status bits.
在该操作模式中，优先转发状态指示每个端点的优先转发状态，但是PW的实际转发状态是本地和远程转发状态位比较的结果。
If more than one PW qualifies for the active state, each PW endpoint MUST implement a common mechanism to choose the PW for forwarding. The default mechanism MUST be supported by all implementations, and it operates as follows:
如果有多个PW符合活动状态，则每个PW端点必须实现一个公共机制来选择要转发的PW。所有实现都必须支持默认机制，其操作如下：
1. For a PW using the PWid ID Forwarding Equivalence Class (PWid FEC) [2], the PW with the lowest PWid value is selected.
1. 对于使用PWid转发等价类（PWid FEC）[2]的PW，选择PWid值最低的PW。
2. For a PW using the Generalized PWid FEC [2], each PW in a redundant set is uniquely identified at each PE using the following triplet: AGI::SAII::TAII. The unsigned integer form of the concatenated word can be used in the comparison. However, the Source Attachment Individual Identifier (SAII) and Target Attachment Individual Identifier (TAII) values as seen on a PE node are the mirror values of what the peer PE node sees. So that both PE nodes compare the same value, the PE with the lowest system IP address MUST use the unsigned integer form of AGI::SAII::TAII, while the PE with the highest system IP address MUST use the unsigned integer form of AGI::TAII::SAII. This way, both PE nodes will compare the same values. The PW that corresponds to the minimum of the compared values across all PWs in the redundant set is selected.
2. 对于使用广义PWid FEC[2]的PW，冗余集中的每个PW在每个PE处使用以下三元组进行唯一标识：AGI:：SAII:：TAII。连接字的无符号整数形式可用于比较。但是，在PE节点上看到的源附件个体标识符（SAII）和目标附件个体标识符（TAII）值是对等PE节点看到的镜像值。为了使两个PE节点比较相同的值，系统IP地址最低的PE必须使用AGI:：SAII:：TAII的无符号整数形式，而系统IP地址最高的PE必须使用AGI:：TAII:：SAII的无符号整数形式。这样，两个PE节点将比较相同的值。选择与冗余集中所有PW的最小比较值相对应的PW。
In the case where the system IP address is not known, it is RECOMMENDED to implement the active PW selection mechanism described next.
在系统IP地址未知的情况下，建议实施下面描述的活动PW选择机制。
In the case of segmented PW, the operator needs to make sure that the PWid or AGI::SAII::TAII of the redundant PWs within the first and last segment are ordered consistently such that the same end-to-end MS-PW gets selected. Otherwise, it is RECOMMENDED to implement the active PW selection mechanism described next.
对于分段PW，操作员需要确保第一个和最后一个段内冗余PW的PWid或AGI:：SAII:：TAII顺序一致，以便选择相同的端到端MS-PW。否则，建议实施下文所述的主动PW选择机制。
The PW endpoints MAY also implement the following active PW selection mechanism:
PW端点还可以实现以下活动PW选择机制：
1. If the PW endpoint is configured with the precedence parameter on each PW in the redundant set, it selects the PW with the lowest configured precedence value.
1. 如果PW端点在冗余集中的每个PW上配置了优先级参数，则它将选择配置优先级值最低的PW。
2. If the PW endpoint is configured with one PW as primary and one or more PWs as secondary, it selects the primary PW in preference to all secondary PWs. If a primary PW is not available, it selects the secondary PW with the lowest precedence value. If the primary PW becomes available, a PW endpoint reverts to it immediately or after the expiration of a configurable delay.
2. 如果PW端点配置有一个PW作为主PW和一个或多个PW作为辅助PW，则它会优先选择主PW而不是所有辅助PW。如果主PW不可用，则选择优先级值最低的辅助PW。如果主PW变为可用，PW端点将立即或在可配置延迟到期后恢复到该PW。
3. This active PW selection mechanism assumes the precedence parameter values are configured consistently at both PW endpoints and that unique values are assigned to the PWs in the same redundant set to achieve tiebreaking using this mechanism.
3. 此活动PW选择机制假定在两个PW端点上一致配置优先参数值，并且为同一冗余集中的PW分配唯一值，以使用此机制实现分段。
There are scenarios with dual-homing of a CE to PE nodes where each PE node needs to advertise active Preferential Forwarding status on more than one PW in the redundant set. However, a PE MUST always select a single PW for forwarding using the above active PW selection algorithm. An example of such a case is described in 15.2.
存在CE到PE节点双重归宿的场景，其中每个PE节点需要在冗余集中的多个PW上公布活动优先转发状态。但是，PE必须始终使用上述活动PW选择算法选择单个PW进行转发。15.2中描述了此类情况的一个示例。
There are scenarios where each PE needs to advertise active Preferential Forwarding status on a single PW in the redundant set. In order to ensure that both PE nodes make the same selection, they MUST use the above active PW selection algorithm to determine the PW eligible for active state. An example of such a case is described in 15.5.
在某些情况下，每个PE需要在冗余集中的单个PW上公布活动优先转发状态。为了确保两个PE节点进行相同的选择，它们必须使用上述活动PW选择算法来确定符合活动状态的PW。15.5中描述了此类情况的一个示例。
In steady state with consistent configuration, a PE will always find an active PW. However, it is possible that such a PW is not found due to a misconfiguration. In the event that an active PW is not found, a management notification SHOULD be generated. If a management notification for failure to find an active PW was generated and an active PW is subsequently found, a management notification SHOULD be generated, so clearing the previous failure indication. Additionally, a PE MAY use the request switchover procedures described in Section 6.3 to have both PE nodes switch to a common PW.
在具有一致配置的稳定状态下，PE始终会发现一个活动PW。但是，由于配置错误，可能未找到此类PW。如果未找到活动PW，则应生成管理通知。如果生成了查找活动PW失败的管理通知，并且随后发现了活动PW，则应生成管理通知，以便清除以前的故障指示。此外，PE可以使用第6.3节中描述的请求切换程序，使两个PE节点切换到公共PW。
There may also be transient conditions where endpoints do not share a common view of the active/standby state of the PWs. This could be caused by propagation delay of the Targeted Label Distribution Protocol (T-LDP) status messages between endpoints. In this case, the behavior of the receiving endpoint is outside the scope of this document.
也可能存在端点不共享PWs活动/备用状态的公共视图的瞬态情况。这可能是由于端点之间目标标签分发协议（T-LDP）状态消息的传播延迟造成的。在这种情况下，接收端点的行为超出了本文档的范围。
Thus, in this mode of operation, the following definition of active and standby PW states apply:
因此，在这种操作模式下，以下活动和备用PW状态的定义适用：
o Active State
o 活动状态
A PW is considered to be in active state when the PW labels are exchanged between its two endpoints and the status bits exchanged between the endpoints indicate the PW is up and its Preferential Forwarding status is active at both endpoints. In this state user traffic can flow over the PW in both directions. As described in Section 5.1, the PE nodes MUST implement a common mechanism to select one PW for forwarding in case multiple PWs qualify for the active state.
当PW标签在其两个端点之间交换并且在端点之间交换的状态位指示PW已启动且其优先转发状态在两个端点处都处于活动状态时，PW被视为处于活动状态。在这种状态下，用户流量可以在两个方向上流过PW。如第5.1节所述，PE节点必须实现一种通用机制，以便在多个PW符合活动状态的情况下选择一个PW进行转发。
o Standby State
o 待命状态
A PW is considered to be in standby state when the PW labels are exchanged between its two endpoints, but the Preferential Forwarding status bits exchanged indicate the PW Preferential Forwarding status is standby at one or both endpoints. In this state, the endpoints MUST NOT forward data traffic over the PW but MAY allow PW OAM packets, e.g., Virtual Connection Connectivity Verification (VCCV) packets [11], to be sent and received in order to test the liveliness of standby PWs. The endpoints of the PW MAY also allow the forwarding of specific control plane packets of applications using the PW. The specification of applications and the allowed control plane packets are outside the scope of this document. If the PW is a spoke in H-VPLS, any Media Access Control (MAC) addresses learned via the PW SHOULD be flushed when it transitions to standby state, according to the procedures in RFC 4762 [3] and in [10].
当PW标签在其两个端点之间交换时，PW被视为处于待机状态，但交换的优先转发状态位指示PW优先转发状态在一个或两个端点处处于待机状态。在此状态下，端点不得通过PW转发数据流量，但可允许发送和接收PW OAM数据包，例如，虚拟连接连接验证（VCCV）数据包[11]，以测试备用PW的活跃度。PW的端点还可以允许使用PW转发应用的特定控制平面分组。应用规范和允许的控制平面数据包不在本文件范围内。如果PW是H-VPLS中的分支，则根据RFC 4762[3]和[10]中的程序，通过PW学习的任何媒体访问控制（MAC）地址应在转换到待机状态时刷新。
One endpoint node of the redundant set of PWs is designated the master and is responsible for selecting which PW both endpoints must use to forward user traffic.
冗余PW集的一个端点节点被指定为主节点，并负责选择两个端点必须使用哪个PW转发用户流量。
The master indicates the forwarding state in the PW Preferential Forwarding status bit. The other endpoint node, the slave, MUST follow the decision of the master node based on the received status bits. In other words, the Preferential Forwarding status bit sent by the master node indicates the actual forwarding state of the PW at the master node.
主机在PW优先转发状态位中指示转发状态。另一个端点节点（从节点）必须遵循主节点基于接收到的状态位的决定。换句话说，主节点发送的优先转发状态比特指示主节点处的PW的实际转发状态。
There is a single PE master PW endpoint node and one or many PE PW endpoint slave nodes. The assignment of master/slave roles to the PW endpoints is performed by local configuration. Note that the behavior described in this section assumes correct configuration of
存在单个PE主PW端点节点和一个或多个PE PW端点从节点。通过本地配置将主/从角色分配给PW端点。请注意，本节中描述的行为假定
the master and slave endpoints. This document does not define a mechanism to detect errors in the configuration, and misconfiguration might lead to protection switchover failing to work correctly. Furthermore, this document does not specify the procedures for a backup master node. In deployments where PE node protection is required, it is recommended to use the independent mode of operation as in the application described in Section 15.2.
主端点和从端点。本文档未定义检测配置错误的机制，错误配置可能导致保护切换无法正常工作。此外，本文档未指定备份主节点的过程。在需要PE节点保护的部署中，建议使用第15.2节所述的独立操作模式。
One endpoint of the PW, the master, actively selects which PW to activate and uses it for forwarding user traffic. This status is indicated to the slave node by setting the Preferential Forwarding status bit in the status bit TLV to active. It does not forward user traffic to any other of the PW's in the redundant set to the slave node and indicates this by setting the Preferential Forwarding status bit in the status bit TLV to standby for those PWs. The master node MUST ignore any PW Preferential Forwarding status bits received from the slave nodes.
PW的一个端点，即主节点，主动选择要激活的PW并将其用于转发用户流量。通过将状态位TLV中的优先转发状态位设置为active（活动），将该状态指示给从属节点。它不会将用户流量转发到冗余集中的任何其他PW到从属节点，并通过将状态位TLV中的优先转发状态位设置为这些PW的备用来表示这一点。主节点必须忽略从从从节点接收的任何PW优先转发状态位。
If more than one PW qualifies for the active state, the master PW endpoint node selects one. There is no requirement to specify a default active PW selection mechanism in this case; however, for consistency across implementations, the master PW endpoint SHOULD implement the default active PW selection mechanism described in Section 5.1.
如果有多个PW符合激活状态，则主PW端点节点将选择一个。在这种情况下，无需指定默认的活动PW选择机制；然而，为了实现一致性，主PW端点应实现第5.1节中描述的默认活动PW选择机制。
If the master PW endpoint implements the active PW selection mechanism based on primary/secondary and precedence parameters, it MUST comply with the following behavior:
如果主PW端点基于主/辅参数和优先参数实现活动PW选择机制，则它必须符合以下行为：
1. If the PW endpoint is configured with the precedence parameter on each PW in the redundant set, it MUST select the PW with the lowest configured precedence value.
1. 如果PW端点在冗余集中的每个PW上配置了优先级参数，则必须选择配置优先级值最低的PW。
2. If the PW endpoint is configured with one PW as primary and one or more PWs as secondary, it MUST select the primary PW in preference to all secondary PWs. If a primary PW is not available, it MUST use the secondary PW with the lowest precedence value. If the primary PW becomes available, a PW endpoint MUST revert to it immediately or after the expiration of a configurable delay.
2. 如果PW端点配置有一个PW作为主PW和一个或多个PW作为辅助PW，则它必须优先选择主PW而不是所有辅助PW。如果主PW不可用，则必须使用优先级最低的辅助PW。如果主PW变为可用，PW端点必须立即或在可配置延迟到期后恢复到它。
The slave endpoint(s) are required to act on the status bits received from the master. When the received status bit transitions from active to standby, a slave node MUST stop forwarding over the previously active PW. When the received status bit transitions from standby to active for a given PW, the slave node MUST start forwarding user traffic over this PW.
从属端点需要对从主端点接收的状态位进行操作。当接收到的状态位从活动变为备用时，从属节点必须停止通过先前活动的PW进行转发。当接收到的状态位针对给定PW从待机转换为活动时，从属节点必须开始通过该PW转发用户通信量。
In this mode of operation, the following definition of active and standby PW states apply:
在该操作模式下，以下主动和备用PW状态定义适用：
o Active State
o 活动状态
A PW is considered to be in active state when the PW labels are exchanged between its two endpoints, and the status bits exchanged between the endpoints indicate the PW is up at both endpoints, and the Preferential Forwarding status at the master endpoint is active. In this state, user traffic can flow over the PW in both directions.
当PW标签在其两个端点之间交换时，PW被视为处于活动状态，并且在端点之间交换的状态位指示PW在两个端点处都处于启动状态，并且主端点处的优先转发状态为活动状态。在此状态下，用户流量可以在两个方向上流过PW。
o Standby State
o 待命状态
A PW is considered to be in standby state when the PW labels are exchanged between its two endpoints, and the status bits exchanged between the endpoints indicate the Preferential Forwarding status at the master endpoint is standby. In this state, the endpoints MUST NOT forward data traffic over the PW but MAY allow PW OAM packets, e.g., VCCV, to be sent and received. The endpoints of the PW MAY also allow the forwarding of specific control plane packets of applications using the PW. The specification of applications and the allowed control plane packets are outside the scope of this document. If the PW is a spoke in H-VPLS, any MAC addresses learned via the PW SHOULD be flushed when it transitions to standby state according to the procedures in RFC 4762 [3] and [10].
当PW标签在其两个端点之间交换时，PW被认为处于待机状态，并且端点之间交换的状态位指示主端点处的优先转发状态为待机。在此状态下，端点不得通过PW转发数据通信量，但可允许发送和接收PW OAM分组，例如VCCV。PW的端点还可以允许使用PW转发应用的特定控制平面分组。应用规范和允许的控制平面数据包不在本文件范围内。如果PW是H-VPLS中的分支，则根据RFC 4762[3]和[10]中的程序，当PW过渡到待机状态时，应刷新通过PW获知的任何MAC地址。
This section describes the extensions to PW status signaling and the processing rules for these extensions. It defines a new PW Preferential Forwarding status bit that is to be used with the PW Status TLV specified in RFC 4447 [2].
本节描述PW状态信令的扩展以及这些扩展的处理规则。它定义了一个新的PW优先转发状态位，该位将与RFC 4447[2]中指定的PW状态TLV一起使用。
The PW Preferential Forwarding bit, when set, is used to signal either the preferred or actual active/standby forwarding state of the PW by one PE to the far-end PE. The actual semantics of the value being signaled vary according to whether the PW is acting in master/slave or independent mode.
设置PW优先转发位时，用于通过一个PE向远端PE发送PW的优先或实际主/备用转发状态的信号。被发信号的值的实际语义根据PW是在主/从模式还是独立模式下工作而变化。
PEs that contain PW endpoints independently select which PW they intend to use for forwarding, depending on the specific application (example applications are described in [8]). They advertise the corresponding preferred active/standby forwarding state for each PW. An active Preferential Forwarding state is indicated by clearing the PW Preferential Forwarding status bit in the PW Status TLV. A standby Preferential Forwarding state is indicated by setting the PW
包含PW端点的PE根据特定的应用程序（示例应用程序在[8]中描述）独立选择它们打算用于转发的PW。它们为每个PW通告相应的首选主动/备用转发状态。通过清除PW状态TLV中的PW优先转发状态位来指示活动优先转发状态。通过设置PW指示待机优先转发状态
Preferential Forwarding status bit in the PW Status TLV. This advertisement occurs in both the initial label mapping message and in a subsequent notification message when the forwarding state transitions as a result of a state change in the specific application.
PW状态TLV中的优先转发状态位。当转发状态由于特定应用程序中的状态更改而转换时，此播发在初始标签映射消息和后续通知消息中发生。
Each PW endpoint compares the updated local and remote status and effectively activates the PW, which is up at both endpoints and which shows both local active and remote active Preferential Forwarding states. The PE nodes MUST implement a common mechanism to select one PW for forwarding in case multiple PWs qualify for the active state, as explained in Section 5.1.
每个PW端点比较更新的本地和远程状态，并有效地激活PW，该PW在两个端点上都处于启动状态，并显示本地活动和远程活动优先转发状态。如第5.1节所述，PE节点必须实现一种通用机制，以在多个PW符合活动状态的情况下选择一个PW进行转发。
When a PW is in active state, the PEs can forward user packets, OAM packets, and other control plane packets over the PW.
当PW处于活动状态时，PEs可以通过PW转发用户分组、OAM分组和其他控制平面分组。
When a PW is in standby state, the PEs MUST NOT forward user packets over the PW but MAY forward PW OAM packets and specific control plane packets.
当PW处于待机状态时，PEs不得通过PW转发用户数据包，但可以转发PW OAM数据包和特定控制平面数据包。
For MS-PWs, S-PEs MUST relay the PW status notification containing both the existing status bits and the new Preferential Forwarding status bits between ingress and egress PWs as per the procedures defined in [4].
对于MS PWs，S-PEs必须按照[4]中定义的程序，在入口和出口PWs之间中继包含现有状态位和新优先转发状态位的PW状态通知。
Whenever the master PW endpoint selects or deselects a PW for forwarding user traffic at its end, it explicitly notifies the event to the remote slave endpoint. The slave endpoint carries out the corresponding action on receiving the PW state change notification.
每当主PW端点选择或取消选择PW以在其端转发用户流量时，它都会将事件显式通知远程从属端点。从属端点在接收到PW状态更改通知时执行相应的操作。
If the PW Preferential Forwarding bit in PW Status TLV received by the slave is set, it indicates that the PW at the master end is not used for forwarding and is thus kept in the standby state. The PW MUST NOT be used for forwarding at slave endpoint. Clearing the PW Preferential Forwarding bit in PW Status TLV indicates that the PW at the master endpoint is used for forwarding and is in active state, and the receiving slave endpoint MUST activate the PW if it was previously not used for forwarding.
如果设置了从机接收的处于PW状态TLV的PW优先转发位，则表明主端的PW不用于转发，因此保持在待机状态。PW不得用于在从属端点进行转发。清除PW Status TLV中的PW优先转发位表示主端点处的PW用于转发且处于活动状态，并且接收从端点必须激活PW（如果它以前未用于转发）。
When this mechanism is used, a common Group ID in the PWid FEC element or a PW Grouping ID TLV in the Generalized PWid FEC element, as defined in [2], MAY be used to signal PWs in groups in order to minimize the number of LDP status messages that MUST be sent. When PWs are provisioned with such grouping, a termination point sends a single "wildcard" notification message to denote this change in status for all affected PWs. This status message contains either the
当使用该机制时，可使用PWid FEC元素中的公共组ID或广义PWid FEC元素中的PW分组ID TLV（如[2]中所定义）来向分组中的PW发送信号，以最小化必须发送的LDP状态消息的数量。当为PW提供此类分组时，终止点发送单个“通配符”通知消息，以表示所有受影响PW的状态更改。此状态消息包含
PWid FEC TLV with only the Group ID or the Generalized PWid FEC TLV with only the PW Grouping ID TLV. As mentioned in [2], the Group ID field of the PWid FEC element, or the PW Grouping ID TLV in the Generalized PWid FEC element, can be used to send status notification for an arbitrary set of PWs.
仅具有组ID的PWid FEC TLV或仅具有PW分组ID TLV的通用PWid FEC TLV。如[2]中所述，PWid FEC元素的组ID字段或通用PWid FEC元素中的PW分组ID TLV可用于发送任意PW集的状态通知。
For MS-PWs, S-PEs MUST relay the PW status notification containing both the existing and the new Preferential Forwarding status bits between ingress and egress PW segments, as per the procedures defined in [4].
对于MS PWs，S-PEs必须按照[4]中定义的程序，在入口和出口PW段之间中继包含现有和新优先转发状态位的PW状态通知。
It is convenient to describe the PW state change behavior in terms of a state machine (Table 1). The PW state machine is explained in detail in the two defined states, and the behavior is presented as a state transition table. The same state machine is applicable to PW groups.
用状态机来描述PW状态变化行为很方便（表1）。PW状态机在两个定义的状态中进行了详细解释，其行为以状态转换表的形式呈现。相同的状态机适用于PW组。
STATE EVENT NEW STATE
状态事件新状态
ACTIVE PW put in standby (master) STANDBY Action: Transmit PW Preferential Forwarding bit set
活动PW投入待机（主）待机动作：发送PW优先转发位集
Receive PW Preferential Forwarding STANDBY bit set (slave) Action: Stop forwarding over PW
接收PW优先转发备用位集（从）操作：通过PW停止转发
Receive PW Preferential Forwarding ACTIVE bit set but bit not supported Action: None
接收PW优先转发活动位集，但位不受支持操作：无
Receive PW Preferential Forwarding ACTIVE bit clear Action: None.
接收PW优先转发活动位清除操作：无。
STANDBY PW activated (master) ACTIVE Action: Transmit PW Preferential Forwarding bit clear
备用PW激活（主）激活操作：传输PW优先转发位清除
Receive PW Preferential Forwarding ACTIVE bit clear (slave) Action: Activate PW
接收PW优先转发活动位清除（从）操作：激活PW
Receive PW Preferential Forwarding STANDBY bit clear but bit not supported Action: None
接收PW优先转发备用位清除但位不受支持操作：无
Receive PW Preferential Forwarding STANDBY bit set Action: None
接收PW优先转发备用位集操作：无
Table 1. PW State Transition Table in Master/Slave Mode
表1。主/从模式下的PW状态转换表
There are PW redundancy applications that require that PE nodes coordinate the switchover to a PW such that both endpoints will forward over the same PW at any given time. One such application for redundant MS-PW is identified in [8]. Multiple MS-PWs are configured between a pair of T-PE nodes. The paths of these MS-PWs are diverse and are switched at different S-PE nodes. Only one of these MS-PWs is active at any given time. The others are put in standby. The endpoints follow the independent mode procedures to use the PW, which is both up and for which both endpoints advertise an active Preferential Forwarding status bit.
有一些PW冗余应用程序要求PE节点协调切换到PW，以便两个端点在任何给定时间都在同一PW上转发。[8]中确定了冗余MS-PW的一种应用。在一对T-PE节点之间配置多个MS PW。这些MS-pw的路径是多样的，并且在不同的S-PE节点上切换。在任何给定时间，这些MS PWs中只有一个处于活动状态。其他人则处于待命状态。端点遵循独立模式过程来使用PW，PW是向上的，并且两个端点都为其播发活动优先转发状态位。
The trigger for sending a request to switchover by one endpoint of the MS-PW can be an operational event. For example, a failure that causes the endpoints to be unable to find a common PW for which both endpoints advertise an active Preferential Forwarding status bit. The other trigger is the execution of an administrative maintenance operation by the network operator in order to move the traffic away from the nodes or links currently used by the active PW.
MS-PW的一个端点发送切换请求的触发器可以是操作事件。例如，导致端点无法找到两个端点都播发活动优先转发状态位的公共PW的故障。另一个触发是由网络运营商执行管理维护操作，以便将流量从活动PW当前使用的节点或链路移开。
Unlike the case of a master/slave mode of operation, the endpoint requesting the switchover requires explicit acknowledgment from the peer endpoint that the request can be honored before it switches to another PW. Furthermore, any of the endpoints can make the request to switch over.
与主/从操作模式的情况不同，请求切换的端点需要对等端点的明确确认，即请求可以在切换到另一个PW之前得到满足。此外，任何端点都可以请求切换。
This document specifies a second status bit that is used by a PE to request that its peer PE switch over to use a different active PW. This bit is referred to as the Request Switchover status bit. The Preferential Forwarding status bit continues to be used by each endpoint to indicate its current local settings of the active/standby state of each PW in the redundant set. In other words, as in the independent mode, it indicates to the far-end which of the PWs is being used to forward packets and which is being put in standby. It can thus be used as a way for the far-end to acknowledge the requested switchover operation.
本文档指定第二个状态位，PE使用该状态位请求其对等PE切换到使用不同的活动PW。该位称为请求切换状态位。每个端点继续使用优先转发状态位来指示冗余集中每个PW的活动/备用状态的当前本地设置。换句话说，如同在独立模式中一样，它向远端指示哪个pw正被用于转发分组，哪个处于待机状态。因此，它可以作为远端确认请求的切换操作的一种方式。
A PE MAY support the Request Switchover bit. A PE that receives the Request Switchover bit and that does not support it will ignore it.
PE可以支持请求切换位。接收到请求切换位且不支持该位的PE将忽略该位。
If the Request Switchover bit is supported by both sending and receiving PEs, the following procedures MUST be followed by both endpoints of a PW to coordinate the switchover of the PW.
如果发送和接收PEs都支持请求切换位，则PW的两个端点必须遵循以下步骤来协调PW的切换。
S-PEs nodes MUST relay the PW status notification containing the existing status bits, as well as the new Preferential Forwarding and Request Switchover status bits between ingress and egress PW segments as per the procedures defined in [4].
S-PEs节点必须按照[4]中定义的程序，中继包含现有状态位的PW状态通知，以及入口和出口PW段之间的新优先转发和请求切换状态位。
a. The requesting endpoint sends a Status TLV in the LDP notification message with the Request Switchover bit set on the PW to which it desires to switch.
a. 请求端点在LDP通知消息中发送状态TLV，并在其希望切换到的PW上设置请求切换位。
b. The endpoint does not activate, forwarding on that PW at this point in time. It MAY, however, enable receiving on that PW. Thus, the Preferential Forwarding status bit still reflects the currently used PW.
b. 端点未激活，此时在该PW上转发。但是，它可以在该PW上启用接收。因此，优先转发状态比特仍然反映当前使用的PW。
c. The requesting endpoint starts a timer while waiting for the remote endpoint to acknowledge the request. This timer SHOULD be configurable with a default value of 3 seconds.
c. 请求端点在等待远程端点确认请求时启动计时器。此计时器应可配置为默认值3秒。
d. If, while waiting for the acknowledgment, the requesting endpoint receives a request from its peer to switch over to the same or a different PW, it MUST perform the following:
d. 如果在等待确认时，请求端点从其对等方接收到切换到相同或不同PW的请求，则它必须执行以下操作：
i. If its address is higher than that of the peer, this endpoint ignores the request and continues to wait for the acknowledgment from its peer.
i. 如果其地址高于对等方的地址，则该端点将忽略该请求并继续等待来自其对等方的确认。
ii. If its system IP address is lower than that of its peer, it aborts the timer and immediately starts the procedures of the receiving endpoint in Section 6.3.2.
二,。如果其系统IP地址低于其对等方的IP地址，则会中止计时器并立即启动第6.3.2节中接收端点的程序。
e. If, while waiting for the acknowledgment, the requesting endpoint receives a status notification message from its peer with the Preferential Forwarding status bit cleared in the requested PW, it MUST treat this as an explicit acknowledgment of the request and MUST perform the following:
e. 如果在等待确认时，请求端点从其对等方接收到状态通知消息，且优先转发状态位在请求的PW中被清除，则它必须将此视为对请求的明确确认，并且必须执行以下操作：
i. Abort the timer.
i. 中止计时器。
ii. Activate the PW.
二,。启动PW。
iii. Send an update status notification message with the Preferential Forwarding status bit and the Request Switchover bit clear on the newly active PW and send an update status notification message with the Preferential Forwarding status bit set in the previously active PW.
iii.在新激活的PW上发送带有优先转发状态位和请求切换位清除的更新状态通知消息，并发送带有先前激活的PW中设置的优先转发状态位的更新状态通知消息。
f. If, while waiting for the acknowledgment, the requesting endpoint detects that the requested PW went into down state locally, and could use an alternate PW that is up, it MUST perform the following:
f. 如果在等待确认时，请求端点检测到请求的PW在本地进入关闭状态，并且可以使用启动的备用PW，则它必须执行以下操作：
i. Abort the timer.
i. 中止计时器。
ii. Issue a new request to switchover to the alternate PW.
二,。发出新请求以切换到备用PW。
iii. Restart the timer.
iii.重新启动计时器。
g. If, while waiting for the acknowledgment, the requesting endpoint detects that the requested PW went into the down state locally, and could not use an alternate PW that is up, it MUST perform the following:
g. 如果在等待确认时，请求端点检测到请求的PW在本地进入关闭状态，并且无法使用启动的备用PW，则它必须执行以下操作：
i. Abort the timer.
i. 中止计时器。
ii. Send an update status notification message with the Preferential Forwarding status bit unchanged and the Request Switchover bit reset for the requested PW.
二,。发送更新状态通知消息，优先转发状态位保持不变，请求的PW的请求切换位重置。
h. If, while waiting for the acknowledgment, the timer expires, the requesting endpoint MUST assume that the request was rejected and MAY issue a new request.
h. 如果在等待确认时计时器过期，则请求端点必须假定请求已被拒绝，并可能发出新请求。
i. If the requesting node receives the acknowledgment after the request expired, it will treat it as if the remote endpoint unilaterally switched between the PWs without issuing a request. In that case, it MAY issue a new request and follow the requesting endpoint procedures to synchronize which PW to use for the transmit and receive directions of the emulated service.
i. 如果请求节点在请求过期后接收到确认，它将把它视为远程端点在PWs之间单方面切换而不发出请求。在这种情况下，它可以发出新的请求并遵循请求端点过程来同步哪个PW用于模拟服务的发送和接收方向。
a. Upon receiving a status notification message with the Request Switchover bit set on a PW different from the currently active one, and the requested PW is up, the receiving endpoint MUST perform the following:
a. 接收到状态通知消息时，如果请求切换位设置在与当前活动PW不同的PW上，并且请求的PW已启动，则接收端点必须执行以下操作：
i. Activate the PW.
i. 启动PW。
ii. Send an update status notification message with the Preferential Forwarding status bit clear and the Request Switchover bit reset on the newly active PW , and send an update status notification message with the Preferential Forwarding status bit set in the previously active PW.
二,。在新激活的PW上发送带有优先转发状态位清除和请求切换位重置的更新状态通知消息，并发送带有先前激活的PW中设置的优先转发状态位的更新状态通知消息。
iii. Upon receiving a status notification message with the Request Switchover bit set on a PW, which is different from the currently active PW but is down, the receiving endpoint MUST ignore the request.
iii.在接收到PW上设置了请求切换位的状态通知消息时，该消息与当前活动PW不同，但处于关闭状态，接收端点必须忽略该请求。
The generation and processing of the PW Status TLV MUST follow the procedures in RFC 4447 [2]. The PW Status TLV is sent on the active PW and standby PWs to make sure the remote AC and PW states are always known to the local PE node.
PW状态TLV的生成和处理必须遵循RFC 4447[2]中的程序。在活动PW和备用PW上发送PW状态TLV，以确保本地PE节点始终知道远程AC和PW状态。
The generation and processing of PW Status TLV by an S-PE node in a MS-PW MUST follow the procedures in [4].
MS-PW中的S-PE节点生成和处理PW状态TLV必须遵循[4]中的程序。
The procedures for determining and mapping PW and AC states MUST follow the rules in [5] with the following modifications.
确定和映射PW和AC状态的程序必须遵循[5]中的规则，并进行以下修改。
A PE enters the AC receive (or transmit) defect state for a PW service when one or more of the conditions specified for this PW service in [5] are met.
当满足[5]中规定的PW服务的一个或多个条件时，PE进入PW服务的AC接收（或传输）缺陷状态。
When a PE enters the AC receive (or transmit) defect state for a PW, it MUST send a forward (reverse) defect indication to the remote peers over all PWs in the redundant set that are associated with this AC.
当PE进入PW的AC接收（或传输）缺陷状态时，它必须通过冗余集中与此AC相关的所有PW向远程对等方发送前向（反向）缺陷指示。
When a PE exits the AC receive (or transmit) defect state for a PW service, it MUST clear the forward (or reverse) defect indication to the remote peers over all PWs in the redundant set that are associated with this AC.
当PE退出PW服务的AC接收（或传输）缺陷状态时，它必须清除与此AC相关联的冗余集中所有PW上的远程对等方的正向（或反向）缺陷指示。
A PE enters the PW receive (or transmit) defect state for a PW service when one or more of the conditions specified in Section 8.3.1 (Section 8.3.2) in [5] are met for each of the PWs in the redundant set.
当冗余集中的每个PW满足[5]中第8.3.1节（第8.3.2节）中规定的一个或多个条件时，PE进入PW服务的PW接收（或传输）缺陷状态。
When a PE enters the PW receive (or transmit) defect state for a PW service associated with an AC, it MUST send a reverse (or forward) defect indication over one or more of the PWs in the redundant set associated with the same AC if the PW failure was detected by this PE without receiving a forward defect indication from the remote PE [5].
当PE进入与AC相关联的PW服务的PW接收（或传输）缺陷状态时，如果该PE检测到PW故障而未接收到来自远程PE的正向缺陷指示，则必须通过与同一AC相关联的冗余集中的一个或多个PW发送反向（或正向）缺陷指示[5]。
When a PE exits the PW receive (or transmit) defect state for a PW, it MUST clear the reverse (or forward) defect indication over any PW in the redundant associated with the same AC set if applicable.
当PE退出PW的PW接收（或传输）缺陷状态时，它必须清除与同一交流机组相关的冗余中任何PW上的反向（或正向）缺陷指示（如适用）。
The mechanisms defined in this document are to be used in applications where standby state signaling of a PW or PW group is required. Both PWid FEC and Generalized PWid FEC are supported. All PWs that are part of a redundant set MUST use the same FEC type. When the set uses the PWid FEC element, each PW is uniquely identified by its PW ID. When the redundant set uses the Generalized
本文件中定义的机制将用于需要PW或PW组备用状态信令的应用中。支持PWid FEC和通用PWid FEC。作为冗余集一部分的所有PW必须使用相同的FEC类型。当集合使用PWid FEC元素时，每个PW由其PW ID唯一标识。当冗余集合使用广义
PWid FEC element, each PW MUST have a unique identifier that consists of the triplet AGI::SAII::TAII.
PWid FEC元素，每个PW必须具有由三元组AGI:：SAII:：TAII组成的唯一标识符。
A PE implementation that uses the mechanisms described in this document MUST negotiate the use of PW Status TLV between its T-LDP peers, as per RFC 4447 [2]. If the PW Status TLV is found to be not supported by either of its endpoints after status negotiation procedures, then the mechanisms specified in this document cannot be used.
根据RFC 4447[2]，使用本文件所述机制的PE实施必须在其T-LDP对等方之间协商PW状态TLV的使用。如果在状态协商过程后发现其任一端点都不支持PW状态TLV，则不能使用本文档中指定的机制。
A PE implementation that is compliant with RFC 4447 [2] and that does not support the generation or processing of the Preferential Forwarding status bit or of the Request Switchover status bit MUST ignore these status bits if they are set by a peer PE. This document in fact updates RFC 4447 by prescribing the same behavior for any status bit not originally defined in RFC 4447.
符合RFC 4447[2]且不支持优先转发状态位或请求切换状态位的生成或处理的PE实现必须忽略这些状态位（如果它们由对等PE设置）。本文档实际上更新了RFC 4447，为RFC 4447中最初未定义的任何状态位规定了相同的行为。
Finally, this document updates RFC 4447 by defining that a status bit can indicate a status other than a fault or can indicate an instruction to the peer PE. As a result, a PE implementation compliant to RFC 4447 MUST process each status bit it supports when set according to the rules specific to that status bit.
最后，本文档通过定义状态位可以指示故障以外的状态，或者可以向对等PE指示指令来更新RFC 4447。因此，当根据特定于该状态位的规则进行设置时，符合RFC 4447的PE实现必须处理其支持的每个状态位。
LDP extensions/options that protect PWs must be implemented because the status bits defined in this document have the same security considerations as the PW setup and maintenance protocol defined in RFC 4447 [2]. It should be noted that the security of a PW redundant set is only as good as the weakest security on any of its members.
必须实施保护PW的LDP扩展/选项，因为本文件中定义的状态位与RFC 4447[2]中定义的PW设置和维护协议具有相同的安全考虑因素。应该注意的是，PW冗余集的安全性仅与其任何成员上最弱的安全性相同。
New MIB objects for the support of PW redundancy will be defined in a separate document.
用于支持PW冗余的新MIB对象将在单独的文档中定义。
This document defines the following PW status codes for the PW redundancy application. IANA has allocated these from the "Pseudowire Status Codes Registry".
本文件为PW冗余应用程序定义了以下PW状态代码。IANA已从“伪线路状态代码注册表”中分配了这些代码。
0x00000020 When the bit is set, it indicates PW forwarding standby".
0x00000020位设置时，表示PW转发待机”。
When the bit is cleared, it indicates PW forwarding active".
当该位被清除时，表示PW转发活动”。
0x00000040 When the bit is set, it represents Request Switchover to this PW.
0x00000040设置该位时，表示请求切换到此PW。
When the bit is cleared, it represents no specific action.
当该位被清除时，它不表示任何特定动作。
The editors would like to thank Matthew Bocci, Pranjal Kumar Dutta, Giles Heron, Marc Lasserre, Luca Martini, Thomas Nadeau, Jonathan Newton, Hamid Ould-Brahim, Olen Stokes, and Daniel Cohn who made a contribution to the development of this document.
编辑们要感谢Matthew Bocci、Pranjal Kumar Dutta、Giles Heron、Marc Lasserre、Luca Martini、Thomas Nadeau、Jonathan Newton、Hamid Ould Brahim、Olen Stokes和Daniel Cohn，他们为本文件的编写做出了贡献。
Matthew Bocci Alcatel-Lucent EMail: matthew.bocci@alcatel-lucent.com
Matthew Bocci Alcatel-Lucent电子邮件：Matthew。bocci@alcatel-朗讯网
Pranjal Kumar Dutta Alcatel-Lucent EMail: pranjal.dutta@alcatel-lucent.com
Pranjal Kumar Dutta Alcatel-Lucent电子邮件：Pranjal。dutta@alcatel-朗讯网
Giles Heron Cisco Systems, Inc. giles.heron@gmail.com
Giles Heron思科系统公司，Giles。heron@gmail.com
Marc Lasserre Alcatel-Lucent EMail: marc.lasserre@alcatel-lucent.com
马克·拉塞尔·阿尔卡特·朗讯电子邮件：马克。lasserre@alcatel-朗讯网
Luca Martini Cisco Systems, Inc. EMail: lmartini@cisco.com
Luca Martini Cisco Systems，Inc.电子邮件：lmartini@cisco.com
Thomas Nadeau Juniper Networks EMail: tnadeau@lucidvision.com
Thomas Nadeau Juniper Networks电子邮件：tnadeau@lucidvision.com
Jonathan Newton Cable & Wireless Worldwide EMail: Jonathan.Newton@cw.com
Jonathan Newton有线和无线全球电子邮件：Jonathan。Newton@cw.com
Hamid Ould-Brahim EMail: ouldh@yahoo.com
哈米德·乌尔德·布拉希姆电子邮件：ouldh@yahoo.com
Olen Stokes Extreme Networks EMail: ostokes@extremenetworks.com
Olen Stokes极限网络电子邮件：ostokes@extremenetworks.com
Daniel Cohn Orckit daniel.cohn.ietf@gmail.com.
丹尼尔·科恩。ietf@gmail.com.
The authors would like to thank the following individuals for their valuable comments and suggestions, which improved the document both technically and editorially:
作者要感谢以下个人提出的宝贵意见和建议，这些意见和建议从技术和编辑两方面改进了本文件：
Vach Kompella, Kendall Harvey, Tiberiu Grigoriu, John Rigby, Prashanth Ishwar, Neil Hart, Kajal Saha, Florin Balus, Philippe Niger, Dave McDysan, Roman Krzanowski, Italo Busi, Robert Rennison, and Nicolai Leymann.
Vach Kompella、Kendall Harvey、Tiberiu Grigoriu、John Rigby、Prashanth Ishwar、Neil Hart、Kajal Saha、Florin Balus、Philippe Niger、Dave McDysan、Roman Krzanowski、Italo Busi、Robert Rennison和Nicolai Leymann。
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[1] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[2] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[2] Martini，L.，Ed.，Rosen，E.，El Aawar，N.，Smith，T.，和G.Heron，“使用标签分发协议（LDP）的伪线设置和维护”，RFC 4447，2006年4月。
[3] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007.
[3] Lasserre，M.，Ed.，和V.Kompella，Ed.，“使用标签分发协议（LDP）信令的虚拟专用LAN服务（VPLS）”，RFC 4762，2007年1月。
[4] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
[4] Martini，L.，Metz，C.，Nadeau，T.，Bocci，M.和M.Aissaoui，“分段伪线”，RFC 60732011年1月。
[5] Aissaoui, M., Busschbach, P., Martini, L., Morrow, M., Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping", RFC 6310, July 2011.
[5] 艾萨维，M.，布施巴赫，P.，马提尼，L.，莫罗，M.，纳多，T.，和Y（J）。Stein，“伪线（PW）操作、管理和维护（OAM）消息映射”，RFC63102011年7月。
[6] Bocci, M. and S. Bryant, "An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, October 2009.
[6] Bocci，M.和S.Bryant，“多段伪线边到边仿真的体系结构”，RFC 5659，2009年10月。
[7] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[7] Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，2006年4月。
[8] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire Redundancy", RFC 6718, August 2012.
[8] Muley，P.，Aissaoui，M.和M.Bocci，“伪线冗余”，RFC 67182012年8月。
[9] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[9] Bryant，S.，Ed.，和P.Pate，Ed.，“伪线仿真边到边（PWE3）架构”，RFC 3985，2005年3月。
[10] Dutta, P., Balus, F., Calvignac, G., and O. Stokes "LDP Extensions for Optimized MAC Address Withdrawal in H-VPLS", Work in Progress, October 2011.
[10] Dutta，P.，Balus，F.，Calvignac，G.，和O.Stokes，“H-VPLS中优化MAC地址提取的LDP扩展”，正在进行的工作，2011年10月。
[11] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, December 2007.
[11] Nadeau，T.，Ed.，和C.Pignataro，Ed.，“伪线虚拟电路连接验证（VCCV）：伪线的控制通道”，RFC 5085，2007年12月。
This section shows how the mechanisms described in this document are used to achieve the desired protection behavior for some of the applications described in "PW Redundancy" [8].
本节说明如何使用本文档中描述的机制为“PW冗余”[8]中描述的一些应用程序实现所需的保护行为。
The following figure illustrates an application of SS-PW redundancy.
下图说明了SS-PW冗余的应用。
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| | | +-----+
| |----------|....|...PW1.(active)...|....|----------| |
| | | |==================| | | CE2 |
| CE1 | +----+ |PE2 | | |
| | +----+ | | +-----+
| | | |==================| |
| |----------|....|...PW2.(standby)..| |
+-----+ | | PE3|==================| |
AC +----+ +----+
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| | | +-----+
| |----------|....|...PW1.(active)...|....|----------| |
| | | |==================| | | CE2 |
| CE1 | +----+ |PE2 | | |
| | +----+ | | +-----+
| | | |==================| |
| |----------|....|...PW2.(standby)..| |
+-----+ | | PE3|==================| |
AC +----+ +----+
Figure 2. Multi-Homed CE with SS-PW Redundancy
图2。具有SS-PW冗余的多宿CE
The application in Figure 2 makes use of the independent mode of operation.
图2中的应用程序使用独立的操作模式。
CE1 is dual-homed to PE1 and to PE3 by attachment circuits. The method for dual-homing of CE1 to PE1 and to PE3 nodes and the protocols used are outside the scope of this document (see [8]).
CE1通过连接电路与PE1和PE3双宿。CE1至PE1和PE3节点的双重归宿方法以及使用的协议不在本文件的范围内（见[8]）。
In this example, the AC from CE1 to PE1 is active, while the AC from CE1 to PE3 is standby, as determined by the redundancy protocol running on the ACs. Thus, in normal operation, PE1 and PE3 will advertise an active and standby Preferential Forwarding status bit, respectively, to PE2, reflecting the forwarding state of the two ACs to CE1 as determined by the AC dual-homing protocol. PE2 advertises a Preferential Forwarding status bit of active on both PW1 and PW2, since the AC to CE2 is single-homed. As both the local and remote UP/DOWN status and Preferential Forwarding status for PW1 are up and active, traffic is forwarded over PW1 in both directions.
在本例中，从CE1到PE1的AC是活动的，而从CE1到PE3的AC是备用的，这由ACs上运行的冗余协议确定。因此，在正常操作中，PE1和PE3将分别向PE2播发活动和备用优先转发状态比特，反映由AC双归宿协议确定的两个AC到CE1的转发状态。PE2在PW1和PW2上公布活动的优先转发状态位，因为AC到CE2是单宿的。由于PW1的本地和远程向上/向下状态以及优先转发状态都处于向上和活动状态，因此流量在两个方向上通过PW1进行转发。
On failure of the AC between CE1 and PE1, the forwarding state of the AC on PE3 transitions to active. PE3 then announces the newly changed Preferential Forwarding status bit of active to PE2. PE1 will advertise a PW status notification message, indicating that the AC between CE1 and PE1 is down. PE2 matches the local and remote Preferential Forwarding status of active and status of "Pseudowire forwarding" and selects PW2 as the new active PW to which to send traffic.
当CE1和PE1之间的AC发生故障时，PE3上AC的转发状态转换为激活状态。然后，PE3向PE2宣布新更改的活动优先转发状态位。PE1将播发PW状态通知消息，指示CE1和PE1之间的AC关闭。PE2匹配活动的本地和远程优先转发状态以及“伪线转发”状态，并选择PW2作为要向其发送流量的新活动PW。
On failure of the PE1 node, PE3 will detect it and will transition the forwarding state of its AC to active. The method by which PE3 detects that PE1 is down is outside the scope of this document. PE3 then announces the newly changed Preferential Forwarding status bit of active to PE2. PE3 and PE2 match the local and remote Preferential Forwarding status of active and UP/DOWN status "Pseudowire forwarding" and select PW2 as the new active PW to which to send traffic. Note that PE2 may have detected that the PW to PE1 went down via T-LDP Hello timeout or via other means. However, it will not be able to forward user traffic until it receives the updated status bit from PE3.
当PE1节点发生故障时，PE3将检测到该节点，并将其AC的转发状态转换为活动状态。PE3检测PE1停机的方法不在本文件范围内。然后，PE3向PE2宣布新更改的活动优先转发状态位。PE3和PE2匹配活动和向上/向下状态“伪线转发”的本地和远程优先转发状态，并选择PW2作为要向其发送流量的新活动PW。注意，PE2可能已经通过T-LDP Hello超时或通过其他方式检测到PW到PE1下降。但是，在从PE3接收到更新的状态位之前，它将无法转发用户流量。
Note that, in this example, the receipt of the AC status on the CE1-PE1 link is normally sufficient for PE2 to switch to PW2. However, the operator may want to trigger the switchover of the PW for administrative reasons, e.g., maintenance; thus, the use of the Preferential Forwarding status bit is required to notify PE2 to trigger the switchover.
注意，在此示例中，CE1-PE1链路上接收到的AC状态通常足以使PE2切换到PW2。但是，操作员可能出于管理原因（例如维护）希望触发PW的切换；因此，需要使用优先转发状态位来通知PE2以触发切换。
Note that the primary/secondary procedures do not apply in this case as the PW Preferential Forwarding status is driven by the AC forwarding state, as determined by the AC dual-homing protocol used.
注意，主要/次要程序在这种情况下不适用，因为PW优先转发状态由AC转发状态驱动，如所使用的AC双归宿协议所确定。
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V (not shown) V V |
V AC +----+ +----+ AC V
+-----+ | |....|.......PW1........|....| | +-----+
| |----------| PE1|...... .........| PE3|----------| |
| CE1 | +----+ \ / PW3 +----+ | CE2 |
| | +----+ X +----+ | |
| | | |....../ \..PW4....| | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | |....|.....PW2..........|....| | +-----+
AC +----+ +----+ AC
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V (not shown) V V |
V AC +----+ +----+ AC V
+-----+ | |....|.......PW1........|....| | +-----+
| |----------| PE1|...... .........| PE3|----------| |
| CE1 | +----+ \ / PW3 +----+ | CE2 |
| | +----+ X +----+ | |
| | | |....../ \..PW4....| | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | |....|.....PW2..........|....| | +-----+
AC +----+ +----+ AC
Figure 3. Multiple Multi-Homed CEs with SS-PW Redundancy
图3。具有SS-PW冗余的多个多宿CE
The application in Figure 3 makes use of the independent mode of operation.
图3中的应用程序使用独立的操作模式。
CE1 is dual-homed to PE1 and PE2. CE2 is dual-homed to PE3 and PE4. The method for dual-homing and the used protocols are outside the scope of this document. Note that the PSN tunnels are not shown in this figure for clarity. However, it can be assumed that each of the PWs shown is encapsulated in a separate PSN tunnel.
CE1是PE1和PE2的双重宿主。CE2是PE3和PE4的双重宿主。双归宿方法和使用的协议不在本文件范围内。请注意，为清晰起见，本图中未显示PSN隧道。然而，可以假设所示的每个PW封装在单独的PSN隧道中。
Assume that the AC from CE1 to PE1 is active and from CE1 to PE2 it is standby; furthermore, assume that the AC from CE2 to PE3 is standby and from CE2 to PE4 it is active. The method of deriving the active/standby status of the AC is outside the scope of this document.
假设从CE1到PE1的交流为有功，从CE1到PE2的交流为备用；此外，假设从CE2到PE3的交流是备用的，从CE2到PE4的交流是活动的。推导AC的活动/备用状态的方法不在本文档的范围内。
PE1 advertises the Preferential Forwarding status active and UP/DOWN status "Pseudowire forwarding" for pseudowires PW1 and PW4 connected to PE3 and PE4. This status reflects the forwarding state of the AC attached to PE1. PE2 advertises Preferential Forwarding status standby and UP/DOWN status "Pseudowire forwarding" for pseudowires PW2 and PW3 to PE3 and PE4. PE3 advertises Preferential Forwarding status standby and UP/DOWN status "Pseudowire forwarding" for pseudowires PW1 and PW3 to PE1 and PE2. PE4 advertises the Preferential Forwarding status active and UP/DOWN status "Pseudowire forwarding" for pseudowires PW2 and PW4 to PE2 and PE1, respectively. Thus, by matching the local and remote Preferential Forwarding status of active and UP/DOWN status of
PE1为连接到PE3和PE4的伪线PW1和PW4播发优先转发状态活动和向上/向下状态“伪线转发”。此状态反映连接到PE1的AC的转发状态。PE2向PE3和PE4宣传伪线PW2和PW3的优先转发状态待机和向上/向下状态“伪线转发”。PE3向PE1和PE2宣传伪线PW1和PW3的优先转发状态待机和向上/向下状态“伪线转发”。PE4分别向PE2和PE1宣传伪线PW2和PW4的优先转发状态活动和向上/向下状态“伪线转发”。因此，通过匹配本地和远程优先转发状态的活动和上/下状态的
"Pseudowire forwarding" of pseudowires, the PE nodes determine which PW should be in the active state. In this case, it is PW4 that will be selected.
“伪线转发”对于伪线，PE节点确定哪个PW应处于活动状态。在这种情况下，将选择PW4。
On failure of the AC between CE1 and PE1, the forwarding state of the AC on PE2 is changed to active. PE2 then announces the newly changed Preferential Forwarding status bit of active to PE3 and PE4. PE1 will advertise a PW status notification message, indicating that the AC between CE1 and PE1 is down. PE2 and PE4 match the local and remote Preferential Forwarding status of active and UP/DOWN status "Pseudowire forwarding" and select PW2 as the new active PW to which to send traffic.
当CE1和PE1之间的AC发生故障时，PE2上AC的转发状态变为激活。然后，PE2向PE3和PE4宣布新更改的活动优先转发状态位。PE1将播发PW状态通知消息，指示CE1和PE1之间的AC关闭。PE2和PE4匹配活动和向上/向下状态“伪线转发”的本地和远程优先转发状态，并选择PW2作为要向其发送流量的新活动PW。
On failure of the PE1 node, PE2 will detect the failure and will transition the forwarding state of its AC to active. The method by which PE2 detects that PE1 is down is outside the scope of this document. PE2 then announces the newly changed Preferential Forwarding status bit of active to PE3 and PE4. PE2 and PE4 match the local and remote Preferential Forwarding status of active and UP/DOWN status "Pseudowire forwarding" and select PW2 as the new active PW to which to send traffic. Note that PE3 and PE4 may have detected that the PW to PE1 went down via T-LDP Hello timeout or via other means. However, they will not be able to forward user traffic until they have received the updated status bit from PE2.
当PE1节点发生故障时，PE2将检测到故障，并将其AC的转发状态转换为活动状态。PE2检测PE1停机的方法不在本文件范围内。然后，PE2向PE3和PE4宣布新更改的活动优先转发状态位。PE2和PE4匹配活动和向上/向下状态“伪线转发”的本地和远程优先转发状态，并选择PW2作为要向其发送流量的新活动PW。注意，PE3和PE4可能已经通过T-LDP Hello timeout或通过其他方式检测到PW到PE1下降。但是，在从PE2接收到更新的状态位之前，他们将无法转发用户流量。
Because each dual-homing algorithm running on the two node sets, i.e., {CE1, PE1, PE2} and {CE2, PE3, PE4}, selects the active AC independently, there is a need to signal the active status of the AC such that the PE nodes can select a common active PW for end-to-end forwarding between CE1 and CE2 as per the procedures in the independent mode.
由于在两个节点集（即{CE1，PE1，PE2}和{CE2，PE3，PE4}）上运行的每个双归宿算法独立地选择活动AC，因此需要向AC的活动状态发送信号，以便PE节点可以按照独立模式中的过程为CE1和CE2之间的端到端转发选择公共活动PW。
Note that no primary/secondary procedures, as defined in Sections 5.1 and 5.2, apply in this use case as the active/standby status is driven by the AC forwarding state, as determined by the AC dual-homing protocol used.
注意，第5.1节和第5.2节中定义的主/辅程序不适用于本用例，因为主/备用状态由AC转发状态驱动，由使用的AC双归宿协议确定。
The following figure illustrates an application of MS-PW redundancy.
下图说明了MS-PW冗余的应用。
Native |<-----------Pseudowire ------------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|PW1-Seg2.......|-------| |
| | | |=========| |=========| | | |
| CE1| +-----+ +-----+ +-----+ | |
| | |.| +-----+ +-----+ | CE2|
| | |.|===========| |=========| | | |
| | |.....PW2-Seg1......|.PW2-Seg2......|-------| |
+----+ |=============|S-PE2|=========|T-PE4| | +----+
+-----+ +-----+ AC
Native |<-----------Pseudowire ------------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|PW1-Seg2.......|-------| |
| | | |=========| |=========| | | |
| CE1| +-----+ +-----+ +-----+ | |
| | |.| +-----+ +-----+ | CE2|
| | |.|===========| |=========| | | |
| | |.....PW2-Seg1......|.PW2-Seg2......|-------| |
+----+ |=============|S-PE2|=========|T-PE4| | +----+
+-----+ +-----+ AC
Figure 4. Multi-Homed CE with MS-PW Redundancy
图4。具有MS-PW冗余的多宿CE
The application in Figure 4 makes use of the independent mode of operation. It extends the application described in Section 15.1. 15.1 of this document and in [8] by adding a pair of S-PE nodes to switch the segments of PW1 and PW2.
图4中的应用程序使用独立的操作模式。它扩展了第15.1节中描述的应用程序。通过添加一对S-PE节点来切换PW1和PW2的段。
CE2 is dual-homed to T-PE2 and T-PE4. PW1 and PW2 are used to extend the resilient connectivity all the way to T-PE1. PW1 has two segments and is an active pseudowire, while PW2 has two segments and is a standby pseudowire. This application requires support for MS-PW with segments of the same type as described in [4].
CE2是T-PE2和T-PE4的双宿主。PW1和PW2用于将弹性连接一直延伸到T-PE1。PW1有两段，是一条活动伪线，而PW2有两段，是一条备用伪线。此应用程序需要支持MS-PW，其段类型与[4]中所述相同。
The operation in this case is the same as in the case of SS-PW, as described in Section 15.1. The only difference is that the S-PE nodes need to relay the PW status notification containing both the UP/DOWN and forwarding status to the T-PE nodes.
这种情况下的操作与SS-PW的操作相同，如第15.1节所述。唯一的区别是S-PE节点需要将包含向上/向下和转发状态的PW状态通知中继到T-PE节点。
The following figure illustrates an application of MS-PW redundancy with 1:1 PW protection.
下图说明了MS-PW冗余与1:1 PW保护的应用。
Native |<-----------Pseudowire ------------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ |
| |=============| |=============| |
| |.....PW3-Seg1......|.PW3-Seg2....| |
| |.|===========|S-PE3|===========|.| |
| |.| +-----+ |.| |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|PW1-Seg2.......|-------| |
| | | |=========| |=========| | | |
| CE1| +-----+ +-----+ +-----+ | |
| | |.| |.| +-----+ +-----+ | CE2|
| | |.| |.|=========| |=========| | | |
| | |.| |...PW2-Seg1......|.PW2-Seg2......|-------| |
+----+ |.| |===========|S-PE2|=========|T-PE4| | +----+
|.| +-----+ +-----+ AC
|.| +-----+ |.|
|.|=============| |===========|.|
|.......PW4-Seg1......|.PW4-Seg2....|
|===============|S-PE4|=============|
+-----+
Native |<-----------Pseudowire ------------->| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ |
| |=============| |=============| |
| |.....PW3-Seg1......|.PW3-Seg2....| |
| |.|===========|S-PE3|===========|.| |
| |.| +-----+ |.| |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|PW1-Seg2.......|-------| |
| | | |=========| |=========| | | |
| CE1| +-----+ +-----+ +-----+ | |
| | |.| |.| +-----+ +-----+ | CE2|
| | |.| |.|=========| |=========| | | |
| | |.| |...PW2-Seg1......|.PW2-Seg2......|-------| |
+----+ |.| |===========|S-PE2|=========|T-PE4| | +----+
|.| +-----+ +-----+ AC
|.| +-----+ |.|
|.|=============| |===========|.|
|.......PW4-Seg1......|.PW4-Seg2....|
|===============|S-PE4|=============|
+-----+
Figure 5. Multi-Homed CE with MS-PW Redundancy and Protection
图5。具有MS-PW冗余和保护的多宿CE
The application in Figure 5 makes use of the independent mode of operation.
图5中的应用程序使用独立的操作模式。
CE2 is dual-homed to T-PE2 and T-PE4. The PW pairs {PW1,PW3} and {PW2,PW4} are used to extend the resilient connectivity all the way to T-PE1, like in the case in Section 15.3, with the addition that this setup provides for S-PE node protection.
CE2是T-PE2和T-PE4的双宿主。PW对{PW1，PW3}和{PW2，PW4}用于将弹性连接一直延伸到T-PE1，如第15.3节中所述，此外，该设置还提供了S-PE节点保护。
CE1 is connected to T-PE1 while CE2 is dual-homed to T-PE2 and T-PE4. There are four segmented PWs. PW1 and PW2 are primary PWs and are used to support CE2 multi-homing. PW3 and PW4 are secondary PWs and are used to support 1:1 PW protection. PW1, PW2, PW3, and PW4 have two segments and they are switched at S-PE1, S-PE2, S-PE3, and S-PE4, respectively.
CE1与T-PE1相连，而CE2与T-PE2和T-PE4相连。有四个分段PW。PW1和PW2是主要PW，用于支持CE2多归宿。PW3和PW4是次级PW，用于支持1:1 PW保护。PW1、PW2、PW3和PW4有两段，分别在S-PE1、S-PE2、S-PE3和S-PE4处切换。
It is possible that S-PE1 coincides with S-PE4 and/or SP-2 coincides with S-PE3, in particular, where the two PSN domains are interconnected via two nodes. However, Figure 5 shows four separate S-PE nodes for clarity.
特别是在两个PSN域通过两个节点互连的情况下，S-PE1可能与S-PE4重合和/或SP-2可能与S-PE3重合。然而，为了清晰起见，图5显示了四个独立的S-PE节点。
The behavior of this setup is exactly the same as the setup in Section 15.3 except that T-PE1 will always see a pair of PWs eligible for the active state, for example, the pair {PW1,PW3} when the AC between CE2 and T-PE2 is in active state. Thus, it is important that both T-PE1 and T-PE2 implement a common mechanism to choose one the two PWs for forwarding, as explained in Section 5.1. Similarly, T-PE1 and T-PE4 must use the same mechanism to select among the pair {PW2,PW4} when the AC between CE2 and T-PE4 is in active state.
该设置的行为与第15.3节中的设置完全相同，除了T-PE1将始终看到一对符合激活状态的PW，例如，当CE2和T-PE2之间的AC处于激活状态时，对{PW1，PW3}。因此，重要的是，T-PE1和T-PE2实现一个共同的机制，从两个PW中选择一个进行转发，如第5.1节所述。同样，当CE2和T-PE4之间的AC处于激活状态时，T-PE1和T-PE4必须使用相同的机制在对{PW2，PW4}中进行选择。
The following is an application of the independent mode of operation, along with the request switchover procedures in order to provide N:1 PW protection. A revertive behavior to a primary PW is shown as an example of configuring and using the primary/secondary procedures described in Sections 5.1. and 5.2.
以下是独立运行模式的应用，以及提供N:1 PW保护的请求切换程序。作为配置和使用第5.1节中描述的主要/次要程序的示例，显示了主要PW的回复行为。和5.2。
Native |<------------Pseudowire ------------>| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Native |<------------Pseudowire ------------>| Native
Service | | Service
(AC) | |<-PSN1-->| |<-PSN2-->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ |
+----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+
| |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| |
| CE1| | |=========| |=========| | | CE2|
| | +-----+ +-----+ +-----+ | |
+----+ |.||.| |.||.| +----+
|.||.| +-----+ |.||.|
|.||.|=========| |========== .||.|
|.||...PW2-Seg1......|.PW2-Seg2...||.|
|.| ===========|S-PE2|============ |.|
|.| +-----+ |.|
|.|============+-----+============= .|
|.....PW3-Seg1.| | PW3-Seg2......|
==============|S-PE3|===============
| |
+-----+
Figure 6. Single-Homed CE with MS-PW Redundancy
图6。具有MS-PW冗余的单宿CE
CE1 is connected to PE1 in provider edge 1 and CE2 to PE2 in provider edge 2, respectively. There are three segmented PWs: a primary PW, PW1, is switched at S-PE1 and has the lowest precedence value of
CE1分别连接到提供程序边缘1中的PE1和CE2到提供程序边缘2中的PE2。有三个分段PW：主PW PW1在S-PE1处切换，优先级最低为
zero; a secondary PW, PW2, which is switched at S-PE2 and has a precedence of 1; and another secondary PW, PW3, which is switched at S-PE3 and has a precedence of 2.
零次级PW，PW2，在S-PE2处切换，优先级为1；以及另一个次级PW，PW3，其在S-PE3处切换并且具有2的优先级。
The precedence is locally configured at the endpoints of the PW, i.e., T-PE1 and T-PE2. The lower the precedence value, the higher the priority.
优先级在PW的端点（即T-PE1和T-PE2）进行本地配置。优先级值越低，优先级越高。
T-PE1 and T-PE2 will select the PW they intend to activate based on their local and remote UP/DOWN state, as well as the local precedence configuration. In this case, they will both advertise Preferential Forwarding status bit of active on PW1 and of standby on PW2 and PW3 using priority derived from local precedence configuration. Assuming all PWs are up, T-PE1 and T-PE2 will use PW1 to forward user packets.
T-PE1和T-PE2将根据其本地和远程向上/向下状态以及本地优先配置，选择其打算激活的PW。在这种情况下，它们都将使用从本地优先级配置派生的优先级在PW1上公布活动的优先转发状态位，在PW2和PW3上公布备用的优先转发状态位。假设所有PW都已启动，T-PE1和T-PE2将使用PW1转发用户数据包。
If PW1 fails, then the T-PE detecting the failure will send a status notification to the remote T-PE with a Local PSN-facing PW (ingress) Receive Fault bit set, a Local PSN-facing PW (egress) Transmit Fault bit set, or a Pseudowire Not Forwarding bit set. In addition, it will set the Preferential Forwarding status bit on PW1 to standby. It will also advertise the Preferential Forwarding status bit on PW2 as active, as it has the next-lowest precedence value. T-PE2 will also perform the same steps as soon as it is informed of the failure of PW1. Both T-PE nodes will perform a match on the Preferential Forwarding status of active and UP/DOWN status of "Pseudowire forwarding" and will use PW2 to forward user packets.
如果PW1发生故障，则检测到故障的T-PE将向远程T-PE发送状态通知，并设置面向本地PSN的PW（入口）接收故障位集、面向本地PSN的PW（出口）传输故障位集或不转发伪线位集。此外，它将PW1上的优先转发状态位设置为待机。它还将在PW2上公布优先转发状态位为活动，因为它具有下一个最低优先级值。一旦通知T-PE2 PW1故障，T-PE2也将执行相同的步骤。两个T-PE节点将对活动的优先转发状态和“伪线转发”的向上/向下状态执行匹配，并将使用PW2转发用户分组。
However, this does not guarantee that the T-PEs will choose the same PW from the redundant set to forward on, for a given emulated service, at all times. This may be due to a mismatch of the configuration of the PW precedence in each T-PE. This may also be due to a failure that caused the endpoints to not be able to match the active Preferential Forwarding status bit and UP/DOWN status bits. In this case, T-PE1 and/or T-PE2 can invoke the request switchover/acknowledgment procedures to synchronize the choice of PW to forward on in both directions.
然而，这并不能保证T-PEs将始终从冗余集中选择相同的PW，以便为给定的模拟服务转发。这可能是由于每个T-PE中PW优先级的配置不匹配造成的。这也可能是由于导致端点无法匹配活动优先转发状态位和向上/向下状态位的故障造成的。在这种情况下，T-PE1和/或T-PE2可以调用请求切换/确认过程，以在两个方向上同步选择要转发的PW。
The trigger for sending a request to switch over can also be the execution of an administrative maintenance operation by the network operator in order to move the traffic away from the T-PE/S-PE nodes/links to be serviced.
发送切换请求的触发器也可以是网络运营商执行管理维护操作，以便将流量从要服务的T-PE/S-PE节点/链路移开。
In case the Request Switchover is sent by both endpoints simultaneously, both T-PEs send status notification with the newly selected PW with Request Switchover bit set, waiting for a response from the other endpoint. In such a situation, the T-PE with greater
如果两个端点同时发送请求切换，则两个T-PEs都会发送状态通知，并设置新选择的PW和请求切换位，等待另一个端点的响应。在这种情况下，T-PE具有更大的
system address request is given precedence. This helps in synchronizing PWs in the event of mismatch of precedence configuration as well.
系统地址请求具有优先权。这有助于在优先级配置不匹配的情况下同步PWs。
On recovery of the primary PW, PW1 is selected to forward traffic and the secondary PW, PW2, is set to standby.
在主PW恢复时，选择PW1转发流量，并将辅助PW PW2设置为备用。
The following figure illustrates the application of use of PW redundancy in H-VPLS for the purpose of dual-homing an MTU-s node to PE nodes using PW spokes. This application makes use of the master/slave mode of operation.
下图说明了在H-VPLS中使用PW冗余的应用，目的是使用PW辐条将MTU-s节点双归宿到PE节点。此应用程序使用主/从操作模式。
PE1-rs
+--------+
| VSI |
Active PW | -- |
Group..........|../ \..|.
CE-1 . | \ / | .
\ . | -- | .
\ . +--------+ .
\ MTU-s . . . PE3-rs
+--------+ . . . +--------+
| VSI | . . H-VPlS .| VSI |
| -- ..|.. . Core |.. -- |
| / \ | . PWs | / \ |
| \ /..|.. . | \ / |
| -- | . . .|.. -- |
+--------+ . . . +--------+
/ . . .
/ . +--------+ .
/ . | VSI | .
CE-2 . | -- | .
..........|../ \..|.
Standby PW | \ / |
Group | -- |
+--------+
PE2-rs
PE1-rs
+--------+
| VSI |
Active PW | -- |
Group..........|../ \..|.
CE-1 . | \ / | .
\ . | -- | .
\ . +--------+ .
\ MTU-s . . . PE3-rs
+--------+ . . . +--------+
| VSI | . . H-VPlS .| VSI |
| -- ..|.. . Core |.. -- |
| / \ | . PWs | / \ |
| \ /..|.. . | \ / |
| -- | . . .|.. -- |
+--------+ . . . +--------+
/ . . .
/ . +--------+ .
/ . | VSI | .
CE-2 . | -- | .
..........|../ \..|.
Standby PW | \ / |
Group | -- |
+--------+
PE2-rs
A.6. Multi-Homed MTU-s in H-VPLS Core
A.6. H-VPLS核心中的多宿MTU-s
MTU-s is dual-homed to PE1-rs and PE2-rs. The primary spoke PWs from MTU-s are connected to PE1-rs, while the secondary PWs are connected to PE2. PE1-rs and PE2-rs are connected to H-VPLS core on the other side of the network. MTU-s communicates to PE1-rs and PE2-rs the forwarding status of its member PWs for a set of Virtual Switch Instances (VSIs) having common status active/standby. It may be
MTU-s与PE1-rs和PE2-rs双宿。MTU-s的主辐条PW连接至PE1-rs，而辅助PW连接至PE2。PE1 rs和PE2 rs连接到网络另一端的H-VPLS核心。MTU-s向PE1 rs和PE2 rs传送其成员PWs的转发状态，以获得一组具有公共状态active/standby的虚拟交换机实例（VSI）。可能是
signaled using PW grouping with a common group-id in the PWid FEC element or Grouping TLV in the Generalized PWid FEC element, as defined in [2] to scale better. MTU-s derives the status of the PWs based on local policy configuration. In this example, the primary/secondary procedures as defined in Section 5.2 are used, but this can be based on any other policy.
使用PWid FEC元素中具有公共组id的PW分组或广义PWid FEC元素中的分组TLV发出信号，如[2]中所定义，以更好地扩展。MTU-s根据本地策略配置导出PWs的状态。在本例中，使用了第5.2节中定义的主要/次要程序，但这可以基于任何其他政策。
Whenever MTU-s performs a switchover, it sends a wildcard notification message to PE2-rs for the previously standby PW group containing PW Status TLV with PW Preferential Forwarding bit cleared. On receiving the notification, PE-2rs unblocks all member PWs identified by the PW group and the state of the PW group changes from standby to active. All procedures described in Section 6.2 are applicable.
每当MTU-s执行切换时，它都会向PE2 rs发送一条通配符通知消息，用于先前备用PW组，其中包含PW状态TLV，PW优先转发位已清除。收到通知后，PE-2rs解锁PW组标识的所有成员PW，PW组的状态从待机变为活动。第6.2节所述的所有程序均适用。
The use of the Preferential Forwarding status bit in master/slave mode is similar to Topology Change Notification in the IEEE Ethernet Bridges controlled by Rapid Spanning Tree Protocol (RSTP) but is restricted over a single hop. When these procedures are implemented, PE-rs devices are aware of switchovers at MTU-s and could generate MAC Withdraw messages to trigger MAC flushing within the H-VPLS full mesh. By default, MTU-s devices should still trigger MAC Withdraw messages, as currently defined in [3], to prevent two copies of MAC Withdraws being sent: one by MTU-s and another one by PE-rs nodes. Mechanisms to disable a MAC Withdraw trigger in certain devices is out of the scope of this document.
主/从模式下优先转发状态位的使用类似于由快速生成树协议（RSTP）控制的IEEE以太网网桥中的拓扑更改通知，但仅限于单跳。当实施这些程序时，PE-rs设备意识到MTU-s处的切换，并可生成MAC撤销消息以触发H-VPLS全网内的MAC刷新。默认情况下，MTU-s设备仍应触发MAC撤回消息，如[3]中当前所定义，以防止发送MAC撤回的两个副本：一个由MTU-s发送，另一个由PE rs节点发送。在某些设备中禁用MAC撤销触发器的机制不在本文档的范围内。
Authors' Addresses
作者地址
Praveen Muley Alcatel-lucent 701 E. Middlefield Road Mountain View, CA, 94043, USA
Praveen Muley Alcatel-lucent 701美国加利福尼亚州米德尔菲尔德路东山景城，邮编94043
EMail: praveen.muley@alcatel-lucent.com
EMail: praveen.muley@alcatel-lucent.com
Mustapha Aissaoui Alcatel-lucent 600 March Rd Kanata, ON, Canada K2K 2E6
Mustapha Aissaoui Alcatel-lucent加拿大安大略省卡纳塔市3月路600号K2K 2E6
EMail: mustapha.aissaoui@alcatel-lucent.com
EMail: mustapha.aissaoui@alcatel-lucent.com