Internet Engineering Task Force (IETF) J. Dong
Request for Comments: 7795 H. Wang
Category: Standards Track Huawei Technologies
ISSN: 2070-1721 February 2016
Internet Engineering Task Force (IETF) J. Dong
Request for Comments: 7795 H. Wang
Category: Standards Track Huawei Technologies
ISSN: 2070-1721 February 2016
Pseudowire Redundancy on the Switching Provider Edge (S-PE)
交换提供程序边缘（S-PE）上的伪线冗余
Abstract
摘要
This document describes Multi-Segment Pseudowire (MS-PW) protection scenarios in which pseudowire redundancy is provided on the Switching Provider Edge (S-PE) as defined in RFC 5659. Operations of the S-PEs that provide PW redundancy are specified in this document. Signaling of the Preferential Forwarding status as defined in RFCs 6870 and 6478 is reused. This document does not require any change to the Terminating Provider Edges (T-PEs) of MS-PW.
本文档描述了多段伪线（MS-PW）保护场景，其中在RFC 5659中定义的交换提供商边缘（S-PE）上提供伪线冗余。本文件规定了提供PW冗余的S-PEs的操作。重复使用RFCs 6870和6478中定义的优先转发状态的信令。本文件不要求对MS-PW的端接提供商边缘（T-PE）进行任何更改。
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/rfc7795.
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/rfc7795.
Copyright Notice
版权公告
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2016 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Typical Scenarios of PW Redundancy on S-PE . . . . . . . . . 3
2.1. MS-PW Redundancy on S-PE . . . . . . . . . . . . . . . . 3
2.2. MS-PW Redundancy on S-PE with S-PE Protection . . . . . . 4
3. S-PE Operations . . . . . . . . . . . . . . . . . . . . . . . 4
4. Applications of PW Redundancy on S-PE . . . . . . . . . . . . 5
4.1. Applications in Scenario 1 . . . . . . . . . . . . . . . 5
4.2. Applications in Scenario 2 . . . . . . . . . . . . . . . 6
5. VCCV Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Typical Scenarios of PW Redundancy on S-PE . . . . . . . . . 3
2.1. MS-PW Redundancy on S-PE . . . . . . . . . . . . . . . . 3
2.2. MS-PW Redundancy on S-PE with S-PE Protection . . . . . . 4
3. S-PE Operations . . . . . . . . . . . . . . . . . . . . . . . 4
4. Applications of PW Redundancy on S-PE . . . . . . . . . . . . 5
4.1. Applications in Scenario 1 . . . . . . . . . . . . . . . 5
4.2. Applications in Scenario 2 . . . . . . . . . . . . . . . 6
5. VCCV Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
[RFC6718] describes the framework and requirements for pseudowire (PW) redundancy, and [RFC6870] specifies a PW redundancy mechanism for scenarios where a set of redundant PWs are configured between Provider Edge (PE) nodes in Single-Segment Pseudowire (SS-PW) [RFC3985] applications, or between Terminating Provider Edge (T-PE) nodes in Multi-Segment Pseudowire (MS-PW) [RFC5659] applications.
[RFC6718]描述了伪线（PW）冗余的框架和要求，[RFC6870]为在单段伪线（SS-PW）[RFC3985]应用程序中的提供程序边缘（PE）节点之间或在终止提供程序边缘（T-PE）之间配置一组冗余PW的场景指定了PW冗余机制多段伪线（MS-PW）[RFC5659]应用中的节点。
In some MS-PW scenarios, there are benefits of providing PW redundancy on Switching Provider Edges (S-PEs), such as reducing the burden on the access T-PE nodes and enabling faster protection switching compared to the end-to-end MS-PW protection mechanisms.
在一些MS-PW场景中，在交换提供程序边缘（S-PE）上提供PW冗余有很多好处，例如，与端到端MS-PW保护机制相比，减少了接入T-PE节点的负担，实现了更快的保护切换。
This document describes some scenarios in which PW redundancy is provided on S-PEs and specifies the operations of the S-PEs. The S-PEs connect to the neighboring T-PEs or S-PEs with PW segments. For the S-PE that provides PW redundancy for an MS-PW, there is a single PW segment on one side, which is called the single-homed side, and there are multiple PW segments on the other side, which is called the multi-homed side. The scenario in which the S-PE has two multi-homed sides is out of scope. Signaling of the Preferential Forwarding status as defined in [RFC6870] and [RFC6478] is reused. This document does not require any change to the T-PEs of MS-PW.
本文件描述了在S-PEs上提供PW冗余的一些场景，并规定了S-PEs的操作。S-PEs通过PW段连接到相邻的T-PEs或S-PEs。对于为MS-PW提供PW冗余的S-PE，一侧有一个PW段，称为单驻留侧，另一侧有多个PW段，称为多驻留侧。S-PE有两个多宿端的场景超出范围。重复使用[RFC6870]和[RFC6478]中定义的优先转发状态的信令。本文件不要求对MS-PW的T-PEs进行任何更改。
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 [RFC2119].
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[RFC2119]中所述进行解释。
In some MS-PW deployment scenarios, there are benefits of providing PW redundancy on S-PEs. This section describes typical scenarios of PW redundancy on S-PE.
在一些MS-PW部署场景中，在S-PEs上提供PW冗余有很多好处。本节描述S-PE上PW冗余的典型场景。
+-----+ AC
+---+ +-----+ | | | +---+
| | | |------|T-PE2|-----| |
| | AC +-----+ | ..PW-Seg2.......| | |
| | | |....PW-Seg1..... | +-----+ | |
|CE1|-----|T-PE1|------|S-PE1| |CE2|
| | | | | . | +-----+ | |
| | +-----+ | ..PW-Seg3.......| | |
| | | |------|T-PE3|-----| |
+---+ +-----+ | | | +---+
+-----+ AC
+-----+ AC
+---+ +-----+ | | | +---+
| | | |------|T-PE2|-----| |
| | AC +-----+ | ..PW-Seg2.......| | |
| | | |....PW-Seg1..... | +-----+ | |
|CE1|-----|T-PE1|------|S-PE1| |CE2|
| | | | | . | +-----+ | |
| | +-----+ | ..PW-Seg3.......| | |
| | | |------|T-PE3|-----| |
+---+ +-----+ | | | +---+
+-----+ AC
Figure 1: MS-PW Redundancy on S-PE
图1:S-PE上的MS-PW冗余
As illustrated in Figure 1, Customer Edge (CE) node CE1 is connected to T-PE1 while CE2 is dual-homed to T-PE2 and T-PE3. T-PE1 is connected to S-PE1 only, and S-PE1 is connected to both T-PE2 and T-PE3. The MS-PW is switched on S-PE1, and PW segments PW-Seg2 and PW-Seg3 provide resiliency on S-PE1 for the failure of T-PE2, T-PE3, or the connected Attachment Circuits (ACs). PW-Seg2 is selected as the primary PW segment, and PW-Seg3 is the secondary PW segment.
如图1所示，客户边缘（CE）节点CE1连接到T-PE1，而CE2双宿到T-PE2和T-PE3。T-PE1仅连接到S-PE1，S-PE1同时连接到T-PE2和T-PE3。MS-PW在S-PE1上切换，PW段PW-Seg2和PW-Seg3在T-PE2、T-PE3或连接的连接电路（ACs）故障时在S-PE1上提供弹性。主PW段选择PW-Seg2，次PW段选择PW-Seg3。
MS-PW redundancy on S-PE is beneficial for the scenario in Figure 1 since T-PE1 as an access node may not support PW redundancy. Besides, with PW redundancy on S-PE, the number of PW segments required between T-PE1 and S-PE1 is only half of the number of PW segments needed when end-to-end MS-PW redundancy is used. In addition, in this scenario, PW redundancy on S-PE could provide faster protection switching, compared with end-to-end protection switching of MS-PW.
S-PE上的MS-PW冗余有利于图1中的场景，因为T-PE1作为接入节点可能不支持PW冗余。此外，对于S-PE上的PW冗余，T-PE1和S-PE1之间所需的PW段数量仅为使用端到端MS-PW冗余时所需PW段数量的一半。此外，在这种情况下，与MS-PW的端到端保护切换相比，S-PE上的PW冗余可以提供更快的保护切换。
+---+ +-----+ +-----+ +-----+
| | | | | | | |
| | AC |......PW1-Seg1......PW1-Seg2........|
| | | | . | | . | | |
|CE1|-----|T-PE1|------|S-PE1|-----------|T-PE2| AC
| | | . | | . | PW1-Seg3 | | | +---+
| | | . | | ......... ......|-----| |
| | | . | | | . .| | | |
+---+ +---.-+ +-----+ . . +-----+ | |
|. . . |CE2|
|. .. | |
|. +-----+ . . +-----+ | |
|. | | . .| |-----| |
|...PW2-Seg1.......... ......| | +---+
| | . | PW2-Seg2 | | AC
----------|S-PE2|-----------|T-PE3|
| . | | |
| .....PW2-Seg3........|
| | | |
+-----+ +-----+
+---+ +-----+ +-----+ +-----+
| | | | | | | |
| | AC |......PW1-Seg1......PW1-Seg2........|
| | | | . | | . | | |
|CE1|-----|T-PE1|------|S-PE1|-----------|T-PE2| AC
| | | . | | . | PW1-Seg3 | | | +---+
| | | . | | ......... ......|-----| |
| | | . | | | . .| | | |
+---+ +---.-+ +-----+ . . +-----+ | |
|. . . |CE2|
|. .. | |
|. +-----+ . . +-----+ | |
|. | | . .| |-----| |
|...PW2-Seg1.......... ......| | +---+
| | . | PW2-Seg2 | | AC
----------|S-PE2|-----------|T-PE3|
| . | | |
| .....PW2-Seg3........|
| | | |
+-----+ +-----+
Figure 2: MS-PW Redundancy on S-PE with S-PE Protection
图2：带S-PE保护的S-PE上的MS-PW冗余
As illustrated in Figure 2, CE1 is connected to T-PE1 while CE2 is dual-homed to T-PE2 and T-PE3. T-PE1 is connected to both S-PE1 and S-PE2, and both S-PE1 and S-PE2 are connected to both T-PE2 and T-PE3. There are two MS-PWs that are switched at S-PE1 and S-PE2, respectively, to provide S-PE node protection. For PW1, S-PE1 provides resiliency using PW1-Seg2 and PW1-Seg3. For PW2, S-PE2 provides resiliency using PW2-Seg2 and PW2-Seg3. PW1 is the primary MS-PW, and PW1-Seg2 between S-PE1 and T-PE2 is the primary PW segment. PW2 is the secondary MS-PW.
如图2所示，CE1与T-PE1相连，而CE2与T-PE2和T-PE3相连。T-PE1连接到S-PE1和S-PE2，S-PE1和S-PE2都连接到T-PE2和T-PE3。有两个MS PW分别在S-PE1和S-PE2处切换，以提供S-PE节点保护。对于PW1，S-PE1使用PW1-Seg2和PW1-Seg3提供弹性。对于PW2，S-PE2使用PW2-Seg2和PW2-Seg3提供弹性。PW1为主要MS-PW，S-PE1和T-PE2之间的PW1-Seg2为主要PW段。PW2是次级MS-PW。
MS-PW redundancy on S-PE is beneficial for this scenario because it reduces the number of end-to-end MS-PWs required for both T-PE and S-PE protection. In addition, PW redundancy on S-PE could provide faster protection switching, compared with end-to-end protection switching of MS-PW.
S-PE上的MS-PW冗余有利于这种情况，因为它减少了T-PE和S-PE保护所需的端到端MS-PW的数量。此外，与MS-PW的端到端保护切换相比，S-PE上的PW冗余可以提供更快的保护切换。
For an S-PE that provides PW redundancy for MS-PW, it is important to advertise the proper preferential forwarding status to the PW segments on both sides and perform protection switching according to the received status information. Note that when PW redundancy for MS-PW is provided on S-PE, the optional S-PE Bypass mode as defined
对于为MS-PW提供PW冗余的S-PE，重要的是向两侧的PW段通告适当的优先转发状态，并根据接收到的状态信息执行保护切换。注意，当MS-PW的PW冗余在S-PE上提供时，可选的S-PE旁路模式
in [RFC6478] MUST NOT be used; otherwise, the S-PE will not receive the PW status messages originated by T-PEs. This section specifies the operations of S-PEs on which PW redundancy is provisioned. This section does not make any change to the T-PEs of MS-PW.
在[RFC6478]中不得使用；否则，S-PE将不会接收由T-PE发出的PW状态消息。本节规定了提供PW冗余的S-PE的操作。本节未对MS-PW的T-PEs进行任何更改。
The S-PEs connect to the neighboring T-PEs or other S-PEs on two sides with PW segments. For the S-PE that provides PW redundancy for an MS-PW, on one side there is a single PW segment, which is called the single-homed side, and on the other side there are multiple PW segments, which is called the multi-homed side. The scenario in which the S-PE has two multi-homed sides is out of scope.
S-PEs通过PW段连接到相邻的T-PEs或两侧的其他S-PEs。对于为MS-PW提供PW冗余的S-PE，一侧有一个PW段，称为单驻留侧，另一侧有多个PW段，称为多驻留侧。S-PE有两个多宿端的场景超出范围。
The S-PE that provides PW redundancy MUST work in Slave mode for the single-homed side, and MUST work in Independent mode for the multi-homed side. Consequently, the T-PE on the single-homed side MUST work in the Master mode, and the T-PEs on the multi-homed side MUST work in the Independent mode. The signaling of the Preferential Forwarding bit as defined in [RFC6870] and [RFC6478] is reused.
提供PW冗余的S-PE必须在单宿端的从属模式下工作，在多宿端的独立模式下工作。因此，单宿侧的T-PE必须在主模式下工作，而多宿侧的T-PE必须在独立模式下工作。重复使用[RFC6870]和[RFC6478]中定义的优先转发位的信令。
The S-PE MUST pass the Preferential Forwarding status received from the single-homed side unchanged to all the PW segments on the multi-homed side. The S-PE MUST advertise the Standby Preferential Forwarding status to the single-homed side if it receives Standby status from all the PW segments on the multi-homed side, and it MUST advertise the Active Preferential Forwarding status to the single-homed side if it receives Active status from any of the PW segments on the multi-homed side. For the single-homed side, the active PW segment is determined by the T-PE on this side, which works in the Master mode. On the multi-homed side, since both the S-PE and T-PEs work in the Independent mode, the PW segment which has both the local and remote Up/Down status as Up and both the local and remote Preferential Forwarding status as Active MUST be selected for traffic forwarding. When a switchover happens on the S-PE, if the S-PE supports the SP-PE TLV processing as defined in [RFC6073], it SHOULD advertise the updated SP-PE TLVs by sending a Label Mapping message to the T-PEs.
S-PE必须将从单宿侧接收到的优先转发状态不变地传递给多宿侧的所有PW段。如果S-PE从多宿侧的所有PW段接收到待机状态，则必须向单宿侧播发待机优先转发状态；如果S-PE从多宿侧的任何PW段接收到活动状态，则必须向单宿侧播发活动优先转发状态。对于单宿侧，活动PW段由该侧的T-PE确定，其在主模式下工作。在多宿端，由于S-PE和T-PE均在独立模式下工作，因此必须选择本地和远程向上/向下状态均为向上且本地和远程优先转发状态均为活动的PW段进行流量转发。当S-PE上发生切换时，如果S-PE支持[RFC6073]中定义的SP-PE TLV处理，则应通过向T-PE发送标签映射消息来公布更新的SP-PE TLV。
For the scenario in Figure 1, assume the AC from CE2 to T-PE2 is active. In normal operation, S-PE1 would receive the Active Preferential Forwarding status bit on the single-homed side from T-PE1, then it would advertise the Active Preferential Forwarding status bit on both PW-Seg2 and PW-Seg3. T-PE2 and T-PE3 would advertise the Active and Standby Preferential Forwarding status bit to S-PE1, respectively, reflecting the forwarding state of the two
对于图1中的场景，假设从CE2到T-PE2的AC处于活动状态。在正常操作中，S-PE1将从T-PE1接收单宿侧的活动优先转发状态位，然后在PW-Seg2和PW-Seg3上公布活动优先转发状态位。T-PE2和T-PE3将分别向S-PE1通告活动和备用优先转发状态位，反映这两个位置的转发状态
ACs connected to CE2. By matching the local and remote Up/Down status and Preferential Forwarding status, PW-Seg2 would be used for traffic forwarding.
ACs连接到CE2。通过匹配本地和远程上/下状态和优先转发状态，PW-Seg2将用于流量转发。
On failure of the AC between CE2 and T-PE2, the forwarding state of AC on T-PE3 is changed to Active. T-PE3 then advertises the Active Preferential Forwarding status to S-PE1, and T-PE2 would advertise a PW status Notification message to S-PE1, indicating that the AC between CE2 and T-PE2 is down. S-PE1 would perform the switchover according to the updated local and remote Preferential Forwarding status and the status of "Pseudowire forwarding", and select PW-Seg3 as the new PW segment for traffic forwarding. Since S-PE1 still connects to an Active PW segment on the multi-homed side, it will not advertise any change of the PW status to T-PE1. If S-PE1 supports the SP-PE TLV processing as defined in [RFC6073], it would advertise the updated SP-PE TLVs by sending a Label Mapping message to T-PE1.
当CE2和T-PE2之间的AC发生故障时，T-PE3上AC的转发状态变为激活。然后，T-PE3向S-PE1播发活动优先转发状态，T-PE2将向S-PE1播发PW状态通知消息，指示CE2和T-PE2之间的AC下降。S-PE1将根据更新后的本地和远程优先转发状态以及“伪线转发”状态进行切换，并选择PW-Seg3作为新的PW段进行业务转发。由于S-PE1仍连接到多宿侧的活动PW段，因此不会向T-PE1公布PW状态的任何更改。如果S-PE1支持[RFC6073]中定义的SP-PE TLV处理，它将通过向T-PE1发送标签映射消息来公布更新的SP-PE TLV。
For the scenario of Figure 2, assume the AC from CE2 to T-PE2 is active. T-PE1 works in Master mode and it would advertise the Active and Standby Preferential Forwarding status bit to S-PE1 and S-PE2 respectively according to configuration. According to the received Preferential Forwarding status bit, S-PE1 would advertise the Active Preferential Forwarding status bit to both T-PE2 and T-PE3, and S-PE2 would advertise the Standby Preferential Forwarding status bit to both T-PE2 and T-PE3. T-PE2 would advertise the Active Preferential Forwarding status bit to both S-PE1 and S-PE2, and T-PE3 would advertise the Standby Preferential Forwarding status bit to both S-PE1 and S-PE2, reflecting the forwarding state of the two ACs connected to CE2. By matching the local and remote Up/Down Status and Preferential Forwarding status, PW1-Seg2 from S-PE1 to T-PE2 would be used for traffic forwarding. Since S-PE1 connects to the Active PW segment on the multi-homed side, it would advertise the Active Preferential Forwarding status bit to T-PE1, and S-PE2 would advertise the Standby Preferential Forwarding status bit to T-PE1 because it does not have any Active PW segment on the multi-homed side.
对于图2的场景，假设从CE2到T-PE2的AC处于活动状态。T-PE1工作在主模式，根据配置分别向S-PE1和S-PE2播发主备优先转发状态位。根据接收到的优先转发状态位，S-PE1将向T-PE2和T-PE3播发活动优先转发状态位，S-PE2将向T-PE2和T-PE3播发备用优先转发状态位。T-PE2将向S-PE1和S-PE2播发活动优先转发状态位，T-PE3将向S-PE1和S-PE2播发备用优先转发状态位，反映连接到CE2的两个ACs的转发状态。通过匹配本地和远程上/下状态以及优先转发状态，将使用从S-PE1到T-PE2的PW1-Seg2进行流量转发。由于S-PE1连接到多宿侧的活动PW段，它将向T-PE1播发活动优先转发状态位，而S-PE2将向T-PE1播发备用优先转发状态位，因为它在多宿侧没有任何活动PW段。
On failure of the AC between CE2 and T-PE2, the forwarding state of AC on T-PE3 is changed to Active. T-PE3 would then advertise the Active Preferential Forwarding status bit to both S-PE1 and S-PE2, and T-PE2 would advertise a PW status Notification message to both S-PE1 and S-PE2, indicating that the AC between CE2 and T-PE2 is down. S-PE1 would perform the switchover according to the updated local and remote Preferential Forwarding status and the status of "Pseudowire forwarding", and select PW1-Seg3 for traffic forwarding. Since S-PE1 still has an Active PW segment on the multi-homed side,
当CE2和T-PE2之间的AC发生故障时，T-PE3上AC的转发状态变为激活。然后，T-PE3将向S-PE1和S-PE2播发活动优先转发状态位，T-PE2将向S-PE1和S-PE2播发PW状态通知消息，指示CE2和T-PE2之间的AC下降。S-PE1将根据更新后的本地和远程优先转发状态以及“伪线转发”状态进行切换，并选择PW1-Seg3进行流量转发。由于S-PE1在多宿侧仍有一个活动PW段，
it would not advertise any change of the PW status to T-PE1. If S-PE1 supports the SP-PE TLV processing as defined in [RFC6073], it would advertise the updated SP-PE TLVs by sending a Label Mapping message to T-PE1.
它不会向T-PE1公布PW状态的任何变化。如果S-PE1支持[RFC6073]中定义的SP-PE TLV处理，它将通过向T-PE1发送标签映射消息来公布更新的SP-PE TLV。
If S-PE1 fails, T-PE1 would notice this through some detection mechanism and then advertise the Active Preferential Forwarding status bit to S-PE2, and PW2-Seg1 would be selected by T-PE1 for traffic forwarding. On receipt of the newly changed Preferential Forwarding status, S-PE2 would advertise the Active Preferential Forwarding status to both T-PE2 and T-PE3. T-PE2 and T-PE3 would also notice the failure of S-PE1 by some detection mechanism. Then by matching the local and remote Up/Down and Preferential Forwarding status, PW2-Seg2 would be selected for traffic forwarding.
如果S-PE1失败，T-PE1将通过某种检测机制注意到这一点，然后向S-PE2播发活动优先转发状态位，T-PE1将选择PW2-Seg1进行流量转发。在收到新更改的优先转发状态后，S-PE2将向T-PE2和T-PE3公布活动的优先转发状态。T-PE2和T-PE3也会通过某种检测机制注意到S-PE1的故障。然后通过匹配本地和远程上/下和优先转发状态，选择PW2-Seg2进行流量转发。
For PW Virtual Circuit Connectivity Verification (VCCV) [RFC5085], the Control Channel (CC) type 1 "PW ACH" can be used with the S-PE redundancy mechanism. VCCV CC type 2 "Router Alert Label" is not supported for MS-PW as specified in [RFC6073]. If VCCV CC type 3 "TTL Expiry" is to be used, the PW label TTL MUST be set to the appropriate value to reach the target PE. The hop count from one T-PE to the target PE can be obtained via SP-PE TLVs, through MS-PW path trace, or based on management-plane information.
对于PW虚拟电路连接验证（VCCV）[RFC5085]，类型1“PW ACH”的控制通道（CC）可与S-PE冗余机制一起使用。[RFC6073]中规定的MS-PW不支持VCCV CC类型2“路由器警报标签”。如果要使用VCCV CC类型3“TTL到期”，则必须将PW标签TTL设置为适当的值，以达到目标PE。从一个T-PE到目标PE的跳数可以通过SP-PE TLV、MS-PW路径跟踪或基于管理平面信息获得。
Since PW redundancy is provided on the S-PE nodes of MS-PWs, it is important that the security mechanisms as defined in [RFC4447], [RFC6073], and [RFC6478] be implemented to ensure that the S-PE nodes and the messages sent and received by the S-PE nodes are not compromised.
由于MS PWs的S-PE节点上提供了PW冗余，因此必须实施[RFC4447]、[RFC6073]和[RFC6478]中定义的安全机制，以确保S-PE节点以及S-PE节点发送和接收的消息不会受到损害。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，DOI 10.17487/RFC2119，1997年3月<http://www.rfc-editor.org/info/rfc2119>.
[RFC4447] 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, DOI 10.17487/RFC4447, April 2006, <http://www.rfc-editor.org/info/rfc4447>.
[RFC4447]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，DOI 10.17487/RFC4447，2006年4月<http://www.rfc-editor.org/info/rfc4447>.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, DOI 10.17487/RFC6073, January 2011, <http://www.rfc-editor.org/info/rfc6073>.
[RFC6073]Martini，L.，Metz，C.，Nadeau，T.，Bocci，M.和M.Aissaoui，“分段伪线”，RFC 6073，DOI 10.17487/RFC6073，2011年1月<http://www.rfc-editor.org/info/rfc6073>.
[RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci, "Pseudowire Status for Static Pseudowires", RFC 6478, DOI 10.17487/RFC6478, May 2012, <http://www.rfc-editor.org/info/rfc6478>.
[RFC6478]Martini，L.，Swallow，G.，Heron，G.，和M.Bocci，“静态伪线的伪线状态”，RFC 6478，DOI 10.17487/RFC6478，2012年5月<http://www.rfc-editor.org/info/rfc6478>.
[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>.
[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>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, December 2007, <http://www.rfc-editor.org/info/rfc5085>.
[RFC5085]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，DOI 10.17487/RFC5085，2007年12月<http://www.rfc-editor.org/info/rfc5085>.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, DOI 10.17487/RFC5659, October 2009, <http://www.rfc-editor.org/info/rfc5659>.
[RFC5659]Bocci，M.和S.Bryant，“多段伪线边到边仿真的体系结构”，RFC 5659，DOI 10.17487/RFC5659，2009年10月<http://www.rfc-editor.org/info/rfc5659>.
[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>.
Acknowledgements
致谢
The authors would like to thank Mach Chen, Lizhong Jin, Mustapha Aissaoui, Luca Martini, Matthew Bocci, and Stewart Bryant for their valuable comments and discussions.
作者要感谢Mach Chen、Lizhong Jin、Mustapha Aissaoui、Luca Martini、Matthew Bocci和Stewart Bryant的宝贵评论和讨论。
Authors' Addresses
作者地址
Jie Dong Huawei Technologies Huawei Building, No.156 Beiqing Rd. Beijing 100095 China
中国北京市北青路156号华为大厦华东华为技术有限公司100095
Email: jie.dong@huawei.com
Email: jie.dong@huawei.com
Haibo Wang Huawei Technologies Huawei Building, No.156 Beiqing Rd. Beijing 100095 China
中国北京市北青路156号华为大厦，邮编：100095
Email: rainsword.wang@huawei.com
Email: rainsword.wang@huawei.com