Internet Engineering Task Force (IETF) Y. Shen
Request for Comments: 8104 Juniper Networks
Category: Standards Track R. Aggarwal
ISSN: 2070-1721 Arktan, Inc.
W. Henderickx
Nokia
Y. Jiang
Huawei Technologies Co., Ltd.
March 2017
Internet Engineering Task Force (IETF) Y. Shen
Request for Comments: 8104 Juniper Networks
Category: Standards Track R. Aggarwal
ISSN: 2070-1721 Arktan, Inc.
W. Henderickx
Nokia
Y. Jiang
Huawei Technologies Co., Ltd.
March 2017
Pseudowire (PW) Endpoint Fast Failure Protection
伪线（PW）端点快速故障保护
Abstract
摘要
This document specifies a fast mechanism for protecting pseudowires (PWs) transported by IP/MPLS tunnels against egress endpoint failures, including egress attachment circuit (AC) failure, egress provider edge (PE) failure, multi-segment PW terminating PE failure, and multi-segment PW switching PE failure. Operating on the basis of multihomed customer edge (CE), redundant PWs, upstream label assignment, and context-specific label switching, the mechanism enables local repair to be performed by the router upstream adjacent to a failure. The router can restore a PW in the order of tens of milliseconds, by rerouting traffic around the failure to a protector through a pre-established bypass tunnel. Therefore, the mechanism can be used to reduce traffic loss before global repair reacts to the failure and the network converges on the topology changes due to the failure.
本文件规定了一种快速机制，用于保护IP/MPLS隧道传输的伪线（PW）免受出口端点故障的影响，包括出口连接电路（AC）故障、出口提供商边缘（PE）故障、多段PW端接PE故障和多段PW交换PE故障。该机制基于多宿客户边缘（CE）、冗余PWs、上游标签分配和特定于上下文的标签交换，使故障附近的路由器上游能够执行本地修复。路由器可以通过预先建立的旁路隧道将故障周围的流量重新路由到保护器，以数十毫秒的顺序恢复PW。因此，该机制可用于在全局修复对故障做出反应之前减少通信量损失，并使网络收敛于因故障而导致的拓扑变化。
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 7841.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 7841第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8104.
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/rfc8104.
Copyright Notice
版权公告
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2017 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (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
2. Specification of Requirements . . . . . . . . . . . . . . . . 5
3. Reference Models for Egress Endpoint Failures . . . . . . . . 5
3.1. Single-Segment PW . . . . . . . . . . . . . . . . . . . . 6
3.2. Multi-Segment PW . . . . . . . . . . . . . . . . . . . . 9
4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 10
4.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Local Repair . . . . . . . . . . . . . . . . . . . . . . 11
4.3. Context Identifier . . . . . . . . . . . . . . . . . . . 14
4.3.1. Semantics . . . . . . . . . . . . . . . . . . . . . . 15
4.3.2. FEC . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.3. IGP Advertisement and Path Computation . . . . . . . 16
4.4. Protection Models . . . . . . . . . . . . . . . . . . . . 17
4.4.1. Co-located Protector . . . . . . . . . . . . . . . . 17
4.4.2. Centralized Protector . . . . . . . . . . . . . . . . 19
4.5. Transport Tunnel . . . . . . . . . . . . . . . . . . . . 20
4.6. Bypass Tunnel . . . . . . . . . . . . . . . . . . . . . . 21
4.7. Examples of Forwarding State . . . . . . . . . . . . . . 22
4.7.1. Co-located Protector Model . . . . . . . . . . . . . 22
4.7.2. Centralized Protector Model . . . . . . . . . . . . . 26
5. Restorative and Revertive Behaviors . . . . . . . . . . . . . 29
6. LDP Extensions . . . . . . . . . . . . . . . . . . . . . . . 30
6.1. Egress Protection Capability TLV . . . . . . . . . . . . 31
6.2. PW Label Distribution from Primary PE to Protector . . . 32
6.3. PW Label Distribution from Backup PE to Protector . . . . 33
6.4. Protection FEC Element TLV . . . . . . . . . . . . . . . 34
6.4.1. Encoding Format for PWid with IPv4 PE Addresses . . . 35
6.4.2. Encoding Format for Generalized PWid with IPv4 PE
Addresses . . . . . . . . . . . . . . . . . . . . . . 36
6.4.3. Encoding Format for PWid with IPv6 PE Addresses . . . 37
6.4.4. Encoding Format for Generalized PWid with IPv6 PE
Addresses . . . . . . . . . . . . . . . . . . . . . . 38
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
8. Security Considerations . . . . . . . . . . . . . . . . . . . 40
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.1. Normative References . . . . . . . . . . . . . . . . . . 40
9.2. Informative References . . . . . . . . . . . . . . . . . 41
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Specification of Requirements . . . . . . . . . . . . . . . . 5
3. Reference Models for Egress Endpoint Failures . . . . . . . . 5
3.1. Single-Segment PW . . . . . . . . . . . . . . . . . . . . 6
3.2. Multi-Segment PW . . . . . . . . . . . . . . . . . . . . 9
4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 10
4.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Local Repair . . . . . . . . . . . . . . . . . . . . . . 11
4.3. Context Identifier . . . . . . . . . . . . . . . . . . . 14
4.3.1. Semantics . . . . . . . . . . . . . . . . . . . . . . 15
4.3.2. FEC . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.3. IGP Advertisement and Path Computation . . . . . . . 16
4.4. Protection Models . . . . . . . . . . . . . . . . . . . . 17
4.4.1. Co-located Protector . . . . . . . . . . . . . . . . 17
4.4.2. Centralized Protector . . . . . . . . . . . . . . . . 19
4.5. Transport Tunnel . . . . . . . . . . . . . . . . . . . . 20
4.6. Bypass Tunnel . . . . . . . . . . . . . . . . . . . . . . 21
4.7. Examples of Forwarding State . . . . . . . . . . . . . . 22
4.7.1. Co-located Protector Model . . . . . . . . . . . . . 22
4.7.2. Centralized Protector Model . . . . . . . . . . . . . 26
5. Restorative and Revertive Behaviors . . . . . . . . . . . . . 29
6. LDP Extensions . . . . . . . . . . . . . . . . . . . . . . . 30
6.1. Egress Protection Capability TLV . . . . . . . . . . . . 31
6.2. PW Label Distribution from Primary PE to Protector . . . 32
6.3. PW Label Distribution from Backup PE to Protector . . . . 33
6.4. Protection FEC Element TLV . . . . . . . . . . . . . . . 34
6.4.1. Encoding Format for PWid with IPv4 PE Addresses . . . 35
6.4.2. Encoding Format for Generalized PWid with IPv4 PE
Addresses . . . . . . . . . . . . . . . . . . . . . . 36
6.4.3. Encoding Format for PWid with IPv6 PE Addresses . . . 37
6.4.4. Encoding Format for Generalized PWid with IPv6 PE
Addresses . . . . . . . . . . . . . . . . . . . . . . 38
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
8. Security Considerations . . . . . . . . . . . . . . . . . . . 40
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.1. Normative References . . . . . . . . . . . . . . . . . . 40
9.2. Informative References . . . . . . . . . . . . . . . . . 41
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
Per [RFC3985], [RFC8077], and [RFC5659], a pseudowire (PW) or PW segment can be thought of as a connection between a pair of forwarders hosted by two PEs, carrying an emulated Layer 2 service over a packet switched network (PSN). In the single-segment PW (SS-PW) case, a forwarder binds a PW to an attachment circuit (AC). In the multi-segment PW (MS-PW) case, a forwarder on a terminating PE (T-PE) binds a PW segment to an AC, while a forwarder on a switching PE (S-PE) binds one PW segment to another PW segment. In each direction between the PEs, PW packets are transported by a PSN tunnel, which is also called a transport tunnel.
根据[RFC3985]、[RFC8077]和[RFC5659]，可以将伪线（PW）或PW段视为由两个PE承载的一对转发器之间的连接，通过分组交换网络（PSN）承载模拟的第2层服务。在单段PW（SS-PW）情况下，转发器将PW绑定到连接电路（AC）。在多段PW（MS-PW）情况下，终端PE（T-PE）上的转发器将PW段绑定到AC，而交换PE（S-PE）上的转发器将一个PW段绑定到另一个PW段。在PEs之间的每个方向上，PW分组由PSN隧道传输，该隧道也称为传输隧道。
In order to protect the PW service against network failures, it is necessary to protect every link and node along the entire data path. For the traffic in a given direction, this includes ingress AC, ingress (T-)PE, intermediate routers of the transport tunnel, S-PEs, egress (T-)PE, and egress AC. To minimize service disruption upon a failure, it is also desirable that each of these components is protected by a fast protection mechanism based on local repair. Such mechanisms generally involve a bypass path that is pre-computed and pre-installed in the data plane on the router upstream adjacent to an anticipated failure. This router is referred to as a "point of local repair" (PLR). The bypass path has the property that it can guide traffic around the failure, while remaining unaffected by the topology changes resulting from the failure. When the failure occurs, the PLR can invoke the bypass path to achieve fast restoration for the service.
为了保护PW服务不受网络故障的影响，有必要保护整个数据路径上的每个链路和节点。对于给定方向上的业务，这包括入口AC、入口（T-）PE、传输隧道的中间路由器、S-PE、出口（T-）PE和出口AC。为了最大限度地减少故障时的服务中断，还希望这些组件中的每一个都由基于本地修复的快速保护机制进行保护。这种机制通常涉及一个旁路路径，该旁路路径预先计算并预先安装在路由器上游靠近预期故障的数据平面上。该路由器被称为“本地维修点”（PLR）。旁路路径的特性是，它可以引导故障周围的通信量，同时不受故障导致的拓扑更改的影响。当故障发生时，PLR可以调用旁路路径来实现服务的快速恢复。
Today, fast protection against ingress AC failure and ingress (T-)PE failure can be achieved by using a multihomed CE and redundant ACs, such as a multi-chassis link aggregation group (MC-LAG). Fast protection against the failure of an intermediate router of the transport tunnel can be achieved through RSVP fast reroute [RFC4090] or IP/LDP fast reroute [RFC5286] [RFC5714]. However, there is no equivalent mechanism that can be used against an egress AC failure, an egress (T-)PE failure, or an S-PE failure. For these failures, service restoration has to rely on global repair or control-plane convergence. Global repair normally involves the ingress CE or the ingress (T-)PE switching traffic to an alternative path, based on remote failure detection via PW status notification, end-to-end Operations, Administration, and Maintenance (OAM), and others. Control-plane convergence relies on control protocols to react on the topology changes due to a failure. Compared to local repair, these mechanisms are relatively slow in reacting to a failure and restoring traffic.
如今，可以通过使用多宿CE和冗余ACs（如多机箱链路聚合组（MC-LAG））实现针对入口AC故障和入口（T-）PE故障的快速保护。可通过RSVP快速重路由[RFC4090]或IP/LDP快速重路由[RFC5286][RFC5714]实现针对传输隧道中间路由器故障的快速保护。然而，没有可用于防止出口AC故障、出口（T-）PE故障或S-PE故障的等效机制。对于这些故障，服务恢复必须依赖于全局修复或控制平面收敛。全局修复通常涉及入口CE或入口（T-）PE将流量切换到备用路径，基于通过PW状态通知、端到端操作、管理和维护（OAM）等进行的远程故障检测。控制平面收敛依赖于控制协议对故障引起的拓扑变化作出反应。与本地修复相比，这些机制在对故障作出反应和恢复流量方面相对较慢。
This document addresses the above need. It specifies a fast protection mechanism based on local repair to protect PWs against the following endpoint failures:
本文件解决了上述需要。它指定了一种基于本地修复的快速保护机制，以针对以下端点故障保护PWs：
a. Egress AC failure.
a. 出口交流故障。
b. Egress PE failure: Link or node failure of an egress PE of an SS-PW or a T-PE of an MS-PW.
b. 出口PE故障：SS-PW的出口PE或MS-PW的T-PE的链路或节点故障。
c. Switching PE failure: Link or node failure of an S-PE of an MS-PW.
c. 交换PE故障：MS-PW的S-PE链路或节点故障。
The mechanism is applicable to LDP-signaled PWs. It is relevant to networks with redundant PWs and multihomed CEs. It is designed on the basis of MPLS upstream label assignment and context-specific label switching [RFC5331]. Fast protection refers to its ability to restore traffic in the order of tens of milliseconds. Compared with global repair and control-plane convergence, this mechanism can provide faster service restoration. However, it is intended to complement these mechanisms, rather than replacing them, as networks rely on them to eventually move traffic to fully functional alternative paths.
该机制适用于LDP信号PWs。它与具有冗余PWs和多址CEs的网络相关。它基于MPLS上游标签分配和上下文特定标签交换[RFC5331]进行设计。快速保护是指它能够以数十毫秒的顺序恢复流量。与全局修复和控制平面收敛相比，该机制可以提供更快的服务恢复。然而，它的目的是补充这些机制，而不是取代它们，因为网络依赖它们最终将流量移动到功能齐全的备用路径。
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 [RFC2119].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[RFC2119]中所述进行解释。
This document refers to the following topologies to describe egress endpoint failures and protection procedures.
本文档引用以下拓扑来描述出口端点故障和保护程序。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 -------------- P1 ---------------- PE2 -
/ \
/ \
CE1 CE2
\ /
\ /
- PE3 -------------- P2 ---------------- PE4 -
- PE1 -------------- P1 ---------------- PE2 -
/ \
/ \
CE1 CE2
\ /
\ /
- PE3 -------------- P2 ---------------- PE4 -
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
Figure 1
图1
In Figure 1, the IP/MPLS network consists of PE and P routers. It provides a PW service between CE1 and CE2. Each CE is multihomed via two ACs to two PEs. This forms two divergent paths between the CEs. The first path uses PW1 between PE1 and PE2, and the second path uses PW2 between PE3 and PE4. For clarity, the transport tunnels of the PWs and other links between the routers are not shown in this figure.
在图1中，IP/MPLS网络由PE和P路由器组成。它在CE1和CE2之间提供PW服务。每个CE通过两个ACs到两个PE进行多址。这在CEs之间形成了两条不同的路径。第一条路径在PE1和PE2之间使用PW1，第二条路径在PE3和PE4之间使用PW2。为清楚起见，本图中未显示PWs的传输隧道和路由器之间的其他链路。
In general, a CE may operate the ACs in two modes when sending traffic to the remote CE, i.e., active-standby mode and active-active mode.
通常，当向远程CE发送通信量时，CE可以在两种模式下操作ACs，即，主备用模式和主-主模式。
o In the active-standby mode, the CE chooses one AC as the active AC and the corresponding path as the active path, and it uses the other AC as the standby AC and the corresponding path as the standby path. The CE only sends traffic on the active AC as long as the active path is operational. The CE will only send traffic on the standby AC after it detects a failure of the active path. Note that the CE may receive traffic on the active or standby AC, depending on whether the remote CE chooses the same active path for the traffic of the reverse direction. In this document, even if both CEs choose the same active path, each CE should still anticipate receiving traffic on a standby AC, because the traffic may be redirected to the standby path by the fast protection mechanism.
o 在主备模式下，CE选择一个AC作为主AC，相应路径作为主路径，并使用另一个AC作为备用AC，相应路径作为备用路径。只要活动路径可用，CE仅在活动AC上发送通信量。CE仅在检测到活动路径故障后在备用AC上发送通信量。注意，CE可以在主AC或备用AC上接收通信量，这取决于远程CE是否为反向通信量选择相同的活动路径。在本文档中，即使两个CE选择相同的活动路径，每个CE仍应预期在备用AC上接收通信量，因为通信量可通过快速保护机制重定向到备用路径。
o In the active-active mode, the CE treats both ACs and their corresponding paths as active and sends traffic on both ACs in a load-balancing fashion. In the reverse direction, the CE may receive traffic on both ACs.
o 在主动-主动模式下，CE将两个ACs及其对应路径视为主动，并以负载平衡方式在两个ACs上发送流量。在相反方向上，CE可以在两个ac上接收业务。
The above modes assume the traffic to be data traffic, which is not bound to a specific AC. This does not include control-protocol
上述模式假设流量为数据流量，不绑定到特定AC。这不包括控制协议
traffic between the CEs, when the CE-CE control-protocol sessions or adjacencies established on the two ACs are considered as distinct rather than having a primary and backup relationship. In general, a dual-homed CE should not make any explicit or implicit assumptions regarding the specific AC from which it receives packets from the remote CE.
当在两个ACs上建立的CE-CE控制协议会话或邻接被认为是不同的而不是具有主和备份关系时，CEs之间的通信量。通常，双宿CE不应就其从远程CE接收数据包的特定AC做出任何明确或隐含的假设。
For either mode, when considering the traffic flowing in a given direction over an active path, this document views the ACs, PEs, and PWs as serving primary or backup roles. In particular, the ACs, PEs, and PWs along this active path have primary roles, while those along the other path have backup roles. Note that in the active-active mode, each AC, PE, and PW on an active path has a primary role and also a backup role protecting the other path, which is also active.
对于任一模式，当考虑在活动路径上沿给定方向流动的流量时，本文档将ACs、PEs和PWs视为主要或备用角色。特别是，此活动路径上的ACs、PEs和PW具有主要角色，而其他路径上的ACs、PEs和PW具有备份角色。请注意，在主动-主动模式下，主动路径上的每个AC、PE和PW都有一个主角色和一个备份角色，用于保护另一条同样处于活动状态的路径。
For Figure 1, the following roles are assumed for the traffic going from CE1 to CE2 via PW1.
对于图1，对于通过PW1从CE1到CE2的流量，假设以下角色。
Primary ingress AC: CE1-PE1
主入口AC:CE1-PE1
Primary ingress PE: PE1
主入口PE:PE1
Primary PW: PW1
初级PW:PW1
Primary egress PE: PE2
一次出口PE:PE2
Primary egress AC: PE2-CE2
一次出口AC:PE2-CE2
Backup ingress AC: CE1-PE3
备用入口AC:CE1-PE3
Backup ingress PE: PE3
备份入口PE:PE3
Backup PW: PW2
备份PW:PW2
Backup egress PE: PE4
备用出口PE:PE4
Backup egress AC: PE4-CE2
备用出口AC:PE4-CE2
Based on this schema, this document describes egress endpoint failures and the fast protection mechanism on the per-active-path and per-direction basis. In this case, an egress AC failure refers to the failure of the AC PE2-CE2, and an egress node failure refers to the failure of PE2. The ultimate goal is that when a failure occurs, the traffic should be locally repaired, so that it can eventually reach CE2 via the backup egress PE (PE4) and the backup egress AC (PE4-CE2).
基于此模式，本文描述了每活动路径和每方向上的出口端点故障和快速保护机制。在这种情况下，出口AC故障指的是AC PE2-CE2的故障，出口节点故障指的是PE2的故障。最终目标是，当发生故障时，应在本地修复通信量，以便最终通过备用出口PE（PE4）和备用出口AC（PE4-CE2）到达CE2。
Subsequent to the local repair, either the current active path should heal after the control plane converges on the new topology or the ingress CE should switch traffic from the primary path to the backup path, depending on the failure scenario. In the latter case, the ingress CE may perform the path switchover triggered by end-to-end OAM (in-band or out-band), PW status notification, CE-PE control protocols (e.g., the Link Aggregation Control Protocol (LACP)), and others. In the active-standby mode, this will promote the standby path to a new active path. In the active-active mode, it will make the other active path carry all the traffic between the two CEs. In any case, this phase of restoration falls into the control-plane convergence and global repair category; hence, it is out of the scope of this document. The purpose of the fast protection mechanism in this document is to reduce traffic loss before this phase of restoration takes place.
在本地修复之后，当前活动路径应在控制平面会聚到新拓扑上后恢复，或者入口CE应根据故障场景将流量从主路径切换到备份路径。在后一种情况下，入口CE可以执行由端到端OAM（带内或带外）、PW状态通知、CE-PE控制协议（例如，链路聚合控制协议（LACP））等触发的路径切换。在主动待机模式下，这将使待机路径升级为新的主动路径。在主动模式下，它将使另一条主动路径承载两个CE之间的所有流量。在任何情况下，此恢复阶段都属于控制平面收敛和全局修复类别；因此，它不在本文件的范围内。本文件中快速保护机制的目的是在该恢复阶段发生之前减少交通损失。
Note that in Figure 1, if the traffic in the reverse direction (i.e., from CE2 to CE1) traverses the AC CE2-PE2 and PE2 as an active path, the failure of PE2 and the failure of the AC PE2-CE2 will be considered as ingress failures of the traffic. If CE2 can detect the failures, it may protect the traffic by switching it to the backup path via the AC CE2-PE4 and PE4. However, this is categorized as ingress endpoint failure protection; hence, it is not handled by the mechanism described in this document.
注意，在图1中，如果反向（即从CE2到CE1）的流量作为活动路径穿过AC CE2-PE2和PE2，则PE2的故障和AC PE2-CE2的故障将被视为流量的进入故障。如果CE2能够检测到故障，它可以通过AC CE2-PE4和PE4将流量切换到备份路径来保护流量。然而，这被归类为入口端点故障保护；因此，本文件中描述的机制无法处理该问题。
Figure 2 shows another possible scenario, where CE1 is single-homed to PE1, while CE2 remains multihomed to PE2 and PE4. From the perspective of egress endpoint protection for the traffic going from CE1 to CE2 over PW1, this scenario is the same as the scenario shown in Figure 1.
图2显示了另一种可能的场景，其中CE1是单宿PE1，而CE2仍然是多宿PE2和PE4。从通过PW1从CE1到CE2的流量的出口端点保护的角度来看，该场景与图1所示的场景相同。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
------------- P1 ---------------- PE2 -
/ \
/ \
CE1 -- PE1 CE2
\ /
\ /
------------- P2 ---------------- PE4 -
------------- P1 ---------------- PE2 -
/ \
/ \
CE1 -- PE1 CE2
\ /
\ /
------------- P2 ---------------- PE4 -
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
Figure 2
图2
For clarity, primary egress AC, primary egress PE, backup egress AC, and backup egress PE may simply be referred to as primary AC, primary PE, backup AC, and backup PE, respectively, when the context of a discussion is egress endpoint.
为清楚起见，当讨论的上下文是出口端点时，主出口AC、主出口PE、备份出口AC和备份出口PE可以分别简单地称为主AC、主PE、备份AC和备份PE。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 -------------- SPE1 --------------- TPE2 -
/ \
/ \
CE1 CE2
\ /
\ /
- TPE3 -------------- SPE2 --------------- TPE4 -
- TPE1 -------------- SPE1 --------------- TPE2 -
/ \
/ \
CE1 CE2
\ /
\ /
- TPE3 -------------- SPE2 --------------- TPE4 -
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
Figure 3
图3
Figure 3 shows a topology that is similar to Figure 1 but in an MS-PW environment. PW1 and PW2 are both MS-PWs. PW1 is established between TPE1 and TPE2 and switched between segments SEG1 and SEG2 at SPE1. PW2 is established between TPE3 and TPE4 and switched between segments SEG3 and SEG4 at SPE2. CE1 is multihomed to TPE1 and TPE3. CE2 is multihomed to TPE2 and TPE4. For clarity, the transport tunnels of the PW segments are not shown in this figure.
图3显示了一个与图1相似但在MS-PW环境中的拓扑。PW1和PW2都是MS PWs。PW1在TPE1和TPE2之间建立，并在SPE1的SEG1段和SEG2段之间切换。PW2在TPE3和TPE4之间建立，并在SPE2的SEG3段和SEG4段之间切换。CE1多宿于TPE1和TPE3。CE2多宿于TPE2和TPE4。为清楚起见，本图未显示PW段的运输隧道。
In this document, the following primary and backup roles are assigned for the traffic going from CE1 to CE2:
在本文档中，为从CE1到CE2的流量分配了以下主要角色和备份角色：
Primary ingress AC: CE1-TPE1
主入口AC:CE1-TPE1
Primary ingress T-PE: TPE1
主入口T-PE:TPE1
Primary PW: PW1
初级PW:PW1
Primary S-PE: SPE1
初级S-PE:SPE1
Primary egress T-PE: TPE2
一次出口T-PE:TPE2
Primary egress AC: TPE2-CE2
主出口AC:TPE2-CE2
Backup ingress AC: CE1-TPE3
备份入口AC:CE1-TPE3
Backup ingress T-PE: TPE3
备份入口T-PE:TPE3
Backup PW: PW2
备份PW:PW2
Backup S-PE: SPE2
备份S-PE:SPE2
Backup egress T-PE: TPE4
备用出口T-PE:TPE4
Backup egress AC: TPE4-CE2
备用出口AC:TPE4-CE2
In this case, an egress AC failure refers to the failure of the AC TPE2-CE2. An egress node failure refers to the failure of TPE2. An S-PE failure refers to the failure of SPE1.
在这种情况下，出口AC故障指AC TPE2-CE2的故障。出口节点故障是指TPE2的故障。S-PE故障是指SPE1的故障。
For consistency with the SS-PW scenario, primary T-PEs and primary S-PEs may simply be referred to as primary PEs in this document, where specifics are not required. Similarly, backup T-PEs and backup S-PEs may be referred to as backup PEs.
为了与SS-PW方案保持一致，本文件中的主要T-PE和主要S-PE可简称为主要PE，无需具体说明。类似地，备用T-PE和备用S-PE可称为备用PE。
The fast protection mechanism in this document provides three types of protection for PWs, corresponding to the three types of failures described in Section 1:
本文件中的快速保护机制为PWs提供了三种类型的保护，对应于第1节中描述的三种类型的故障：
a. Egress AC protection
a. 出口交流保护
b. Egress (T-)PE node protection
b. 出口（T-）PE节点保护
c. S-PE node protection
c. S-PE节点保护
The mechanism is applicable to LDP-signaled PWs in an environment where an egress CE is multihomed to a primary PE and a backup PE and there exists a backup PW, as described in Section 3. The procedure for S-PE node protection is applicable when there exists a backup S-PE on the backup PW.
如第3节所述，该机制适用于出口与主PE和备份PE多址且存在备份PW的环境中的LDP信号PW。当备份PW上存在备份S-PE时，S-PE节点保护程序适用。
The mechanism assumes IP/MPLS transport tunnels and is applicable to tunnels with single path and equal-cost multipaths (ECMPs). As an example of ECMPs, imagine a tunnel carrying one or multiple PWs and traversing a router with ECMPs to a primary PE. The ECMPs consist of at least one direct link to the PE and some multi-hop paths to the PE. Due to the direct link, the router is considered as a penultimate hop of the tunnel and can perform local detection and repair for an egress node failure. The router normally uses a hashing algorithm to distribute PW packets over the ECMPs, on a
该机制假设IP/MPLS传输隧道，适用于具有单路径和等成本多路径（ECMPs）的隧道。作为ECMPs的一个示例，想象一个隧道承载一个或多个PW，并使用ECMPs穿过路由器到达主PE。ECMPs包括至少一条到PE的直接链路和一些到PE的多跳路径。由于直接链路，路由器被视为隧道的倒数第二跳，可以对出口节点故障执行本地检测和修复。路由器通常使用散列算法将PW数据包分发到ECMPs上，以
per-PW or per-flow basis. Upon a failure of the direct link, i.e., transit link failure, the router removes the link from the hashing algorithm, which automatically redistributes the traffic of the link to the other paths of the ECMPs, achieving local repair. This scenario is not the focus of this document. Upon a failure of the PE, i.e., egress node failure, the router SHOULD perform local repair by rerouting the entire traffic of the ECMPs, as the failure will affect every path. If the router does not have a fast or reliable mechanism to detect the egress node failure, it is RECOMMENDED that the router SHOULD treat the failure of the direct link as an egress node failure.
每PW或每流量基础。当直接链路发生故障，即传输链路故障时，路由器从散列算法中删除链路，散列算法自动将链路流量重新分配到ECMP的其他路径，从而实现本地修复。此场景不是本文档的重点。当PE发生故障，即出口节点故障时，路由器应通过重新路由ECMP的整个流量来执行本地修复，因为故障将影响每条路径。如果路由器没有快速或可靠的机制来检测出口节点故障，建议路由器将直接链路故障视为出口节点故障。
The mechanism is applicable to both best-effort and traffic engineering (TE) transport tunnels. For TE transport tunnels that require bandwidth protection, TE bypass tunnels with reserved bandwidth MAY be used to avoid congestion for rerouted traffic.
该机制适用于尽力而为和交通工程（TE）运输隧道。对于需要带宽保护的TE传输隧道，可以使用具有保留带宽的TE旁路隧道来避免重路由流量的拥塞。
It is also RECOMMENDED that the mechanism SHOULD be used in conjunction with global repair and control-plane convergence, in such a manner that the mechanism temporarily repairs a failed path by using a bypass tunnel, and global repair and control-plane convergence eventually move traffic to a fully functional alternative path.
还建议该机制应与全局维修和控制平面会聚一起使用，以便该机制通过使用旁通隧道临时维修故障路径，并且全局维修和控制平面会聚最终将交通转移到功能齐全的备用路径。
The fast protection ability of the mechanism comes from local repair performed by routers upstream adjacent to failures. Each of these routers is referred to as a PLR. A PLR MUST be able to detect a failure by using a rapid mechanism, such as physical-layer failure detection, Bidirectional Forwarding Detection (BFD) [RFC5880], Seamless BFD (S-BFD) [RFC7880], and others. In anticipation of the failure, the PLR MUST also pre-establish a bypass tunnel to a "protector" and pre-install a bypass route for the bypass tunnel in the data plane. The protector is either a backup PE or a router that will forward traffic to a backup PE. The bypass tunnel MUST have the property that it will not be affected by the topology changes due to the failure. Specifically, it MUST NOT traverse the primary PE or the penultimate link of the protected transport tunnel or share any shared risk link groups (SRLGs) with the penultimate link. Upon detecting the failure, the PLR invokes the bypass route in the data plane and reroutes PW traffic to the protector through the bypass tunnel. The protector in turn sends the traffic to the target CE. This procedure is referred to as local repair.
该机制的快速保护能力来自于邻近故障的路由器上游执行的本地修复。这些路由器中的每一个都称为PLR。PLR必须能够通过使用快速机制检测故障，如物理层故障检测、双向转发检测（BFD）[RFC5880]、无缝BFD（S-BFD）[RFC7880]等。在预期故障的情况下，PLR还必须预先建立到“保护器”的旁通隧道，并在数据平面中预先安装旁通隧道的旁通路由。保护器是备份PE或将流量转发到备份PE的路由器。旁路隧道必须具有这样的属性，即它不会因故障而受到拓扑更改的影响。具体而言，不得穿过受保护运输隧道的主要PE或倒数第二条链路，或与倒数第二条链路共享任何共享风险链路组（SRLGs）。在检测到故障后，PLR调用数据平面中的旁路路由，并通过旁路隧道将PW流量重新路由到保护器。保护器依次向目标CE发送通信量。此程序称为局部维修。
Different routers may serve as PLR and protector in different scenarios.
不同的路由器可以在不同的场景中充当PLR和保护器。
o In egress AC protection, the PLR is the primary PE, and the protector is the backup PE (Figure 4).
o 在出口交流保护中，PLR是主PE，保护器是备用PE（图4）。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 -------------- P1 ---------------- PE2 -
/ PLR \
/ | \
CE1 bypass| CE2
\ | /
\ | /
- PE3 -------------- P2 ---------------- PE4 -
protector
- PE1 -------------- P1 ---------------- PE2 -
/ PLR \
/ | \
CE1 bypass| CE2
\ | /
\ | /
- PE3 -------------- P2 ---------------- PE4 -
protector
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
Figure 4
图4
o In egress PE node protection, the PLR is the penultimate hop router of the transport tunnel of the primary PW, and the protector is the backup PE (Figure 5).
o 在出口PE节点保护中，PLR是主PW传输隧道的倒数第二个跃点路由器，保护器是备份PE（图5）。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 -------------- P1 ------- P3 ----- PE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- PE3 -------------- P2 ---------------- PE4 -
protector
- PE1 -------------- P1 ------- P3 ----- PE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- PE3 -------------- P2 ---------------- PE4 -
protector
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
Figure 5
图5
o In S-PE node protection, the PLR is the penultimate hop router of the transport tunnel of the primary PW segment, and the protector is the backup S-PE (Figure 6).
o 在S-PE节点保护中，PLR是主PW段传输隧道的倒数第二个跃点路由器，保护器是备用S-PE（图6）。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
protector
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
protector
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
Figure 6
图6
In egress AC protection, a PLR realizes its role based on configuration of a "context identifier", which is introduced in this document (Section 4.3). The PLR establishes a bypass tunnel to the protector in the same fashion as a normal PSN tunnel.
在出口交流保护中，PLR根据本文件（第4.3节）中介绍的“上下文标识符”的配置实现其角色。PLR以与正常PSN通道相同的方式建立到保护器的旁路通道。
In egress PE and S-PE node protection, a PLR is a transit router on the transport tunnel, and it normally does not have knowledge of the PW(s) carried by the transport tunnel. In this document, the PLR simply computes and establishes a node-protection bypass tunnel in the same fashion as the normal IP/MPLS node protection, except that with the notion of the context identifier, the bypass tunnel will be established from the PLR to the protector (Section 4.6). Conversely, when the router is no longer a PLR for egress PE or S-PE node protection due to a change in network topology or the transport tunnel's path, the router should revert to the role of regular transit router, including PLR for transit link and node protection.
在出口PE和S-PE节点保护中，PLR是传输隧道上的传输路由器，通常不知道传输隧道承载的PW。在本文件中，PLR仅以与正常IP/MPLS节点保护相同的方式计算和建立节点保护旁路隧道，除了使用上下文标识符的概念，将建立从PLR到保护器的旁路隧道（第4.6节）。相反，当由于网络拓扑或传输隧道路径的变化，路由器不再是出口PE或S-PE节点保护的PLR时，路由器应恢复为常规传输路由器的角色，包括传输链路和节点保护的PLR。
In local repair, a PLR simply switches all the traffic received on the transport tunnel to the bypass tunnel. This requires that the protector given by the bypass tunnel MUST be intended for all the PWs carried by the transport tunnel. This is achieved by the ingress PE using a context identifier to associate a PW with the specific pair of {primary PE, protector} and map the PW to a transport tunnel destined for the same {primary PE, protector}. The ingress PE MAY map multiple PWs to the transport tunnel, if they share the {primary PE, protector} in common.
在局部维修中，PLR只需将运输隧道上接收的所有交通量切换到旁通隧道。这要求旁通隧道提供的保护装置必须适用于运输隧道携带的所有PW。这是通过入口PE使用上下文标识符将PW与{primary PE，protector}的特定对相关联，并将PW映射到目的地为同一{primary PE，protector}的传输隧道来实现的。入口PE可以将多个PW映射到传输隧道，如果它们共享{primary PE，protector}。
In local repair, the PLR keeps the PW label intact in packets. This obviates the need for the PLR to maintain bypass routes on a per-PW basis and allows bypass tunnel sharing between PWs. On the other hand, this imposes a requirement on the protector that it MUST be able to forward the packets based on a PW label that is assigned by the primary PE and ensure that the traffic MUST reach the target CE via a backup path. From the protector's perspective, this PW label is an upstream assigned label [RFC5331]. To achieve this, the protector MUST learn the PW label from the primary PE prior to the failure and install a proper forwarding state for the PW label in a dedicated label space associated with the primary PE. During local repair, the protector MUST perform PW label lookup in this label space.
在局部维修中，PLR保持PW标签在包装中完好无损。这样就无需PLR在每个PW的基础上维护旁路线路，并允许PW之间共享旁路隧道。另一方面，这对保护器提出了一个要求，即它必须能够基于由主PE分配的PW标签转发分组，并确保通信量必须通过备份路径到达目标CE。从保护者的角度来看，该PW标签是上游分配的标签[RFC5331]。为了实现这一点，保护器必须在发生故障之前从主PE了解PW标签，并在与主PE相关的专用标签空间中为PW标签安装正确的转发状态。在本地维修期间，保护器必须在此标签空间中执行PW标签查找。
The previous examples have shown the scenarios where the protectors are backup (T-/S-)PEs. It is also possible that a protector is a dedicated router to serve such a role, separate from the backup (T-/S-)PE. During local repair, the PLR still reroutes traffic to the protector through a bypass tunnel. The protector then forwards the traffic to the backup (T-/S-)PE, which further forwards the traffic to the target CE via a backup AC or a backup PW segment. More detail is included in Section 4.4.
前面的示例显示了保护器为备用（T-/S-）PE的场景。保护器也可能是一个专用路由器，用于服务于这样的角色，与备份（T-/S-）PE分离。在本地维修期间，PLR仍然通过旁通隧道将流量重新路由到保护器。然后，保护器将流量转发给备份（T-/S-）PE，后者通过备份AC或备份PW段将流量进一步转发给目标CE。更多详情见第4.4节。
A protector may protect multiple primary PEs. The protector MUST maintain a separate label space for each primary PE. Likewise, the PWs terminated on a primary PE may be protected by multiple protectors, each for a subset of the PWs. In any case, a given PW MUST be associated with one and only one pair of {primary PE, protector}.
保护器可保护多个主PE。保护器必须为每个主PE保留单独的标签空间。类似地，端接在主PE上的PW可由多个保护器保护，每个保护器用于PW的子集。在任何情况下，给定的PW必须与一对且仅与一对{primary PE，protector}关联。
This document introduces the notion of a context identifier to facilitate protection establishment. A context identifier is an IPv4/v6 address assigned to each ordered pair of {primary PE, protector}. The address MUST be globally unique or unique in the address space of the network where the primary PE and the protector reside.
本文档介绍了上下文标识符的概念，以便于建立保护。上下文标识符是分配给每个有序的{primary PE，protector}对的IPv4/v6地址。该地址必须是全局唯一的，或者在主PE和保护器所在的网络的地址空间中是唯一的。
The semantics of a context identifier is twofold:
上下文标识符的语义有两个方面：
o A context identifier identifies a primary PE and an associated protector. It represents the primary PE as the PW destination on a per-protector basis. A given primary PE may be protected by multiple protectors, each for a subset of the PWs terminated on the primary PE. A distinct context identifier MUST be assigned to each {primary PE, protector} pair.
o 上下文标识符标识主PE和关联的保护器。它将主PE表示为每个保护器的PW目标。给定的主PE可由多个保护器保护，每个保护器用于在主PE上终止的PW的子集。必须为每个{primary PE，protector}对分配一个不同的上下文标识符。
The ingress PE of a PW learns the context identifier of the PW's {primary PE, protector} from the primary PE via the Interface_ID TLV [RFC3471] [RFC3472] in the LDP Label Mapping message of the PW. The ingress PE then sets up or resolves a transport tunnel with the context identifier, rather than a private IP address of the primary PE, as the destination. This destination not only makes the transport tunnel reach the primary PE but also conveys the identity of the protector to the PLR, which MUST use the context identifier as the destination for the bypass tunnel to the protector. The ingress PE MUST map only the PWs terminated by the exact primary PE and protected by the exact protector to the transport tunnel.
PW的入口PE通过PW的LDP标签映射消息中的接口_ID TLV[RFC3471][RFC3472]从主PE学习PW的{primary PE，protector}的上下文标识符。入口PE然后以上下文标识符（而不是主PE的私有IP地址）作为目的地建立或解析传输隧道。该目的地不仅使传输隧道到达主PE，还将保护器的身份传递给PLR，PLR必须使用上下文标识符作为旁路隧道到保护器的目的地。入口PE必须仅将由确切的主PE端接并由确切的保护器保护的PWs映射到传输隧道。
o A context identifier indicates the primary PE's label space on the protector. The protector may protect PWs for multiple primary PEs. For each primary PE, it MUST maintain a separate label space to store the PW labels assigned by that primary PE. It associates a PW label with a label space via the context identifier of the {primary PE, protector}, as below.
o 上下文标识符指示保护器上主PE的标签空间。保护器可保护多个主PEs的PWs。对于每个主PE，必须保留一个单独的标签空间，以存储该主PE分配的PW标签。它通过{primary PE，protector}的上下文标识符将PW标签与标签空间关联，如下所示。
In addition to the normal LDP PW signaling, the primary PE MUST have a targeted LDP session with the protector and advertise PW labels to the protector via LDP Label Mapping messages (Section 6). The primary PE MUST attach the context identifier to each message. Upon receiving the message, the protector MUST install the advertised PW label in the label space identified by the context identifier.
除了正常的LDP PW信令，主PE必须与保护器有一个目标LDP会话，并通过LDP标签映射消息向保护器公布PW标签（第6节）。主PE必须将上下文标识符附加到每条消息。收到消息后，保护器必须在上下文标识符标识的标签空间中安装播发的PW标签。
When a PLR sets up or resolves a bypass tunnel to the protector, it MUST use the context identifier rather than a private IP address of the protector as the destination. The protector MUST use the bypass tunnel, either the MPLS tunnel label or the IP tunnel destination address, as the pointer to the corresponding label space. The protector MUST forward PW packets received on the bypass tunnel based on label lookup in that label space.
当PLR设置或解析到保护器的旁路隧道时，它必须使用上下文标识符而不是保护器的私有IP地址作为目标。保护器必须使用旁路隧道（MPLS隧道标签或IP隧道目标地址）作为指向相应标签空间的指针。保护器必须根据该标签空间中的标签查找转发在旁路通道上接收的PW数据包。
In an MPLS network, a context identifier represents a Forwarding Equivalence Class (FEC) for transport tunnels and bypass tunnels destined for it. For example, it may be encoded in an LDP Prefix FEC Element or in the "tunnel endpoint address" of an RSVP Session object. The FEC is associated with a unique forwarding state on PLRs and the protector, which cannot be shared with other FECs. Some MPLS protocols (e.g., LDP) support FEC aggregation [RFC3031]. In this case, FEC aggregation MUST NOT be applied to a context identifier's FEC, and every router MUST assign a unique label to the FEC.
在MPLS网络中，上下文标识符表示传输隧道和目的地为其的旁路隧道的转发等价类（FEC）。例如，它可以编码在LDP前缀FEC元素中或RSVP会话对象的“隧道端点地址”中。FEC与PLR和保护器上的唯一转发状态相关联，不能与其他FEC共享。一些MPLS协议（例如LDP）支持FEC聚合[RFC3031]。在这种情况下，FEC聚合不能应用于上下文标识符的FEC，每个路由器必须为FEC分配唯一的标签。
Using a context identifier as the destination for both the transport tunnel and bypass tunnel requires coordination between the primary PE and the protector in IGP advertisement of the context identifier in the routing domain and TE domain. The context identifier should be advertised in such a way that all the routers on the tunnels MUST be able to independently reach the following common view of paths:
使用上下文标识符作为传输隧道和旁路隧道的目的地需要在路由域和TE域中上下文标识符的IGP广告中的主PE和保护器之间进行协调。上下文标识符的公布方式应确保隧道上的所有路由器必须能够独立地到达以下路径的公共视图：
o The transport tunnel MUST have the primary PE as the path endpoint.
o 传输隧道必须将主PE作为路径端点。
o The bypass tunnel MUST have the protector as the path endpoint. In egress PE and S-PE node protection, the path MUST avoid the primary PE.
o 旁路隧道必须具有保护器作为路径端点。在出口PE和S-PE节点保护中，路径必须避开主PE。
There are generally two categories of approaches to achieve the above:
通常有两类方法来实现上述目标：
o The first category does not require an ingress PE or a PLR to have knowledge of the PW egress endpoint protection schema. It does not require any IGP extension for context identifier advertisement. A context identifier is advertised by the primary PE and the protector as an address reachable via both routers. The ingress PE and the PLR can compute paths by using a normal method, such as Dijkstra, constrained shortest path first (CSPF), Loop-Free Alternate (LFA) [RFC5286], and Maximally Redundant Tree (MRT) [RFC7812]. One example is to advertise a context identifier as a virtual proxy node connected to the primary PE and the protector, with the link between the proxy node and the primary PE having a more preferable IGP and TE metric than the link between the proxy node and the protector. The transport tunnel will follow the shortest path or a TE path to the primary PE and be terminated by the primary PE. The PLR will no longer view itself as a penultimate hop of the transport tunnel, but rather two hops away from the proxy node, via the primary PE. Hence, a node-
o 第一类不要求入口PE或PLR了解PW出口端点保护模式。上下文标识符播发不需要任何IGP扩展。主PE和保护器将上下文标识符作为可通过两个路由器访问的地址进行公告。入口PE和PLR可以使用常规方法计算路径，例如Dijkstra、约束最短路径优先（CSPF）、无环备用（LFA）[RFC5286]和最大冗余树（MRT）[RFC7812]。一个示例是将上下文标识符公布为连接到主PE和保护器的虚拟代理节点，其中代理节点和主PE之间的链路具有比代理节点和保护器之间的链路更优选的IGP和TE度量。传输隧道将遵循到主PE的最短路径或TE路径，并由主PE终止。PLR将不再将自身视为传输隧道的倒数第二个跃点，而是通过主PE将其视为距离代理节点两个跃点。因此，一个节点-
protection bypass tunnel will be available via the protector to the proxy node, but it will actually be terminated by the protector.
保护旁路隧道可通过保护器连接到代理节点，但实际上将由保护器终止。
o The second category requires a PLR to have knowledge of the PW egress endpoint protection schema. The primary PE advertises the context identifier as a regular IP address, while the protector advertises it by using an explicit "context identifier object", which MUST be understood by the PLR. The context identifier object requires an IGP extension. In both the routing domain and the TE domain, the context identifier is only reachable via the primary PE. This ensures that the transport tunnel is terminated by the primary PE. The PLR views itself as the penultimate hop of the transport tunnel, and based on the IGP context identifier object, it establishes or resolves a bypass tunnel to the advertiser (i.e., the protector), while avoiding the primary PE.
o 第二类要求PLR了解PW出口端点保护模式。主PE将上下文标识符作为常规IP地址播发，而保护器通过使用明确的“上下文标识符对象”播发，PLR必须理解该对象。上下文标识符对象需要IGP扩展。在路由域和TE域中，只能通过主PE访问上下文标识符。这确保传输隧道由主PE终止。PLR将自身视为传输隧道的倒数第二个跃点，并基于IGP上下文标识符对象，建立或解析到广告客户（即，保护者）的旁路隧道，同时避免主PE。
The mechanism in this document intends to be flexible on the approach used by a network, as long as it satisfies the above requirements for the transport tunnel path and bypass tunnel path. In theory, the network can use one approach for context ID X and another approach for context ID Y. For a given context ID, all relevant routers, including primary PE, protector, and PLR, must support and agree on the chosen approach. The coordination between the routers can be achieved by configuration.
本文件中的机制旨在对网络使用的方法具有灵活性，只要它满足上述对运输隧道路径和旁路隧道路径的要求。理论上，网络可以对上下文ID X使用一种方法，对上下文ID Y使用另一种方法。对于给定的上下文ID，所有相关路由器，包括主PE、保护器和PLR，必须支持并同意所选方法。路由器之间的协调可以通过配置来实现。
There are two protection models based on the location of a protector: the co-located protector model and the centralized protector model. A network MAY use either model or both.
根据保护器的位置，有两种保护模型：同地保护器模型和集中式保护器模型。网络可以使用任何一种模型，也可以同时使用这两种模型。
In this model, the protector is a backup PE that is directly connected to the target CE via a backup AC, or it is a backup S-PE on a backup PW. That is, the protector is co-located with the backup (S-)PE. Examples of this model are shown in Figures 4, 5, and 6 in Section 4.2.
在该型号中，保护器是一个备份PE，通过备份AC直接连接到目标CE，或者是备份PW上的备份S-PE。也就是说，保护器与备用（S-）PE位于同一位置。该模型的示例如第4.2节中的图4、图5和图6所示。
In egress AC protection and egress PE node protection, when a protector receives traffic from the PLR, it forwards the traffic to the CE via the backup AC. This is shown in Figure 7, where PE2 is the PLR for egress AC failure, P3 is the PLR for PE2 failure, and PE4 (backup PE) is the protector.
在出口AC保护和出口PE节点保护中，当保护器从PLR接收流量时，它通过备用AC将流量转发给CE。如图7所示，其中PE2是出口AC故障的PLR，P3是PE2故障的PLR，PE4（备用PE）是保护器。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 -------------- P1 ------- P3 ----- PE2 ----
/ PLR \ PLR \
/ \ | \
CE1 bypass\ |bypass CE2
\ \ | /
\ \ | /
- PE3 -------------- P2 ---------------- PE4 ----
protector
- PE1 -------------- P1 ------- P3 ----- PE2 ----
/ PLR \ PLR \
/ \ | \
CE1 bypass\ |bypass CE2
\ \ | /
\ \ | /
- PE3 -------------- P2 ---------------- PE4 ----
protector
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
Figure 7
图7
In S-PE node protection, when a protector receives traffic from the PLR, it forwards the traffic over the next segment of the backup PW. The T-PE of the backup PW in turn forwards the traffic to the CE via a backup AC. This is shown in Figure 8, where P1 is the PLR for SPE1 failure, and SPE2 (backup S-PE) is the protector for SPE1. SPE2 receives traffic from P1, swaps SEG1's label to SEG4's label, and forwards the traffic over a transport tunnel to TPE4.
在S-PE节点保护中，当保护器从PLR接收流量时，它将流量转发到备份PW的下一段。备用PW的T-PE依次通过备用AC将流量转发给CE。如图8所示，其中P1是SPE1故障的PLR，SPE2（备用S-PE）是SPE1的保护器。SPE2从P1接收流量，将SEG1的标签交换到SEG4的标签，并通过传输隧道将流量转发到TPE4。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
protector
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass\ CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
protector
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
Figure 8
图8
In the co-located protector model, the number of context identifiers needed by a network is the number of distinct {primary PE, backup PE} pairs. From the perspective of scalability, the model is suitable for networks where the number of primary PEs and the average number of backup PEs per primary PE are both relatively low.
在共存保护器模型中，网络所需的上下文标识符的数量是不同的{primary PE，backup PE}对的数量。从可扩展性的角度来看，该模型适用于主PE数量和每个主PE的平均备份PE数量都相对较低的网络。
In this model, the protector is a dedicated P router or PE router that serves the role. In egress AC protection and egress PE node protection, the protector may or may not be a backup PE directly connected to the target CE. In S-PE node protection, the protector may or may not be a backup S-PE on the backup PW.
在这个模型中，保护器是一个专用的P路由器或PE路由器，为这个角色服务。在出口AC保护和出口PE节点保护中，保护器可以是也可以不是直接连接到目标CE的备份PE。在S-PE节点保护中，保护器可能是也可能不是备份PW上的备份S-PE。
In egress AC protection and egress PE node protection, if the protector is not directly connected to the CE, it forwards the traffic to a backup PE, which in turn forwards the traffic to the CE via a backup AC. This is shown in Figure 9, where the protector receives traffic from P3 (PLR for egress PE failure) or PE2 (PLR for egress AC failure), swaps PW1's label to PW2's label, and forwards the traffic via a transport tunnel to PE4 (backup PE). The protector may be protecting other PWs and other primary PEs as well; for clarity, this is not shown in the figure.
在出口AC保护和出口PE节点保护中，如果保护器未直接连接到CE，则将流量转发给备份PE，备份PE又通过备份AC将流量转发给CE。如图9所示，其中保护器接收来自P3（出口PE故障的PLR）或PE2（出口AC故障的PLR）的流量，将PW1的标签交换到PW2的标签，并通过传输隧道将流量转发到PE4（备用PE）。保护器也可以保护其他PW和其他初级PE；为清楚起见，图中未显示这一点。
|<------------- PW1 --------------->|
|<------------- PW1 --------------->|
- PE1 ------------- P1 ------- P3 ----- PE2 --
/ PLR \ PLR \
/ \ / \
/ bypass\ /bypass \
/ \ / \
CE1 protector CE2
\ \ /
\ transport\ /
\ tunnel \ /
\ \ /
- PE3 ------------- P2 -----------------PE4 --
- PE1 ------------- P1 ------- P3 ----- PE2 --
/ PLR \ PLR \
/ \ / \
/ bypass\ /bypass \
/ \ / \
CE1 protector CE2
\ \ /
\ transport\ /
\ tunnel \ /
\ \ /
- PE3 ------------- P2 -----------------PE4 --
|<------------- PW2 --------------->|
|<------------- PW2 --------------->|
Figure 9
图9
In S-PE node protection, if the protector is not a backup S-PE, it forwards the traffic to the backup S-PE, which in turn forwards the traffic over the next segment of the backup PW. Finally, the T-PE of the backup PW forwards the traffic to the CE via the backup AC. This is shown in Figure 10, where the protector receives traffic from P1 (PLR), swaps SEG1's label to SEG3's label, and forwards the traffic via a transport tunnel to SPE2 (backup S-PE). SPE2 in turn performs MS-PW switching from SEG3's label to SEG4's label and forwards the traffic over a transport tunnel to TPE4 (backup T-PE). The protector may be protecting other PW segments and other primary S-PEs as well; for clarity, this is not shown in the figure.
在S-PE节点保护中，如果保护器不是备份S-PE，它会将通信量转发给备份S-PE，而备份S-PE又会将通信量转发到备份PW的下一段。最后，备用PW的T-PE通过备用AC将流量转发给CE。如图10所示，保护器从P1（PLR）接收流量，将SEG1的标签交换给SEG3的标签，并通过传输隧道将流量转发给SPE2（备用s-PE）。SPE2依次执行从SEG3标签到SEG4标签的MS-PW切换，并通过传输隧道将流量转发到TPE4（备用T-PE）。保护器也可以保护其他PW段和其他主S-PE；为清楚起见，图中未显示这一点。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
/ bypass\ \
/ \ \
CE1 protector CE2
\ \ /
\ transport\ /
\ tunnel \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
- TPE1 ----- P1 ----- SPE1 -------------- TPE2 -
/ PLR \ \
/ \ \
/ bypass\ \
/ \ \
CE1 protector CE2
\ \ /
\ transport\ /
\ tunnel \ /
\ \ /
- TPE3 --------------- SPE2 -------------- TPE4 -
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
Figure 10
图10
The centralized protector model allows multiple primary PEs to share one protector. Each primary PE may need only one protector. Therefore, the number of context identifiers needed by a network may be bound to the number of primary PEs.
集中式保护器模型允许多个主PE共享一个保护器。每个主PE可能只需要一个保护器。因此，网络所需的上下文标识符的数量可以绑定到主PEs的数量。
A PW is associated with a pair of {primary PE, protector}, which is represented by a unique context identifier. The ingress PE of the PW sets up or resolves a transport tunnel by using the context identifier rather than a private IP address of the primary PE as the destination. This not only ensures that the PW is transported to the primary PE but also facilitates bypass tunnel establishment at PLR, because the context identifier contains the identity of the protector as well. This is also the case for a multi-segment PW, where the ingress PE and egress PE are T-/S-PEs.
PW与一对{primary PE，protector}关联，该对由唯一的上下文标识符表示。PW的入口PE通过使用上下文标识符而不是主PE的私有IP地址作为目的地来建立或解析传输隧道。这不仅确保PW被传输到主PE，而且有助于在PLR建立旁路通道，因为上下文标识符也包含保护器的标识。这也是多段PW的情况，其中入口PE和出口PE为T-/S-PE。
An ingress PE learns the association between a PW and a context identifier from the primary PE, which MUST advertise the context identifier as a "third-party next hop" via the IPv4/v6 Interface_ID TLV [RFC3471] [RFC3472] in the LDP Label Mapping message of the PW.
入口PE从主PE学习PW和上下文标识符之间的关联，主PE必须通过PW的LDP标签映射消息中的IPv4/v6接口_ID TLV[RFC3471][RFC3472]将上下文标识符作为“第三方下一跳”公布。
In an ECMP scenario, a transport tunnel may have multiple penultimate hop routers. Each of them SHOULD act as a PLR independently. Also in an ECMP scenario, a penultimate hop router may have ECMPs to the primary PE. At least one path of the ECMPs must be a direct link to the primary PE, qualifying the router as a penultimate hop. The other paths of the ECMPs may be direct links or indirect paths to the
在ECMP场景中，传输隧道可能有多个倒数第二跳路由器。它们中的每一个都应该独立地充当PLR。同样在ECMP场景中，倒数第二跳路由器可能具有到主PE的ECMP。ECMPs的至少一条路径必须是到主PE的直接链路，从而将路由器限定为倒数第二个跃点。ECMPs的其他路径可以是直接链路或到服务器的间接路径
primary PE. In egress PE node protection and S-PE node protection, when a node failure is detected, or a link failure is detected on a direct link and treated as a node failure, the penultimate hop router SHOULD act as a PLR and reroute the entire traffic of the ECMPs to the protector.
初级体育。在出口PE节点保护和S-PE节点保护中，当检测到节点故障或在直接链路上检测到链路故障并将其视为节点故障时，倒数第二个跃点路由器应充当PLR，并将ECMP的整个流量重新路由到保护器。
A PLR may protect multiple PWs associated with one or multiple pairs of {primary PE, protector}. The PLR MUST establish a bypass tunnel to each protector for each context identifier associated with that protector. The destination of the bypass tunnel MUST be the context identifier (Section 4.3.1). Since the PLR is a transit router of the transport tunnel, it SHOULD derive the context identifier from the destination of the transport tunnel.
PLR可保护与一对或多对{primary PE，protector}相关联的多个PW。PLR必须为每个与保护器关联的上下文标识符建立到每个保护器的旁路通道。旁通隧道的目的地必须是上下文标识符（第4.3.1节）。由于PLR是传输隧道的传输路由器，它应该从传输隧道的目的地派生上下文标识符。
For example, in Figures 7 and 9, a bypass tunnel is established from PE2 (PLR for egress AC failure) to the protector, and another bypass tunnel is established from P3 (PLR for egress node failure) to the protector. In Figures 8 and 10, a bypass tunnel is established from P1 (PLR for S-PE failure) to the protector.
例如，在图7和图9中，从PE2（出口AC故障的PLR）到保护器建立旁路隧道，从P3（出口节点故障的PLR）到保护器建立另一旁路隧道。在图8和图10中，建立了从P1（S-PE故障的PLR）到保护器的旁通通道。
In local repair, a PLR reroutes traffic to the protector through a bypass tunnel, with the PW label intact in the packets. This normally involves pushing a label to the label stack, if the bypass tunnel is an MPLS tunnel, or pushing an IP header to the packets, if the bypass tunnel is an IP tunnel. Upon receipt of the packets, the protector forwards them based on the PW label. Specifically, the protector uses the bypass tunnel as a context to determine the primary PE's label space. If the bypass tunnel is an MPLS tunnel, the protector should have assigned a non-reserved label to the bypass tunnel; hence, this label can serve as the context. This label is also called a "context label", as it is actually bound to the context identifier. If the bypass tunnel is an IP tunnel, the context identifier should be the destination address of the IP header.
在本地修复中，PLR通过旁路隧道将流量重新路由到保护器，包中的PW标签完好无损。这通常涉及将标签推送到标签堆栈（如果旁通隧道是MPLS隧道），或者将IP头推送到数据包（如果旁通隧道是IP隧道）。收到数据包后，保护器根据PW标签转发数据包。具体而言，保护器使用旁路通道作为上下文来确定主PE的标签空间。如果旁路隧道是MPLS隧道，则保护器应为旁路隧道分配非保留标签；因此，这个标签可以作为上下文。此标签也称为“上下文标签”，因为它实际上绑定到上下文标识符。如果旁路隧道是IP隧道，则上下文标识符应该是IP头的目标地址。
To be useful for local repair, a bypass tunnel MUST have the property that it is not affected by any topology changes caused by the failure. It MUST NOT traverse the primary PE or the penultimate link of the transport tunnel, or share any SRLG with the penultimate link. A bypass tunnel may be a TE tunnel with reserved bandwidth to avoid traffic congestion for rerouted traffic. A bypass tunnel should remain effective during local repair, until the traffic is moved to an alternative path, i.e., either the same PW over a fully functional transport tunnel or another fully functional PW.
为了便于本地修复，旁通隧道必须具有不受故障引起的任何拓扑更改影响的特性。不得穿过运输隧道的主要PE或倒数第二条链路，或与倒数第二条链路共用任何SRLG。旁路隧道可以是具有保留带宽的TE隧道，以避免重路由流量的流量拥塞。在局部维修期间，旁通隧道应保持有效，直到交通被转移到替代路径，即，在全功能运输隧道上的相同PW或另一个全功能PW上。
There is little or no benefit to protect a bypass tunnel. Therefore, a bypass tunnel SHOULD NOT be protected against a transit link failure, transit node failure, or egress node failure.
保护旁通隧道几乎没有好处。因此，不应针对传输链路故障、传输节点故障或出口节点故障保护旁通隧道。
This section provides some detailed examples of forwarding state on the PLR, protector, and other relevant routers.
本节提供了PLR、保护器和其他相关路由器上转发状态的一些详细示例。
A protector learns PW labels from all the primary PEs that it protects (Section 6.2) and maintains the PW labels in separate label spaces on a per-primary-PE basis. In the control plane, each label space is identified by the context identifier of the corresponding {primary PE, protector}. In the forwarding plane, the label space is indicated by the bypass tunnel(s) destined for the context identifier.
保护器从其保护的所有主要PE（第6.2节）中学习PW标签，并根据每个主要PE在单独的标签空间中维护PW标签。在控制平面中，每个标签空间由对应的{primary PE，protector}的上下文标识符标识。在转发平面中，标签空间由目的地为上下文标识符的旁路隧道指示。
In Figure 11, PE4 is a co-located protector that protects PW1 against egress AC failure and egress node failure. It maintains a label space for PE2, which is identified by the context identifier of {PE2, PE4}. It learns PW1's label from PE2 and installs a forwarding entry for the label in that label space. The next hop of the forwarding entry indicates a label pop with an outgoing interface pointing to the backup AC PE4-CE2.
在图11中，PE4是一个共位保护器，用于保护PW1免受出口AC故障和出口节点故障的影响。它为PE2维护一个标签空间，该标签空间由上下文标识符{PE2，PE4}标识。它从PE2中学习PW1的标签，并在该标签空间中为该标签安装转发条目。转发条目的下一个跃点表示标签pop，其传出接口指向备份AC PE4-CE2。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 -------------- P1 ------- P3 ----- PE2 ------
/ PLR \ PLR \
/ \ | \
/ \ | \
CE1 bypass P4 P5 bypass CE2
\ \ | /
\ \ | /
\ \ | /
- PE3 -------------- P2 ---------------- PE4 ------
protector
- PE1 -------------- P1 ------- P3 ----- PE2 ------
/ PLR \ PLR \
/ \ | \
/ \ | \
CE1 bypass P4 P5 bypass CE2
\ \ | /
\ \ | /
\ \ | /
- PE3 -------------- P2 ---------------- PE4 ------
protector
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
PW1's label assigned by PE2: 100
PW2's label assigned by PE4: 200
On P3: </t>
Incoming label of transport tunnel to PE2: 1000
Outgoing label of transport tunnel to PE2: implicit null
Outgoing label of bypass tunnel to PE4: 2000
On PE2:
Outgoing label of bypass tunnel to PE4: 3000
On PE4:
Context label (incoming label of bypass tunnels): 999
PW1's label assigned by PE2: 100
PW2's label assigned by PE4: 200
On P3: </t>
Incoming label of transport tunnel to PE2: 1000
Outgoing label of transport tunnel to PE2: implicit null
Outgoing label of bypass tunnel to PE4: 2000
On PE2:
Outgoing label of bypass tunnel to PE4: 3000
On PE4:
Context label (incoming label of bypass tunnels): 999
Forwarding state on P3: label 1000 -- primary next hop: pop, to PE2 backup next hop: swap 2000, to P4
P3上的转发状态：标签1000——主下一跳：pop，到PE2备份下一跳：swap 2000，到P4
Forwarding state on PE2: label 100 -- primary next hop: pop, to CE2 backup next hop: push 3000, to P5
PE2上的转发状态：标签100——主下一跳：pop，到CE2备份下一跳：推送3000，到P5
Forwarding state on P4: label 2000 -- next hop: swap 999, to PE4
P4上的转发状态：标签2000——下一跳：交换999，到PE4
Forwarding state on P5: label 3000 -- next hop: swap 999, to PE4
P5上的转发状态：标签3000——下一跳：交换999，到PE4
Forwarding state on PE4:
label 200 -- next hop: pop, to CE2
label 999 -- next hop: label table of PE2's label space
Forwarding state on PE4:
label 200 -- next hop: pop, to CE2
label 999 -- next hop: label table of PE2's label space
Label table of PE2's label space on PE4: label 100 -- next hop: pop, to CE2
PE4上PE2标签空间的标签表：标签100——下一跳：pop，到CE2
Figure 11
图11
In Figure 12, SPE2 is a co-located protector that protects PW1 against S-PE failure. It maintains a label space for SPE1, which is identified by the context identifier of {SPE1, SPE2}. It learns SEG1's label from SPE1 and installs a forwarding entry in the label space. The next hop of the forwarding entry indicates a label swap to SEG4's label and a label push with the label of a transport tunnel to TPE4.
在图12中，SPE2是一个位于同一位置的保护器，用于保护PW1免受S-PE故障的影响。它为SPE1维护一个标签空间，该空间由{SPE1，SPE2}的上下文标识符标识。它从SPE1学习SEG1的标签，并在标签空间中安装转发条目。转发条目的下一个跃点表示到SEG4标签的标签交换和到TPE4的传输隧道标签的标签推送。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 ----- P1 ----- SPE1 --- P3 ------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass P2 CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 --- P4 ------- TPE4 -
protector
- TPE1 ----- P1 ----- SPE1 --- P3 ------- TPE2 -
/ PLR \ \
/ \ \
CE1 bypass P2 CE2
\ \ /
\ \ /
- TPE3 --------------- SPE2 --- P4 ------- TPE4 -
protector
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
SEG1's label assigned by SPE1: 100 SEG2's label assigned by TPE2: 200 SEG3's label assigned by SPE2: 300 SEG4's label assigned by TPE4: 400 On P1: Incoming label of transport tunnel to SPE1: 1000 Outgoing label of transport tunnel to SPE1: implicit null Outgoing label of bypass tunnel to SPE2: 2000 On SPE1: Outgoing label of transport tunnel to TPE2: 3000 On SPE2: Outgoing label of transport tunnel to TPE4: 4000 Context label (incoming label of bypass tunnel): 999
SPE1分配的SEG1标签：100 TPE2分配的SEG2标签：200 SPE2分配的SEG3标签：300 TPE4:400在P1上分配的SEG1标签：传输隧道的传入标签到SPE1:1000传输隧道的传出标签到SPE1：旁路隧道的隐式空传出标签到SPE2:2000在SPE1：传输隧道的传出标签到SPE2上的TPE2:3000：运输隧道的输出标签至TPE4:4000上下文标签（旁通隧道的输入标签）：999
Forwarding state on P1: label 1000 -- primary next hop: pop, to SPE1 backup next hop: swap 2000, to P2
P1上的转发状态：标签1000--主下一跳：pop，到SPE1备份下一跳：swap 2000，到P2
Forwarding state on SPE1: label 100 -- next hop: swap 200, push 3000, to P3
SPE1上的转发状态：标签100——下一跳：交换200，推送3000，到P3
Forwarding state on P2: label 2000 -- next hop: swap 999, to SPE2
P2上的转发状态：标签2000--下一跳：交换999，到SPE2
Forwarding state on SPE2:
label 300 -- next hop: swap 400, push 4000, to P4
label 999 -- next hop: label table of SPE1's label space
Forwarding state on SPE2:
label 300 -- next hop: swap 400, push 4000, to P4
label 999 -- next hop: label table of SPE1's label space
Label table of SPE1's label space on SPE2: label 100 -- next hop: swap 400, push 4000, to P4
SPE2上SPE1标签空间的标签表：标签100——下一跳：交换400，推送4000，到P4
Figure 12
图12
In the centralized protector model, for each primary PW of which the protector is not a backup (S-)PE, the protector MUST also learn the label of the backup PW from the backup (S-)PE (Section 6.3). This is the backup (S-)PE that the protector will forward traffic to. The protector MUST install a forwarding entry with a label swap from the primary PW's label to the backup PW's label and a label push with the label of a transport tunnel to the backup (S-)PE.
在集中式保护器模型中，对于保护器不是备份（S-）PE的每个主PW，保护器还必须从备份（S-）PE中学习备份PW的标签（第6.3节）。这是保护程序将流量转发到的备份（S-）PE。保护器必须安装一个转发条目，该条目带有从主PW标签到备份PW标签的标签交换，以及一个带有传输隧道标签到备份（s-）PE的标签推送。
In Figure 13, the protector is a centralized protector that protects PW1 against egress AC failure and egress node failure. It maintains a label space for PE2, which is identified by the context identifier of {PE2, protector}. It learns PW1's label from PE2 and PW2's label from PE4. It installs a forwarding entry for PW1's label in the label space. The next hop of the forwarding entry indicates a label swap to PW2's label and a label push with the label of a transport tunnel to PE4.
在图13中，保护器是一个集中式保护器，用于保护PW1免受出口AC故障和出口节点故障的影响。它为PE2维护一个标签空间，该空间由上下文标识符{PE2，protector}标识。它从PE2学习PW1的标签，从PE4学习PW2的标签。它在标签空间中为PW1的标签安装转发条目。转发条目的下一个跃点表示到PW2标签的标签交换和到PE4的传输隧道标签的标签推送。
|<-------------- PW1 --------------->|
|<-------------- PW1 --------------->|
- PE1 ------------- P1 ------- P3 ------ PE2 ----
/ PLR \ PLR \
/ \ / \
/ bypass P5 P6 bypass \
/ \ / \
/ \/ \
CE1 protector CE2
\ \ /
\ transport \ /
\ tunnel P7 /
\ \ /
\ \ /
- PE3 ------------- P2 ----------------- PE4 ----
- PE1 ------------- P1 ------- P3 ------ PE2 ----
/ PLR \ PLR \
/ \ / \
/ bypass P5 P6 bypass \
/ \ / \
/ \/ \
CE1 protector CE2
\ \ /
\ transport \ /
\ tunnel P7 /
\ \ /
\ \ /
- PE3 ------------- P2 ----------------- PE4 ----
|<-------------- PW2 --------------->|
|<-------------- PW2 --------------->|
PW1's label assigned by PE2: 100 PW2's label assigned by PE4: 200 On P3: Incoming label of transport tunnel to PE2: 1000 Outgoing label of transport tunnel to PE2: implicit null Outgoing label of bypass tunnel to protector: 2000 On PE2: Outgoing label of bypass tunnel to protector: 3000 On protector: Context label (incoming label of bypass tunnels): 999 Outgoing label of transport tunnel to PE4: 4000
PE2分配的PW1标签：100 P3上PE4:200分配的PW2标签：运输隧道进线标签到PE2:1000运输隧道出线标签到PE2：旁路隧道到保护器的隐式空出线标签：PE2上2000：旁路隧道到保护器的出线标签：保护器上3000：上下文标签（旁路隧道进线标签）：999至PE4的运输隧道出站标签：4000
Forwarding state on P3: label 1000 -- primary next hop: pop, to PE2 backup next hop: swap 2000, to P5
P3上的转发状态：标签1000——主下一跳：pop，到PE2备份下一跳：交换2000，到P5
Forwarding state on PE2: label 100 -- primary next hop: pop, to CE2 backup next hop: push 3000, to P6
PE2上的转发状态：标签100——主下一跳：pop，到CE2备份下一跳：推送3000，到P6
Forwarding state on P5: label 2000 -- next hop: swap 999, to protector
P5上的转发状态：标签2000——下一跳：交换999，到保护器
Forwarding state on P6: label 3000 -- next hop: swap 999, to protector
P6上的转发状态：标签3000——下一跳：交换999，到保护器
Forwarding state on P7: label 4000 -- next hop: pop, to PE4
P7上的转发状态：标签4000——下一跳：pop，到PE4
Forwarding state on PE4: label 200 -- next hop: pop, to CE2
PE4上的转发状态：标签200——下一跳：pop，到CE2
Forwarding state on protector: label 999 -- next hop: label table of PE2's label space
保护器上的转发状态：标签999——下一跳：PE2标签空间的标签表
Label table of PE2's label space on protector: label 100 -- next hop: swap 200, push 4000, to P7
保护器上PE2标签空间的标签表：标签100——下一跳：交换200，推送4000，到P7
Figure 13
图13
In Figure 14, the protector is a centralized protector that protects the PW segment SEG1 of PW1 against the node failure of SPE1. It maintains a label space for SPE1, which is identified by the context identifier of {SPE1, protector}. It learns SEG1's label from SPE1 and SEG3's label from SPE2. It installs a forwarding entry for SEG1's label in the label space. The next hop of the forwarding entry indicates a label swap to SEG3's label and a label push with the label of a transport tunnel to TPE4.
在图14中，保护器是一个集中式保护器，用于保护PW1的PW段SEG1免受SPE1节点故障的影响。它为SPE1维护一个标签空间，该空间由上下文标识符{SPE1，protector}标识。它从SPE1学习SEG1的标签，从SPE2学习SEG3的标签。它在标签空间中安装SEG1标签的转发条目。转发条目的下一个跃点表示到SEG3标签的标签交换和到TPE4的传输隧道标签的标签推送。
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
|<--------------- PW1 --------------->|
|<----- SEG1 ----->|<----- SEG2 ----->|
- TPE1 ----- P1 ----- SPE1 --- P2 -------- TPE2 -
/ PLR \ \
/ \ \
/ bypass P4 \
/ \ \
/ \ \
CE1 protector CE2
\ \ /
\ \ /
\ transport P5 /
\ tunnel \ /
\ \ /
- TPE3 -------------- SPE2 --- P3 -------- TPE4 -
- TPE1 ----- P1 ----- SPE1 --- P2 -------- TPE2 -
/ PLR \ \
/ \ \
/ bypass P4 \
/ \ \
/ \ \
CE1 protector CE2
\ \ /
\ \ /
\ transport P5 /
\ tunnel \ /
\ \ /
- TPE3 -------------- SPE2 --- P3 -------- TPE4 -
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
|<----- SEG3 ----->|<----- SEG4 ----->|
|<--------------- PW2 --------------->|
SEG1's label assigned by SPE1: 100 SEG2's label assigned by TPE2: 200 SEG3's label assigned by SPE2: 300 SEG4's label assigned by TPE4: 400 On P1: Incoming label of transport tunnel to SPE1: 1000 Outgoing label of transport tunnel to SPE1: implicit null Outgoing label of bypass tunnel to protector: 2000 On SPE1: Outgoing label of transport tunnel to TPE2: 3000 On SPE2: Outgoing label of transport tunnel to TPE4: 4000 On protector: Context label (incoming label of bypass tunnel): 999 Outgoing label of transport tunnel to SPE2: 5000
SPE1分配的SEG1标签：100 TPE2分配的SEG2标签：200 SPE2分配的SEG3标签：300 TPE4分配的SEG4标签：P1上的400：运输隧道的传入标签到SPE1:1000运输隧道的传出标签到SPE1：旁路隧道到保护器的隐式空传出标签：SPE1上的2000：运输隧道的传出标签至SPE2上的TPE2:3000：运输隧道的输出标签至保护器上的TPE4:4000：上下文标签（旁通隧道的输入标签）：999至SPE2的运输隧道的输出标签：5000
Forwarding state on P1: label 1000 -- primary next hop: pop, to SPE1 backup next hop: swap 2000, to P4
P1上的转发状态：标签1000--主下一个跃点：pop，到SPE1备份下一个跃点：swap 2000，到P4
Forwarding state on SPE1: label 100 -- next hop: swap 200, push 3000, to P2
SPE1上的转发状态：标签100——下一跳：交换200，推送3000，到P2
Forwarding state on P4: label 2000 -- next hop: swap 999, to protector
P4上的转发状态：标签2000——下一跳：交换999，到保护器
Forwarding state on P5: label 5000 -- next hop: pop, to SPE2
P5上的转发状态：标签5000——下一跳：pop，到SPE2
Forwarding state on SPE2: label 300 -- next hop: swap 400, push 4000, to P3
SPE2上的转发状态：标签300——下一跳：交换400，推送4000，到P3
Forwarding state on protector: label 999 -- next hop: label table of SPE1's label space
保护器上的转发状态：标签999--下一跳：SPE1标签空间的标签表
Label table of SPE1's label space on protector: label 100 -- next hop: swap 300, push 5000, to P5
保护器上SPE1标签空间的标签表：标签100——下一跳：交换300，推送5000，到P5
Figure 14
图14
Subsequent to local repair, there are three strategies for a network to restore traffic to a fully functional alternative path:
在本地修复之后，网络有三种策略可将流量恢复到功能齐全的备用路径：
o Global repair
o 全局修复
If the ingress CE is multihomed (Figure 1), it MAY switch the traffic to the backup AC, which is bound to the backup PW. Alternatively, if the ingress PE hosts a backup PW (Figure 2), the ingress PE MAY switch the traffic to the backup PW. These procedures are referred to as global repair. Possible triggers of global repair include PW status notification, Virtual Circuit Connectivity Verification (VCCV) [RFC5085] [RFC5885], BFD, end-to-end OAM between CEs, and others.
如果入口CE是多址的（图1），它可以将通信量切换到备份AC，备份AC绑定到备份PW。或者，如果入口PE承载备份PW（图2），入口PE可以将通信量切换到备份PW。这些程序称为全局修复。全局修复的可能触发因素包括PW状态通知、虚拟电路连接验证（VCCV）[RFC5085][RFC5885]、BFD、CEs之间的端到端OAM等。
o Control-plane convergence
o 控制平面收敛
In egress PE node protection and S-PE node protection, it is possible that the failure is limited to the link between the PLR and the primary PE, whereas the primary PE is still operational. In this case, the PLR or an upstream router on the transport tunnel MAY reroute the tunnel around the link via an alternative path to the primary PE. Thus, the transport tunnel can heal and continue to carry the PW to the primary PE. This procedure is driven by control-plane convergence on the new topology.
在出口PE节点保护和S-PE节点保护中，故障可能限于PLR和主PE之间的链路，而主PE仍在运行。在这种情况下，传输隧道上的PLR或上游路由器可以经由到主PE的替代路径围绕链路重新路由隧道。因此，输送通道可以愈合并继续将PW输送至主要PE。此过程由新拓扑上的控制平面收敛驱动。
o Local reversion
o 局部回归
The PLR MAY move traffic back to the primary PW, after the failure is resolved. In egress AC protection, upon detecting that the primary AC is restored, the PLR MAY start forwarding traffic over the AC again. Likewise, in egress PE node protection and S-PE node protection, upon detecting that the primary PE is restored, the PLR MAY re-establish the transport tunnel to the primary PE and move the traffic from the bypass tunnel back to the transport tunnel. These procedures are referred to as local reversion.
故障解决后，PLR可将通信量移回主PW。在出口AC保护中，在检测到主AC被恢复时，PLR可以再次开始通过AC转发业务。类似地，在出口PE节点保护和S-PE节点保护中，在检测到主PE被恢复时，PLR可以重新建立到主PE的传输隧道，并将业务从旁路隧道移回传输隧道。这些程序称为局部复原。
It is RECOMMENDED that the fast protection mechanism SHOULD be used in conjunction with global repair. Particularly in the case of egress PE and S-PE node failures, if the ingress PE or the protector loses communication with the egress PE or S-PE for an extensive period of time, the LDP session may go down. Consequently, the ingress PE may bring down the primary PW completely, or the protector may remove the forwarding entry of the primary PW label. In either case, the service will be disrupted. In other words, although the mechanism can temporarily repair traffic, control-plane state may eventually expire if the failure persists. Therefore, global repair SHOULD take place in a timely manner to move traffic to a fully functional alternative path.
建议将快速保护机制与全局修复结合使用。特别是在出口PE和S-PE节点故障的情况下，如果入口PE或保护器丢失与出口PE或S-PE的通信达很长一段时间，则LDP会话可能下降。因此，入口PE可以完全关闭主PW，或者保护器可以移除主PW标签的转发条目。无论哪种情况，服务都将中断。换句话说，尽管该机制可以临时修复通信量，但如果故障持续存在，控制平面状态最终可能会过期。因此，应及时进行全局修复，以将交通转移到功能完备的替代路径。
Control-plane convergence may automatically happen as control-plane protocols react to the new topology. However, it is only applicable to the specific link failure scenario described above.
当控制平面协议对新拓扑作出反应时，控制平面收敛可能会自动发生。但是，它仅适用于上述特定链路故障场景。
Local reversion is optional. In the circumstances where the failure is caused by resource flapping, local reversion MAY be dampened to limit potential disruption. Local reversion MAY be disabled completely by configuration.
本地恢复是可选的。在故障是由资源摆动引起的情况下，可以抑制局部回复，以限制潜在的中断。本地恢复可通过配置完全禁用。
As described in previous sections, a targeted LDP session MUST be established between each pair of primary PE and protector. The primary PE sends a Label Mapping message over this session to advertise primary PW labels to the protector. In the centralized protector model, a targeted LDP session MUST also be established between a backup (S-)PE and the protector. The backup PE sends a Label Mapping message over this session to advertise backup PW labels to the protector.
如前几节所述，必须在每对主PE和保护器之间建立目标LDP会话。主PE在此会话上发送标签映射消息，以向保护器播发主PW标签。在集中式保护器模型中，还必须在备份（S-）PE和保护器之间建立目标LDP会话。备份PE在此会话上发送标签映射消息，以向保护器播发备份PW标签。
To support the procedures, this document defines a new "Protection FEC Element" TLV. The Label Mapping messages of both the LDP sessions above MUST carry this TLV to identify a primary PW. Specifically, in the centralized protector model, the Protection FEC Element TLV advertised by a backup (S-)PE MUST match the one advertised by the primary PE, so that the protector can associate the primary PW's label with the backup PW's label and perform a label swap. The backup (S-)PE builds such a Protection FEC Element TLV based on local configuration.
为了支持这些程序，本文件定义了一个新的“保护FEC元件”TLV。上述两个LDP会话的标签映射消息必须携带该TLV以识别主PW。具体而言，在集中式保护器模型中，备份（S-）PE播发的保护FEC元素TLV必须与主PE播发的保护FEC元素TLV匹配，以便保护器可以将主PW的标签与备份PW的标签关联，并执行标签交换。备份（S-）PE基于本地配置构建这样一个保护FEC元素TLV。
This document also defines a new "Egress Protection Capability" TLV as a new type of Capability Parameter TLV [RFC5561], to allow a protector to announce its capability of processing the above Protection FEC Element TLV and performing context-specific label switching for PW labels.
本文件还将新的“出口保护能力”TLV定义为一种新类型的能力参数TLV[RFC5561]，以允许保护器宣布其处理上述保护FEC元素TLV并对PW标签执行上下文特定标签切换的能力。
The procedures in this section are only applicable if the protector advertises the Egress Protection Capability TLV, the primary PE supports the advertisement of the Protection FEC Element TLV, and in the centralized protector model, the backup PE also supports the advertisement of the Protection FEC Element TLV.
本节中的程序仅适用于保护器播发出口保护能力TLV，主PE支持保护FEC元件TLV的播发，并且在集中式保护器模型中，备份PE也支持保护FEC元件TLV的播发。
A protector MUST advertise the Egress Protection Capability TLV in its Initialization message and Capability message over the LDP session with a primary PE. In the centralized protector model, the protector MUST also advertise the TLV over the LDP session with a backup PE. The TLV carries one or multiple context identifiers. To the primary PE, the TLV MUST carry the context identifier of the {primary PE, protector}. In the centralized protector model, the TLV MUST carry multiple context identifiers to the backup PE, one for each {primary PE, protector} where the backup PE serves as a backup for the primary PE. This TLV MUST NOT be advertised by the primary PE or the backup PE to the protector.
保护器必须在其初始化消息和通过与主PE的LDP会话的能力消息中公布出口保护能力TLV。在集中式保护器模型中，保护器还必须使用备份PE在LDP会话上公布TLV。TLV携带一个或多个上下文标识符。对于主PE，TLV必须携带{primary PE，protector}的上下文标识符。在集中式保护器模型中，TLV必须向备份PE携带多个上下文标识符，其中备份PE用作主PE的备份，每个{primary PE，protector}对应一个上下文标识符。主PE或备份PE不得向保护器播发此TLV。
The processing of the Egress Protection Capability TLV by a receiving router MUST follow the procedures defined in [RFC5561]. In particular, the router MUST advertise PW information to the protector by using the Protection FEC Element TLV, only after it has received the Egress Protection Capability TLV from the protector. It MUST validate each context identifier included in the TLV and advertise the information of only the PWs that are associated with the context identifier. It MUST withdraw previously advertised Protection FEC TLVs, when the protector has withdrawn a previously advertised context identifier or the entire Egress Protection Capability TLV via a Capability message.
接收路由器对出口保护能力TLV的处理必须遵循[RFC5561]中定义的程序。特别地，路由器必须仅在从保护器接收到出口保护能力TLV之后，通过使用保护FEC元素TLV向保护器通告PW信息。它必须验证TLV中包含的每个上下文标识符，并仅公布与上下文标识符关联的PW的信息。当保护器通过能力消息撤回先前公布的上下文标识符或整个出口保护能力TLV时，必须撤回先前公布的保护FEC TLV。
The encoding of the Egress Protection Capability TLV is defined below. It conforms to the format of Capability Parameter TLV specified in [RFC5561].
出口保护能力TLV的编码定义如下。它符合[RFC5561]中规定的能力参数TLV的格式。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Egress Protection (0x0974)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+ |
| |
~ Capability Data = context identifier(s) ~
| |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Egress Protection (0x0974)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+ |
| |
~ Capability Data = context identifier(s) ~
| |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15
图15
The U-bit MUST be set to 1, so that a receiver MUST silently ignore this TLV if unknown to it and continue processing the rest of the message.
U位必须设置为1，这样，如果接收器未知，则必须默默忽略此TLV，并继续处理消息的其余部分。
The F-bit MUST be set to 0 since this TLV is sent only in Initialization and Capability messages, which are not forwarded.
F位必须设置为0，因为此TLV仅在初始化和功能消息中发送，而不会转发。
The TLV code point is 0x0974.
TLV代码点为0x0974。
The S-bit indicates whether the sender is advertising (S=1) or withdrawing (S=0) the capability.
S位表示发送方是在宣传（S=1）还是在撤回（S=0）该功能。
The Capability Data field is encoded with the context identifiers of the {primary PE, protector} pairs for which the advertiser is the protector.
能力数据字段用广告客户作为保护者的{primary PE，protector}对的上下文标识符编码。
A primary PE MUST advertise a primary PW's label to a protector by sending a Label Mapping message. The message includes a Protection FEC Element TLV (see Section 6.4 for encoding) and an Upstream-Assigned Label TLV [RFC6389] encoded with the PW's label. The combination of the Protection FEC Element TLV and the PW label represents the primary PE's forwarding state for the PW. The Label Mapping message MUST also carry an IPv4/v6 Interface_ID TLV [RFC3471] [RFC6389] encoded with the context identifier of the {primary PE, protector}.
主PE必须通过发送标签映射消息向保护器公布主PW的标签。该信息包括一个保护FEC元件TLV（编码见第6.4节）和一个上游分配标签TLV[RFC6389]，用PW的标签编码。保护FEC元素TLV和PW标签的组合表示PW的主PE的转发状态。标签映射消息还必须携带IPv4/v6接口_idtlv[RFC3471][RFC6389]，该接口用{primary PE，protector}的上下文标识符编码。
The protector that receives this Label Mapping message MUST install a forwarding entry for the PW label in the label space identified by the context identifier. The next hop of the forwarding entry MUST ensure that packets are sent towards the target CE via a backup AC or
接收此标签映射消息的保护器必须在上下文标识符标识的标签空间中为PW标签安装转发条目。转发条目的下一跳必须确保通过备份AC或IP向目标CE发送数据包
a backup (S-)PE, depending on the protection scenario. The protector MUST silently discard a Label Mapping message if the included context identifier is unknown to it.
备份（S-）PE，具体取决于保护方案。如果所包含的上下文标识符未知，则保护程序必须以静默方式放弃标签映射消息。
In the centralized protector model, a backup PE MUST advertise a backup PW's label to the protector by sending a Label Mapping message. The message includes a Protection FEC Element TLV and a Generic Label TLV encoded with the backup PW's label. This Protection FEC Element MUST be identical to the Protection FEC Element TLV that the primary PE advertises to the protector (Section 6.2). This is achieved through configuration on the backup PE. The context identifier MUST NOT be encoded in an Interface_ID TLV in this message.
在集中式保护器模型中，备份PE必须通过发送标签映射消息向保护器公布备份PW的标签。该消息包括一个保护FEC元素TLV和一个用备份PW的标签编码的通用标签TLV。该保护FEC元件必须与主PE向保护器通告的保护FEC元件TLV相同（第6.2节）。这是通过备份PE上的配置实现的。上下文标识符不得编码在此消息中的接口ID TLV中。
The protector that receives this Label Mapping message MUST associate the backup PW with the primary PW, based on the common Protection FEC Element TLV. It MUST distinguish between the Label Mapping message from the primary PE and the Label Mapping message from the backup PE based on the respective presence and absence of a context identifier in the Interface_ID TLV. It MUST install a forwarding entry for the primary PW's label in the label space identified by the context identifier. The next hop of the forwarding entry MUST indicate a label swap to the backup PW's label, followed by a label push or IP header push for a transport tunnel to the backup PE.
接收此标签映射消息的保护器必须基于公共保护FEC元素TLV将备份PW与主PW关联。它必须根据接口_ID TLV中上下文标识符的存在与否，区分来自主PE的标签映射消息和来自备份PE的标签映射消息。它必须在上下文标识符标识的标签空间中为主PW的标签安装转发条目。转发条目的下一个跃点必须指示标签交换到备份PW的标签，然后是标签推送或IP头推送，用于到备份PE的传输隧道。
The Protection FEC Element TLV has type 0x83. Its format is defined below:
保护FEC元件TLV的类型为0x83。其格式定义如下：
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Encoding Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
~ PW Information ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Encoding Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
~ PW Information ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16
图16
- Encoding Type
- 编码类型
Type of encoding format of the PW Information field. The following types are defined, corresponding to the PWid FEC Element and Generalized PWid FEC Element defined in [RFC8077].
PW信息字段的编码格式类型。定义了以下类型，对应于[RFC8077]中定义的PWid FEC元素和广义PWid FEC元素。
1 - PWid FEC Element with IPv4 PE addresses (Section 6.4.1).
1-具有IPv4 PE地址的PWid FEC元素（第6.4.1节）。
2 - Generalized PWid FEC Element with IPv4 PE addresses (Section 6.4.2).
2-具有IPv4 PE地址的通用PWid FEC元素（第6.4.2节）。
3 - PWid FEC Element with IPv6 PE addresses (Section 6.4.3).
3-具有IPv6 PE地址的PWid FEC元件（第6.4.3节）。
4 - Generalized PWid FEC Element with IPv6 PE addresses (Section 6.4.4).
4-具有IPv6 PE地址的通用PWid FEC元素（第6.4.4节）。
- Length
- 长
Length of the PW Information field in octets.
PW信息字段的长度（以八位字节为单位）。
- PW Information
- PW信息
Field of variable length that specifies a PW.
指定PW的可变长度字段。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(1) | Length(20) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(1) | Length(20) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17
图17
- Ingress PE IPv4 Address
- 入口PE IPv4地址
IPv4 address of the ingress PE of PW.
PW的入口PE的IPv4地址。
- Egress PE IPv4 Address
- 出口PE IPv4地址
IPv4 address of the egress PE of PW.
PW出口PE的IPv4地址。
- Group ID
- 组ID
An arbitrary 32-bit value that represents a group of PWs and that is used to create groups in the PW space.
表示一组PW的任意32位值，用于在PW空间中创建组。
- PW ID
- PW ID
A non-zero 32-bit connection ID that, together with the PW Type field, identifies a particular PW.
一种非零32位连接ID，与PW类型字段一起标识特定PW。
- Control word bit (C)
- 控制字位（C）
A bit that flags the presence of a control word on this PW. If C = 1, control word is present; if C = 0, control word is not present.
标记此PW上是否存在控制字的位。如果C=1，则存在控制字；如果C=0，则控制字不存在。
- PW Type
- PW型
A 15-bit quantity that represents the type of PW.
表示PW类型的15位数量。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress PE IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18
图18
- Ingress PE IPv4 Address
- 入口PE IPv4地址
IPv4 address of the ingress PE of PW.
PW的入口PE的IPv4地址。
- Egress PE IPv4 Address
- 出口PE IPv4地址
IPv4 address of the egress PE of PW.
PW出口PE的IPv4地址。
- Control word bit (C)
- 控制字位（C）
A bit that flags the presence of a control word on this PW. If C = 1, control word is present; if C = 0, control word is not present.
标记此PW上是否存在控制字的位。如果C=1，则存在控制字；如果C=0，则控制字不存在。
- PW Type
- PW型
A 15-bit quantity that represents the type of PW.
表示PW类型的15位数量。
- AGI Type, Length, AGI Value
- AGI类型、长度、AGI值
Attachment Group Identifier of PW.
PW的附件组标识符。
- AII Type, Length, SAII Value
- 所有类型、长度、SAII值
Source Attachment Individual Identifier of PW.
源附件PW的单个标识符。
- AII Type, Length, TAII Value
- 所有类型、长度、TAII值
Target Attachment Individual Identifier of PW.
目标附件PW的单个标识符。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(3) | Length(44) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Ingress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Egress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(3) | Length(44) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Ingress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Egress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19
图19
- Ingress PE IPv6 Address
- 入口PE IPv6地址
IPv6 address of the ingress PE of PW; 16 octets.
PW入口PE的IPv6地址；16个八位组。
- Egress PE IPv6 Address
- 出口PE IPv6地址
IPv6 address of the egress PE of PW; 16 octets.
PW出口PE的IPv6地址；16个八位组。
- Group ID
- 组ID
An arbitrary 32-bit value that represents a group of PWs and that is used to create groups in the PW space.
表示一组PW的任意32位值，用于在PW空间中创建组。
- PW ID
- PW ID
A non-zero 32-bit connection ID that, together with the PW Type field, identifies a particular PW.
一种非零32位连接ID，与PW类型字段一起标识特定PW。
- Control word bit (C)
- 控制字位（C）
A bit that flags the presence of a control word on this PW. If C = 1, control word is present; if C = 0, control word is not present.
标记此PW上是否存在控制字的位。如果C=1，则存在控制字；如果C=0，则控制字不存在。
- PW Type
- PW型
A 15-bit quantity that represents the type of PW.
表示PW类型的15位数量。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Ingress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Egress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(0x83) | Reserved | Enc Type(4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Ingress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Egress PE IPv6 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| PW Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | TAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20
图20
- Ingress PE IPv6 Address
- 入口PE IPv6地址
IPv6 address of the ingress PE of PW; 16 octets.
PW入口PE的IPv6地址；16个八位组。
- Egress PE IPv6 Address
- 出口PE IPv6地址
IPv6 address of the egress PE of PW; 16 octets.
PW出口PE的IPv6地址；16个八位组。
- Control word bit (C)
- 控制字位（C）
A bit that flags the presence of a control word on this PW. If C = 1, control word is present; if C = 0, control word is not present.
标记此PW上是否存在控制字的位。如果C=1，则存在控制字；如果C=0，则控制字不存在。
- PW Type
- PW型
A 15-bit quantity that represents the type of PW.
表示PW类型的15位数量。
- AGI Type, Length, AGI Value
- AGI类型、长度、AGI值
Attachment Group Identifier of PW.
PW的附件组标识符。
- AII Type, Length, SAII Value
- 所有类型、长度、SAII值
Source Attachment Individual Identifier of PW.
源附件PW的单个标识符。
- AII Type, Length, TAII Value
- 所有类型、长度、TAII值
Target Attachment Individual Identifier of PW.
目标附件PW的单个标识符。
This document defines a new Egress Protection Capability TLV in Section 6. IANA has assigned value 0x0974 for it in the "TLV Type Name Space" registry.
本文件在第6节中定义了新的出口保护能力TLV。IANA在“TLV类型名称空间”注册表中为其分配了值0x0974。
This document defines a new Protection FEC Element TLV in Section 6. IANA assigned value 0x83 for it in the "Forwarding Equivalence Class (FEC) Type Name Space" registry per RFC 7358. IANA has updated the registry to also reference this document.
本文件在第6节中定义了新的FEC保护元件TLV。IANA根据RFC 7358在“转发等价类（FEC）类型名称空间”注册表中为其分配了值0x83。IANA已更新了注册表，以同时参考本文件。
In this document, PW traffic can be temporarily rerouted by a PLR to a protector. In the centralized protector scenario, the traffic can be further rerouted to a backup PE. In the control plane, there is a targeted LDP session between a primary PE and a protector. In the centralized protector scenario, there is also a targeted LDP session between a backup PE and a protector. In all scenarios, traffic rerouting via PLRs, protectors, and backup PEs is planned and anticipated, and backup PEs can be used anyway to host PWs and LDP sessions. Hence, the rerouted traffic and the LDP sessions introduced in this document should not be viewed as a new security threat.
在本文件中，可通过PLR将PW通信暂时重新路由至保护器。在集中式保护器方案中，流量可以进一步重新路由到备份PE。在控制平面中，在主PE和保护器之间存在目标LDP会话。在集中式保护器方案中，备份PE和保护器之间还有一个目标LDP会话。在所有情况下，都计划并预期通过PLR、保护器和备份PEs的流量重新路由，并且备份PEs可用于承载PWs和LDP会话。因此，本文件中介绍的重路由流量和LDP会话不应被视为新的安全威胁。
In general, [RFC5920] describes the security framework for MPLS networks. [RFC3209] describes the security considerations for RSVP Label Switched Paths (LSPs). [RFC5036] describes the security considerations for the base LDP specification. [RFC5561] describes the security considerations that apply when using the LDP capability mechanism. All these security frameworks and considerations apply to this document as well.
通常，[RFC5920]描述了MPLS网络的安全框架。[RFC3209]描述了RSVP标签交换路径（LSP）的安全注意事项。[RFC5036]描述了基本LDP规范的安全注意事项。[RFC5561]描述了使用LDP能力机制时应用的安全注意事项。所有这些安全框架和注意事项也适用于本文档。
[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>.
[RFC8077] Martini, L., Ed. and G. Heron, Ed., "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017, <http://www.rfc-editor.org/info/rfc8077>.
[RFC8077]Martini，L.，Ed.和G.Heron，Ed.，“使用标签分发协议（LDP）的伪线设置和维护”，STD 84，RFC 8077，DOI 10.17487/RFC8077，2017年2月<http://www.rfc-editor.org/info/rfc8077>.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream Label Assignment and Context-Specific Label Space", RFC 5331, DOI 10.17487/RFC5331, August 2008, <http://www.rfc-editor.org/info/rfc5331>.
[RFC5331]Aggarwal，R.，Rekhter，Y.，和E.Rosen，“MPLS上游标签分配和上下文特定标签空间”，RFC 5331，DOI 10.17487/RFC5331，2008年8月<http://www.rfc-editor.org/info/rfc5331>.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL. Le Roux, "LDP Capabilities", RFC 5561, DOI 10.17487/RFC5561, July 2009, <http://www.rfc-editor.org/info/rfc5561>.
[RFC5561]托马斯，B.，拉扎，K.，阿加瓦尔，S.，阿加瓦尔，R.，和JL。Le Roux，“LDP能力”，RFC 5561，DOI 10.17487/RFC55611909年7月<http://www.rfc-editor.org/info/rfc5561>.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, DOI 10.17487/RFC3471, January 2003, <http://www.rfc-editor.org/info/rfc3471>.
[RFC3471]Berger，L.，Ed.“通用多协议标签交换（GMPLS）信令功能描述”，RFC 3471，DOI 10.17487/RFC3471，2003年1月<http://www.rfc-editor.org/info/rfc3471>.
[RFC3472] Ashwood-Smith, P., Ed. and L. Berger, Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Constraint-based Routed Label Distribution Protocol (CR-LDP) Extensions", RFC 3472, DOI 10.17487/RFC3472, January 2003, <http://www.rfc-editor.org/info/rfc3472>.
[RFC3472]Ashwood Smith，P.，Ed.和L.Berger，Ed.，“基于广义多协议标签交换（GMPLS）信令约束的路由标签分发协议（CR-LDP）扩展”，RFC 3472，DOI 10.17487/RFC3472，2003年1月<http://www.rfc-editor.org/info/rfc3472>.
[RFC6389] Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label Assignment for LDP", RFC 6389, DOI 10.17487/RFC6389, November 2011, <http://www.rfc-editor.org/info/rfc6389>.
[RFC6389]阿加瓦尔，R.和JL。Le Roux，“LDP的MPLS上游标签分配”，RFC 6389，DOI 10.17487/RFC6389，2011年11月<http://www.rfc-editor.org/info/rfc6389>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, DOI 10.17487/RFC4090, May 2005, <http://www.rfc-editor.org/info/rfc4090>.
[RFC4090]Pan，P.，Ed.，Swallow，G.，Ed.，和A.Atlas，Ed.，“LSP隧道RSVP-TE的快速重路由扩展”，RFC 4090，DOI 10.17487/RFC4090，2005年5月<http://www.rfc-editor.org/info/rfc4090>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, DOI 10.17487/RFC5286, September 2008, <http://www.rfc-editor.org/info/rfc5286>.
[RFC5286]Atlas，A.，Ed.和A.Zinin，Ed.，“IP快速重路由的基本规范：无环路交替”，RFC 5286，DOI 10.17487/RFC5286，2008年9月<http://www.rfc-editor.org/info/rfc5286>.
[RFC7812] Atlas, A., Bowers, C., and G. Enyedi, "An Architecture for IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-FRR)", RFC 7812, DOI 10.17487/RFC7812, June 2016, <http://www.rfc-editor.org/info/rfc7812>.
[RFC7812]Atlas，A.，Bowers，C.，和G.Enyedi，“使用最大冗余树的IP/LDP快速重路由架构（MRT-FRR）”，RFC 7812，DOI 10.17487/RFC7812，2016年6月<http://www.rfc-editor.org/info/rfc7812>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <http://www.rfc-editor.org/info/rfc3031>.
[RFC3031]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 3031，DOI 10.17487/RFC3031，2001年1月<http://www.rfc-editor.org/info/rfc3031>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010, <http://www.rfc-editor.org/info/rfc5920>.
[RFC5920]方，L.，编辑，“MPLS和GMPLS网络的安全框架”，RFC 5920，DOI 10.17487/RFC5920，2010年7月<http://www.rfc-editor.org/info/rfc5920>.
[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>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, <http://www.rfc-editor.org/info/rfc3209>.
[RFC3209]Awduche，D.，Berger，L.，Gan，D.，Li，T.，Srinivasan，V.，和G.Swallow，“RSVP-TE：LSP隧道RSVP的扩展”，RFC 3209，DOI 10.17487/RFC3209，2001年12月<http://www.rfc-editor.org/info/rfc3209>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007, <http://www.rfc-editor.org/info/rfc5036>.
[RFC5036]Andersson，L.，Ed.，Minei，I.，Ed.，和B.Thomas，Ed.“LDP规范”，RFC 5036，DOI 10.17487/RFC5036，2007年10月<http://www.rfc-editor.org/info/rfc5036>.
[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>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714, DOI 10.17487/RFC5714, January 2010, <http://www.rfc-editor.org/info/rfc5714>.
[RFC5714]Shand，M.和S.Bryant，“IP快速重路由框架”，RFC 5714，DOI 10.17487/RFC5714，2010年1月<http://www.rfc-editor.org/info/rfc5714>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, <http://www.rfc-editor.org/info/rfc5880>.
[RFC5880]Katz，D.和D.Ward，“双向转发检测（BFD）”，RFC 5880，DOI 10.17487/RFC5880，2010年6月<http://www.rfc-editor.org/info/rfc5880>.
[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>.
[RFC5885] Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)", RFC 5885, DOI 10.17487/RFC5885, June 2010, <http://www.rfc-editor.org/info/rfc5885>.
[RFC5885]Nadeau，T.，Ed.和C.Pignataro，Ed.，“伪线虚拟电路连接验证（VCCV）的双向转发检测（BFD）”，RFC 5885，DOI 10.17487/RFC5885，2010年6月<http://www.rfc-editor.org/info/rfc5885>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. Pallagatti, "Seamless Bidirectional Forwarding Detection (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, <http://www.rfc-editor.org/info/rfc7880>.
[RFC7880]Pignataro，C.，Ward，D.，Akiya，N.，Bhatia，M.，和S.Pallagati，“无缝双向转发检测（S-BFD）”，RFC 7880，DOI 10.17487/RFC78802016年7月<http://www.rfc-editor.org/info/rfc7880>.
Acknowledgements
致谢
This document leverages work done by Hannes Gredler, Yakov Rekhter, Minto Jeyananth, Kevin Wang, and several others on MPLS edge protection. Thanks to Nischal Sheth and Bhupesh Kothari for their contributions. Thanks to John E. Drake, Andrew G. Malis, Alexander Vainshtein, Stewart Bryant, and Mach(Guoyi) Chen for valuable comments that helped shape this document and improve its clarity.
本文档利用了Hannes Gredler、Yakov Rekhter、Minto Jeyananth、Kevin Wang和其他几个人在MPLS边缘保护方面所做的工作。感谢Nischal Sheth和Bhupesh Kothari的贡献。感谢John E.Drake、Andrew G.Malis、Alexander Vainstein、Stewart Bryant和Mach（Guoyi）Chen的宝贵意见，这些意见有助于形成本文件并提高其清晰度。
Authors' Addresses
作者地址
Yimin Shen Juniper Networks 10 Technology Park Drive Westford, MA 01886 United States of America
美国马萨诸塞州韦斯特福德科技园大道10号伊敏·申·杜松网络公司01886
Phone: +1 9785890722
Email: yshen@juniper.net
Phone: +1 9785890722
Email: yshen@juniper.net
Rahul Aggarwal Arktan, Inc.
Rahul Aggarwal Arktan公司。
Email: raggarwa_1@yahoo.com
Email: raggarwa_1@yahoo.com
Wim Henderickx Nokia Copernicuslaan 50 2018 Antwerp Belgium
Wim Henderickx诺基亚哥白尼50 2018比利时安特卫普
Email: wim.henderickx@nokia.com
Email: wim.henderickx@nokia.com
Yuanlong Jiang Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129 China
中国深圳市龙岗区坂田远龙江华为技术有限公司518129
Email: jiangyuanlong@huawei.com
Email: jiangyuanlong@huawei.com