Internet Engineering Task Force (IETF) R. Aggarwal
Request for Comments: 5884 K. Kompella
Updates: 1122 Juniper Networks
Category: Standards Track T. Nadeau
ISSN: 2070-1721 BT
G. Swallow
Cisco Systems, Inc.
June 2010
Internet Engineering Task Force (IETF) R. Aggarwal
Request for Comments: 5884 K. Kompella
Updates: 1122 Juniper Networks
Category: Standards Track T. Nadeau
ISSN: 2070-1721 BT
G. Swallow
Cisco Systems, Inc.
June 2010
Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)
MPLS标签交换路径（LSP）的双向转发检测（BFD）
Abstract
摘要
One desirable application of Bidirectional Forwarding Detection (BFD) is to detect a Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) data plane failure. LSP Ping is an existing mechanism for detecting MPLS data plane failures and for verifying the MPLS LSP data plane against the control plane. BFD can be used for the former, but not for the latter. However, the control plane processing required for BFD Control packets is relatively smaller than the processing required for LSP Ping messages. A combination of LSP Ping and BFD can be used to provide faster data plane failure detection and/or make it possible to provide such detection on a greater number of LSPs. This document describes the applicability of BFD in relation to LSP Ping for this application. It also describes procedures for using BFD in this environment.
双向转发检测（BFD）的一个理想应用是检测多协议标签交换（MPLS）标签交换路径（LSP）数据平面故障。LSP Ping是一种现有的机制，用于检测MPLS数据平面故障并根据控制平面验证MPLS LSP数据平面。BFD可用于前者，但不能用于后者。然而，BFD控制分组所需的控制平面处理相对小于LSP Ping消息所需的处理。LSP Ping和BFD的组合可用于提供更快的数据平面故障检测和/或使在更多LSP上提供此类检测成为可能。本文件描述了BFD在该应用中与LSP Ping相关的适用性。它还描述了在此环境中使用BFD的过程。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5884.
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/rfc5884.
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版权公告
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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。
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
本文件可能包含2008年11月10日之前发布或公开的IETF文件或IETF贡献中的材料。控制某些材料版权的人员可能未授予IETF信托允许在IETF标准流程之外修改此类材料的权利。在未从控制此类材料版权的人员处获得充分许可的情况下，不得在IETF标准流程之外修改本文件，也不得在IETF标准流程之外创建其衍生作品，除了将其格式化以RFC形式发布或将其翻译成英语以外的其他语言。
Table of Contents
目录
1. Introduction ....................................................3
2. Specification of Requirements ...................................3
3. Applicability ...................................................3
3.1. BFD for MPLS LSPs: Motivation ..............................3
3.2. Using BFD in Conjunction with LSP Ping .....................5
4. Theory of Operation .............................................6
5. Initialization and Demultiplexing ...............................7
6. Session Establishment ...........................................7
6.1. BFD Discriminator TLV in LSP Ping ..........................8
7. Encapsulation ...................................................8
8. Security Considerations .........................................9
9. IANA Considerations ............................................10
10. Acknowledgments ...............................................10
11. References ....................................................10
11.1. Normative References .....................................10
11.2. Informative References ...................................10
1. Introduction ....................................................3
2. Specification of Requirements ...................................3
3. Applicability ...................................................3
3.1. BFD for MPLS LSPs: Motivation ..............................3
3.2. Using BFD in Conjunction with LSP Ping .....................5
4. Theory of Operation .............................................6
5. Initialization and Demultiplexing ...............................7
6. Session Establishment ...........................................7
6.1. BFD Discriminator TLV in LSP Ping ..........................8
7. Encapsulation ...................................................8
8. Security Considerations .........................................9
9. IANA Considerations ............................................10
10. Acknowledgments ...............................................10
11. References ....................................................10
11.1. Normative References .....................................10
11.2. Informative References ...................................10
One desirable application of Bidirectional Forwarding Detection (BFD) is to track the liveness of a Multiprotocol Label Switching (MPLS) Label Switched Path (LSP). In particular, BFD can be used to detect a data plane failure in the forwarding path of an MPLS LSP. LSP Ping [RFC4379] is an existing mechanism for detecting MPLS LSP data plane failures and for verifying the MPLS LSP data plane against the control plane. This document describes the applicability of BFD in relation to LSP Ping for detecting MPLS LSP data plane failures. It also describes procedures for using BFD for detecting MPLS LSP data plane failures.
双向转发检测（BFD）的一个理想应用是跟踪多协议标签交换（MPLS）标签交换路径（LSP）的活跃度。具体而言，BFD可用于检测MPLS LSP的转发路径中的数据平面故障。LSP Ping[RFC4379]是一种现有机制，用于检测MPLS LSP数据平面故障，并根据控制平面验证MPLS LSP数据平面。本文档描述了BFD在检测MPLS LSP数据平面故障时与LSP Ping相关的适用性。它还描述了使用BFD检测MPLS LSP数据平面故障的过程。
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。
In the event of an MPLS LSP failing to deliver data traffic, it may not always be possible to detect the failure using the MPLS control plane. For instance, the control plane of the MPLS LSP may be functional while the data plane may be mis-forwarding or dropping data. Hence, there is a need for a mechanism to detect a data plane failure in the MPLS LSP path [RFC4377].
在MPLS LSP未能交付数据通信量的情况下，可能并不总是能够使用MPLS控制平面来检测故障。例如，MPLS LSP的控制平面可以是功能性的，而数据平面可以是误转发或丢弃数据。因此，需要一种机制来检测MPLS LSP路径[RFC4377]中的数据平面故障。
LSP Ping described in [RFC4379] is an existing mechanism for detecting an MPLS LSP data plane failure. In addition, LSP Ping also provides a mechanism for verifying the MPLS control plane against the data plane. This is done by ensuring that the LSP is mapped to the same Forwarding Equivalence Class (FEC), at the egress, as the ingress.
[RFC4379]中描述的LSP Ping是用于检测MPLS LSP数据平面故障的现有机制。此外，LSP Ping还提供了一种根据数据平面验证MPLS控制平面的机制。这是通过确保LSP在出口处映射到与入口相同的转发等价类（FEC）来实现的。
BFD cannot be used for verifying the MPLS control plane against the data plane. However, BFD can be used to detect a data plane failure in the forwarding path of an MPLS LSP. The LSP may be associated with any of the following FECs:
BFD不能用于对照数据平面验证MPLS控制平面。然而，BFD可用于检测MPLS LSP的转发路径中的数据平面故障。LSP可与以下任何fec相关联：
a) Resource Reservation Protocol (RSVP) LSP_Tunnel IPv4/IPv6 Session [RFC3209]
a) 资源预留协议（RSVP）LSP_隧道IPv4/IPv6会话[RFC3209]
b) Label Distribution Protocol (LDP) IPv4/IPv6 prefix [RFC5036]
b) 标签分发协议（LDP）IPv4/IPv6前缀[RFC5036]
c) Virtual Private Network (VPN) IPv4/IPv6 prefix [RFC4364]
c) 虚拟专用网络（VPN）IPv4/IPv6前缀[RFC4364]
d) Layer 2 VPN [L2-VPN]
d) 第二层VPN[L2-VPN]
e) Pseudowires based on PWid FEC and Generalized PWid FEC [RFC4447]
e) 基于PWid FEC和广义PWid FEC的伪线[RFC4447]
f) Border Gateway Protocol (BGP) labeled prefixes [RFC3107]
f) 带前缀的边界网关协议（BGP）[RFC3107]
LSP Ping includes extensive control plane verification. BFD, on the other hand, was designed as a lightweight means of testing only the data plane. As a result, LSP Ping is computationally more expensive than BFD for detecting MPLS LSP data plane faults. BFD is also more suitable for being implemented in hardware or firmware due to its fixed packet format. Thus, the use of BFD for detecting MPLS LSP data plane faults has the following advantages:
LSP Ping包括广泛的控制平面验证。另一方面，BFD被设计成只测试数据平面的轻量级方法。因此，在检测MPLS LSP数据平面故障时，LSP Ping在计算上比BFD更昂贵。由于其固定的数据包格式，BFD也更适合在硬件或固件中实现。因此，使用BFD检测MPLS LSP数据平面故障具有以下优点：
a) Support for fault detection for greater number of LSPs.
a) 支持更多LSP的故障检测。
b) Fast detection. Detection with sub-second granularity is considered as fast detection. LSP Ping is intended to be used in an environment where fault detection messages are exchanged, either for diagnostic purposes or for infrequent periodic fault detection, in the order of tens of seconds or minutes. Hence, it is not appropriate for fast detection. BFD, on the other hand, is designed for sub-second fault detection intervals. Following are some potential cases when fast detection may be desirable for MPLS LSPs:
b) 快速检测。亚秒级粒度的检测被认为是快速检测。LSP Ping旨在用于交换故障检测消息的环境中，无论是出于诊断目的，还是为了不频繁的周期性故障检测，交换时间为几十秒或几分钟。因此，它不适合快速检测。另一方面，BFD设计用于亚秒级故障检测间隔。以下是MPLS LSP可能需要快速检测的一些潜在情况：
1. In the case of a bypass LSP used for a facility-based link or node protection [RFC4090]. In this case, the bypass LSP is essentially being used as an alternate link to protect one or more LSPs. It represents an aggregate and is used to carry data traffic belonging to one or more LSPs, when the link or the node being protected fails. Hence, fast failure detection of the bypass LSP may be desirable particularly in the event of link or node failure when the data traffic is moved to the bypass LSP.
1. 如果旁路LSP用于基于设施的链路或节点保护[RFC4090]。在这种情况下，旁路LSP基本上被用作保护一个或多个LSP的备用链路。它表示聚合，用于在链路或受保护节点发生故障时承载属于一个或多个LSP的数据流量。因此，尤其在数据业务被移动到旁路LSP时发生链路或节点故障的情况下，可能需要旁路LSP的快速故障检测。
2. MPLS Pseudowires (PWs). Fast detection may be desired for MPLS PWs depending on i) the model used to layer the MPLS network with the Layer 2 network, and ii) the service that the PW is emulating. For a non-overlay model between the Layer 2 network and the MPLS network, the provider may rely on PW fault detection to provide service status to the end-systems. Also, in that case, interworking scenarios such as ATM/Frame Relay interworking may force periodic PW fault detection messages. Depending on the requirements of the service that the MPLS PW is emulating, fast failure detection may be desirable.
2. MPLS伪线（PWs）。MPLS PW可能需要快速检测，这取决于i）用于将MPLS网络与第2层网络分层的模型，以及ii）PW正在模拟的服务。对于第2层网络和MPLS网络之间的非重叠模型，提供商可以依赖PW故障检测向终端系统提供服务状态。此外，在这种情况下，诸如ATM/帧中继互通之类的互通场景可能会强制执行周期性PW故障检测消息。根据MPLS PW正在模拟的服务的需求，可能需要快速故障检测。
There may be other potential cases where fast failure detection is desired for MPLS LSPs.
对于MPLS LSP，还可能存在需要快速故障检测的其他潜在情况。
BFD can be used for MPLS LSP data plane fault detection. However, it does not have all the functionality of LSP Ping. In particular, it cannot be used for verifying the control plane against the data plane. LSP Ping performs the following functions that are outside the scope of BFD:
BFD可用于MPLS LSP数据平面故障检测。但是，它并不具备LSP Ping的所有功能。特别是，它不能用于对照数据平面验证控制平面。LSP Ping执行以下超出BFD范围的功能：
a) Association of an LSP Ping Echo request message with a FEC. In the case of Penultimate Hop Popping (PHP) or when the egress Label Switching Router (LSR) distributes an explicit null label to the penultimate hop router, for a single label stack LSP, the only way to associate a fault detection message with a FEC is by carrying the FEC in the message. LSP Ping provides this functionality. Next-hop label allocation also makes it necessary to carry the FEC in the fault detection message as the label alone is not sufficient to identify the LSP being verified. In addition, presence of the FEC in the Echo request message makes it possible to verify the control plane against the data plane at the egress LSR.
a) LSP Ping回显请求消息与FEC的关联。在倒数第二跳弹出（PHP）的情况下，或者当出口标签交换路由器（LSR）向倒数第二跳路由器分发显式空标签时，对于单标签堆栈LSP，将故障检测消息与FEC关联的唯一方法是通过在消息中携带FEC。LSP Ping提供了此功能。下一跳标签分配还需要在故障检测消息中携带FEC，因为仅标签不足以识别正在验证的LSP。此外，Echo请求消息中FEC的存在使得能够对照出口LSR处的数据平面来验证控制平面。
b) Equal Cost Multi-Path (ECMP) considerations. LSP Ping traceroute makes it possible to probe multiple alternate paths for LDP IP FECs.
b) 等成本多路径（ECMP）注意事项。LSP Ping跟踪路由使探测LDP IP FEC的多条备用路径成为可能。
c) Traceroute. LSP Ping supports traceroute for a FEC and it can be used for fault isolation.
c) 追踪路线。LSP Ping支持FEC的跟踪路由，可用于故障隔离。
Hence, BFD is used in conjunction with LSP Ping for MPLS LSP fault detection:
因此，BFD与LSP Ping一起用于MPLS LSP故障检测：
i) LSP Ping is used for bootstrapping the BFD session as described later in this document.
i) LSP Ping用于引导BFD会话，如本文档后面所述。
ii) BFD is used to exchange fault detection (i.e., BFD session) packets at the required detection interval.
ii）BFD用于按要求的检测间隔交换故障检测（即BFD会话）数据包。
iii) LSP Ping is used to periodically verify the control plane against the data plane by ensuring that the LSP is mapped to the same FEC, at the egress, as the ingress.
iii）LSP Ping用于通过确保LSP映射到出口处与入口处相同的FEC，根据数据平面定期验证控制平面。
To use BFD for fault detection on an MPLS LSP, a BFD session MUST be established for that particular MPLS LSP. BFD Control packets MUST be sent along the same data path as the LSP being verified and are processed by the BFD processing module of the egress LSR. If the LSP is associated with multiple FECs, a BFD session SHOULD be established for each FEC. For instance, this may happen in the case of next-hop label allocation. Hence, the operation is conceptually similar to the data plane fault detection procedures of LSP Ping.
要在MPLS LSP上使用BFD进行故障检测，必须为该特定MPLS LSP建立BFD会话。BFD控制数据包必须沿着与正在验证的LSP相同的数据路径发送，并由出口LSR的BFD处理模块处理。如果LSP与多个FEC关联，则应为每个FEC建立BFD会话。例如，这可能发生在下一跳标签分配的情况下。因此，该操作在概念上类似于LSP Ping的数据平面故障检测过程。
If MPLS fast-reroute is being used for the MPLS LSP, the use of BFD for fault detection can result in false fault detections if the BFD fault detection interval is less than the MPLS fast-reroute switchover time. When MPLS fast-reroute is triggered because of a link or node failure, BFD Control packets will be dropped until traffic is switched on to the backup LSP. If the time taken to perform the switchover exceeds the BFD fault detection interval, a fault will be declared even though the MPLS LSP is being locally repaired. To avoid this, the BFD fault detection interval should be greater than the fast-reroute switchover time. An implementation SHOULD provide configuration options to control the BFD fault detection interval.
如果MPLS LSP使用MPLS快速重路由，如果BFD故障检测间隔小于MPLS快速重路由切换时间，则使用BFD进行故障检测可能导致错误故障检测。当由于链路或节点故障触发MPLS快速重路由时，BFD控制数据包将被丢弃，直到流量切换到备份LSP。如果执行切换所需的时间超过BFD故障检测间隔，则即使MPLS LSP正在本地修复，也会宣布故障。为避免这种情况，BFD故障检测间隔应大于快速重路由切换时间。实施应提供配置选项，以控制BFD故障检测间隔。
If there are multiple alternate paths from an ingress LSR to an egress LSR for an LDP IP FEC, LSP Ping traceroute MAY be used to determine each of these alternate paths. A BFD session SHOULD be established for each alternate path that is discovered.
如果对于LDP IP FEC存在从入口LSR到出口LSR的多个备用路径，则LSP Ping跟踪路由可用于确定这些备用路径中的每一个。应为发现的每个备用路径建立BFD会话。
Periodic LSP Ping Echo request messages SHOULD be sent by the ingress LSR to the egress LSR along the same data path as the LSP. This is to periodically verify the control plane against the data plane by ensuring that the LSP is mapped to the same FEC, at the egress, as the ingress. The rate of generation of these LSP Ping Echo request messages SHOULD be significantly less than the rate of generation of the BFD Control packets. An implementation MAY provide configuration options to control the rate of generation of the periodic LSP Ping Echo request messages.
入口LSR应沿与LSP相同的数据路径向出口LSR发送定期LSP Ping Echo请求消息。这是通过确保LSP被映射到出口处与入口处相同的FEC，根据数据平面周期性地验证控制平面。这些LSP Ping Echo请求消息的生成速率应明显小于BFD控制数据包的生成速率。实现可以提供配置选项来控制周期性LSP Ping Echo请求消息的生成速率。
To enable fault detection procedures specified in this document, for a particular MPLS LSP, this document requires the ingress and egress LSRs to be configured. This includes configuration for supporting BFD and LSP Ping as specified in this document. It also includes configuration that enables the ingress LSR to determine the method used by the egress LSR to identify Operations, Administration, and Maintenance (OAM) packets, e.g., whether the Time to Live (TTL) of the innermost MPLS label needs to be set to 1 to enable the egress
为了启用本文档中指定的故障检测程序，对于特定MPLS LSP，本文档要求配置入口和出口LSR。这包括本文档中规定的支持BFD和LSP Ping的配置。它还包括使入口LSR能够确定出口LSR用于识别操作、管理和维护（OAM）分组的方法的配置，例如，是否需要将最内层MPLS标签的生存时间（TTL）设置为1以启用出口
LSR to identify the OAM packet. For fault detection for MPLS PWs, this document assumes that the PW control channel type [RFC5085] is configured and the support of LSP Ping is also configured.
LSR用于标识OAM数据包。对于MPLS PWs的故障检测，本文档假设配置了PW控制通道类型[RFC5085]，并且还配置了对LSP Ping的支持。
A BFD session may be established for a FEC associated with an MPLS LSP. As described above, in the case of PHP or when the egress LSR distributes an explicit null label to the penultimate hop router, or next-hop label allocation, the BFD Control packet received by the egress LSR does not contain sufficient information to associate it with a BFD session. Hence, the demultiplexing MUST be done using the remote discriminator field in the received BFD Control packet. The exchange of BFD discriminators for this purpose is described in the next section.
可以为与MPLS LSP相关联的FEC建立BFD会话。如上所述，在PHP的情况下，或者当出口LSR向倒数第二跳路由器分发显式空标签或下一跳标签分配时，出口LSR接收的BFD控制分组不包含足够的信息以将其与BFD会话相关联。因此，解复用必须使用接收到的BFD控制包中的远程鉴别器字段来完成。下一节将介绍为此目的交换BFD鉴别器。
A BFD session is bootstrapped using LSP Ping. This specification describes procedures only for BFD asynchronous mode. BFD demand mode is outside the scope of this specification. Further, the use of the Echo function is outside the scope of this specification. The initiation of fault detection for a particular <MPLS LSP, FEC> combination results in the exchange of LSP Ping Echo request and Echo reply packets, in the ping mode, between the ingress and egress LSRs for that <MPLS LSP, FEC>. To establish a BFD session, an LSP Ping Echo request message MUST carry the local discriminator assigned by the ingress LSR for the BFD session. This MUST subsequently be used as the My Discriminator field in the BFD session packets sent by the ingress LSR.
BFD会话是使用LSP Ping引导的。本规范仅描述BFD异步模式的程序。BFD需求模式不在本规范范围内。此外，回声功能的使用不在本规范的范围内。对特定<MPLS LSP，FEC>组合的故障检测的启动导致在Ping模式下在该<MPLS LSP，FEC>的入口和出口lsr之间交换LSP Ping Echo请求和Echo reply分组。要建立BFD会话，LSP Ping Echo请求消息必须携带入口LSR为BFD会话分配的本地鉴别器。该字段随后必须用作入口LSR发送的BFD会话数据包中的My Discriminator字段。
On receipt of the LSP Ping Echo request message, the egress LSR MUST send a BFD Control packet to the ingress LSR, if the validation of the FEC in the LSP Ping Echo request message succeeds. This BFD Control packet MUST set the Your Discriminator field to the discriminator received from the ingress LSR in the LSP Ping Echo request message. The egress LSR MAY respond with an LSP Ping Echo reply message that carries the local discriminator assigned by it for the BFD session. The local discriminator assigned by the egress LSR MUST be used as the My Discriminator field in the BFD session packets sent by the egress LSR.
在接收到LSP Ping Echo请求消息时，如果LSP Ping Echo请求消息中的FEC验证成功，则出口LSR必须向入口LSR发送BFD控制分组。此BFD控制数据包必须将您的鉴别器字段设置为从LSP Ping Echo请求消息中的入口LSR接收的鉴别器。出口LSR可以使用LSP Ping Echo应答消息进行响应，该消息携带其为BFD会话分配的本地鉴别器。出口LSR分配的本地鉴别器必须用作出口LSR发送的BFD会话数据包中的My鉴别器字段。
The ingress LSR follows the procedures in [BFD] to send BFD Control packets to the egress LSR in response to the BFD Control packets received from the egress LSR. The BFD Control packets from the ingress to the egress LSR MUST set the local discriminator of the egress LSR, in the Your Discriminator field. The egress LSR demultiplexes the BFD session based on the received Your
入口LSR遵循[BFD]中的过程，响应于从出口LSR接收的BFD控制分组，向出口LSR发送BFD控制分组。从入口到出口LSR的BFD控制数据包必须在您的鉴别器字段中设置出口LSR的本地鉴别器。出口LSR根据接收到的数据解复用BFD会话
Discriminator field. As mentioned above, the egress LSR MUST send Control packets to the ingress LSR with the Your Discriminator field set to the local discriminator of the ingress LSR. The ingress LSR uses this to demultiplex the BFD session.
鉴别器字段。如上所述，出口LSR必须向入口LSR发送控制数据包，并且您的鉴别器字段设置为入口LSR的本地鉴别器。入口LSR使用它来解复用BFD会话。
LSP Ping Echo request and Echo reply messages carry a BFD discriminator TLV for the purpose of session establishment as described above. IANA has assigned a type value of 15 to this TLV. This TLV has a length of 4. The value contains the 4-byte local discriminator that the LSR, sending the LSP Ping message, associates with the BFD session.
LSP Ping Echo请求和Echo应答消息携带BFD鉴别器TLV，用于如上所述的会话建立。IANA已将类型值15分配给该TLV。该TLV的长度为4。该值包含发送LSP Ping消息的LSR与BFD会话关联的4字节本地鉴别器。
If the BFD session is not in UP state, the periodic LSP Ping Echo request messages MUST include the BFD Discriminator TLV.
如果BFD会话未处于启动状态，则定期LSP Ping Echo请求消息必须包括BFD鉴别器TLV。
BFD Control packets sent by the ingress LSR MUST be encapsulated in the MPLS label stack that corresponds to the FEC for which fault detection is being performed. If the label stack has a depth greater than one, the TTL of the inner MPLS label MAY be set to 1. This may be necessary for certain FECs to enable the egress LSR's control plane to receive the packet [RFC4379]. For MPLS PWs, alternatively, the presence of a fault detection message may be indicated by setting a bit in the control word [RFC5085].
入口LSR发送的BFD控制数据包必须封装在MPLS标签堆栈中，该标签堆栈对应于正在执行故障检测的FEC。如果标签堆栈的深度大于1，则内部MPLS标签的TTL可以设置为1。这对于某些fec来说可能是必要的，以使出口LSR的控制平面能够接收分组[RFC4379]。对于MPLS PWs，或者，可以通过在控制字[RFC5085]中设置位来指示故障检测消息的存在。
The BFD Control packet sent by the ingress LSR MUST be a UDP packet with a well-known destination port 3784 [BFD-IP] and a source port assigned by the sender as per the procedures in [BFD-IP]. The source IP address is a routable address of the sender. The destination IP address MUST be randomly chosen from the 127/8 range for IPv4 and from the 0:0:0:0:0:FFFF:7F00/104 range for IPv6 with the following exception. If the FEC is an LDP IP FEC, the ingress LSR may discover multiple alternate paths to the egress LSR for this FEC using LSP Ping traceroute. In this case, the destination IP address, used in a BFD session established for one such alternate path, is the address in the 127/8 range for IPv4 or 0:0:0:0:0:FFFF:7F00/104 range for IPv6 discovered by LSP Ping traceroute [RFC4379] to exercise that particular alternate path.
入口LSR发送的BFD控制数据包必须是UDP数据包，具有已知的目标端口3784[BFD-IP]和发送方根据[BFD-IP]中的程序分配的源端口。源IP地址是发送方的可路由地址。目标IP地址必须从IPv4的127/8范围和IPv6的0:0:0:0:FFFF:7F00/104范围中随机选择，但以下情况除外。如果FEC是LDP-IP-FEC，则入口LSR可以使用LSP-Ping跟踪路由为该FEC发现到出口LSR的多个备选路径。在这种情况下，在为一条此类备用路径建立的BFD会话中使用的目标IP地址是由LSP Ping traceroute[RFC4379]发现的IPv4 127/8范围内的地址，或IPv6 0:0:0:0:FFFF:7F00/104范围内的地址，以执行该特定备用路径。
The motivation for using the address range 127/8 is the same as specified in Section 2.1 of [RFC4379]. This is an exception to the behavior defined in [RFC1122].
使用地址范围127/8的动机与[RFC4379]第2.1节中的规定相同。这是[RFC1122]中定义的行为的例外。
The IP TTL or hop limit MUST be set to 1 [RFC4379].
IP TTL或跃点限制必须设置为1[RFC4379]。
BFD Control packets sent by the egress LSR are UDP packets. The source IP address is a routable address of the replier.
出口LSR发送的BFD控制数据包是UDP数据包。源IP地址是应答器的可路由地址。
The BFD Control packet sent by the egress LSR to the ingress LSR MAY be routed based on the destination IP address as per the procedures in [BFD-MHOP]. If this is the case, the destination IP address MUST be set to the source IP address of the LSP Ping Echo request message, received by the egress LSR from the ingress LSR.
出口LSR发送到入口LSR的BFD控制分组可以按照[BFD-MHOP]中的过程基于目的地IP地址进行路由。如果是这种情况，则必须将目标IP地址设置为LSP Ping Echo请求消息的源IP地址，该消息由出口LSR从入口LSR接收。
Or the BFD Control packet sent by the egress LSR to the ingress LSR MAY be encapsulated in an MPLS label stack. In this case, the presence of the fault detection message is indicated as described above. This may be the case if the FEC for which the fault detection is being performed corresponds to a bidirectional LSP or an MPLS PW. This may also be the case when there is a return LSP from the egress LSR to the ingress LSR. In this case, the destination IP address MUST be randomly chosen from the 127/8 range for IPv4 and from the 0:0:0:0:0:FFFF:7F00/104 range for IPv6.
或者，由出口LSR发送到入口LSR的BFD控制分组可以封装在MPLS标签栈中。在这种情况下，如上所述指示故障检测消息的存在。如果正在执行故障检测的FEC对应于双向LSP或MPLS PW，则可能是这种情况。这也可能是当存在从出口LSR到入口LSR的返回LSP时的情况。在这种情况下，必须从IPv4的127/8范围和IPv6的0:0:0:0:FFFF:7F00/104范围中随机选择目标IP地址。
The BFD Control packet sent by the egress LSR MUST have a well-known destination port 4784, if it is routed [BFD-MHOP], or it MUST have a well-known destination port 3784 [BFD-IP] if it is encapsulated in a MPLS label stack. The source port MUST be assigned by the egress LSR as per the procedures in [BFD-IP].
出口LSR发送的BFD控制分组如果路由[BFD-MHOP]，则必须具有众所周知的目的地端口4784；如果封装在MPLS标签堆栈中，则必须具有众所周知的目的地端口3784[BFD-IP]。源端口必须由出口LSR按照[BFD-IP]中的程序分配。
Note that once the BFD session for the MPLS LSP is UP, either end of the BFD session MUST NOT change the source IP address and the local discriminator values of the BFD Control packets it generates, unless it first brings down the session. This implies that an LSR MUST ignore BFD packets for a given session, demultiplexed using the received Your Discriminator field, if the session is in UP state and if the My Discriminator or the Source IP address fields of the received packet do not match the values associated with the session.
请注意，一旦MPLS LSP的BFD会话启动，BFD会话的任何一端都不得更改其生成的BFD控制数据包的源IP地址和本地鉴别器值，除非它首先关闭会话。这意味着LSR必须忽略给定会话的BFD数据包，如果会话处于UP状态，并且如果接收数据包的My Discriminator或Source IP address字段与会话相关的值不匹配，则使用received Your Discriminator字段进行解复用。
Security considerations discussed in [BFD], [BFD-MHOP], and [RFC4379] apply to this document. For BFD Control packets sent by the ingress LSR or when the BFD Control packet sent by the egress LSR are encapsulated in an MPLS label stack, MPLS security considerations apply. These are discussed in [MPLS-SEC]. When BFD Control packets sent by the egress LSR are routed, the authentication considerations discussed in [BFD-MHOP] should be followed.
[BFD]、[BFD-MHOP]和[RFC4379]中讨论的安全注意事项适用于本文件。对于入口LSR发送的BFD控制数据包，或者当出口LSR发送的BFD控制数据包被封装在MPLS标签堆栈中时，MPLS安全注意事项适用。这些在[MPLS-SEC]中讨论。当路由出口LSR发送的BFD控制数据包时，应遵循[BFD-MHOP]中讨论的认证注意事项。
This document introduces a BFD discriminator TLV in LSP Ping. The BFD Discriminator has been assigned a value of 15 from the LSP Ping TLVs and sub-TLVs registry maintained by IANA.
本文介绍了LSP Ping中的BFD鉴别器TLV。已从IANA维护的LSP Ping TLV和子TLV注册表中为BFD鉴别器分配了15的值。
We would like to thank Yakov Rekhter, Dave Katz, and Ina Minei for contributing to the discussions that formed the basis of this document and for their comments. Thanks to Dimitri Papadimitriou for his comments and review. Thanks to Carlos Pignataro for his comments and review.
我们要感谢雅科夫·雷赫特、戴夫·卡茨和伊娜·米尼对构成本文件基础的讨论所作的贡献以及他们的评论。感谢Dimitri Papadimitriou的评论和评论。感谢卡洛斯·皮格纳塔罗的评论和评论。
[BFD] Katz, D. and D. Ward, "Bidirectional Forwarding Detection", RFC 5880, June 2010.
[BFD]Katz，D.和D.Ward，“双向转发检测”，RFC 58802010年6月。
[BFD-IP] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June 2010.
[BFD-IP]Katz，D.和D.Ward，“IPv4和IPv6（单跳）的双向转发检测（BFD）”，RFC 58812010年6月。
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
[RFC4379]Kompella，K.和G.Swallow，“检测多协议标签交换（MPLS）数据平面故障”，RFC 4379，2006年2月。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1122]Braden，R.，Ed.“互联网主机的要求-通信层”，STD 3，RFC 1122，1989年10月。
[BFD-MHOP] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for Multihop Paths", RFC 5883, June 2010.
[BFD-MHOP]Katz，D.和D.Ward，“多跳路径的双向转发检测（BFD）”，RFC 5883，2010年6月。
[RFC5085] Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, December 2007.
[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 5085，2007年12月。
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3209]Awduche，D.，Berger，L.，Gan，D.，Li，T.，Srinivasan，V.，和G.Swallow，“RSVP-TE：LSP隧道RSVP的扩展”，RFC 3209，2001年12月。
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.
[RFC4090]Pan，P.，Ed.，Swallow，G.，Ed.，和A.Atlas，Ed.，“LSP隧道RSVP-TE快速重路由扩展”，RFC 40902005年5月。
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, October 2007.
[RFC5036]Andersson，L.，Ed.，Minei，I.，Ed.，和B.Thomas，Ed.，“LDP规范”，RFC 5036，2007年10月。
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, February 2006.
[RFC4364]Rosen，E.和Y.Rekhter，“BGP/MPLS IP虚拟专用网络（VPN）”，RFC 4364，2006年2月。
[L2-VPN] Kompella, K., Leelanivas, M., Vohra, Q., Achirica, J., Bonica, R., Cooper, D., Liljenstolpe, C., Metz, E., Ould-Brahim, H., Sargor, C., Shah, H., Srinivasan, and Z. Zhang, "Layer 2 VPNs Over Tunnels", Work in Progress, February 2003.
[L2-VPN]Kompella，K.，Leelanivas，M.，Vohra，Q.，Achirica，J.，Bonica，R.，Cooper，D.，Liljenstolpe，C.，Metz，E.，Ould Brahim，H.，Sargor，C.，Shah，H.，Srinivasan和Z.Zhang，“隧道上的第2层VPN”，正在进行的工作，2003年2月。
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4447]Martini，L.，Ed.，Rosen，E.，El Aawar，N.，Smith，T.，和G.Heron，“使用标签分发协议（LDP）的伪线设置和维护”，RFC 4447，2006年4月。
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, May 2001.
[RFC3107]Rekhter，Y.和E.Rosen，“在BGP-4中携带标签信息”，RFC 3107，2001年5月。
[RFC4377] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S. Matsushima, "Operations and Management (OAM) Requirements for Multi-Protocol Label Switched (MPLS) Networks", RFC 4377, February 2006.
[RFC4377]Nadeau，T.，Morrow，M.，Swallow，G.，Allan，D.，和S.Matsushima，“多协议标签交换（MPLS）网络的运营和管理（OAM）要求”，RFC 4377，2006年2月。
[MPLS-SEC] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", Work in Progress, October 2009.
[MPLS-SEC]Fang，L.，编辑，“MPLS和GMPLS网络的安全框架”，正在进行的工作，2009年10月。
Authors' Addresses
作者地址
Rahul Aggarwal Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 USA
Rahul Aggarwal Juniper Networks 1194 N.Mathilda Ave.Sunnyvale，加利福尼亚州94089
EMail: rahul@juniper.net
EMail: rahul@juniper.net
Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 USA
Kireeti Kompella Juniper Networks 1194 N.Mathilda Ave.Sunnyvale，加利福尼亚州94089
EMail: kireeti@juniper.net
EMail: kireeti@juniper.net
Thomas D. Nadeau BT BT Centre 81 Newgate Street London EC1A 7AJ UK
Thomas D.Nadeau英国电信中心伦敦纽盖特街81号EC1A 7AJ英国
EMail: tom.nadeau@bt.com
EMail: tom.nadeau@bt.com
George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxborough, MA 01719 USA
George Swallow Cisco Systems，Inc.美国马萨诸塞州Boxborough市比弗布鲁克路300号，邮编01719
EMail: swallow@cisco.com
EMail: swallow@cisco.com