Internet Engineering Task Force (IETF) V. Govindan
Request for Comments: 7885 C. Pignataro
Updates: 5885 Cisco
Category: Standards Track July 2016
ISSN: 2070-1721
Internet Engineering Task Force (IETF) V. Govindan
Request for Comments: 7885 C. Pignataro
Updates: 5885 Cisco
Category: Standards Track July 2016
ISSN: 2070-1721
Seamless Bidirectional Forwarding Detection (S-BFD) for Virtual Circuit Connectivity Verification (VCCV)
用于虚拟电路连接验证（VCCV）的无缝双向转发检测（S-BFD）
Abstract
摘要
This document defines Seamless BFD (S-BFD) for VCCV by extending the procedures and Connectivity Verification (CV) types already defined for Bidirectional Forwarding Detection (BFD) for Virtual Circuit Connectivity Verification (VCCV).
本文件通过扩展虚拟电路连接验证（VCCV）双向转发检测（BFD）的程序和连接验证（CV）类型，定义了VCCV的无缝BFD（S-BFD）。
This document updates RFC 5885 by extending the CV Type values and the capability selection.
本文档通过扩展CV类型值和能力选择来更新RFC 5885。
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/rfc7885.
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/rfc7885.
Copyright Notice
版权公告
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2016 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Background ......................................................3
2. S-BFD Connectivity Verification .................................3
2.1. Co-existence of S-BFD and BFD Capabilities .................4
2.2. S-BFD CV Operation .........................................4
2.2.1. S-BFD Initiator Operation ...........................4
2.2.2. S-BFD Reflector Operation ...........................5
2.2.2.1. Demultiplexing .............................5
2.2.2.2. Transmission of Control Packets ............5
2.2.2.3. Advertisement of Target
Discriminators Using LDP ...................5
2.2.2.4. Advertisement of Target
Discriminators Using L2TP ..................6
2.2.2.5. Provisioning of Target Discriminators ......6
2.3. S-BFD Encapsulation ........................................6
3. Capability Selection ............................................7
4. Security Considerations .........................................7
5. IANA Considerations .............................................8
5.1. MPLS CV Types for the VCCV Interface Parameters Sub-TLV ....8
5.2. L2TPv3 CV Types for the VCCV Capability AVP ................8
5.3. PW Associated Channel Type .................................9
6. References ......................................................9
6.1. Normative References .......................................9
6.2. Informative References ....................................10
Acknowledgements ..................................................11
Contributors ......................................................11
Authors' Addresses ................................................11
1. Background ......................................................3
2. S-BFD Connectivity Verification .................................3
2.1. Co-existence of S-BFD and BFD Capabilities .................4
2.2. S-BFD CV Operation .........................................4
2.2.1. S-BFD Initiator Operation ...........................4
2.2.2. S-BFD Reflector Operation ...........................5
2.2.2.1. Demultiplexing .............................5
2.2.2.2. Transmission of Control Packets ............5
2.2.2.3. Advertisement of Target
Discriminators Using LDP ...................5
2.2.2.4. Advertisement of Target
Discriminators Using L2TP ..................6
2.2.2.5. Provisioning of Target Discriminators ......6
2.3. S-BFD Encapsulation ........................................6
3. Capability Selection ............................................7
4. Security Considerations .........................................7
5. IANA Considerations .............................................8
5.1. MPLS CV Types for the VCCV Interface Parameters Sub-TLV ....8
5.2. L2TPv3 CV Types for the VCCV Capability AVP ................8
5.3. PW Associated Channel Type .................................9
6. References ......................................................9
6.1. Normative References .......................................9
6.2. Informative References ....................................10
Acknowledgements ..................................................11
Contributors ......................................................11
Authors' Addresses ................................................11
Bidirectional Forwarding Detection (BFD) for Virtual Circuit Connectivity Verification (VCCV) [RFC5885] defines the CV Types for BFD using VCCV, protocol operation, and the required packet encapsulation formats. This document extends those procedures and CV Type values to enable Seamless BFD (S-BFD) [RFC7880] operation for VCCV.
用于虚拟电路连接验证（VCCV）的双向转发检测（BFD）[RFC5885]使用VCCV、协议操作和所需的数据包封装格式定义BFD的CV类型。本文件扩展了这些程序和CV类型值，以实现VCCV的无缝BFD（S-BFD）[RFC7880]操作。
The new S-BFD CV Types are Pseudowire (PW) demultiplexer agnostic and hence are applicable for both MPLS and Layer Two Tunneling Protocol version 3 (L2TPv3) PW demultiplexers. This document concerns itself with the S-BFD VCCV operation over Single-Segment PWs (SS-PWs). The scope of this document is as follows:
新的S-BFD CV类型与伪线（PW）解复用器无关，因此适用于MPLS和第二层隧道协议版本3（L2TPv3）PW解复用器。本文件涉及单段PWs（SS PWs）上的S-BFD VCCV操作。本文件的范围如下：
o This specification describes procedures for S-BFD asynchronous mode only.
o 本规范仅描述S-BFD异步模式的程序。
o S-BFD Echo mode is outside the scope of this specification.
o S-BFD回波模式不在本规范范围内。
o S-BFD operation for fault detection and status signaling is outside the scope of this specification.
o 用于故障检测和状态信号的S-BFD操作不在本规范的范围内。
This document specifies the use of a single S-BFD Discriminator per PW. There are cases where multiple S-BFD Discriminators per PW can be useful. One such case involves using different S-BFD Discriminators per Flow within a Flow-Aware Transport (FAT) PW [RFC6391]; however, the mapping between Flows and discriminators is a prerequisite. FAT PWs can be supported as described in Section 7 of [RFC6391], which details Operations, Administration, and Maintenance (OAM) considerations for FAT PWs.
本文件规定了每个PW使用一个S-BFD鉴别器。在某些情况下，每个PW有多个S-BFD鉴别器是有用的。其中一种情况涉及在流感知传输（FAT）PW[RFC6391]内对每个流使用不同的S-BFD鉴别器；但是，流和鉴别器之间的映射是一个先决条件。可按照[RFC6391]第7节的说明支持FAT PWs，该节详细说明了FAT PWs的操作、管理和维护（OAM）注意事项。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "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”、“建议”、“不建议”、“可”和“可选”应按照[RFC2119]中的说明进行解释。
The S-BFD protocol provides continuity check services by monitoring the S-BFD Control packets sent and received over the VCCV channel of the PW. The term "Connectivity Verification" (CV) is used throughout this document to be consistent with [RFC5885].
S-BFD协议通过监测通过PW的VCCV信道发送和接收的S-BFD控制数据包来提供连续性检查服务。本文件中使用的术语“连接验证”（CV）与[RFC5885]一致。
This section defines the CV Types to be used for S-BFD. It also defines the procedures for the S-BFD reflector and S-BFD initiator operation.
本节定义了S-BFD使用的CV类型。它还定义了S-BFD反射器和S-BFD启动器操作的程序。
Two CV Types are defined for S-BFD. Table 1 summarizes the S-BFD CV Types, grouping them by encapsulation (i.e., with IP/UDP headers, without IP/UDP headers) for fault detection only. S-BFD for fault detection and status signaling is outside the scope of this specification.
S-BFD定义了两种CV类型。表1总结了S-BFD CV类型，通过封装（即，使用IP/UDP报头，不使用IP/UDP报头）将其分组，仅用于故障检测。用于故障检测和状态信号的S-BFD不在本规范的范围内。
+-----------------------------------------+-----------+-------------+
| | Fault | Fault |
| | Detection | Detection |
| | Only | and Status |
| | | Signaling |
+-----------------------------------------+-----------+-------------+
| S-BFD IP/UDP encapsulation (with IP/UDP | 0x40 | N/A |
| headers) | | |
| | | |
| S-BFD PW-ACH encapsulation when using | 0x80 | N/A |
| MPLS PW or S-BFD L2-Specific Sublayer | | |
| (L2SS) encapsulation when using L2TP PW | | |
| (without IP/UDP headers) | | |
+-----------------------------------------+-----------+-------------+
+-----------------------------------------+-----------+-------------+
| | Fault | Fault |
| | Detection | Detection |
| | Only | and Status |
| | | Signaling |
+-----------------------------------------+-----------+-------------+
| S-BFD IP/UDP encapsulation (with IP/UDP | 0x40 | N/A |
| headers) | | |
| | | |
| S-BFD PW-ACH encapsulation when using | 0x80 | N/A |
| MPLS PW or S-BFD L2-Specific Sublayer | | |
| (L2SS) encapsulation when using L2TP PW | | |
| (without IP/UDP headers) | | |
+-----------------------------------------+-----------+-------------+
Table 1: Bitmask Values for S-BFD CV Types
表1:S-BFD CV类型的位掩码值
IANA has assigned two new bits to indicate S-BFD operation.
IANA分配了两个新位来指示S-BFD操作。
Since the CV Types for S-BFD and BFD are unique, BFD and S-BFD capabilities can be advertised concurrently.
由于S-BFD和BFD的CV类型是唯一的，因此可以同时公布BFD和S-BFD能力。
The S-BFD initiator SHOULD bootstrap S-BFD sessions after it learns the discriminator of the remote target identifier. This can be achieved, for example, through one or more of the following methods. (This list is not exhaustive.)
S-BFD启动器应在学习到远程目标标识符的鉴别器后引导S-BFD会话。这可以通过以下一种或多种方法实现。（此列表并非详尽无遗。）
1. Advertisements of S-BFD Discriminators made through a PW signaling protocol -- for example, AVPs/TLVs defined in L2TP/LDP.
1. 通过PW信令协议发布S-BFD鉴别器广告——例如，L2TP/LDP中定义的AVPs/TLV。
2. Provisioning of S-BFD Discriminators by manual configuration of the Provider Edge (PE) or L2TP Control Connection Endpoints (LCCEs).
2. 通过手动配置提供程序边缘（PE）或L2TP控制连接端点（LCCE），提供S-BFD鉴别器。
3. Assignment of S-BFD Discriminators by a controller.
3. 控制器分配S-BFD鉴别器。
4. Probing remote S-BFD Discriminators through a mechanism such as S-BFD Alert Discriminators [SBFD-ALERT-DISCRIM].
4. 通过S-BFD警报鉴别器等机制探测远程S-BFD鉴别器[SBFD-Alert-DISCRIM]。
The S-BFD initiator operation MUST be done as specified in Section 7.3 of [RFC7880].
S-BFD启动器操作必须按照[RFC7880]第7.3节的规定进行。
When a PW signaling protocol such as LDP or L2TPv3 is in use, the S-BFD reflector can advertise its target discriminators using that signaling protocol. When static PWs are in use, the target discriminator of S-BFD needs to be provisioned on the S-BFD initiator nodes.
当使用诸如LDP或L2TPv3之类的PW信令协议时，S-BFD反射器可以使用该信令协议通告其目标鉴别器。当使用静态PWs时，需要在S-BFD启动器节点上配置S-BFD的目标鉴别器。
All point-to-point PWs are bidirectional; the S-BFD reflector therefore reflects the S-BFD packet back to the initiator using the VCCV channel of the reverse direction of the PW on which it was received.
所有点对点PWs都是双向的；因此，S-BFD反射器使用接收S-BFD数据包的PW反向的VCCV信道将S-BFD数据包反射回启动器。
The reflector has enough information to reflect the S-BFD Async packet received by it back to the S-BFD initiator using the PW context (e.g., fields of the L2TPv3 headers).
反射器具有足够的信息，可以使用PW上下文（例如L2TPv3报头的字段）将其接收到的S-BFD异步数据包反射回S-BFD启动器。
The S-BFD reflector operation for BFD protocol fields MUST be performed as specified in [RFC7880].
BFD协议字段的S-BFD反射器操作必须按照[RFC7880]中的规定执行。
Demultiplexing of S-BFD is achieved using the PW context, following the procedures in Section 7.1 of [RFC7880].
按照[RFC7880]第7.1节中的程序，使用PW上下文实现S-BFD的解复用。
S-BFD reflector procedures as described in [RFC7880] apply for S-BFD using VCCV.
[RFC7880]中所述的S-BFD反射器程序适用于使用VCCV的S-BFD。
The advertisement of the target discriminator using LDP is left for further study. It should be noted that S-BFD can still be used with signaled PWs over an MPLS Packet Switched Network (PSN) by provisioning the S-BFD Discriminators or by learning the S-BFD Discriminators via some other means.
使用LDP的目标鉴别器的广告留待进一步研究。应当注意的是，通过提供S-BFD鉴别器或者通过一些其他手段学习S-BFD鉴别器，S-BFD仍然可以与MPLS分组交换网络（PSN）上的信号pw一起使用。
The S-BFD reflector MUST use the AVP defined in [RFC7886] for advertising its target discriminators using L2TP.
S-BFD反射器必须使用[RFC7886]中定义的AVP，以使用L2TP宣传其目标鉴别器。
S-BFD target discriminators MAY be provisioned when static PWs are used.
当使用静态PW时，可提供S-BFD目标鉴别器。
Unless specified differently below, the encapsulation of S-BFD packets is identical to the method specified in Section 3.2 of [RFC5885] and in [RFC5880] for the encapsulation of BFD packets.
除非下文另有规定，否则S-BFD数据包的封装与[RFC5885]第3.2节和[RFC5880]中规定的BFD数据包封装方法相同。
o IP/UDP BFD encapsulation (BFD with IP/UDP headers):
o IP/UDP BFD封装（带有IP/UDP头的BFD）：
* The destination UDP port for the IP-encapsulated S-BFD packet MUST be 7784 [RFC7881].
* IP封装的S-BFD数据包的目标UDP端口必须为7784[RFC7881]。
* The contents of the S-BFD Control packets MUST be set according to Section 7.3.2 of [RFC7880].
* 必须根据[RFC7880]第7.3.2节设置S-BFD控制数据包的内容。
* The Time to Live (TTL) (IPv4) or Hop Limit (IPv6) is set to 255.
* 生存时间（TTL）（IPv4）或跃点限制（IPv6）设置为255。
o PW-ACH/L2SS BFD encapsulation (BFD without IP/UDP headers):
o PW-ACH/L2SS BFD封装（不带IP/UDP头的BFD）：
* The encapsulation of S-BFD packets using this format MUST be performed according to Section 3.2 of [RFC5885], with the exception of the value for the PW-ACH/L2SS type.
* 使用此格式的S-BFD数据包的封装必须根据[RFC5885]第3.2节进行，PW-ACH/L2SS类型的值除外。
* When VCCV carries PW-ACH/L2SS-encapsulated S-BFD (i.e., "raw" S-BFD), the Channel Type of PW-ACH (the PW Control Word (CW)) or L2SS MUST be set to 0x0008 to indicate "S-BFD Control, PW-ACH/L2SS-encapsulated" (i.e., S-BFD without IP/UDP headers; see Section 5.3). This is done to allow the identification of the encapsulated S-BFD payload when demultiplexing the VCCV control channel.
* 当VCCV携带PW-ACH/L2SS封装的S-BFD（即“原始”S-BFD）时，PW-ACH（PW控制字（CW））或L2SS的通道类型必须设置为0x0008，以指示“S-BFD控制，PW-ACH/L2SS封装”（即不带IP/UDP头的S-BFD；见第5.3节）。这样做是为了在解复用VCCV控制信道时识别封装的S-BFD有效负载。
When multiple S-BFD CV Types are advertised, and after applying the rules in [RFC5885], the set that both ends of the PW have in common is determined. If the two ends have more than one S-BFD CV Type in common, the following list of S-BFD CV Types is considered in order, from the lowest list number CV Type to the highest list number CV Type, and the CV Type with the lowest list number is used:
当播发多个S-BFD CV类型时，在应用[RFC5885]中的规则后，确定PW两端共有的集合。如果两端共有多个S-BFD CV类型，则按顺序考虑以下S-BFD CV类型列表，从列表编号最低的CV类型到列表编号最高的CV类型，并使用列表编号最低的CV类型：
1. 0x40 - S-BFD IP/UDP-encapsulated, for PW Fault Detection only.
1. 0x40-S-BFD IP/UDP封装，仅用于PW故障检测。
2. 0x80 - S-BFD PW-ACH/L2SS-encapsulated (without IP/UDP headers), for PW Fault Detection only.
2. 0x80-S-BFD PW-ACH/L2SS封装（无IP/UDP报头），仅用于PW故障检测。
The order of capability selection between S-BFD and BFD is defined as follows:
S-BFD和BFD之间的能力选择顺序定义如下：
+---------------------------+---------+-----------+-----------------+
| Advertised capabilities | BFD | S-BFD | Both S-BFD and |
| of PE1/PE2 | Only | Only | BFD |
+---------------------------+---------+-----------+-----------------+
| BFD Only | BFD | None | BFD Only |
| | | | |
| S-BFD Only | None | S-BFD | S-BFD Only |
| | | | |
| Both S-BFD and BFD | BFD | S-BFD | Both S-BFD and |
| | Only | Only | BFD |
+---------------------------+---------+-----------+-----------------+
+---------------------------+---------+-----------+-----------------+
| Advertised capabilities | BFD | S-BFD | Both S-BFD and |
| of PE1/PE2 | Only | Only | BFD |
+---------------------------+---------+-----------+-----------------+
| BFD Only | BFD | None | BFD Only |
| | | | |
| S-BFD Only | None | S-BFD | S-BFD Only |
| | | | |
| Both S-BFD and BFD | BFD | S-BFD | Both S-BFD and |
| | Only | Only | BFD |
+---------------------------+---------+-----------+-----------------+
Table 2: Capability Selection Matrix for BFD and S-BFD
表2：BFD和S-BFD的能力选择矩阵
Security considerations for VCCV are addressed in Section 10 of [RFC5085]. The introduction of the S-BFD CV Types does not present any new security risks for VCCV. Implementations of the additional CV Types defined herein are subject to the same security considerations as those defined in [RFC5085] as well as [RFC7880].
[RFC5085]第10节介绍了VCCV的安全注意事项。S-BFD CV类型的引入不会给VCCV带来任何新的安全风险。本文定义的附加CV类型的实现受到与[RFC5085]和[RFC7880]中定义的相同的安全考虑的约束。
The IP/UDP encapsulation of S-BFD makes use of the TTL / Hop Limit procedures described in the Generalized TTL Security Mechanism (GTSM) specification [RFC5082] as a security mechanism.
S-BFD的IP/UDP封装利用通用TTL安全机制（GTSM）规范[RFC5082]中描述的TTL/Hop限制过程作为安全机制。
This specification does not raise any additional security issues beyond these.
除此之外，本规范不会提出任何其他安全问题。
The VCCV Interface Parameters Sub-TLV codepoint is defined in [RFC4446], and the "MPLS VCCV Connectivity Verification (CV) Types" registry is defined in [RFC5085].
[RFC4446]中定义了VCCV接口参数子TLV代码点，而[RFC5085]中定义了“MPLS VCCV连接验证（CV）类型”注册表。
This section lists the new S-BFD CV Types.
本节列出了新的S-BFD CV类型。
IANA has augmented the "MPLS VCCV Connectivity Verification (CV) Types" registry in the "Pseudowire Name Spaces (PWE3)" registry [IANA-PWE3]. These are bitfield values. CV Type values are specified in Section 2 of this document.
IANA扩充了“伪线名称空间（PWE3）”注册表[IANA-PWE3]中的“MPLS VCCV连接验证（CV）类型”注册表。这些是位字段值。本文件第2节规定了CV类型值。
MPLS VCCV Connectivity Verification (CV) Types:
MPLS VCCV连接验证（CV）类型：
Bit (Value) Description Reference
=========== =========== ==============
6 (0x40) S-BFD IP/UDP-encapsulated, RFC 7885
for PW Fault Detection only
Bit (Value) Description Reference
=========== =========== ==============
6 (0x40) S-BFD IP/UDP-encapsulated, RFC 7885
for PW Fault Detection only
7 (0x80) S-BFD PW-ACH-encapsulated, RFC 7885 for PW Fault Detection only
7（0x80）S-BFD PW ACH封装，RFC 7885仅用于PW故障检测
This section lists the new S-BFD "L2TPv3 Connectivity Verification (CV) Types" that have been added to the existing "VCCV Capability AVP (Attribute Type 96) Values" registry in the "Layer Two Tunneling Protocol 'L2TP'" registry [IANA-L2TP]. IANA has assigned the following L2TPv3 Connectivity Verification (CV) Types in the "VCCV Capability AVP (Attribute Type 96) Values" registry.
本节列出了添加到“第二层隧道协议‘L2TP’”注册表[IANA-L2TP]中现有“VCCV能力AVP（属性类型96）值”注册表中的新S-BFD“L2TPv3连接验证（CV）类型”。IANA已在“VCCV能力AVP（属性类型96）值”注册表中分配了以下L2TPv3连接验证（CV）类型。
VCCV Capability AVP (Attribute Type 96) Values
----------------------------------------------
VCCV Capability AVP (Attribute Type 96) Values
----------------------------------------------
L2TPv3 Connectivity Verification (CV) Types:
L2TPv3连接验证（CV）类型：
Bit (Value) Description Reference
=========== =========== ==============
6 (0x40) S-BFD IP/UDP-encapsulated, RFC 7885
for PW Fault Detection only
Bit (Value) Description Reference
=========== =========== ==============
6 (0x40) S-BFD IP/UDP-encapsulated, RFC 7885
for PW Fault Detection only
7 (0x80) S-BFD L2SS-encapsulated, RFC 7885 for PW Fault Detection only
7（0x80）S-BFD L2SS封装，RFC 7885仅用于PW故障检测
As per the IANA considerations in [RFC5586], IANA has allocated a Channel Type in the "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types)" registry [IANA-G-ACh].
根据[RFC5586]中的IANA注意事项，IANA已在“MPLS通用关联信道（G-ACh）类型（包括伪线关联信道类型）”注册表[IANA-G-ACh]中分配信道类型。
IANA has assigned a new Pseudowire Associated Channel Type value, as follows:
IANA已指定一个新的伪线关联通道类型值，如下所示：
Value Description Reference
------ ---------------------------------- ---------------
0x0008 S-BFD Control, PW-ACH/L2SS RFC 7885
encapsulation
(without IP/UDP Headers)
Value Description Reference
------ ---------------------------------- ---------------
0x0008 S-BFD Control, PW-ACH/L2SS RFC 7885
encapsulation
(without IP/UDP Headers)
[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>.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, DOI 10.17487/RFC4446, April 2006, <http://www.rfc-editor.org/info/rfc4446>.
[RFC4446]Martini，L.，“伪线边到边仿真（PWE3）的IANA分配”，BCP 116，RFC 4446，DOI 10.17487/RFC4446，2006年4月<http://www.rfc-editor.org/info/rfc4446>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007, <http://www.rfc-editor.org/info/rfc5082>.
[RFC5082]Gill，V.，Heasley，J.，Meyer，D.，Savola，P.，Ed.，和C.Pignataro，“广义TTL安全机制（GTSM）”，RFC 5082，DOI 10.17487/RFC5082，2007年10月<http://www.rfc-editor.org/info/rfc5082>.
[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>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009, <http://www.rfc-editor.org/info/rfc5586>.
[RFC5586]Bocci，M.，Ed.，Vigoureux，M.，Ed.，和S.Bryant，Ed.，“MPLS通用关联信道”，RFC 5586，DOI 10.17487/RFC55862009年6月<http://www.rfc-editor.org/info/rfc5586>.
[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>.
[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.，“用于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>.
[RFC7881] Pignataro, C., Ward, D., and N. Akiya, "Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6, and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016, <http://www.rfc-editor.org/info/rfc7881>.
[RFC7881]Pignataro，C.，Ward，D.，和N.Akiya，“IPv4，IPv6和MPLS的无缝双向转发检测（S-BFD）”，RFC 7881，DOI 10.17487/RFC7881，2016年7月<http://www.rfc-editor.org/info/rfc7881>.
[RFC7886] Govindan, V. and C. Pignataro, "Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in the Layer Two Tunneling Protocol Version 3 (L2TPv3)", RFC 7886, DOI 10.17487/RFC7886, July 2016, <http://www.rfc-editor.org/info/rfc7886>.
[RFC7886]Govindan，V.和C.Pignataro，“第二层隧道协议版本3（L2TPv3）中的广告无缝双向转发检测（S-BFD）鉴别器”，RFC 7886，DOI 10.17487/RFC7886，2016年7月<http://www.rfc-editor.org/info/rfc7886>.
[IANA-G-ACh] Internet Assigned Numbers Authority, "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudowire Associated Channel Types)", <http://www.iana.org/assignments/g-ach-parameters>.
[IANA-G-ACh]互联网分配号码管理局，“MPLS通用关联信道（G-ACh）类型（包括伪线关联信道类型）”<http://www.iana.org/assignments/g-ach-parameters>.
[IANA-L2TP] Internet Assigned Numbers Authority, "Layer Two Tunneling Protocol 'L2TP'", <http://www.iana.org/assignments/l2tp-parameters>.
[IANA-L2TP]互联网分配号码管理局，“第二层隧道协议‘L2TP’”<http://www.iana.org/assignments/l2tp-parameters>.
[IANA-PWE3] Internet Assigned Numbers Authority, "Pseudowire Name Spaces (PWE3)", <http://www.iana.org/assignments/pwe3-parameters>.
[IANA-PWE3]互联网分配号码管理局，“伪线名称空间（PWE3）”<http://www.iana.org/assignments/pwe3-parameters>.
[RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V., Regan, J., and S. Amante, "Flow-Aware Transport of Pseudowires over an MPLS Packet Switched Network", RFC 6391, DOI 10.17487/RFC6391, November 2011, <http://www.rfc-editor.org/info/rfc6391>.
[RFC6391]Bryant，S.，Ed.，Filsfils，C.，Drafz，U.，Kompella，V.，Regan，J.，和S.Amante，“MPLS分组交换网络上伪线的流感知传输”，RFC 6391，DOI 10.17487/RFC63911911<http://www.rfc-editor.org/info/rfc6391>.
[SBFD-ALERT-DISCRIM] Akiya, N., Pignataro, C., and D. Ward, "Seamless Bidirectional Forwarding Detection (S-BFD) Alert Discriminator", Work in Progress, draft-akiya-bfd-seamless-alert-discrim-03, October 2014.
[SBFD-ALERT-DISCRIM]北阿基亚、北卡罗来纳州皮格纳塔罗和D.沃德，“无缝双向转发检测（S-BFD）警报鉴别器”，正在进行的工作，草稿-Akiya-BFD-无缝-ALERT-DISCRIM-032014年10月。
Acknowledgements
致谢
The authors would like to thank Nobo Akiya, Stewart Bryant, Greg Mirsky, Pawel Sowinski, Yuanlong Jiang, Andrew Malis, and Alexander Vainshtein for providing input to this document, performing thorough reviews, and providing useful comments.
作者要感谢Nobo Akiya、Stewart Bryant、Greg Mirsky、Pawel Sowinski、姜元龙、Andrew Malis和Alexander Vainstein为本文件提供了投入，进行了全面审查，并提供了有用的意见。
Contributors
贡献者
Mallik Mudigonda Cisco Systems, Inc.
Mallik Mudigonda思科系统公司。
Email: mmudigon@cisco.com
Email: mmudigon@cisco.com
Authors' Addresses
作者地址
Vengada Prasad Govindan Cisco Systems, Inc.
Vengada Prasad Govindan思科系统公司。
Email: venggovi@cisco.com
Email: venggovi@cisco.com
Carlos Pignataro Cisco Systems, Inc.
卡洛斯·皮格纳塔罗思科系统公司。
Email: cpignata@cisco.com
Email: cpignata@cisco.com