Internet Engineering Task Force (IETF) L. Martini
Request for Comments: 6478 G. Swallow
Updates: 5885 G. Heron
Category: Standards Track Cisco
ISSN: 2070-1721 M. Bocci
Alcatel-Lucent
May 2012
Internet Engineering Task Force (IETF) L. Martini
Request for Comments: 6478 G. Swallow
Updates: 5885 G. Heron
Category: Standards Track Cisco
ISSN: 2070-1721 M. Bocci
Alcatel-Lucent
May 2012
Pseudowire Status for Static Pseudowires
静态伪线的伪线状态
Abstract
摘要
This document specifies a mechanism to signal Pseudowire (PW) status messages using a PW associated channel (ACh). Such a mechanism is suitable for use where no PW dynamic control plane exits, known as static PWs, or where a Terminating Provider Edge (T-PE) needs to send a PW status message directly to a far-end T-PE. The mechanism allows PW Operations, Administration, and Maintenance (OAM) message mapping and PW redundancy to operate on static PWs. This document also updates RFC 5885 in the case when Bi-directional Forwarding Detection (BFD) is used to convey PW status-signaling information.
本文档指定了一种使用PW关联通道（ACh）向伪线（PW）状态消息发送信号的机制。这种机制适用于不存在PW动态控制平面（称为静态PWs）的情况，或者终端提供商边缘（T-PE）需要直接向远端T-PE发送PW状态消息的情况。该机制允许PW操作、管理和维护（OAM）消息映射和PW冗余在静态PWs上运行。当双向转发检测（BFD）用于传送PW状态信令信息时，本文档还更新了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 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/rfc6478.
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/rfc6478.
Copyright Notice
版权公告
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2011 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 ....................................................3
2. Specification of Requirements ...................................3
3. Terminology .....................................................3
4. Applicability ...................................................3
5. Pseudowire Status Operation .....................................4
5.1. PW OAM Message .............................................4
5.2. Sending a PW Status Message ................................5
5.3. PW OAM Status Message Transmit and Receive .................6
5.3.1. Acknowledgment of PW Status .........................7
5.4. MPLS Label Stack ...........................................7
5.4.1. Label Stack for a Message Destined to the Next PE ...8
5.4.2. Label Stack for a Message Destined to the Egress PE .8
5.5. S-PE Bypass Mode ...........................................8
5.5.1. S-PE Bypass Mode LDP Flag Bit .......................9
6. S-PE Operation .................................................10
6.1. Static PW to Another Static PW ............................10
6.2. Dynamic PW to Static PW or Vice Versa .....................10
7. Security Considerations ........................................11
8. IANA Considerations ............................................11
9. References .....................................................11
9.1. Normative References ......................................11
9.2. Informative References ....................................12
1. Introduction ....................................................3
2. Specification of Requirements ...................................3
3. Terminology .....................................................3
4. Applicability ...................................................3
5. Pseudowire Status Operation .....................................4
5.1. PW OAM Message .............................................4
5.2. Sending a PW Status Message ................................5
5.3. PW OAM Status Message Transmit and Receive .................6
5.3.1. Acknowledgment of PW Status .........................7
5.4. MPLS Label Stack ...........................................7
5.4.1. Label Stack for a Message Destined to the Next PE ...8
5.4.2. Label Stack for a Message Destined to the Egress PE .8
5.5. S-PE Bypass Mode ...........................................8
5.5.1. S-PE Bypass Mode LDP Flag Bit .......................9
6. S-PE Operation .................................................10
6.1. Static PW to Another Static PW ............................10
6.2. Dynamic PW to Static PW or Vice Versa .....................10
7. Security Considerations ........................................11
8. IANA Considerations ............................................11
9. References .....................................................11
9.1. Normative References ......................................11
9.2. Informative References ....................................12
The default control plane for Pseudowire (PW) technology, as defined in [RFC4447], is based on the Label Distribution Protocol (LDP). However, that document also describes a static provisioning mode without a control plane. When a static PW is used, there is no method to transmit the status of the PW or attachment circuit (AC) between the two Provider Edge (PE) devices at each end of the PW. This document defines a method to transport the PW status codes defined in Section 5.4.2 of [RFC4447] and elsewhere [REDUNDANCY] in-band with the PW data using a generic associated channel [RFC5586].
[RFC4447]中定义的伪线（PW）技术的默认控制平面基于标签分发协议（LDP）。但是，该文档还描述了没有控制平面的静态配置模式。当使用静态PW时，没有方法在PW两端的两个提供商边缘（PE）设备之间传输PW或连接电路（AC）的状态。本文件定义了使用通用相关信道[RFC5586]在带内传输[RFC4447]第5.4.2节和其他地方[REDUNDANCY]中定义的PW状态代码和PW数据的方法。
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。
ACh: Associated Channel
相关信道
ACH: Associated Channel Header
ACH：关联通道头
FEC: Forwarding Equivalence Class
转发等价类
LDP: Label Distribution Protocol
标签分发协议
LSP: Label Switching Path
标签交换路径
MS-PW: Multi-Segment Pseudowire
MS-PW：多段伪导线
PE: Provider Edge
PE：提供程序边缘
PW: Pseudowire
伪线
SS-PW: Single-Segment Pseudowire
SS-PW：单段伪导线
S-PE: Switching Provider Edge Node of MS-PW
S-PE:MS-PW的交换提供程序边缘节点
T-PE: Terminating Provider Edge Node of MS-PW
T-PE：终止MS-PW的提供程序边缘节点
As described in [RFC4447] and [RFC6310], a PE that establishes an MPLS PW using means other than LDP, e.g., by static configuration, MUST support some alternative method of status reporting. The
如[RFC4447]和[RFC6310]中所述，使用LDP以外的方式（例如通过静态配置）建立MPLS PW的PE必须支持某种状态报告的替代方法。这个
procedures described in this document are for use when PWs are statically configured and an LDP control plane is not available.
本文件中描述的程序适用于PWs静态配置且LDP控制平面不可用的情况。
As defined in [RFC4447], a PE that establishes a PW using LDP MUST use the PW status TLV mechanism for AC and PW status and defect notification on that PW. In order to avoid duplicate notifications and potentially conflicting notifications, such PEs MUST NOT use the mechanisms described in this document for those PWs, except that the S-PE bypass mode described in Section 5.5 MAY be used when both T-PEs at each end of the PW use LDP to establish the PW.
如[RFC4447]中所定义，使用LDP建立PW的PE必须使用PW状态TLV机制，用于AC和PW状态以及该PW上的缺陷通知。为避免重复通知和潜在冲突通知，此类PE不得使用本文件中针对这些PW所述的机制，除非当PW两端的T-PE使用LDP建立PW时，可使用第5.5节中所述的S-PE旁路模式。
In order to protect against duplicate notifications and potentially conflicting notifications, when the Pseudowire Status protocol for Static Pseudowires described in this document is used, the BFD VCCV (Virtual Circuit Connectivity Verification) status-signaling mechanisms described in [RFC5885] (CV Types 0x08 and 0x20) MUST NOT be used. BFD VCCV for fault detection (CV types 0x04 and 0x10) MAY still be used.
为了防止重复通知和潜在冲突通知，当使用本文档中描述的静态伪线的伪线状态协议时，不得使用[RFC5885]（CV类型0x08和0x20）中描述的BFD VCCV（虚拟电路连接验证）状态信令机制。故障检测用BFD VCCV（CV类型0x04和0x10）仍可使用。
The PW status TLV as defined in Section 5.4.2 of [RFC4447] is transported in a PW OAM message using the PW ACH.
[RFC4447]第5.4.2节中定义的PW状态TLV使用PW ACH在PW OAM消息中传输。
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | 0x0027 PW OAM Message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh Timer | TLV Length |A| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ TLVs ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | 0x0027 PW OAM Message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh Timer | TLV Length |A| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ TLVs ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ACh PW OAM Message Packet Header
图1:ACh PW OAM消息包头
The first 32 bits are the standard ACH header construct as defined in [RFC5586].
前32位是[RFC5586]中定义的标准ACH头结构。
The first nibble (0001b) indicates the ACH instead of PW data. The version and the reserved values are both set to 0 as specified in [RFC4385].
第一个半字节（0001b）表示ACH而不是PW数据。版本和保留值均设置为[RFC4385]中规定的0。
The refresh timer is an unsigned integer and specifies refresh time in seconds with a range from 1 to 65535. The value 0 means that the refresh timer is set to infinity, and the PW OAM message will never be refreshed, and will never timeout.
刷新计时器是一个无符号整数，以秒为单位指定刷新时间，范围从1到65535。值0表示刷新计时器设置为无穷大，PW OAM消息将永远不会刷新，也永远不会超时。
The TLV length field indicates the length of all TLVs only. This document defines only the transport of the PW status TLV, as defined in Section 5.4.2, [RFC4447], in the TLV field. In the future, additional TLVs may be defined to be used in this field with code points allocated from the IANA registry called "LDP TLV Type Name Space".
TLV长度字段仅指示所有TLV的长度。本文件仅在TLV字段中定义了第5.4.2节[RFC4447]中定义的PW状态TLV的传输。将来，可能会定义额外的TLV用于该字段，代码点从IANA注册中心分配，称为“LDP TLV类型名称空间”。
The A flag bit is used to indicate an acknowledgment of the PW status TLV included. The rest of the flag bits are reserved and they MUST be set to 0 on transmit, and ignored upon receipt. When the A bit is set, the refresh timer value is a requested timer value.
A标志位用于指示对包含的PW状态TLV的确认。其余的标志位是保留的，传输时必须设置为0，接收时忽略。设置A位时，刷新计时器值是请求的计时器值。
The PW OAM Message code point value is 0x0027.
PW OAM消息代码点值为0x0027。
The PW Status messages are sent in-band using the PW OAM message containing the PW Status TLV for a particular PW, as defined in [RFC4447]. The PW Status TLV format is almost as defined in [RFC4447] and is repeated here for the reader's convenience:
按照[RFC4447]中的定义，使用包含特定PW的PW状态TLV的PW OAM消息在频带内发送PW状态消息。PW Status TLV格式几乎与[RFC4447]中的定义相同，为方便读者，在此重复：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Res| PW Status (0x096A) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Res| PW Status (0x096A) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PW Status TLV Format
图2:PW状态TLV格式
Unlike the case in [RFC4447], here, the first 2 bits are reserved, and MUST be set to zero on transmit and ignored on receipt.
与[RFC4447]中的情况不同，此处前2位是保留的，必须在传输时设置为零，在接收时忽略。
The PW Status TLV is prepended with a PW OAM message header and sent on the ACh of the PW to which the status update applies.
PW状态TLV以PW OAM消息头作为前缀，并在状态更新适用的PW的ACh上发送。
To clear a particular status indication, the PE needs to send a new PW OAM message containing a PW Status TLV with the corresponding bit cleared as defined in [RFC4447].
要清除特定的状态指示，PE需要发送一条新的PW OAM消息，其中包含PW状态TLV，并清除[RFC4447]中定义的相应位。
The procedures described in [RFC6073] that apply to an S-PE and PW using an LDP control plane also apply when sending PW status using
[RFC6073]中描述的适用于使用LDP控制平面的S-PE和PW的程序也适用于使用LDP控制平面发送PW状态时
the PW OAM channel. The OPTIONAL procedures using the SP-PE TLV described in [RFC6073] can also be applied when sending PW status using the PW OAM channel.
PW OAM通道。[RFC6073]中描述的使用SP-PE TLV的可选程序也可在使用PW OAM信道发送PW状态时应用。
The detailed message transmit and message receive procedures are specified in the next section. PW OAM status messages MUST NOT be used as a connectivity verification method.
详细的消息发送和消息接收程序将在下一节中指定。PW OAM状态消息不得用作连接验证方法。
Unlike the PW status procedures defined in [RFC4447], with this method there is no TCP/IP session or session management. Therefore, unlike the TCP/IP case, where each message is sent only once, the PW OAM message containing the PW status TLV needs to be transmitted repeatedly to ensure reliable message delivery. If a malformed TLV or an unknown TLV is received in a PW OAM status message, the TLV MUST be ignored, and the PE SHOULD report the event to the operator.
与[RFC4447]中定义的PW状态过程不同，此方法没有TCP/IP会话或会话管理。因此，与TCP/IP情况不同，每个消息只发送一次，包含PW状态TLV的PW OAM消息需要重复传输，以确保可靠的消息传递。如果在PW OAM状态消息中接收到格式错误的TLV或未知TLV，则必须忽略TLV，PE应将事件报告给操作员。
A PW OAM message containing a PW status TLV with a new status bit set or reset will be transmitted immediately by the PE. Unless the message is acknowledged within a second, the PW OAM message will then be repeated twice more at an initial interval of one second. Subsequently, the PW OAM message will be transmitted with an interval specified by the refresh timer value in the packet. Note that this value MAY be updated in the new PW OAM message packet, in which case the new refresh timer value becomes the new packet transmit interval.
PE将立即发送包含PW状态TLV的PW OAM消息，该消息具有设置或重置的新状态位。除非消息在一秒钟内得到确认，否则PW OAM消息将以1秒的初始间隔再重复两次。随后，将以分组中的刷新定时器值指定的间隔来发送PW OAM消息。注意，该值可以在新的PW OAM消息分组中更新，在这种情况下，新的刷新定时器值成为新分组发送间隔。
The suggested default value for the refresh timer is 600 seconds. This default is adequate for typical deployments, and PEs are designed to take into account processing these messages at the required rate.
刷新计时器的建议默认值为600秒。此默认值适用于典型部署，PEs的设计考虑以所需速率处理这些消息。
When a PW OAM message containing a status TLV is received, a timer is started according to the refresh rate specified in the packet. If another non-zero PW status message is not received within 3.5 times the specified timer value, the status condition will timeout in 3.5 times the last refresh timer value received, and the default status of zero is assumed on the PW. It is also a good practice to introduce some jitter in the delay between refresh transmissions, as long as the maximum jitter delay is within the prescribed maximum refresh time of 3.5 times the specified timer value for 3 consecutive refresh packets.
当接收到包含状态TLV的PW OAM消息时，根据数据包中指定的刷新率启动计时器。如果在指定计时器值的3.5倍内未收到另一个非零PW状态消息，则状态条件将在收到的上次刷新计时器值的3.5倍内超时，PW上的默认状态为零。在刷新传输之间的延迟中引入一些抖动也是一种良好的做法，只要最大抖动延迟在规定的最大刷新时间内，即3个连续刷新数据包的指定计时器值的3.5倍。
To clear a particular status fault, the PE need only send an updated message with the corresponding bit cleared. If the PW status code is zero, the PW OAM message will be sent like any other PW OAM status message using the procedures described above; however, transmission will cease after 3 PW status messages have been sent at one second
要清除特定的状态故障，PE只需发送一条已更新的消息，并清除相应的位。如果PW状态代码为零，则PW OAM消息将像任何其他PW OAM状态消息一样使用上述程序发送；但是，在每秒发送3个PW状态消息后，传输将停止
intervals and before the refresh timer expires. A PW status message of zero MAY be acknowledged using the procedures described in Section 5.3.1. If it is acknowledged, then a timer value of zero MUST be used. This SHOULD cause the PE sending the PW status notification message with a PW status code equal to zero to stop sending and to continue normal operation.
刷新计时器到期前的间隔和。可使用第5.3.1节所述程序确认零PW状态信息。如果已确认，则必须使用零计时器值。这将导致发送PW状态代码等于零的PW状态通知消息的PE停止发送并继续正常运行。
A PE receiving a PW OAM message containing a PW status message MAY acknowledge the PW status message by simply building a reply packet with the same format and status code as the received PW OAM message, but with the A bit set, and transmitting it on the PW ACh back to the source of the PW OAM message. The receiving PE MAY use the refresh timer field in the acknowledgement packet to request a new refresh interval from the originator of the PW OAM message. The timer value set in the reply packet SHOULD then be used by the originator of the PW OAM message as the new transmit interval. If the requested refresh timer value is to be used, then, when the the current timer expires, the PW OAM message transmission interval is set to the new value and the new value is sent in the PW OAM message. If the transmitting PE does not want to use the new timer value (for local policy reasons, or because it simply cannot support it), it MUST refresh the PW OAM message with the timer value it desires. The receiving PE will then set its timeout timer according to the new refresh timer value that is in the packet received, regardless of what timer value it requested. The receiving PE MUST NOT request a new refresh timer value more than once per refresh interval.
接收包含PW状态消息的PW OAM消息的PE可以通过简单地构建具有与接收到的PW OAM消息相同的格式和状态代码但设置了位的应答包，并在PW ACh上将其发送回PW OAM消息的源来确认PW状态消息。接收PE可以使用确认分组中的刷新计时器字段来请求来自PW OAM消息的发起方的新刷新间隔。然后，PW OAM消息的发起者应使用应答数据包中设置的计时器值作为新的传输间隔。如果要使用请求的刷新计时器值，则当当前计时器过期时，PW OAM消息传输间隔设置为新值，并在PW OAM消息中发送新值。如果发送PE不想使用新的计时器值（出于本地策略原因，或者因为它根本不支持新的计时器值），则必须使用所需的计时器值刷新PW OAM消息。然后，接收PE将根据接收到的数据包中的新刷新计时器值设置其超时计时器，而不管其请求的计时器值是什么。接收PE不得在每个刷新间隔多次请求新的刷新计时器值。
The suggested default value for the refresh timer value in the acknowledgment packet is 600 seconds.
确认数据包中刷新计时器值的建议默认值为600秒。
If the sender PE receives an acknowledgment message that does not match the current active PW status message being sent, it simply ignores the acknowledgment packet.
如果发送方PE接收到与当前正在发送的活动PW状态消息不匹配的确认消息，它将忽略确认数据包。
If a PE that has received a non-zero status code for a PW detects by any means that the far end PE has become unreachable, it will follow the standard defect entry procedures of [RFC6310], Section 6.2.
如果接收到PW非零状态代码的PE通过任何方式检测到远端PE无法访问，则其将遵循[RFC6310]第6.2节的标准缺陷输入程序。
With one exception, all PW OAM status messages are sent to the adjacent PE across the PSN tunnel. In many cases, the transmitting PE has no way to determine whether the adjacent PE is an S-PE or a T-PE. This is a necessary behavior to preserve backward compatibility with PEs that do not understand MS-PWs. In the procedures described in this document, there are two possible
除了一个例外，所有PW OAM状态消息都通过PSN隧道发送到相邻的PE。在许多情况下，发送PE无法确定相邻PE是S-PE还是T-PE。这是与不了解MS PWs的PE保持向后兼容性的必要行为。在本文件所述的程序中，有两种可能
destinations for the PW OAM status messages: the adjacent PE or the T-PE. Sending a PW status message directly to the T-PE is an enhanced method that is only applicable using PW OAM status messages sent in the PW ACH.
PW OAM状态消息的目的地：相邻PE或T-PE。直接向T-PE发送PW状态消息是一种增强方法，仅适用于使用PW ACH中发送的PW OAM状态消息。
A PE that needs to forward a PW OAM status message to the adjacent PE across the PSN tunnel MUST set the PW label TTL field to 1. Furthermore, if the control word is not in use on the particular PW, the PE MUST place the GAL reserved label [RFC5586] below the PW label with the TTL field set to 1.
需要通过PSN隧道将PW OAM状态消息转发给相邻PE的PE必须将PW label TTL字段设置为1。此外，如果控制字未在特定PW上使用，PE必须将GAL保留标签[RFC5586]放置在PW标签下方，TTL字段设置为1。
This is also known as "S-PE bypass mode"; see below. A T-PE that requires sending a PW OAM status message directly to the corresponding T-PE at the other end of the PW MUST set the TTL of the PW label to a value that is sufficient to reach the corresponding T-PE. This value will be greater than one, but will be set according to the local policy on the transmitting T-PE. Furthermore, if the control word is not in use on the particular PW, the PE MUST also place the GAL reserved label [RFC5586] below the PW label with the TTL field set to 1.
这也称为“S-PE旁路模式”；见下文。需要直接向PW另一端的相应T-PE发送PW OAM状态消息的T-PE必须将PW标签的TTL设置为足以到达相应T-PE的值。该值将大于1，但将根据传输T-PE上的本地策略进行设置。此外，如果控制字未在特定PW上使用，PE还必须将GAL保留标签[RFC5586]放置在PW标签下方，TTL字段设置为1。
S-PE bypass mode enables a T-PE that uses LDP as the PW setup and control protocol to bypass all S-PEs that might be present along the MS-PW and to send a message directly to the remote T-PE. This is used for very fast message transmission in-band with the PW PDUs. This mode is OPTIONAL and MUST be supported by both T-PEs to be enabled. This mode MUST NOT be used if the first PW segment connected to each T-PE is not using LDP.
S-PE旁路模式使使用LDP作为PW设置和控制协议的T-PE能够绕过MS-PW沿线可能存在的所有S-PE，并直接向远程T-PE发送消息。这用于PW PDU的带内非常快速的消息传输。此模式为可选模式，必须由两个T-PE支持才能启用。如果连接到每个T-PE的第一个PW段未使用LDP，则不得使用该模式。
Note that this method MUST NOT be used to send messages that are permitted to originate at an S-PE. Otherwise, race conditions could occur between messages sent via the control plane by S-PEs and messages sent via the data plane by T-PEs.
请注意，此方法不得用于发送允许在S-PE上发起的消息。否则，S-PEs通过控制平面发送的消息和T-PEs通过数据平面发送的消息之间可能会出现竞争条件。
Status codes, except for those listed below, MUST NOT be sent using the S-PE bypass procedure and MUST be ignored on reception.
状态代码（以下列出的代码除外）不得使用S-PE旁路程序发送，接收时必须忽略。
0x00000002 - Local Attachment Circuit (ingress) Receive Fault
0x00000002-本地连接电路（入口）接收故障
0x00000004 - Local Attachment Circuit (egress) Transmit Fault
0x00000004-本地连接电路（出口）传输故障
0x00000020 - PW forwarding standby
0x00000020-PW转发待机
0x00000040 - Request switchover to this PW
0x00000040-请求切换到此PW
Note that since "clear all failures" may be sent by an S-PE, it MUST NOT be sent using the S-PE bypass mode.
请注意，由于“清除所有故障”可能由S-PE发送，因此不得使用S-PE旁路模式发送。
When S-PE bypass mode is enabled, all PW Status TLVs received using this method have priority over PW Status TLVs sent via control protocols such as LDP [RFC4447]. However, the same PW Status TLVs MUST also be sent in LDP to keep the S-PEs state updated.
启用S-PE旁路模式时，使用此方法接收的所有PW状态TLV优先于通过LDP[RFC4447]等控制协议发送的PW状态TLV。但是，同样的PW状态TLV也必须在LDP中发送，以保持S-PEs状态的更新。
When a PW Segment along an MS-PW is using the LDP control protocol and wishes to request the use of the S-PE bypass status message mode, it sets the B bit in the generic protocol flags interface parameters sub-TLV as shown in Figure 3. This flag can only be set by a T-PE using LDP as the PW configuration and management protocol. If the S-PE bypass mode LDP flag bit in the generic protocol flags interface parameter does not match in the FEC advertisement for directions of a specific PW, that PW MUST NOT be enabled.
当沿着MS-PW的PW段使用LDP控制协议并希望请求使用S-PE旁路状态消息模式时，它在通用协议标志接口参数子TLV中设置B位，如图3所示。该标志只能由使用LDP作为PW配置和管理协议的T-PE设置。如果通用协议标志接口参数中的S-PE旁路模式LDP标志位在FEC公告中与特定PW的方向不匹配，则不得启用该PW。
The interface parameter is defined as follows:
接口参数定义如下：
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=0x18 | Length=4 |R R R R R R R R R R R R R R R B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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=0x18 | Length=4 |R R R R R R R R R R R R R R R B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PW Generic Protocol Flags Sub-TLV
图3:PW通用协议标志子TLV
TLV Type
TLV型
Type 0x18 - PW Generic Protocol Flags.
类型0x18-PW通用协议标志。
Length
长
TLV length is always 4 octets.
TLV长度始终为4个八位字节。
Flags
旗帜
Bit B, in position 31 above, is set to request the S-PE bypass mode. R bits are to be allocated by IANA as described in the IANA section. If they are not allocated, they are to be considered as reserved for future use and MUST be zero on transmission and ignored on reception of this TLV.
位于上述位置31的位B设置为请求S-PE旁路模式。R位由IANA分配，如IANA部分所述。如果未分配，则视为保留供将来使用，且在传输时必须为零，在接收该TLV时忽略。
If the T-PE receives an LDP label mapping message containing a generic protocol flags interface parameter TLV with the bit B set, then the T-PE receiving the label mapping message MAY send S-PE bypass status messages in the PW ACh. If bit B of said TLV is not set, or the TLV is not present, then the T-PE receiving the label mapping message MUST NOT send S-PE bypass status messages in the PW ACh.
如果T-PE接收到LDP标签映射消息，其中包含设置了位B的通用协议标志接口参数TLV，则接收标签映射消息的T-PE可以在PW ACh中发送S-PE旁路状态消息。如果未设置所述TLV的位B，或TLV不存在，则接收标签映射消息的T-PE不得在PW ACh中发送S-PE旁路状态消息。
The S-PE will operate according to the procedures defined in [RFC6073]. The following additional procedures apply to the case where a static PW segment is switched to a dynamic PW segment that uses LDP, and the case where a static PW segment is switched to another static PW segment.
S-PE将按照[RFC6073]中规定的程序运行。以下附加程序适用于静态PW段切换到使用LDP的动态PW段的情况，以及静态PW段切换到另一个静态PW段的情况。
The procedures that are described in [RFC6073] Section 10 also apply to the case of a static PW switched to another static PW. The LDP header is simply replaced by the PW OAM header; otherwise, the packet format will be identical. The information that is necessary to form an SP-PE TLV MUST be configured in the S-PE, or no SP-PE TLV will be sent. [RFC6073] defines the IANA "Pseudowire Switching Point PE TLV Type" registry. In order to support the static PW configuration and addressing scheme, the following new code point has been assigned:
[RFC6073]第10节中描述的程序也适用于静态PW切换到另一静态PW的情况。LDP报头被PW-OAM报头简单地替换；否则，数据包格式将相同。必须在S-PE中配置形成SP-PE TLV所需的信息，否则不会发送SP-PE TLV。[RFC6073]定义IANA“伪线交换点PE TLV类型”注册表。为了支持静态PW配置和寻址方案，已分配以下新代码点：
Type Length Description
---- ------ -----------
0x07 24 Static PW/MPLS-TP PW segment ID of last
PW segment traversed
Type Length Description
---- ------ -----------
0x07 24 Static PW/MPLS-TP PW segment ID of last
PW segment traversed
The format of this TLV is that of the "Static Pseudowire Sub-TLV" defined in [RFC6426].
该TLV的格式为[RFC6426]中定义的“静态伪线子TLV”。
The procedures that are described in Section 10 of [RFC6073] also apply to this situation. However, if the PW label of the LDP-controlled PW segment is withdrawn by the adjacent PE, the S-PE will set the PW status code "0x00000001 - Pseudowire Not Forwarding" to the adjacent PW on the static PW segment.
[RFC6073]第10节中描述的程序也适用于这种情况。但是，如果相邻PE撤销LDP控制的PW段的PW标签，则S-PE将在静态PW段上向相邻PW设置PW状态代码“0x00000001-伪线不转发”。
The S-PE will only withdraw its label for the dynamic, LDP-controlled PW segment if the S-PE is not provisioned.
如果未设置S-PE，则S-PE将仅撤销其动态LDP控制PW段的标签。
The security measures described in [RFC4447], [RFC5085], and [RFC6073] are adequate for the proposed mechanism.
[RFC4447]、[RFC5085]和[RFC6073]中描述的安全措施适用于提议的机制。
IANA has set up the registry of "PW Generic Protocol Flags". These are bit strings of length 16. Bit 0 is defined in this document. Bits 1 through 15 are to be assigned by IANA using the "IETF Review" policy defined in [RFC5226].
IANA已经建立了“PW通用协议标志”的注册中心。这些是长度为16的位字符串。位0在本文档中定义。IANA将使用[RFC5226]中定义的“IETF审查”策略分配位1至15。
Any requests for allocation from this registry require a description of up to 65 characters.
来自此注册表的任何分配请求都需要最多65个字符的描述。
Initial PW Generic Protocol Flags value allocations are as follows:
初始PW通用协议标志值分配如下：
Bit Mask Description
====================================================================
0x0001 - S-PE bypass mode [RFC6478]
Bit Mask Description
====================================================================
0x0001 - S-PE bypass mode [RFC6478]
This document uses a new Associated Channel Type. IANA already maintains the "Pseudowire Associated Channel Types" registry. The value 0x0027 has been assigned with the description "PW OAM Message".
此文档使用新的关联频道类型。IANA已经维护了“伪线关联通道类型”注册表。值0x0027已分配有描述“PW OAM消息”。
This document uses a new Pseudowire Switching Point PE TLV Type. IANA already maintains the "Pseudowire Switching Point PE sub-TLV Type" registry. A value of 0x07 has been assigned with the description "Static PW/MPLS-TP PW segment ID of last PW segment traversed".
本文档使用一种新的伪线切换点PE TLV类型。IANA已经维护了“伪线交换点PE子TLV类型”注册表。已为0x07的值分配了描述“最后经过的PW段的静态PW/MPLS-TP PW段ID”。
This document uses a new interface parameter type. IANA already maintains the "Pseudowire Interface Parameters Sub-TLV type Registry". A value of 0x18 has been assigned with the description "PW Generic Protocol Flags".
此文档使用新的接口参数类型。IANA已经维护了“伪线接口参数子TLV类型注册表”。已为0x18的值分配了描述“PW通用协议标志”。
[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。
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006.
[RFC4385]Bryant，S.，Swallow，G.，Martini，L.，和D.McPherson，“用于MPLS PSN的伪线仿真边到边（PWE3）控制字”，RFC 43852006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。
[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。
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC5226]Narten，T.和H.Alvestrand，“在RFCs中编写IANA注意事项部分的指南”，BCP 26，RFC 5226，2008年5月。
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
[RFC6073]Martini，L.，Metz，C.，Nadeau，T.，Bocci，M.和M.Aissaoui，“分段伪线”，RFC 60732011年1月。
[RFC6310] Aissaoui, M., Busschbach, P., Martini, L., Morrow, M., Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping", RFC 6310, July 2011.
[RFC6310]Aissaoui，M.，Busschbach，P.，Martini，L.，Morrow，M.，Nadeau，T.，和Y（J）。Stein，“伪线（PW）操作、管理和维护（OAM）消息映射”，RFC63102011年7月。
[RFC6426] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS On-Demand Connectivity Verification and Route Tracing", RFC 6426, November 2011.
[RFC6426]Gray，E.，Bahadur，N.，Boutros，S.，和R.Aggarwal，“MPLS按需连接验证和路由跟踪”，RFC 6426，2011年11月。
[REDUNDANCY] Muley, P., Ed., and M. Aissaoui, Ed., "Pseudowire Preferential Forwarding Status Bit", Work in Progress, September 2011.
[冗余]Muley，P.，Ed.，和M.Aissaoui，Ed.，“伪线优先转发状态位”，正在进行的工作，2011年9月。
[RFC5885] Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)", RFC 5885, June 2010.
[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 58852010年6月。
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, June 2009.
[RFC5586]Bocci，M.，Ed.，Vigoureux，M.，Ed.，和S.Bryant，Ed.，“MPLS通用关联信道”，RFC 55862009年6月。
Authors' Addresses
作者地址
Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112 EMail: lmartini@cisco.com
Luca Martini Cisco Systems，Inc.地址：科罗拉多州恩格尔伍德东尼科尔斯大道9155号400室，邮编：80112电子邮件：lmartini@cisco.com
George Swallow Cisco Systems, Inc. 300 Beaver Brook Road Boxborough, Massachusetts 01719 United States EMail: swallow@cisco.com
George Swallow Cisco Systems，Inc.美国马萨诸塞州Boxborough市比弗布鲁克路300号01719电子邮件：swallow@cisco.com
Giles Heron Cisco Systems 9-11 New Square Bedfont Lakes Feltham Middlesex TW14 8HA United Kingdom EMail: giheron@cisco.com
Giles Heron Cisco Systems 9-11 New Square Bedfont Lakes Feltham Middlesex TW14 8英国电子邮件：giheron@cisco.com
Matthew Bocci Alcatel-Lucent Voyager Place Shoppenhangers Road Maidenhead Berks SL6 2PJ United Kingdom EMail: matthew.bocci@alcatel-lucent.com
Matthew Bocci Alcatel-Lucent Voyager Place Shoppenigers Road Maidenhead Berks SL6 2PJ英国电子邮件：Matthew。bocci@alcatel-朗讯网