Internet Engineering Task Force (IETF)                          S. Hegde
Request for Comments: 8379                        Juniper Networks, Inc.
Category: Standards Track                                      P. Sarkar
ISSN: 2070-1721                                             Arrcus, Inc.
                                                              H. Gredler
                                                            RtBrick Inc.
                                                              M. Nanduri
                                                        ebay Corporation
                                                                L. Jalil
                                                                 Verizon
                                                                May 2018
        
Internet Engineering Task Force (IETF)                          S. Hegde
Request for Comments: 8379                        Juniper Networks, Inc.
Category: Standards Track                                      P. Sarkar
ISSN: 2070-1721                                             Arrcus, Inc.
                                                              H. Gredler
                                                            RtBrick Inc.
                                                              M. Nanduri
                                                        ebay Corporation
                                                                L. Jalil
                                                                 Verizon
                                                                May 2018
        

OSPF Graceful Link Shutdown

OSPF优雅链路关闭

Abstract

摘要

When a link is being prepared to be taken out of service, the traffic needs to be diverted from both ends of the link. Increasing the metric to the highest value on one side of the link is not sufficient to divert the traffic flowing in the other direction.

当一条链路准备停止服务时,需要从链路两端转移流量。将链路一侧的度量增加到最大值不足以使流向另一方向的流量分流。

It is useful for the routers in an OSPFv2 or OSPFv3 routing domain to be able to advertise a link as being in a graceful-shutdown state to indicate impending maintenance activity on the link. This information can be used by the network devices to reroute the traffic effectively.

OSPFv2或OSPFv3路由域中的路由器能够将链路通告为处于正常关闭状态,以指示链路上即将发生的维护活动,这是非常有用的。网络设备可以使用此信息有效地重新路由流量。

This document describes the protocol extensions to disseminate graceful-link-shutdown information in OSPFv2 and OSPFv3.

本文档描述了在OSPFv2和OSPFv3中传播链路关闭信息的协议扩展。

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 https://www.rfc-editor.org/info/rfc8379.

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https://www.rfc-editor.org/info/rfc8379.

Copyright Notice

版权公告

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2018 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 (https://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(https://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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Scope  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . .   4
     4.2.  Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . .   4
     4.3.  Local/Remote Interface ID Sub-TLV . . . . . . . . . . . .   5
     4.4.  OSPFv3 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . .   6
     4.5.  BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . .   6
     4.6.  Distinguishing Parallel Links . . . . . . . . . . . . . .   7
   5.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Point-to-Point Links  . . . . . . . . . . . . . . . . . .   8
     5.2.  Broadcast/NBMA Links  . . . . . . . . . . . . . . . . . .   9
     5.3.  Point-to-Multipoint Links . . . . . . . . . . . . . . . .  10
     5.4.  Unnumbered Interfaces . . . . . . . . . . . . . . . . . .  10
     5.5.  Hybrid Broadcast and P2MP Interfaces  . . . . . . . . . .  10
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  10
   7.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Overlay Network . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  Controller-Based Deployments  . . . . . . . . . . . . . .  12
     7.3.  L3VPN Services and Sham Links . . . . . . . . . . . . . .  13
     7.4.  Hub and Spoke Deployment  . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17
        
   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Scope  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . .   4
     4.2.  Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . .   4
     4.3.  Local/Remote Interface ID Sub-TLV . . . . . . . . . . . .   5
     4.4.  OSPFv3 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . .   6
     4.5.  BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . .   6
     4.6.  Distinguishing Parallel Links . . . . . . . . . . . . . .   7
   5.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Point-to-Point Links  . . . . . . . . . . . . . . . . . .   8
     5.2.  Broadcast/NBMA Links  . . . . . . . . . . . . . . . . . .   9
     5.3.  Point-to-Multipoint Links . . . . . . . . . . . . . . . .  10
     5.4.  Unnumbered Interfaces . . . . . . . . . . . . . . . . . .  10
     5.5.  Hybrid Broadcast and P2MP Interfaces  . . . . . . . . . .  10
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  10
   7.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Overlay Network . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  Controller-Based Deployments  . . . . . . . . . . . . . .  12
     7.3.  L3VPN Services and Sham Links . . . . . . . . . . . . . .  13
     7.4.  Hub and Spoke Deployment  . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17
        
1. Introduction
1. 介绍

This document describes a mechanism for gracefully taking a link out of service while allowing it to be used if no other path is available. It also provides a mechanism to divert the traffic from both directions of the link.

本文档描述了一种机制,用于在没有其他路径可用的情况下,在允许使用链接的同时,使链接正常退出服务。它还提供了一种从链路的两个方向转移流量的机制。

Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned by means of pseudowires or L2 circuits. Prior to devices in the underlying network going offline for maintenance, it is useful to divert the traffic away from the node before maintenance is actually performed. Since the nodes in the underlying network are not visible to OSPF, the existing stub-router mechanism described in [RFC6987] cannot be used. In a service provider's network, there may be many CE-to-CE connections that run over a single PE. It is cumbersome to change the metric on every CE-to-CE connection in both directions. This document provides a mechanism to change the metric of the link on the remote side and also use the link as a last-resort link if no alternate paths are available. An application specific to this use case is described in detail in Section 7.1.

许多OSPFv2或OSPFv3部署运行在通过伪线或L2电路提供的覆盖网络上。在底层网络中的设备脱机进行维护之前,在实际执行维护之前将流量从节点转移出去是很有用的。由于底层网络中的节点对OSPF不可见,因此无法使用[RFC6987]中描述的现有存根路由器机制。在服务提供商的网络中,可能有许多通过单个PE运行的CE到CE连接。在两个方向上更改每个CE-to-CE连接上的度量是很麻烦的。本文档提供了一种机制,用于更改远程链路的度量,并在没有备用路径可用时将该链路用作最后的链路。第7.1节详细描述了特定于该用例的应用程序。

This document provides mechanisms to advertise graceful-link-shutdown state in the flexible encodings provided by "OSPFv2 Prefix/Link Attribute Advertisement" [RFC7684] and the E-Router-LSA [RFC8362] for OSPFv3. Throughout this document, OSPF is used when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is used when the text is specific to one version of the OSPF protocol.

本文档提供了在“OSPFv2前缀/链路属性播发”[RFC7684]和OSPFv3的E-Router-LSA[RFC8362]提供的灵活编码中播发优美链路关闭状态的机制。在本文件中,当文本同时适用于OSPFv2和OSPFv3时,将使用OSPF。当文本特定于OSPF协议的一个版本时,使用OSPFv2或OSPFv3。

1.1. Requirements Language
1.1. 需求语言

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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

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”在所有大写字母出现时(如图所示)应按照BCP 14[RFC2119][RFC8174]所述进行解释。

2. Motivation
2. 动机

The motivation of this document is to reduce manual intervention during maintenance activities. The following objectives help to accomplish this in a range of deployment scenarios.

本文件旨在减少维护活动期间的手动干预。以下目标有助于在一系列部署场景中实现这一点。

1. Advertise impending maintenance activity so that traffic from both directions can be diverted away from the link.

1. 宣传即将进行的维护活动,使来自两个方向的交通可以从链路分流。

2. Allow the solution to be backward compatible so that nodes that do not understand the new advertisement do not cause routing loops.

2. 允许解决方案向后兼容,以便不理解新播发的节点不会导致路由循环。

3. Advertise the maintenance activity to other nodes in the network so that Label Switched Path (LSP) ingress routers/controllers can learn about the impending maintenance activity and apply specific policies to reroute the LSPs for deployments based on Traffic Engineering (TE).

3. 向网络中的其他节点公布维护活动,以便标签交换路径(LSP)入口路由器/控制器可以了解即将到来的维护活动,并应用特定策略来重新路由LSP,以便基于流量工程(TE)进行部署。

4. Allow the link to be used as a last-resort link to prevent traffic disruption when alternate paths are not available.

4. 允许将该链路用作万不得已的链路,以防止在备用路径不可用时造成交通中断。

3. Flooding Scope
3. 泛洪范围

The graceful-link-shutdown information is flooded in an area-scoped Extended Link Opaque LSA [RFC7684] for OSPFv2 and in an E-Router-LSA for OSPFv3 [RFC8362]. The Graceful-Link-Shutdown sub-TLV MAY be processed by the head-end nodes or the controller as described in the Section 7. The procedures for processing the Graceful-Link-Shutdown sub-TLV are described in Section 5.

在OSPFv2的区域范围扩展链路不透明LSA[RFC7684]和OSPFv3的E-Router-LSA[RFC8362]中,正常链路关闭信息被淹没。如第7节所述,前端节点或控制器可处理优雅链路关闭子TLV。第5节描述了处理正常链路关闭子TLV的程序。

4. Protocol Extensions
4. 协议扩展
4.1. OSPFv2 Graceful-Link-Shutdown Sub-TLV
4.1. OSPFv2优雅链路关闭子TLV

The Graceful-Link-Shutdown sub-TLV identifies the link as being gracefully shutdown. It is advertised in the Extended Link TLV of the Extended Link Opaque LSA as defined in [RFC7684].

优雅链接关闭子TLV将链接标识为优雅关闭。它在[RFC7684]中定义的扩展链路不透明LSA的扩展链路TLV中公布。

        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        
        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 1: Graceful-Link-Shutdown Sub-TLV for OSPFv2

图1:OSPFv2的优雅链路关闭子TLV

Type: 7

类型:7

Length: 0

长度:0

4.2. Remote IPv4 Address Sub-TLV
4.2. 远程IPv4地址子TLV

This sub-TLV specifies the IPv4 address of the remote endpoint on the link. It is advertised in the Extended Link TLV as defined in [RFC7684]. This sub-TLV is optional and MAY be advertised in an area-scoped Extended Link Opaque LSA to identify the link when there are multiple parallel links between two nodes.

此子TLV指定链路上远程端点的IPv4地址。它在[RFC7684]中定义的扩展链路TLV中公布。此子TLV是可选的,可以在区域范围的扩展链路不透明LSA中公布,以在两个节点之间存在多个并行链路时识别链路。

        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote IPv4 Address                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        
        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote IPv4 Address                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 2: Remote IPv4 Address Sub-TLV

图2:远程IPv4地址子TLV

Type: 8

类型:8

Length: 4

长度:4

Value: Remote IPv4 address. The remote IPv4 address is used to identify a particular link on the remote side when there are multiple parallel links between two nodes.

值:远程IPv4地址。当两个节点之间存在多个并行链路时,远程IPv4地址用于标识远程端的特定链路。

4.3. Local/Remote Interface ID Sub-TLV
4.3. 本地/远程接口ID子TLV

This sub-TLV specifies Local and Remote Interface IDs. It is advertised in the Extended Link TLV as defined in [RFC7684]. This sub-TLV is optional and MAY be advertised in an area-scoped Extended Link Opaque LSA to identify the link when there are multiple parallel unnumbered links between two nodes. The Local Interface ID is generally readily available. One of the mechanisms to obtain the Remote Interface ID is described in [RFC4203].

此子TLV指定本地和远程接口ID。它在[RFC7684]中定义的扩展链路TLV中公布。此子TLV是可选的,可以在区域范围的扩展链路不透明LSA中公布,以在两个节点之间存在多个并行未编号链路时识别链路。本地接口ID通常随时可用。[RFC4203]中描述了获取远程接口ID的机制之一。

        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Local Interface ID                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote Interface ID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        
        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Local Interface ID                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote Interface ID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 3: Local/Remote Interface ID Sub-TLV

图3:本地/远程接口ID子TLV

Type: 9

类型:9

Length: 8

长度:8

Value: 4 octets of the Local Interface ID followed by 4 octets of the Remote Interface ID.

值:本地接口ID的4个八位字节,然后是远程接口ID的4个八位字节。

4.4. OSPFv3 Graceful-Link-Shutdown Sub-TLV
4.4. OSPFv3优雅链路关闭子TLV

The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV as defined in [RFC8362] for OSPFv3. The Router-Link TLV contains the Neighbor Interface ID and can uniquely identify the link on the remote node.

按照OSPFv3的[RFC8362]中的定义,在路由器链路TLV中携带优雅链路关闭子TLV。路由器链路TLV包含邻居接口ID,可以唯一标识远程节点上的链路。

        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        
        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 4: Graceful-Link-Shutdown Sub-TLV for OSPFv3

图4:OSPFv3的优雅链路关闭子TLV

Type: 8

类型:8

Length: 0

长度:0

4.5. BGP-LS Graceful-Link-Shutdown TLV
4.5. BGP-LS优雅链路关闭TLV

BGP-LS as defined in [RFC7752] is a mechanism that distributes network information to the external entities using the BGP routing protocol. Graceful link shutdown is important link information that the external entities can use for various use cases as defined in Section 7. BGP Link Network Layer Reachability Information (NLRI) is used to carry the link information. A new TLV called "Graceful-Link-Shutdown" is defined to describe the link attribute corresponding to graceful-link-shutdown state. The TLV format is as described in Section 3.1 of [RFC7752]. There is no Value field, and the Length field is set to zero for this TLV.

[RFC7752]中定义的BGP-LS是一种使用BGP路由协议将网络信息分发给外部实体的机制。优雅链接关闭是外部实体可用于第7节中定义的各种用例的重要链接信息。BGP链路网络层可达性信息(NLRI)用于承载链路信息。定义了一个新的TLV,称为“优雅链接关闭”,用于描述与优雅链接关闭状态相对应的链接属性。TLV格式如[RFC7752]第3.1节所述。没有值字段,此TLV的长度字段设置为零。

        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        
        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             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 5: Graceful-Link-Shutdown TLV for BGP-LS

图5:BGP-LS的正常链路关闭TLV

Type: 1121

类型:1121

Length: 0

长度:0

4.6. Distinguishing Parallel Links
4.6. 区分平行连杆
                    ++++++++++I.w            I.y+++++++++++
                    |Router A|------------------|Router B |
                    |        |------------------|         |
                    ++++++++++I.x            I.z+++++++++++
        
                    ++++++++++I.w            I.y+++++++++++
                    |Router A|------------------|Router B |
                    |        |------------------|         |
                    ++++++++++I.x            I.z+++++++++++
        

Figure 6: Parallel Links

图6:平行链路

Consider two routers, A and B, connected with two parallel point-to-point interfaces. I.w and I.x represent the interface address on Router A's side, and I.y and I.z represent interface addresses on Router B's side. The Extended Link Opaque LSA as defined in [RFC7684] describes links using Link Type, Link ID, and Link Data. For example, a link with the address I.w is described as below on Router A.

考虑两个路由器A和B,与两个并行的点对点接口连接。I.w和I.x代表路由器A侧的接口地址,I.y和I.z代表路由器B侧的接口地址。[RFC7684]中定义的扩展链路不透明LSA使用链路类型、链路ID和链路数据描述链路。例如,地址I.w的链路在路由器a上描述如下。

Link Type = Point-to-point

链接类型=点对点

Link ID = Router ID of B

链路ID=B的路由器ID

Link Data = I.w

链路数据=I.w

A third node (controller or head-end) in the network cannot distinguish the interface on Router B, which is connected to this particular Interface on Router A based on the link information described above. The interface with address I.y or I.z could be chosen due to this ambiguity. In such cases, a Remote IPv4 Address sub-TLV should be originated and added to the Extended Link TLV. The use cases as described in Section 7 require controller or head-end nodes to interpret the graceful-link-shutdown information and hence the need for the Remote IPv4 Address sub-TLV. I.y is carried in the Extended Link TLV, which unambiguously identifies the interface on the remote side. The OSPFv3 Router-Link TLV as described in [RFC8362] contains an Interface ID and a neighbor's Interface ID, which can uniquely identify connecting the interface on the remote side; hence, OSPFv3 does not require a separate remote IPv6 address to be advertised along with the OSPFv3 Graceful-Link-Shutdown sub-TLV.

网络中的第三节点(控制器或前端)无法区分路由器B上的接口,该接口基于上述链路信息连接到路由器A上的该特定接口。由于这种模糊性,可以选择地址为I.y或I.z的接口。在这种情况下,应发起远程IPv4地址子TLV并将其添加到扩展链路TLV。第7节中描述的用例要求控制器或前端节点解释正常链路关闭信息,因此需要远程IPv4地址子TLV。I.y在扩展链路TLV中携带,该TLV明确标识远程端的接口。[RFC8362]中描述的OSPFv3路由器链路TLV包含一个接口ID和一个邻居的接口ID,该接口ID可以唯一标识连接远程侧的接口;因此,OSPFv3不需要单独的远程IPv6地址与OSPFv3优雅链路关闭子TLV一起发布。

5. Elements of Procedure
5. 程序要素

As defined in [RFC7684], every link on the node will have a separate Extended Link Opaque LSA. The node that has the link to be taken out of service MUST advertise the Graceful-Link-Shutdown sub-TLV in the Extended Link TLV of the Extended Link Opaque LSA for OSPFv2, as defined in [RFC7684], and in the Router-Link TLV of E-Router-LSA for OSPFv3. The Graceful-Link-Shutdown sub-TLV indicates that the link identified by the sub-TLV is subjected to maintenance.

如[RFC7684]中所定义,节点上的每个链路都将有一个单独的扩展链路不透明LSA。具有要停止服务的链路的节点必须在[RFC7684]中定义的OSPFv2的扩展链路不透明LSA的扩展链路TLV和OSPFv3的E-Router-LSA的路由器链路TLV中公布优雅链路关闭子TLV。正常链路关闭子TLV表示子TLV标识的链路正在进行维护。

For the purposes of changing the metric OSPFv2 and OSPFv3 Router-LSAs need to be reoriginated. To change the Traffic Engineering metric, TE Opaque LSAs in OSPFv2 [RFC3630] and Intra-area-TE-LSAs in OSPFv3 [RFC5329] need to be reoriginated.

为了改变指标OSPFv2和OSPFv3,需要对路由器LSA进行重新排序。要更改流量工程度量,需要对OSPFv2[RFC3630]中的TE不透明LSA和OSPFv3[RFC5329]中的区域内TE LSA进行重新排序。

The graceful-link-shutdown information is advertised as a property of the link and is flooded through the area. This information can be used by ingress routers or controllers to take special actions. An application specific to this use case is described in Section 7.2.

正常链路关闭信息作为链路的属性发布,并通过该区域被淹没。入口路由器或控制器可使用此信息采取特殊行动。第7.2节描述了特定于该用例的应用程序。

When a link is ready to carry traffic, the Graceful-Link-Shutdown sub-TLV MUST be removed from the Extended Link TLV/Router-Link TLV, and the corresponding LSAs MUST be readvertised. Similarly, the metric MUST be set to original values, and the corresponding LSAs MUST be readvertised.

当链路准备好承载流量时,必须从扩展链路TLV/路由器链路TLV中删除正常链路关闭子TLV,并且必须读取相应的LSA。同样,必须将度量设置为原始值,并且必须读取相应的LSA。

The procedures described in this document may be used to divert the traffic away from the link in scenarios other than link-shutdown or link-replacement activity.

本文件中描述的程序可用于在链路关闭或链路更换活动以外的情况下转移链路的通信量。

The precise action taken by the remote node at the other end of the link identified for graceful-shutdown depends on the link type.

链路另一端的远程节点在正常关闭时所采取的精确操作取决于链路类型。

5.1. Point-to-Point Links
5.1. 点对点链接

The node that has the link to be taken out of service MUST set the metric of the link to MaxLinkMetric (0xffff) and reoriginate its Router-LSA. The Traffic Engineering metric of the link SHOULD be set to (0xffffffff), and the node SHOULD reoriginate the corresponding TE Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received for a point-to-point link, the remote node MUST identify the local link that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff), and the remote node MUST reoriginate its Router-LSA with the changed metric. When TE is enabled, the Traffic Engineering metric of the link SHOULD be set to (0xffffffff) and follow the procedures in [RFC5817]. Similarly, the

具有要停止服务的链路的节点必须将链路的度量设置为MaxLinkMetric(0xffff),并重新确定其路由器LSA的顺序。链路的流量工程度量应设置为(0xffffffff),节点应重新确定相应TE链路不透明LSA的顺序。当接收到点到点链路的正常链路关闭子TLV时,远程节点必须识别与正常链路相对应的本地链路,并将其度量设置为MaxLinkMetric(0xffff),并且远程节点必须使用更改的度量对其路由器LSA进行重新排序。启用TE时,链路的流量工程度量应设置为(0xffffffff),并遵循[RFC5817]中的步骤。同样地

remote node SHOULD set the Traffic Engineering metric of the link to 0xffffffff and SHOULD reoriginate the TE Link Opaque LSA for the link with the new value.

远程节点应将链路的流量工程度量设置为0xFFFFFF,并应使用新值重新排列链路的TE链路不透明LSA。

The Extended Link Opaque LSAs and the Extended Link TLV are not scoped for multi-topology [RFC4915]. In multi-topology deployments [RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an Extended Link Opaque LSA corresponds to all the topologies that include the link. The receiver node SHOULD change the metric in the reverse direction for all the topologies that include the remote link and reoriginate the Router-LSA as defined in [RFC4915].

扩展链路不透明LSA和扩展链路TLV不适用于多拓扑[RFC4915]。在多拓扑部署[RFC4915]中,扩展链路不透明LSA中公布的优雅链路关闭子TLV对应于包括链路的所有拓扑。接收器节点应按照[RFC4915]中的定义,反向更改包括远程链路的所有拓扑的度量,并重新确定路由器LSA的顺序。

When the originator of the Graceful-Link-Shutdown sub-TLV purges the Extended Link Opaque LSA or reoriginates it without the Graceful-Link-Shutdown sub-TLV, the remote node must reoriginate the appropriate LSAs with the metric and TE metric values set to their original values.

当优雅链接关闭子TLV的发起人清除扩展链接不透明LSA或在没有优雅链接关闭子TLV的情况下对其进行重新排序时,远程节点必须使用设置为其原始值的度量值和TE度量值对适当的LSA进行重新排序。

5.2. Broadcast/NBMA Links
5.2. 广播/NBMA链接

Broadcast or Non-Broadcast Multi-Access (NBMA) networks in OSPF are represented by a star topology where the Designated Router (DR) is the central point to which all other routers on the broadcast or NBMA network logically connect. As a result, routers on the broadcast or NBMA network advertise only their adjacency to the DR. Routers that do not act as DRs do not form or advertise adjacencies with each other. For the broadcast links, the MaxLinkMetric on the remote link cannot be changed since all the neighbors are on same link. Setting the link cost to MaxLinkMetric would impact all paths that traverse any of the neighbors connected on that broadcast link.

OSPF中的广播或非广播多址(NBMA)网络由星形拓扑表示,其中指定的路由器(DR)是广播或NBMA网络上所有其他路由器逻辑连接的中心点。因此,广播或NBMA网络上的路由器仅宣传其与DR的邻接。不充当DR的路由器不会形成或宣传彼此的邻接。对于广播链路,无法更改远程链路上的MaxLinkMetric,因为所有邻居都在同一链路上。将链路成本设置为MaxLinkMetric将影响通过该广播链路上连接的任何邻居的所有路径。

The node that has the link to be taken out of service MUST set the metric of the link to MaxLinkMetric (0xffff) and reoriginate the Router-LSA. The Traffic Engineering metric of the link SHOULD be set to (0xffffffff), and the node SHOULD reoriginate the corresponding TE Link Opaque LSAs. For a broadcast link, the two-part metric as described in [RFC8042] is used. The node originating the Graceful-Link-Shutdown sub-TLV MUST set the metric in the Network-to-Router Metric sub-TLV to MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and reoriginate the corresponding LSAs. The nodes that receive the two-part metric should follow the procedures described in [RFC8042]. The backward-compatibility procedures described in [RFC8042] should be followed to ensure loop-free routing.

具有要停止服务的链路的节点必须将链路的度量设置为MaxLinkMetric(0xffff),并重新确定路由器LSA的顺序。链路的流量工程度量应设置为(0xffffffff),节点应重新确定相应TE链路不透明LSA的顺序。对于广播链路,使用[RFC8042]中所述的两部分度量。发起优雅链路关闭子TLV的节点必须为OSPFv2和OSPFv3将网络中的度量设置为路由器度量子TLV到MaxLinkMetric(0xffff),并重新确定相应LSA的顺序。接收两部分度量的节点应遵循[RFC8042]中描述的步骤。应遵循[RFC8042]中描述的向后兼容性程序,以确保无环路路由。

5.3. Point-to-Multipoint Links
5.3. 点对多点链路

Operation for the point-to-multipoint (P2MP) links is similar to the point-to-point links. When a Graceful-Link-Shutdown sub-TLV is received for a point-to-multipoint link, the remote node MUST identify the neighbor that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff). The remote node MUST reoriginate the Router-LSA with the changed metric for the corresponding neighbor.

点对多点(P2MP)链路的操作与点对点链路类似。当接收到点对多点链路的正常链路关闭子TLV时,远程节点必须识别与正常链路相对应的邻居,并将其度量设置为MaxLinkMetric(0xffff)。远程节点必须使用相应邻居的已更改度量对路由器LSA进行重新排序。

5.4. Unnumbered Interfaces
5.4. 未编号的接口

Unnumbered interfaces do not have a unique IP address and borrow their address from other interfaces. [RFC2328] describes procedures to handle unnumbered interfaces in the context of the Router-LSA. We apply a similar procedure to the Extended Link TLV advertising the Graceful-Link-Shutdown sub-TLV in order to handle unnumbered interfaces. The Link-Data field in the Extended Link TLV includes the Local Interface ID instead of the IP address. The Local/Remote Interface ID sub-TLV MUST be advertised when there are multiple parallel unnumbered interfaces between two nodes. One of the mechanisms to obtain the Interface ID of the remote side is defined in [RFC4203].

未编号的接口没有唯一的IP地址,并从其他接口借用其地址。[RFC2328]描述了在路由器LSA上下文中处理未编号接口的过程。我们将类似的过程应用于扩展链路TLV,该扩展链路TLV宣传优雅链路关闭子TLV,以便处理未编号的接口。扩展链路TLV中的链路数据字段包括本地接口ID,而不是IP地址。当两个节点之间存在多个并行的未编号接口时,必须公布本地/远程接口ID子TLV。[RFC4203]中定义了获取远程端接口ID的机制之一。

5.5. Hybrid Broadcast and P2MP Interfaces
5.5. 混合广播和P2MP接口

Hybrid Broadcast and P2MP interfaces represent a broadcast network modeled as P2MP interfaces. [RFC6845] describes procedures to handle these interfaces. Operation for the Hybrid interfaces is similar to operation for the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is received for a hybrid link, the remote node MUST identify the neighbor that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff). All the remote nodes connected to the originator MUST reoriginate the Router-LSA with the changed metric for the neighbor.

混合广播和P2MP接口表示一个模拟为P2MP接口的广播网络。[RFC6845]描述了处理这些接口的过程。混合接口的操作与P2MP接口的操作类似。当为混合链路接收到优美链路关闭子TLV时,远程节点必须识别对应于优美链路的邻居,并将其度量设置为MaxLinkMetric(0xffff)。连接到发起者的所有远程节点必须使用邻居的已更改度量对路由器LSA进行重新排序。

6. Backward Compatibility
6. 向后兼容性

The mechanisms described in the document are fully backward compatible. It is required that the node adverting the Graceful-Link-Shutdown sub-TLV as well as the node at the remote end of the graceful-shutdown link support the extensions described herein for the traffic to be diverted from the graceful-shutdown link. If the remote node doesn't support the capability, it will still use the graceful-shutdown link, but there are no other adverse effects. In the case of broadcast links using two-part metrics, the backward-compatibility procedures as described in [RFC8042] are applicable.

文档中描述的机制完全向后兼容。要求播发优雅链路关闭子TLV的节点以及优雅链路远程端的节点支持本文所述的扩展,以便从优雅链路分流业务。如果远程节点不支持该功能,它仍将使用优雅的关机链接,但没有其他不利影响。在使用两部分指标的广播链路的情况下,[RFC8042]中描述的向后兼容性程序适用。

7. Applications
7. 应用
7.1. Overlay Network
7.1. 覆盖网络

Many service providers offer L2 services to a customer connecting different locations. The customer's IGP protocol creates a seamless private network (overlay network) across the locations for the customer. Service providers want to offer graceful-shutdown functionality when the PE device is taken out for maintenance. There can be large number of customers attached to a PE node, and the remote endpoints for these L2 attachment circuits are spread across the service provider's network. Changing the metric for all corresponding L2 circuits in both directions is a tedious and error-prone process. The graceful-link-shutdown feature simplifies the process by increasing the metric on the CE-CE overlay link so that traffic in both directions is diverted away from the PE undergoing maintenance. The graceful-link-shutdown feature allows the link to be used as a last-resort link so that traffic is not disrupted when alternate paths are not available.

许多服务提供商向连接不同位置的客户提供L2服务。客户的IGP协议为客户在各个位置创建无缝专用网络(覆盖网络)。当PE设备取出进行维护时,服务提供商希望提供优雅的关机功能。可以有大量客户连接到PE节点,并且这些L2连接电路的远程端点分布在服务提供商的网络中。在两个方向上更改所有相应L2电路的度量是一个繁琐且容易出错的过程。优雅的链路关闭功能通过增加CE-CE覆盖链路上的度量来简化过程,从而使两个方向上的流量从正在维护的PE中分流。优雅的链路关闭功能允许将链路用作最后的链路,以便在备用路径不可用时不会中断通信。

                     ------PE3---------------PE4------CE3
                   /                           \
                 /                               \
              CE1---------PE1----------PE2---------CE2
                                       \
                                        \
                                         ------CE4
        
                     ------PE3---------------PE4------CE3
                   /                           \
                 /                               \
              CE1---------PE1----------PE2---------CE2
                                       \
                                        \
                                         ------CE4
        

CE: Customer Edge PE: Provider Edge

CE:客户边缘PE:提供商边缘

Figure 7: Overlay Network

图7:覆盖网络

In the example shown in Figure 7, when the PE1 node is going out of service for maintenance, a service provider sets the PE1 to stub-router state and communi