Internet Engineering Task Force (IETF) J. Tantsura
Request for Comments: 8491 Apstra, Inc.
Category: Standards Track U. Chunduri
ISSN: 2070-1721 Huawei Technologies
S. Aldrin
Google, Inc.
L. Ginsberg
Cisco Systems
November 2018
Internet Engineering Task Force (IETF) J. Tantsura
Request for Comments: 8491 Apstra, Inc.
Category: Standards Track U. Chunduri
ISSN: 2070-1721 Huawei Technologies
S. Aldrin
Google, Inc.
L. Ginsberg
Cisco Systems
November 2018
Signaling Maximum SID Depth (MSD) Using IS-IS
使用IS-IS发送最大SID深度（MSD）信号
Abstract
摘要
This document defines a way for an Intermediate System to Intermediate System (IS-IS) router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment ID (SID) stack can be supported in a given network. This document only defines one type of MSD: Base MPLS Imposition. However, it defines an encoding that can support other MSD types. This document focuses on MSD use in a network that is Segment Routing (SR) enabled, but MSD may also be useful when SR is not enabled.
本文档定义了一种中间系统到中间系统（IS-IS）路由器在节点和/或链路粒度上公布多种支持的最大SID深度（MSDs）的方法。此类广告允许实体（例如，集中式控制器）确定特定网段ID（SID）堆栈在给定网络中是否受支持。本文件仅定义了一种MSD类型：基本MPLS。但是，它定义了一种可以支持其他MSD类型的编码。本文档重点介绍MSD在启用段路由（SR）的网络中的使用，但在未启用SR时，MSD也可能有用。
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/rfc8491.
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/rfc8491.
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5
4. Procedures for Defining and Using Node and Link MSD
Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6
5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5
4. Procedures for Defining and Using Node and Link MSD
Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6
5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
When Segment Routing (SR) paths are computed by a centralized controller, it is critical that the controller learn the Maximum SID Depth (MSD) that can be imposed at each node/link of a given SR path. This ensures that the Segment Identifier (SID) stack depth of a computed path does not exceed the number of SIDs the node is capable of imposing.
当集中控制器计算段路由（SR）路径时，控制器了解可施加在给定SR路径的每个节点/链路上的最大SID深度（MSD）至关重要。这可确保计算路径的段标识符（SID）堆栈深度不超过节点能够施加的SID数量。
[PCEP-EXT] defines how to signal MSD in the Path Computation Element Communication Protocol (PCEP). However, if PCEP is not supported/ configured on the head-end of an SR tunnel or a Binding-SID anchor node, and the controller does not participate in IGP routing, it has no way of learning the MSD of nodes and links. BGP-LS (Distribution
[PCEP-EXT]定义如何在路径计算元素通信协议（PCEP）中向MSD发送信号。但是，如果在SR隧道或绑定SID锚节点的前端不支持/配置PCEP，并且控制器不参与IGP路由，则无法了解节点和链路的MSD。BGP-LS（分配）
of Link-State and TE Information Using Border Gateway Protocol) [RFC7752] defines a way to expose topology and associated attributes and capabilities of the nodes in that topology to a centralized controller. MSD signaling by BGP-LS has been defined in [MSD-BGP]. Typically, BGP-LS is configured on a small number of nodes that do not necessarily act as head-ends. In order for BGP-LS to signal MSD for all the nodes and links in the network for which MSD is relevant, MSD capabilities SHOULD be advertised by every Intermediate System to Intermediate System (IS-IS) router in the network.
使用边界网关协议（Border Gateway Protocol）[RFC7752]定义了一种向集中式控制器公开拓扑以及该拓扑中节点的相关属性和功能的方法。BGP-LS的MSD信令已在[MSD-BGP]中定义。通常，BGP-LS配置在少数不一定充当前端的节点上。为了让BGP-LS向网络中与MSD相关的所有节点和链路发送MSD信号，网络中的每个中间系统到中间系统（is-is）路由器应公布MSD能力。
Other types of MSDs are known to be useful. For example, [ELC-ISIS] defines Entropy Readable Label Depth (ERLD), which is used by a head-end to insert an Entropy Label (EL) at a depth where it can be read by transit nodes.
已知其他类型的MSDs是有用的。例如，[ELC-ISIS]定义了熵可读标签深度（ERLD），前端使用该深度在传输节点可以读取的深度插入熵标签（EL）。
This document defines an extension to IS-IS used to advertise one or more types of MSDs at node and/or link granularity. It also creates an IANA registry for assigning MSD-Type identifiers and defines the Base MPLS Imposition MSD-Type. In the future, it is expected that new MSD-Types will be defined to signal additional capabilities, e.g., entropy labels, SIDs that can be imposed through recirculation, or SIDs associated with another data plane such as IPv6.
本文档定义了IS-IS的扩展，用于在节点和/或链接粒度上公布一种或多种类型的MSDs。它还创建用于分配MSD类型标识符的IANA注册表，并定义基本MPLS MSD类型。未来，预计将定义新的MSD类型，以显示附加功能，例如熵标签、可通过再循环施加的SID或与另一个数据平面（如IPv6）关联的SID。
MSD advertisements MAY be useful even if Segment Routing itself is not enabled. For example, in a non-SR MPLS network, MSD defines the maximum label depth.
即使未启用段路由本身，MSD播发也可能有用。例如，在非SR MPLS网络中，MSD定义最大标签深度。
BMI: Base MPLS Imposition is the number of MPLS labels that can be imposed inclusive of all service/transport/special labels.
BMI:Base MPLS Imposition是可以强制使用的MPLS标签数，包括所有服务/传输/特殊标签。
MSD: Maximum SID Depth is the number of SIDs supported by a node or a link on a node.
MSD:Maximum SID Depth是节点或节点上的链接支持的SID数。
SID: Segment Identifier is defined in [RFC8402].
SID:段标识符在[RFC8402]中定义。
Label Imposition: Imposition is the act of modifying and/or adding labels to the outgoing label stack associated with a packet. This includes:
标签粘贴：粘贴是修改和/或向与数据包相关的传出标签堆栈添加标签的行为。这包括：
* replacing the label at the top of the label stack with a new label
* 用新标签替换标签堆栈顶部的标签
* pushing one or more new labels onto the label stack
* 将一个或多个新标签推送到标签堆栈上
The number of labels imposed is then the sum of the number of labels that are replaced and the number of labels that are pushed. See [RFC3031] for further details.
然后，施加的标签数量是替换的标签数量和推送的标签数量之和。有关更多详细信息，请参见[RFC3031]。
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。
The Node MSD sub-TLV is defined within the body of the IS-IS Router CAPABILITY TLV [RFC7981] to carry the provisioned SID depth of the router originating the IS-IS Router CAPABILITY TLV. Node MSD is the smallest MSD supported by the node on the set of interfaces configured for use by the advertising IGP instance. MSD values may be learned via a hardware API or may be provisioned.
节点MSD子TLV在is-is路由器能力TLV[RFC7981]的主体内定义，以承载发起is-is路由器能力TLV的路由器的已配置SID深度。节点MSD是该节点在为广告IGP实例使用而配置的一组接口上支持的最小MSD。MSD值可通过硬件API学习或设置。
0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Node MSD Sub-TLV
图1：节点MSD子TLV
Type: 23
类型：23
Length: variable (multiple of 2 octets); represents the total length of the Value field
长度：可变（2个八位字节的倍数）；表示值字段的总长度
Value: field consists of one or more pairs of a 1-octet MSD-Type and 1-octet MSD-Value
值：字段由一对或多对1-octet MSD类型和1-octet MSD值组成
MSD-Type: value defined in the "IGP MSD-Types" registry created by the IANA Considerations section of this document Section 6
MSD类型：本文件第6节IANA注意事项部分创建的“IGP MSD类型”注册表中定义的值
MSD-Value: number in the range of 0-255 (for all MSD-Types, 0 represents the lack of ability to support a SID stack of any depth; any other value represents that of the node. This value MUST represent the lowest value supported by any link configured for use by the advertising IS-IS instance.)
MSD值：0-255范围内的数字（对于所有MSD类型，0表示无法支持任何深度的SID堆栈；任何其他值表示节点的SID堆栈。此值必须表示为广告IS-IS实例使用而配置的任何链接支持的最低值。）
This sub-TLV is optional. The scope of the advertisement is specific to the deployment.
此子TLV是可选的。播发的范围特定于部署。
If there exist multiple Node MSD advertisements for the same MSD-Type originated by the same router, the procedures defined in [RFC7981] apply. These procedures may result in different MSD values being used, for example, by different controllers. This does not, however, create any interoperability issue.
如果同一路由器发起的同一MSD类型存在多个节点MSD播发，则[RFC7981]中定义的过程适用。这些程序可能导致不同的MSD值被使用，例如，由不同的控制器使用。但是，这不会产生任何互操作性问题。
The Link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and 223 to carry the MSD of the interface associated with the link. MSD values may be signaled by the forwarding plane or may be provisioned.
链路MSD子TLV是为TLV 22、23、25、141、222和223定义的，用于承载与链路相关联的接口的MSD。MSD值可以由转发平面发出信号，也可以设置。
0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link MSD Sub-TLV
图2：链接MSD子TLV
Type: 15
类型：15
Length: variable (multiple of 2 octets); represents the total length of the Value field
长度：可变（2个八位字节的倍数）；表示值字段的总长度
Value: field consists of one or more pairs of a 1-octet MSD-Type and 1-octet MSD-Value
值：字段由一对或多对1-octet MSD类型和1-octet MSD值组成
MSD-Type: value defined in the "IGP MSD-Types" registry created by the IANA Considerations section of this document Section 6
MSD类型：本文件第6节IANA注意事项部分创建的“IGP MSD类型”注册表中定义的值
MSD-Value: number in the range of 0-255 (for all MSD-Types, 0 represents the lack of ability to support a SID stack of any depth; any other value represents that of the particular link when used as an outgoing interface.)
MSD值：0-255范围内的数字（对于所有MSD类型，0表示无法支持任何深度的SID堆栈；任何其他值表示用作传出接口时特定链接的SID堆栈。）
This sub-TLV is optional.
此子TLV是可选的。
If multiple Link MSD advertisements for the same MSD-Type and the same link are received, the procedure to select which copy to use is undefined.
如果收到同一MSD类型和同一链接的多个链接MSD播发，则选择使用哪个副本的过程未定义。
If the advertising router performs label imposition in the context of the ingress interface, it is not possible to meaningfully advertise per-link values. In such a case, only the Node MSD SHOULD be advertised.
如果广告路由器在入口接口的上下文中执行标签施加，则不可能有意义地广告每条链路的值。在这种情况下，只应通告节点MSD。
When Link MSD is present for a given MSD-Type, the value of the Link MSD MUST take precedence over the Node MSD. If a Link MSD-Type is not signaled, but the Node MSD-Type is, then the Node MSD-Type value MUST be considered to be the MSD value for that link.
当给定MSD类型存在链接MSD时，链接MSD的值必须优先于节点MSD。如果未通知链路MSD类型，但节点MSD类型为，则必须将节点MSD类型值视为该链路的MSD值。
In order to increase flooding efficiency, it is RECOMMENDED that routers with homogenous Link MSD values advertise just the Node MSD value.
为了提高泛洪效率，建议具有同质链路MSD值的路由器仅公布节点MSD值。
The meaning of the absence of both Node and Link MSD advertisements for a given MSD-Type is specific to the MSD-Type. Generally, it can only be inferred that the advertising node does not support advertisement of that MSD-Type. In some cases, however, the lack of advertisement might imply that the functionality associated with the MSD-Type is not supported. The correct interpretation MUST be specified when an MSD-Type is defined.
给定MSD类型中没有节点和链接MSD播发的含义特定于MSD类型。通常，只能推断广告节点不支持该MSD类型的广告。但是，在某些情况下，缺少广告可能意味着不支持与MSD类型关联的功能。定义MSD类型时，必须指定正确的解释。
Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS labels that can be imposed, including all service/transport/special labels.
基本MPLS实施MSD（BMI-MSD）表示可实施的MPLS标签总数，包括所有服务/传输/特殊标签。
The absence of BMI-MSD advertisements indicates only that the advertising node does not support advertisement of this capability.
缺少BMI-MSD播发仅表示播发节点不支持此功能的播发。
IANA has allocated a sub-TLV type for the new sub-TLV proposed in Section 2 of this document from the "Sub-TLVs for TLV 242 (IS-IS Router CAPABILITY TLV)" registry as defined by [RFC7981].
IANA已从[RFC7981]定义的“TLV 242子TLV（IS-IS路由器能力TLV）”注册表中为本文件第2节中提出的新子TLV分配了子TLV类型。
IANA has allocated the following value:
IANA已分配以下值：
Value Description Reference
----- --------------- -------------
23 Node MSD This document
Value Description Reference
----- --------------- -------------
23 Node MSD This document
Figure 3: Node MSD
图3：节点MSD
IANA has allocated a sub-TLV type as defined in Section 3 from the "Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 (Extended IS reachability, IS Neighbor Attribute, L2 Bundle Member Attributes, inter-AS reachability information, MT-ISN, and MT IS Neighbor Attribute TLVs)" registry.
IANA已从“TLV 22、23、25、141、222和223的子TLV（扩展IS可达性、IS邻居属性、L2捆绑包成员属性、as间可达性信息、MT-ISN和MT是邻居属性TLV）”注册表中分配了第3节中定义的子TLV类型。
IANA has allocated the following value:
IANA已分配以下值：
Value Description Reference
----- --------------- -------------
15 Link MSD This document
Value Description Reference
----- --------------- -------------
15 Link MSD This document
Figure 4: Link MSD
图4：链接MSD
Per-TLV information where Link MSD sub-TLV can be part of:
根据TLV信息，链接MSD子TLV可以是以下内容的一部分：
TLV 22 23 25 141 222 223
--- --------------------
y y y y y y
TLV 22 23 25 141 222 223
--- --------------------
y y y y y y
Figure 5: TLVs Where LINK MSD Sub-TLV Can Be Present
图5：存在链路MSD子TLV的TLV
IANA has created an IANA-managed registry titled "IGP MSD-Types" under the "Interior Gateway Protocol (IGP) Parameters" registry to identify MSD-Types as proposed in Sections 2 and 3. The registration procedure is "Expert Review" as defined in [RFC8126]. Types are an unsigned 8-bit number. The following values are defined by this document:
IANA已在“内部网关协议（IGP）参数”注册表下创建了一个名为“IGP MSD类型”的IANA管理注册表，以识别第2节和第3节中建议的MSD类型。注册程序为[RFC8126]中定义的“专家评审”。类型是一个无符号8位数字。本文件定义了以下值：
Value Name Reference
----- --------------------- -------------
0 Reserved This document
1 Base MPLS Imposition MSD This document
2-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
Value Name Reference
----- --------------------- -------------
0 Reserved This document
1 Base MPLS Imposition MSD This document
2-250 Unassigned
251-254 Experimental Use This document
255 Reserved This document
Figure 6: MSD-Types Codepoints Registry
图6:MSD类型代码点注册表
General guidance for the designated experts is defined in [RFC7370].
[RFC7370]中定义了指定专家的一般指南。
Security considerations as specified by [RFC7981] are applicable to this document.
[RFC7981]规定的安全注意事项适用于本文件。
The advertisement of an incorrect MSD value may have negative consequences. If the value is smaller than supported, path computation may fail to compute a viable path. If the value is larger than supported, an attempt to instantiate a path that can't be supported by the head-end (the node performing the SID imposition) may occur.
公布不正确的MSD值可能会产生负面后果。如果该值小于支持的值，则路径计算可能无法计算可行路径。如果该值大于支持的值，则可能会尝试实例化头端（执行SID强制的节点）不支持的路径。
The presence of this information may also inform an attacker of how to induce any of the aforementioned conditions.
此信息的存在还可能会告知攻击者如何诱发上述任何情况。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://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<https://www.rfc-editor.org/info/rfc2119>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <https://www.rfc-editor.org/info/rfc3031>.
[RFC3031]Rosen，E.，Viswanathan，A.，和R.Callon，“多协议标签交换体系结构”，RFC 3031，DOI 10.17487/RFC3031，2001年1月<https://www.rfc-editor.org/info/rfc3031>.
[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014, <https://www.rfc-editor.org/info/rfc7370>.
[RFC7370]Ginsberg，L.，“IS-IS TLV码点注册表的更新”，RFC 7370，DOI 10.17487/RFC7370，2014年9月<https://www.rfc-editor.org/info/rfc7370>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions for Advertising Router Information", RFC 7981, DOI 10.17487/RFC7981, October 2016, <https://www.rfc-editor.org/info/rfc7981>.
[RFC7981]Ginsberg，L.，Previdi，S.，和M.Chen，“广告路由器信息的IS-IS扩展”，RFC 7981，DOI 10.17487/RFC7981，2016年10月<https://www.rfc-editor.org/info/rfc7981>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
[RFC8126]Cotton，M.，Leiba，B.，和T.Narten，“在RFC中编写IANA考虑事项部分的指南”，BCP 26，RFC 8126，DOI 10.17487/RFC8126，2017年6月<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8174]Leiba，B.，“RFC 2119关键词中大写与小写的歧义”，BCP 14，RFC 8174，DOI 10.17487/RFC8174，2017年5月<https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8402]Filsfils，C.，Ed.，Previdi，S.，Ed.，Ginsberg，L.，Decarene，B.，Litkowski，S.，和R.Shakir，“段路由架构”，RFC 8402，DOI 10.17487/RFC8402，2018年7月<https://www.rfc-editor.org/info/rfc8402>.
[ELC-ISIS] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", Work in Progress, draft-ietf-isis-mpls-elc-06, September 2018.
[ELC-ISIS]Xu，X.，Kini，S.，Sivabalan，S.，Filsfils，C.，和S.Litkowski，“使用IS-IS的信号熵标签能力和熵可读标签深度”，正在进行的工作，草案-ietf-ISIS-mpls-ELC-062018年9月。
[MSD-BGP] Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, "Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link-State", Work in Progress, draft-ietf-idr-bgp-ls-segment-routing-msd-02, August 2018.
[MSD-BGP]Tantsura，J.，Chunduri，U.，Mirsky，G.，和S.Sivabalan，“使用边界网关协议链路状态发送MSD（最大SID深度），正在进行的工作，草案-ietf-idr-BGP-ls-segment-routing-MSD-02，2018年8月。
[PCEP-EXT] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., and J. Hardwick, "PCEP Extensions for Segment Routing", Work in Progress, draft-ietf-pce-segment-routing-13, October 2018.
[PCEP-EXT]Sivabalan，S.，Filsfils，C.，Tantsura，J.，Henderickx，W.，和J.Hardwick，“分段布线的PCEP扩展”，正在进行的工作，草案-ietf-pce-Segment-Routing-132018年10月。
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, <https://www.rfc-editor.org/info/rfc7752>.
[RFC7752]Gredler，H.，Ed.，Medved，J.，Previdi，S.，Farrel，A.，和S.Ray，“使用BGP的链路状态和流量工程（TE）信息的北向分布”，RFC 7752，DOI 10.17487/RFC7752，2016年3月<https://www.rfc-editor.org/info/rfc7752>.
Acknowledgements
致谢
The authors would like to thank Acee Lindem, Ketan Talaulikar, Stephane Litkowski, and Bruno Decraene for their reviews and valuable comments.
作者要感谢Acee Lindem、Ketan Talaulikar、Stephane Litkowski和Bruno DeClaene的评论和宝贵意见。
Contributors
贡献者
The following people contributed to this document:
以下人员对此文件作出了贡献：
Peter Psenak
彼得·普塞纳克
Email: ppsenak@cisco.com
Email: ppsenak@cisco.com
Authors' Addresses
作者地址
Jeff Tantsura Apstra, Inc.
杰夫·坦特拉飞天公司。
Email: jefftant.ietf@gmail.com
Email: jefftant.ietf@gmail.com
Uma Chunduri Huawei Technologies
Uma Chunduri华为技术有限公司
Email: uma.chunduri@huawei.com
Email: uma.chunduri@huawei.com
Sam Aldrin Google, Inc.
山姆·奥尔德林谷歌公司。
Email: aldrin.ietf@gmail.com
Email: aldrin.ietf@gmail.com
Les Ginsberg Cisco Systems
莱斯金斯伯格思科系统公司
Email: ginsberg@cisco.com
Email: ginsberg@cisco.com