Internet Engineering Task Force (IETF) L. Ginsberg, Ed.
Request for Comments: 8401 Cisco Systems
Category: Standards Track A. Przygienda
ISSN: 2070-1721 Juniper Networks
S. Aldrin
Google
J. Zhang
Juniper Networks, Inc.
June 2018
Internet Engineering Task Force (IETF) L. Ginsberg, Ed.
Request for Comments: 8401 Cisco Systems
Category: Standards Track A. Przygienda
ISSN: 2070-1721 Juniper Networks
S. Aldrin
Google
J. Zhang
Juniper Networks, Inc.
June 2018
Bit Index Explicit Replication (BIER) Support via IS-IS
通过IS-IS支持位索引显式复制（BIER）
Abstract
摘要
This document defines IS-IS extensions to support multicast forwarding using the Bit Index Explicit Replication (BIER) architecture.
本文档定义了IS-IS扩展，以支持使用位索引显式复制（BIER）体系结构的多播转发。
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/rfc8401.
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/rfc8401.
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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. BIER Domains and Subdomains . . . . . . . . . . . . . . . 5
4.2. Advertising BIER Information . . . . . . . . . . . . . . 5
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Multi-Topology and Subdomain . . . . . . . . . . . . . . 5
5.2. BFR-id Advertisements . . . . . . . . . . . . . . . . . . 6
5.3. Logging Misconfiguration . . . . . . . . . . . . . . . . 6
5.4. Flooding Reduction . . . . . . . . . . . . . . . . . . . 6
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. BIER Info Sub-TLV . . . . . . . . . . . . . . . . . . . . 7
6.2. BIER MPLS Encapsulation Sub-sub-TLV . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. BIER Domains and Subdomains . . . . . . . . . . . . . . . 5
4.2. Advertising BIER Information . . . . . . . . . . . . . . 5
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Multi-Topology and Subdomain . . . . . . . . . . . . . . 5
5.2. BFR-id Advertisements . . . . . . . . . . . . . . . . . . 6
5.3. Logging Misconfiguration . . . . . . . . . . . . . . . . 6
5.4. Flooding Reduction . . . . . . . . . . . . . . . . . . . 6
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. BIER Info Sub-TLV . . . . . . . . . . . . . . . . . . . . 7
6.2. BIER MPLS Encapsulation Sub-sub-TLV . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
Bit Index Explicit Replication (BIER) [RFC8279] defines an architecture where all intended multicast receivers are encoded as a bitmask in the multicast packet header within different encapsulations such as described in [RFC8296]. A router that receives such a packet will forward the packet based on the bit position in the packet header towards the receiver(s) following a precomputed tree for each of the bits in the packet. Each receiver is represented by a unique bit in the bitmask.
位索引显式复制（BIER）[RFC8279]定义了一种体系结构，其中所有预期的多播接收器都被编码为多播数据包报头中不同封装内的位掩码，如[RFC8296]中所述。接收这样的分组的路由器将基于分组报头中的比特位置沿着分组中每个比特的预计算树向接收机转发分组。每个接收器由位掩码中的唯一位表示。
This document presents necessary extensions to the currently deployed IS-IS for IP [RFC1195] to support distribution of information necessary for operation of BIER domains and subdomains. This document defines a new TLV to be advertised by every router participating in BIER signaling.
本文档介绍了当前部署的IS-IS for IP[RFC1195]的必要扩展，以支持BIER域和子域操作所需的信息分发。本文档定义了一个新的TLV，该TLV将由参与BIER信令的每个路由器发布。
This document defines support for MPLS encapsulation as specified in [RFC8296]. Support for other encapsulation types and the use of multiple encapsulation types are outside the scope of this document.
本文档定义了对[RFC8296]中规定的MPLS封装的支持。对其他封装类型的支持以及对多种封装类型的使用超出了本文档的范围。
Some of the terminology specified in [RFC8279] is replicated here and extended by necessary definitions:
[RFC8279]中规定的一些术语在此重复，并通过必要的定义进行扩展：
BIER: Bit Index Explicit Replication. The overall architecture of forwarding multicast using a bit position.
BIER：位索引显式复制。使用位位置转发多播的总体架构。
BIER-OL: BIER Overlay Signaling. The method for the BFIR to learn about BFERs.
BIER-OL：BIER覆盖信令。BFIR了解BFERs的方法。
BFR: Bit Forwarding Router. A router that participates in Bit Index Multipoint Forwarding. A BFR is identified by a unique BFR-prefix in a BIER domain.
比特转发路由器。参与位索引多点转发的路由器。BFR由BIER域中唯一的BFR前缀标识。
BFIR: Bit Forwarding Ingress Router. The ingress border router that inserts the BitString into the packet. Each BFIR must have a valid BFR-id assigned.
比特转发入口路由器。将位字符串插入数据包的入口边界路由器。每个BFIR必须分配有效的BFR id。
BFER: Bit Forwarding Egress Router. A router that participates in Bit Index Forwarding as a leaf. Each BFER must be a BFR. Each BFER must have a valid BFR-id assigned.
比特转发出口路由器。作为叶参与位索引转发的路由器。每个BFER必须是一个BFR。每个BFER必须分配一个有效的BFR id。
BFT: Bit Forwarding Tree used to reach all BFERs in a domain.
BFT：用于到达域中所有BFER的位转发树。
BIER subdomain: A further distinction within a BIER domain identified by its unique subdomain identifier. A BIER subdomain can support multiple BitString Lengths.
BIER子域：由唯一子域标识符标识的BIER域内的进一步区别。BIER子域可以支持多个位字符串长度。
BFR-id: An optional, unique identifier for a BFR within a BIER subdomain.
BFR id：BIER子域内BFR的可选唯一标识符。
Invalid BFR-id: Unassigned BFR-id. The special value 0 is reserved for this purpose.
无效的BFR id:未分配的BFR-id。为此保留特殊值0。
BAR: BIER Algorithm. Used to calculate underlay next hops.
BAR:BIER算法。用于计算下一跳的参考底图。
IPA: IGP Algorithm. May be used to modify, enhance, or replace the calculation of underlay paths as defined by the BAR value.
IPA:IGP算法。可用于修改、增强或替换由条形图值定义的参考底图路径的计算。
SPF: Shortest Path First routing calculation based on the IGP link metric.
SPF：基于IGP链路度量的最短路径优先路由计算。
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。
This document adds the following entry to the "Sub-TLVs for TLVs 135, 235, 236, and 237" registry.
本文档将以下条目添加到“用于TLV 135、235、236和237的子TLV”注册表中。
Value: 32
数值：32
Name: BIER Info
姓名：BIER Info
This document also introduces a new registry for sub-sub-TLVs for the BIER Info sub-TLV. The registration policy is Expert Review as defined in [RFC8126]. The "Sub-sub-TLVs for BIER Info Sub-TLV" has been created within the "IS-IS TLV Codepoints" registry. The defined value is as follows:
本文档还介绍了BIER Info子TLV子TLV的新注册表。注册政策为[RFC8126]中定义的专家评审。“BIER Info子TLV的子TLV”已在“IS-IS TLV代码点”注册表中创建。定义值如下所示：
Type Name
---- ----
1 BIER MPLS Encapsulation
Type Name
---- ----
1 BIER MPLS Encapsulation
IANA has created the "BIER Algorithms" registry within the "Bit Index Explicit Replication (BIER)" registry. The registration policies [RFC8126] for this registry are:
IANA在“位索引显式复制（BIER）”注册表中创建了“BIER算法”注册表。此注册表的注册策略[RFC8126]为：
"Standards Action" for values 0-127
值0-127的“标准行动”
"Specification Required" for values 128-239
值128-239的“所需规格”
"Experimental Use" for values 240-254
240-254值的“实验用途”
The initial values in the "BIER Algorithms" registry are:
“BIER算法”注册表中的初始值为：
0: No BIER-specific algorithm is used
0:未使用特定于BIER的算法
255: Reserved
255：保留
An IS-IS-signaled BIER domain is aligned with the scope of distribution of BFR-prefixes that identify the BFRs within IS-IS. In such a case, IS-IS acts as the supporting BIER underlay.
IS-IS信号BIER域与标识IS-IS中BFR的BFR前缀的分布范围一致。在这种情况下，IS-IS充当支撑BIER的底层。
Within such a domain, the extensions defined in this document advertise BIER information for one or more BIER subdomains. Each subdomain is uniquely identified by a subdomain-id (SD). Each subdomain is associated with a single IS-IS topology (MT) [RFC5120], which may be any of the topologies supported by IS-IS. Local configuration controls which <MT,SD> pairs are supported by a router. The mapping of subdomains to topologies MUST be consistent within the IS-IS flooding domain used to advertise BIER information.
在这样的域中，本文档中定义的扩展为一个或多个BIER子域发布BIER信息。每个子域由一个子域id（SD）唯一标识。每个子域与单个is-is拓扑（MT）[RFC5120]相关联，该拓扑可以是is-is支持的任何拓扑。本地配置控制路由器支持哪些<MT，SD>对。子域到拓扑的映射必须在用于发布BIER信息的IS-IS泛洪域内保持一致。
Each BIER subdomain has as its unique attributes the encapsulation used and the type of tree it uses to forward BIER frames (currently always SPF). Additionally, per supported BitString length in the subdomain, each router will advertise the necessary label ranges to support it.
每个BIER子域都有其独特的属性，即用于转发BIER帧的封装和树的类型（当前总是SPF）。此外，根据子域中受支持的位字符串长度，每个路由器将公布必要的标签范围以支持它。
BIER information advertisements are associated with a new sub-TLV in the extended reachability TLVs. BIER information is always associated with a host prefix, which MUST be a node address for the advertising node. If this is not the case, the advertisement MUST be ignored. Therefore, the following restrictions apply:
BIER信息广告与扩展可达性TLV中的新子TLV相关联。BIER信息始终与主机前缀关联，主机前缀必须是播发节点的节点地址。如果情况并非如此，则必须忽略广告。因此，以下限制适用：
o Prefix length MUST be 32 for an IPv4 prefix or 128 for an IPv6 prefix.
o IPv4前缀的前缀长度必须为32，IPv6前缀的前缀长度必须为128。
o When the Prefix Attributes Flags sub-TLV [RFC7794] is present, the N flag MUST be set and the R flag MUST NOT be set.
o 当前缀属性标志子TLV[RFC7794]存在时，必须设置N标志而不能设置R标志。
o BIER sub-TLVs MUST be included when a prefix reachability advertisement is leaked between levels.
o 当前缀可达性广告在级别之间泄漏时，必须包括BIER子TLV。
A given subdomain is supported within one and only one topology. All routers in the flooding scope of the BIER sub-TLVs MUST advertise the same subdomain within the same multi-topology. A router receiving an <MT,SD> advertisement that does not match the locally configured pair
给定的子域仅在一个拓扑中受支持。BIER子TLV泛洪范围内的所有路由器必须在同一多拓扑中公布同一子域。接收与本地配置对不匹配的<MT，SD>播发的路由器
MUST report a misconfiguration of the received <MT,SD> pair. All received BIER advertisements associated with the conflicting <MT,SD> pair MUST be ignored. Note that in the presence of such a misconfiguration, this will lead to partitioning of the subdomain.
必须报告收到的<MT，SD>对的配置错误。必须忽略与冲突的<MT，SD>对关联的所有接收到的BIER播发。请注意，如果存在这种错误配置，这将导致子域的分区。
Example:
例子：
The following combination of advertisements are valid: <0,0> <0,1>, and <2,2>.
以下广告组合有效：<0,0><0,1>和<2,2>。
The following combination of advertisements are invalid: <0,0> <0,1>, and <2,0>. Advertisements associated with <0,0> and <2,0> must be ignored.
以下广告组合无效：<0,0><0,1>和<2,0>。必须忽略与<0,0>和<2,0>关联的广告。
If a BFER/BFIR is configured with a BFR-id, then it advertises this value in its BIER advertisements. If no BFR-id is configured, then the value "Invalid BFR-id" is advertised. A valid BFR-id MUST be unique within the flooding scope of the BIER advertisements. All BFERs/BFIRs MUST detect advertisement of duplicate valid BFR-IDs for a given <MT,SD>. When such duplication is detected, all of the routers advertising duplicates MUST be treated as if they did not advertise a valid BFR-id. This implies they cannot act as BFER or BFIR in that <MT,SD>.
如果BFER/BFIR配置了BFR id，则它会在其BIER播发中播发该值。如果未配置BFR id，则会公布值“无效BFR id”。在BIER广告的泛洪范围内，有效的BFR id必须是唯一的。所有BFER/BFIR必须检测给定<MT，SD>的重复有效BFR ID的播发。当检测到这种重复时，所有公布重复的路由器必须被视为没有公布有效的BFR-id。这意味着它们不能在<MT，SD>中充当BFER或BFIR。
Whenever an advertisement is received that violates any of the constraints defined in this document, the receiving router MUST support logging this occurrence. Logging SHOULD be dampened to avoid excessive output.
每当接收到违反本文档中定义的任何约束的广告时，接收路由器必须支持记录此事件。应抑制日志记录，以避免输出过多。
It is expected that changes in the BIER domain information that is advertised by IS-IS occur infrequently. If this expectation is not met for an extended period of time (more than a few seconds of burstiness), changes will increase the number of Link State PDU (LSP) updates and negatively impact performance in the network. Implementations SHOULD protect against this possibility by, for example, dampening updates if they occur over an extended period of time.
预计is-is发布的BIER域信息中的更改很少发生。如果在很长一段时间内（超过几秒钟的突发性）未达到此预期，则更改将增加链路状态PDU（LSP）更新的数量，并对网络中的性能产生负面影响。实现应该防止这种可能性，例如，如果更新发生的时间过长，应该抑制更新。
All IS-IS BIER information is carried within the TLVs 235, 237, [RFC5120], 135 [RFC5305], or 236 [RFC5308].
所有IS-IS BIER信息均在TLV 235、237、[RFC5120]、135[RFC5305]或236[RFC5308]中传输。
This sub-TLV carries the information for the BIER subdomains that the router participates in as a BFR. This sub-TLV MAY appear multiple times in a given prefix-reachability TLV -- once for each subdomain supported in the associated topology.
此子TLV携带路由器作为BFR参与的BIER子域的信息。该子TLV可能在给定的前缀可达性TLV中出现多次——对于关联拓扑中支持的每个子域一次。
The sub-TLV advertises a single <MT,SD> combination followed by optional sub-sub-TLVs as described in the following sections.
子TLV宣传单个<MT，SD>组合，然后是可选的子TLV，如以下章节所述。
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BAR | IPA | subdomain-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BAR | IPA | subdomain-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: As indicated in the IANA section.
类型：如IANA部分所示。
Length: Variable
长度：可变
BAR: BIER Algorithm. Specifies a BIER-specific algorithm used to calculate underlay paths to reach BFERs. Values are allocated from the "BIER Algorithms" registry. 1 octet.
BAR:BIER算法。指定用于计算到达BFER的参考底图路径的BIER特定算法。值是从“BIER算法”注册表分配的。1个八位组。
IPA: IGP Algorithm. Specifies an IGP Algorithm to either modify, enhance, or replace the calculation of underlay paths to reach BFERs as defined by the BAR value. Values are from the IGP Algorithm registry. 1 octet.
IPA:IGP算法。指定IGP算法以修改、增强或替换参考底图路径的计算，以达到由条形图值定义的边界。值来自IGP算法注册表。1个八位组。
subdomain-id: Unique value identifying the BIER subdomain. 1 octet.
子域id：标识BIER子域的唯一值。1个八位组。
BFR-id: A 2-octet field encoding the BFR-id, as documented in [RFC8279]. If no BFR-id has been assigned, the value of this field is set to "Invalid BFR-id", which is defined as illegal in [RFC8279].
BFR id：一个编码BFR id的2个八位组字段，如[RFC8279]中所述。如果未分配BFR id，则此字段的值设置为“无效BFR id”，在[RFC8279]中定义为非法。
The use of non-zero values in either the BAR field or the IPA field is outside the scope of this document. If an implementation does not support the use of non-zero values in these fields but receives a BIER Info sub-TLV containing non-zero values in these fields, it SHOULD treat the advertising router as incapable of supporting BIER (one way of handling incapable routers is documented in Section 6.9 of [RFC8279] and additional methods may be defined in the future).
在BAR字段或IPA字段中使用非零值超出了本文档的范围。如果实施不支持在这些字段中使用非零值，但收到包含这些字段中非零值的BIER Info子TLV，则应将广告路由器视为无法支持BIER（处理无法支持的路由器的一种方法记录在[RFC8279]第6.9节中）将来可能会定义其他方法）。
This sub-sub-TLV carries the information for the BIER MPLS encapsulation including the label range for a specific BitString length for a certain <MT,SD>. It is advertised within the BIER Info sub-TLV (Section 6.1). This sub-sub-TLV MAY appear multiple times within a single BIER Info sub-TLV.
此子TLV包含BIER MPLS封装的信息，包括特定<MT，SD>的特定位字符串长度的标签范围。在BIER Info子条款TLV（第6.1节）中公布。该子TLV可能在单个BIER Info子TLV中出现多次。
If the same BitString length is repeated in multiple sub-sub-TLVs inside the same BIER Info sub-TLV, the BIER Info sub-TLV MUST be ignored.
如果在同一BIER Info子TLV内的多个子TLV中重复相同的位字符串长度，则必须忽略BIER Info子TLV。
Label ranges within all BIER MPLS Encapsulation sub-sub-TLVs across all BIER Info sub-TLVs advertised by the same BFR MUST NOT overlap. If overlap is detected, the advertising router MUST be treated as if it did not advertise any BIER sub-TLVs.
同一BFR发布的所有BIER Info子TLV上所有BIER MPLS封装子TLV内的标签范围不得重叠。如果检测到重叠，则必须将播发路由器视为未播发任何BIER子TLV。
Label values MUST NOT match any of the reserved values defined in [RFC3032].
标签值不得与[RFC3032]中定义的任何保留值匹配。
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: Value of 1 indicating MPLS encapsulation.
类型：值1表示MPLS封装。
Length: 4
长度：4
Max SI: Maximum Set Identifier (Section 1 of [RFC8279]) used in the encapsulation for this BIER subdomain for this BitString length, 1 octet. Each SI maps to a single label in the label range. The first label is for SI=0, the second label is for SI=1, etc. If the label associated with the Maximum Set Identifier exceeds the 20-bit range, the sub-sub-TLV MUST be ignored.
Max SI：用于此位字符串长度的BIER子域封装的最大集合标识符（RFC8279的第1节），1个八位字节。每个SI映射到标签范围内的单个标签。第一个标签用于SI=0，第二个标签用于SI=1，等等。如果与最大集合标识符关联的标签超过20位范围，则必须忽略子TLV。
Local BitString Length (BS Len): Encoded BitString length as per [RFC8296]. 4 bits.
本地位字符串长度（BS Len）：按照[RFC8296]编码的位字符串长度。4位。
Label: First label of the range, 20 bits. The labels are as defined in [RFC8296].
标签：范围的第一个标签，20位。标签的定义见[RFC8296]。
Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
IS-IS的安全问题见[RFC5304]和[RFC5310]。
The Security Considerations section of [RFC8279] discusses the possibility of performing a Denial-of-Service (DoS) attack by setting too many bits in the BitString of a BIER-encapsulated packet. However, this sort of DoS attack cannot be initiated by modifying the IS-IS BIER advertisements specified in this document. A BFIR decides which systems are to receive a BIER-encapsulated packet. In making this decision, it is not influenced by the IS-IS control messages. When creating the encapsulation, the BFIR sets one bit in the encapsulation for each destination system. The information in the IS-IS BIER advertisements is used to construct the forwarding tables that map each bit in the encapsulation into a set of next hops for the host that is identified by that bit, but it is not used by the BFIR to decide which bits to set. Hence, an attack on the IS-IS control plane cannot be used to cause this sort of DoS attack.
[RFC8279]的安全注意事项部分讨论了通过在BIER封装数据包的位字符串中设置过多位来执行拒绝服务（DoS）攻击的可能性。但是，这种DoS攻击不能通过修改本文档中指定的IS-IS BIER播发来发起。BFIR决定哪些系统接收BIER封装的数据包。在作出此决定时，它不受is-is控制消息的影响。创建封装时，BFIR为每个目标系统在封装中设置一位。IS-IS BIER广告中的信息用于构造转发表，该转发表将封装中的每个位映射到由该位标识的主机的一组下一跳，但BFIR不使用该信息来决定要设置的位。因此，对IS-IS控制平面的攻击不能用于引起此类DoS攻击。
While a BIER-encapsulated packet is traversing the network, a BFR that receives a BIER-encapsulated packet with n bits set in its BitString may have to replicate the packet and forward multiple copies. However, a given bit will only be set in one copy of the packet. This means that each transmitted replica of a received packet has fewer bits set (i.e., is targeted to fewer destinations) than the received packet. This is an essential property of the BIER-forwarding process as defined in [RFC8279]. While a failure of this process might cause a DoS attack (as discussed in the Security Considerations of [RFC8279]), such a failure cannot be caused by an attack on the IS-IS control plane.
当BIER封装的数据包穿越网络时，接收BIER封装数据包且其位字符串中设置了n位的BFR可能必须复制该数据包并转发多个副本。但是，给定的位将仅在数据包的一个副本中设置。这意味着接收到的分组的每个传输副本具有比接收到的分组更少的比特集（即，针对更少的目的地）。这是[RFC8279]中定义的BIER转发过程的基本属性。虽然此过程的故障可能会导致DoS攻击（如[RFC8279]的安全注意事项中所述），但此类故障不能由IS-IS控制平面上的攻击引起。
Further discussion of BIER-specific security considerations can be found in [RFC8279].
有关BIER特定安全注意事项的进一步讨论，请参见[RFC8279]。
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC1195]Callon，R.“OSI IS-IS在TCP/IP和双环境中的路由使用”，RFC 1195，DOI 10.17487/RFC1195，1990年12月<https://www.rfc-editor.org/info/rfc1195>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, <https://www.rfc-editor.org/info/rfc3032>.
[RFC3032]Rosen，E.，Tappan，D.，Fedorkow，G.，Rekhter，Y.，Farinaci，D.，Li，T.，和A.Conta，“MPLS标签堆栈编码”，RFC 3032，DOI 10.17487/RFC3032，2001年1月<https://www.rfc-editor.org/info/rfc3032>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, <https://www.rfc-editor.org/info/rfc5120>.
[RFC5120]Przygienda，T.，Shen，N.，和N.Sheth，“M-ISIS：中间系统到中间系统（IS-ISs）的多拓扑（MT）路由”，RFC 5120，DOI 10.17487/RFC5120，2008年2月<https://www.rfc-editor.org/info/rfc5120>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5304]Li，T.和R.Atkinson，“IS-IS加密认证”，RFC 5304，DOI 10.17487/RFC5304，2008年10月<https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5305]Li，T.和H.Smit，“交通工程的IS-IS扩展”，RFC 5305，DOI 10.17487/RFC5305，2008年10月<https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, DOI 10.17487/RFC5308, October 2008, <https://www.rfc-editor.org/info/rfc5308>.
[RFC5308]Hopps，C.，“使用IS-IS路由IPv6”，RFC 5308，DOI 10.17487/RFC5308，2008年10月<https://www.rfc-editor.org/info/rfc5308>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC5310]Bhatia，M.，Manral，V.，Li，T.，Atkinson，R.，White，R.，和M.Fanto，“IS-IS通用密码认证”，RFC 5310，DOI 10.17487/RFC5310，2009年2月<https://www.rfc-editor.org/info/rfc5310>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC7794]Ginsberg，L.，Ed.，Decarene，B.，Previdi，S.，Xu，X.，和U.Chunduri，“扩展IPv4和IPv6可达性的IS-IS前缀属性”，RFC 7794，DOI 10.17487/RFC7794，2016年3月<https://www.rfc-editor.org/info/rfc7794>.
[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>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., Przygienda, T., and S. Aldrin, "Multicast Using Bit Index Explicit Replication (BIER)", RFC 8279, DOI 10.17487/RFC8279, November 2017, <https://www.rfc-editor.org/info/rfc8279>.
[RFC8279]Wijnands，IJ.，Ed.，Rosen，E.，Ed.，Dolganow，A.，Przygienda，T.，和S.Aldrin，“使用位索引显式复制（BIER）的多播”，RFC 8279，DOI 10.17487/RFC8279，2017年11月<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation for Bit Index Explicit Replication (BIER) in MPLS and Non-MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January 2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8296]Wijnands，IJ.，Ed.，Rosen，E.，Ed.，Dolganow，A.，Tantsura，J.，Aldrin，S.，和I.Meilik，“MPLS和非MPLS网络中位索引显式复制（BIER）的封装”，RFC 8296，DOI 10.17487/RFC8296，2018年1月<https://www.rfc-editor.org/info/rfc8296>.
[OPSFv2BIER] Psenak, P., Kumar, N., Wijnands, I., Dolganow, A., Przygienda, T., Zhang, Z., and S. Aldrin, "OSPFv2 Extensions for BIER", Work in Progress, draft-ietf-bier-ospf-bier-extensions-18, June 2018.
[OPSFv2BIER]Psenak，P.，Kumar，N.，Wijnands，I.，Dolganow，A.，Przygienda，T.，Zhang，Z.，和S.Aldrin，“用于BIER的OSPFv2扩展”，正在进行的工作，草案-ietf-BIER-ospf-BIER-Extensions-18，2018年6月。
[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>.
Acknowledgements
致谢
This RFC is aligned with "OSPFv2 Extensions for BIER" [OPSFv2BIER] document as far as the protocol mechanisms overlap.
只要协议机制重叠，本RFC与“BIER的OSPFv2扩展”[OPSFv2BIER]文档保持一致。
Many thanks for comments from (in no particular order) Hannes Gredler, IJsbrand Wijnands, Peter Psenak, and Chris Bowers.
非常感谢Hannes Gredler、IJsbrand Wijnands、Peter Psenak和Chris Bowers（无特殊顺序）的评论。
Special thanks to Eric Rosen.
特别感谢埃里克·罗森。
Authors' Addresses
作者地址
Les Ginsberg (editor) Cisco Systems 510 McCarthy Blvd. Milpitas, CA 95035 United States of America
莱斯·金斯伯格（编辑）思科系统公司麦卡锡大道510号。美国加利福尼亚州米尔皮塔斯95035
Email: ginsberg@cisco.com
Email: ginsberg@cisco.com
Tony Przygienda Juniper Networks
Tony Przygienda Juniper Networks
Email: prz@juniper.net
Email: prz@juniper.net
Sam Aldrin Google 1600 Amphitheatre Parkway Mountain View, CA United States of America
Sam Aldrin谷歌1600圆形剧场公园道山景，加利福尼亚州，美利坚合众国
Email: aldrin.ietf@gmail.com
Email: aldrin.ietf@gmail.com
Jeffrey (Zhaohui) Zhang Juniper Networks, Inc. 10 Technology Park Drive Westford, MA 01886 United States of America
Jeffrey（赵辉）Zhang Juniper Networks，Inc.美国马萨诸塞州韦斯特福德科技园大道10号01886
Email: zzhang@juniper.net
Email: zzhang@juniper.net