Network Working Group T. Przygienda
Request for Comments: 5120 Z2 Sagl
Category: Standards Track N. Shen
Cisco Systems
N. Sheth
Juniper Networks
February 2008
Network Working Group T. Przygienda
Request for Comments: 5120 Z2 Sagl
Category: Standards Track N. Shen
Cisco Systems
N. Sheth
Juniper Networks
February 2008
M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)
M-ISIS：中间系统到中间系统（IS-ISs）的多拓扑（MT）路由
Status of This Memo
关于下段备忘
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Abstract
摘要
This document describes an optional mechanism within Intermediate System to Intermediate Systems (IS-ISs) used today by many ISPs for IGP routing within their clouds. This document describes how to run, within a single IS-IS domain, a set of independent IP topologies that we call Multi-Topologies (MTs). This MT extension can be used for a variety of purposes, such as an in-band management network "on top" of the original IGP topology, maintaining separate IGP routing domains for isolated multicast or IPv6 islands within the backbone, or forcing a subset of an address space to follow a different topology.
本文档描述了中间系统到中间系统（IS ISs）中的一种可选机制，目前许多ISP在其云中用于IGP路由。本文档描述了如何在单个IS-IS域中运行一组独立的IP拓扑，我们称之为多拓扑（MTs）。此MT扩展可用于多种目的，例如原始IGP拓扑的“顶部”带内管理网络、为主干内的隔离多播或IPv6孤岛维护单独的IGP路由域，或强制地址空间的子集遵循不同的拓扑。
Maintaining multiple MTs for IS-IS [ISO10589] [RFC1195] in a backwards-compatible manner necessitates several extensions to the packet encoding and additional Shortest Path First (SPF) procedures. The problem can be partitioned into the forming of adjacencies and advertising of prefixes and reachable intermediate systems within each topology. Having put all the necessary additional information in place, it must be properly used by MT capable SPF computation. The following sections describe each of the problems separately. To simplify the text, "standard" IS-IS topology is defined to be MT ID #0 (zero).
以向后兼容的方式维护IS-IS[ISO10589][RFC1195]的多个MTs需要对数据包编码和额外的最短路径优先（SPF）过程进行若干扩展。该问题可分为邻接的形成、前缀的广告和每个拓扑中可到达的中间系统。将所有必要的附加信息放在适当位置后，必须由具有MT功能的SPF计算正确使用。以下各节分别描述了每个问题。为了简化文本，“标准”IS-IS拓扑定义为MT ID#0（零）。
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 RFC 2119 [RFC2119].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[RFC2119]中所述进行解释。
CSNP Complete Sequence Number Packet. Used to describe all the contents of a link state database of IS-IS.
CSNP完整序列号数据包。用于描述IS-IS链接状态数据库的所有内容。
DIS Designated Intermediate System. The intermediate system elected to advertise the pseudo-node for a broadcast network.
DIS指定的中间系统。选择为广播网络播发伪节点的中间系统。
IIH IS-IS Hello. Packets that are used to discover adjacent intermediate systems.
你好。用于发现相邻中间系统的数据包。
LSP Link State Packet. Packet generated by an intermediate system and lists adjacent systems, prefixes, and other information.
LSP链路状态数据包。由中间系统生成并列出相邻系统、前缀和其他信息的数据包。
PSNP Partial Sequence Number Packet. Used to request information from an adjacent intermediate system's link state database.
PSNP部分序列号数据包。用于从相邻中间系统的链路状态数据库请求信息。
SPF Shortest Path First. An algorithm that takes a database of nodes within a domain and builds a tree of connectivity along the shortest paths through the entire network.
SPF最短路径优先。一种算法，它获取域内节点的数据库，并沿整个网络的最短路径建立连接树。
Each adjacency formed MUST be classified as belonging to a set of MTs on the interface. This is achieved by adding a new TLV into IIH packets that advertises to which topologies the interface belongs. If MT #0 is the only MT on the interface, it is optional to advertise it in the new TLV. Thus, not including such a TLV in the IIH implies MT ID #0 capability only. Through this exchange of MT capabilities, a router is able to advertise the IS TLVs in LSPs with common MT set over those adjacencies.
形成的每个邻接必须分类为属于接口上的一组MT。这是通过在IIH数据包中添加新的TLV来实现的，IIH数据包会公布接口所属的拓扑。如果MT#0是接口上的唯一MT，则可以选择在新TLV中公布它。因此，在IIH中不包括这样的TLV意味着仅具有MT ID#0能力。通过这种MT能力的交换，路由器能够在LSP中公布is TLV，并在这些邻接上设置公共MT。
The case of adjacency contains multiple MTs on an interface, and if there exists an overlapping IP address space among the topologies, additional mechanisms MUST be used to resolve the topology identity of the incoming IP packets on the interface. See further discussion in Section 8.2.2 of this document.
邻接情况下，接口上包含多个MT，如果拓扑之间存在重叠的IP地址空间，则必须使用其他机制来解析接口上传入IP数据包的拓扑标识。见本文件第8.2.2节的进一步讨论。
Adjacencies on point-to-point interfaces are formed as usual with IS-IS routers not implementing MT extensions. If a local router does not participate in certain MTs, it will not advertise those MT IDs in its IIHs and thus will not include that neighbor within its LSPs. On the other hand, if an MT ID is not detected in the remote side's IIHs, the local router MUST NOT include that neighbor within its LSPs. The local router SHOULD NOT form an adjacency if they don't have at least one common MT over the interface.
点到点接口上的邻接通常是在IS-IS路由器未实现MT扩展的情况下形成的。如果本地路由器不参与某些MTs，它将不会在其IIH中公布这些MTID，因此不会将该邻居包含在其LSP中。另一方面，如果在远程侧的iih中未检测到MT ID，则本地路由器不得在其lsp中包括该邻居。如果本地路由器在接口上没有至少一个公共MT，则不应形成邻接。
On a LAN, all the routers on the LAN that implement the MT extension MAY advertise their MT capability TLV in their IIHs. If there is at least one adjacency on the LAN interface that belongs to this MT, the MT capable router MUST include the corresponding MT IS Reachable TLV in its LSP, otherwise it MAY include this MT IS Reachable TLV in its LSP if the LAN interface participates in this MT set.
在LAN上，LAN上实现MT扩展的所有路由器都可以在其IIH中公布其MT能力TLV。如果LAN接口上至少有一个邻接属于此MT，则支持MT的路由器必须在其LSP中包含相应的MT可到达TLV，否则，如果LAN接口参与此MT集，则它可能在其LSP中包含此MT可到达TLV。
Two routers on a LAN SHALL always establish adjacency, regardless of whether or not they have a common MT. This is to ensure all the routers on the LAN can correctly elect the same DIS. The IS SHOULD NOT include the MT IS TLV in its LSP if none of the adjacencies on the LAN contain this MT.
LAN上的两个路由器应始终建立邻接关系，无论它们是否具有公共MT。这是为了确保LAN上的所有路由器都能正确选择相同的DI。如果LAN上的任何相邻区域都不包含此MT，则IS不应在其LSP中包含MT IS TLV。
The DIS, CSNP, and PSNP functions are not changed by MT extension.
MT扩展不会改变DIS、CSNP和PSNP函数。
A router MUST include within its LSPs in the Reachable Intermediate Systems TLV-only adjacent nodes that are participating in the corresponding topology and advertise such TLVs only if it participates itself in the corresponding topology. The Standard Reachable Intermediate Systems TLV is acting here as MT ID #0, the equivalent of the newly introduced MT Reachable Intermediate Systems TLV. A router MUST announce the MT IS TLV when there is at least one adjacency on the interface that belongs to this MT, otherwise it MAY announce the MT IS TLV of an adjacency for a given MT if this interface participates in the LAN.
路由器必须在其可到达中间系统的LSP中仅包括参与相应拓扑的相邻节点TLV，并且仅当其自身参与相应拓扑时才公布此类TLV。标准的可到达中间系统TLV在这里充当MT ID#0，相当于新引入的MT可到达中间系统TLV。当属于此MT的接口上至少有一个邻接时，路由器必须宣布MT为TLV，否则，如果此接口参与LAN，路由器可能会宣布给定MT邻接的MT为TLV。
Since it is not possible to prevent a router that does not understand MT extensions from being responsible for the generation of the according pseudo-node, it is possible to neither introduce special TLVs in the pseudo-node LSPs, nor run distinct DIS elections per MT. Therefore, a generated pseudo-node LSP by DIS MUST contain
由于无法防止不理解MT扩展的路由器负责生成相应的伪节点，因此既不能在伪节点LSP中引入特殊TLV，也不能对每个MT运行不同的DIS选择。因此，DIS生成的伪节点LSP必须包含
in its IS Reachable TLV all nodes on the LAN as usual, regardless of their MT capabilities. In other words, there is no change to the pseudo-node LSP construction.
在its中，可以像往常一样访问LAN上的所有节点，而不管它们的MT能力如何。换句话说，伪节点LSP构造没有变化。
For each of the MTs, a router could become potentially partitioned, overloaded, and attached independently. To prevent unnecessary complexity, MT extensions do not support MT based partition repair. The overload, partition, and attached bits in the LSP header only reflect the status of the default topology.
对于每一个MTs，路由器都可能独立地进行分区、过载和连接。为了避免不必要的复杂性，MT扩展不支持基于MT的分区修复。LSP头中的重载、分区和附加位仅反映默认拓扑的状态。
Attached bit and overload bit are part of the MT TLV being distributed within a node's LSP fragment zero. Since each adjacency can belong to different MTs, it is possible that some MTs are L2 attached, and others are not on the same router. The overload bit in the MT TLV can be used to signal the topology being overloaded. An MT-based system is considered overloaded if the overload bit in the MT is set.
附加位和重载位是MT TLV的一部分，该MT TLV分布在节点的LSP片段零中。由于每个邻接可以属于不同的mt，因此可能有些mt是L2连接的，而其他mt不在同一路由器上。MT TLV中的过载位可用于向过载拓扑发送信号。如果设置了MT中的过载位，则基于MT的系统被视为过载。
Route leaking between the levels SHOULD only be performed within the same MT.
水平之间的路线泄漏只能在同一MT内进行。
Each of the MTs commands its own address space so a new TLV is necessary for prefixes stored in MTs other than MT ID #0. To make the encoding less confusing when same prefixes are present in multiple MTs and accelerate SPF per MT, rather than adding a sub-TLV in Traffic Engineered (TE) extensions, a new TLV is introduced for that purpose that closely follows TE encoding [RFC3784].
每个MTs都有自己的地址空间，因此对于存储在MTs中的前缀（而非MT ID#0），需要一个新的TLV。为了在多个MT中存在相同前缀时减少编码混乱，并加速每MT的SPF，而不是在流量工程（TE）扩展中添加子TLV，为此目的引入了一个新的TLV，该TLV紧随TE编码[RFC3784]。
Each MT MUST run its own instance of the decision process. The pseudo-node LSPs are used by all topologies during computation. Each non-default topology MAY have its attached bit and overload bit set in the MT TLV. A reverse-connectivity check within SPF MUST follow the according MT to assure the bi-directional reachability within the same MT.
每个MT必须运行自己的决策过程实例。在计算过程中，所有拓扑都使用伪节点LSP。每个非默认拓扑都可以在MT TLV中设置其附加位和重载位。SPF内的反向连接检查必须遵循相应的MT，以确保同一MT内的双向可达性。
The results of each computation SHOULD be stored in a separate Routing Information Base (RIB), in normal cases, otherwise overlapping addresses in different topologies could lead to undesirable routing behavior, such as forwarding loops. The forwarding logic and configuration need to ensure the same MT is traversed from the source to the destination for packets. The nexthops derived from the MT SPF MUST belong to the adjacencies
在正常情况下，每次计算的结果应存储在单独的路由信息库（RIB）中，否则不同拓扑中的重叠地址可能会导致不良的路由行为，如转发循环。转发逻辑和配置需要确保数据包从源到目的地经过相同的MT。从MT SPF派生的nexthops必须属于邻接
conforming to the same MT for correct forwarding. It is recommended for the administrators to ensure consistent configuration of all routers in the domain to prevent undesirable forwarding behavior.
符合相同的MT以正确转发。建议管理员确保域中所有路由器的配置一致，以防止不良的转发行为。
No attempt is made in this document to allow one topology to calculate routes using the routing information from another topology inside SPF. Even though it is possible to redistribute and leak routes from another IS-IS topology or from external sources, the exact mechanism is beyond the scope of this document.
本文档中未尝试允许一个拓扑使用SPF内另一个拓扑的路由信息计算路由。即使可以从其他is-is拓扑或外部来源重新分配和泄漏路由，但确切的机制超出了本文档的范围。
Four new TLVs are added to support MT extensions. One of them is common for the LSPs and IIHs. Encoding of Intermediate System TLV and IPv4 Reachable Prefixes is tied to traffic engineering extensions [RFC3784] to simplify the implementation effort. The main reasons we chose to use new TLVs instead of using sub-TLVs inside existing TLV type-22 and type-135 are:
添加了四个新的TLV以支持MT扩展。其中一个对于LSP和IIH来说是常见的。中间系统TLV和IPv4可访问前缀的编码与流量工程扩展[RFC3784]相关联，以简化实现工作。我们选择在现有22型和135型TLV内使用新TLV而不是子TLV的主要原因是：
1. In many cases, multi-topologies are non-congruent, using the sub-TLV approach will not save LSP space;
1. 在许多情况下，多拓扑是非一致的，使用子TLV方法不会节省LSP空间；
2. Many sub-TLVs are already being used in TLV type-22, and many more are being proposed while there is a maximum limit on the TLV size, from the existing TLVs;
2. 22型TLV中已经使用了许多子TLV，并且在现有TLV的TLV尺寸存在最大限制的情况下，正在提出更多子TLV；
3. If traffic engineering or some other applications are being applied per topology level later, the new TLVs can automatically inherit the same attributes already defined for the "standard" topology without going through long standard process to redefine them per topology.
3. 如果以后按拓扑级别应用流量工程或某些其他应用程序，则新TLV可以自动继承已为“标准”拓扑定义的相同属性，而无需经过漫长的标准过程按拓扑重新定义这些属性。
The TLV number of this TLV is 229. It contains one or more MTs; the router is participating in the following structure:
该TLV的TLV编号为229。它包含一个或多个MTs；路由器正在参与以下结构：
x CODE - 229
x LENGTH - total length of the value field, it SHOULD be 2
times the number of MT components.
x VALUE - one or more 2-byte MT components, structured
as follows:
No. of Octets
+--------------------------------+
|O |A |R |R | MT ID | 2
+--------------------------------+
x CODE - 229
x LENGTH - total length of the value field, it SHOULD be 2
times the number of MT components.
x VALUE - one or more 2-byte MT components, structured
as follows:
No. of Octets
+--------------------------------+
|O |A |R |R | MT ID | 2
+--------------------------------+
Bit O represents the OVERLOAD bit for the MT (only valid in LSP fragment zero for MTs other than ID #0, otherwise SHOULD be set to 0 on transmission and ignored on receipt).
位O表示MT的重载位（仅在LSP片段0中对ID#0以外的MT有效，否则在传输时应设置为0，在接收时忽略）。
Bit A represents the ATTACH bit for the MT (only valid in LSP fragment zero for MTs other than ID #0, otherwise SHOULD be set to 0 on transmission and ignored on receipt).
位A表示MT的附加位（仅在LSP片段0中对ID#0以外的MT有效，否则在传输时应设置为0，在接收时忽略）。
Bits R are reserved, SHOULD be set to 0 on transmission and ignored on receipt.
位R是保留的，传输时应设置为0，接收时忽略。
MT ID is a 12-bit field containing the ID of the topology being announced.
MT ID是一个12位字段，包含所宣布拓扑的ID。
This MT TLV can advertise up to 127 MTs. It is announced in IIHs and LSP fragment 0, and can occur multiple times. The resulting MT set SHOULD be the union of all the MT TLV occurrences in the packet. Any other IS-IS PDU occurrence of this TLV MUST be ignored. Lack of MT TLV in hellos and fragment zero LSPs MUST be interpreted as participation of the advertising interface or router in MT ID #0 only. If a router advertises MT TLV, it has to advertise all the MTs it participates in, specifically including topology ID #0 also.
此MT TLV最多可播发127 MT。它在IIHs和LSP片段0中发布，并且可以多次出现。生成的MT集应该是数据包中所有MT TLV事件的并集。必须忽略此TLV的任何其他IS-IS PDU事件。hellos中缺少MT TLV和零片段LSP必须解释为广告接口或路由器仅参与MT ID#0。如果路由器播发MT TLV，它必须播发它参与的所有MT，特别是包括拓扑ID#0。
The TLV number of this TLV is 222. It is aligned with extended IS reachability TLV type 22 beside an additional two bytes in front at the beginning of the TLV.
该TLV的TLV编号为222。它与扩展is可达性TLV类型22对齐，在TLV开头前面的另外两个字节旁边。
x CODE - 222
x LENGTH - total length of the value field
x VALUE - 2-byte MT membership plus the format of extended IS
reachability TLV, structured as follows:
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| extended IS TLV format | 11 - 253
+--------------------------------+
. .
. .
+--------------------------------+
| extended IS TLV format | 11 - 253
+--------------------------------+
x CODE - 222
x LENGTH - total length of the value field
x VALUE - 2-byte MT membership plus the format of extended IS
reachability TLV, structured as follows:
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| extended IS TLV format | 11 - 253
+--------------------------------+
. .
. .
+--------------------------------+
| extended IS TLV format | 11 - 253
+--------------------------------+
Bits R are reserved, SHOULD be set to 0 on transmission and ignored on receipt.
位R是保留的，传输时应设置为0，接收时忽略。
MT ID is a 12-bit field containing the non-zero MT ID of the topology being announced. The TLV MUST be ignored if the ID is zero. This is to ensure the consistent view of the standard unicast topology.
MT ID是一个12位字段，其中包含所宣布拓扑的非零MT ID。如果ID为零，则必须忽略TLV。这是为了确保标准单播拓扑的一致视图。
After the 2-byte MT membership format, the MT IS content is in the same format as extended IS TLV, type 22 [RFC3784]. It can contain up to 23 neighbors of the same MT if no sub-TLVs are used.
在2字节MT成员格式之后，MT IS内容的格式与扩展IS TLV相同，类型为22[RFC3784]。如果不使用子TLV，它最多可以包含同一MT的23个邻居。
This TLV can occur multiple times.
该TLV可能发生多次。
The TLV number of this TLV is 235. It is aligned with extended IP reachability TLV type 135 beside an additional two bytes in front.
该TLV的TLV编号为235。它与扩展IP可达性TLV类型135对齐，并在前面增加了两个字节。
x CODE - 235 x LENGTH - total length of the value field x VALUE - 2-byte MT membership plus the format of extended IP reachability TLV, structured as follows:
x代码-235 x长度-值字段的总长度x值-2字节MT成员资格加上扩展IP可达性TLV的格式，结构如下：
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| extended IP TLV format | 5 - 253
+--------------------------------+
. .
. .
+--------------------------------+
| extended IP TLV format | 5 - 253
+--------------------------------+
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| extended IP TLV format | 5 - 253
+--------------------------------+
. .
. .
+--------------------------------+
| extended IP TLV format | 5 - 253
+--------------------------------+
Bits R are reserved, SHOULD be set to 0 on transmission and ignored on receipt.
位R是保留的，传输时应设置为0，接收时忽略。
MT ID is a 12-bit field containing the non-zero ID of the topology being announced. The TLV MUST be ignored if the ID is zero. This is to ensure the consistent view of the standard unicast topology.
MT ID是一个12位字段，包含所宣布拓扑的非零ID。如果ID为零，则必须忽略TLV。这是为了确保标准单播拓扑的一致视图。
After the 2-byte MT membership format, the MT IPv4 content is in the same format as extended IP reachability TLV, type 135 [RFC3784].
在2字节MT成员资格格式之后，MT IPv4内容的格式与扩展IP可达性TLV相同，类型135[RFC3784]。
This TLV can occur multiple times.
该TLV可能发生多次。
The TLV number of this TLV is 237. It is aligned with IPv6 Reachability TLV type 236 beside an additional two bytes in front.
该TLV的TLV编号为237。它与前面另外两个字节旁边的IPv6可达性TLV类型236一致。
x CODE - 237 x LENGTH - total length of the value field x VALUE - 2-byte MT membership plus the format of IPv6 Reachability TLV, structured as follows:
x代码-237 x长度-值字段的总长度x值-2字节MT成员资格加上IPv6可达性TLV的格式，结构如下：
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| IPv6 Reachability format | 6 - 253
+--------------------------------+
. .
+--------------------------------+
| IPv6 Reachability format | 6 - 253
+--------------------------------+
No. of Octets
+--------------------------------+
|R |R |R |R | MT ID | 2
+--------------------------------+
| IPv6 Reachability format | 6 - 253
+--------------------------------+
. .
+--------------------------------+
| IPv6 Reachability format | 6 - 253
+--------------------------------+
Bits R are reserved, SHOULD be set to 0 on transmission and ignored on receipt.
位R是保留的，传输时应设置为0，接收时忽略。
MT ID is a 12-bit field containing the ID of the topology being announced. The TLV MUST be ignored if the ID is zero.
MT ID是一个12位字段，包含所宣布拓扑的ID。如果ID为零，则必须忽略TLV。
After the 2-byte MT membership format, the MT IPv6 context is in the same format as IPv6 Reachability TLV, type 236 [H01].
在2字节MT成员格式之后，MT IPv6上下文的格式与IPv6可达性TLV相同，类型为236[H01]。
This TLV can occur multiple times.
该TLV可能发生多次。
Certain MT topologies are assigned to serve predetermined purposes:
某些MT拓扑分配用于预定目的：
- MT ID #0: Equivalent to the "standard" topology. - MT ID #1: Reserved for IPv4 in-band management purposes. - MT ID #2: Reserved for IPv6 routing topology. - MT ID #3: Reserved for IPv4 multicast routing topology. - MT ID #4: Reserved for IPv6 multicast routing topology. - MT ID #5: Reserved for IPv6 in-band management purposes. - MT ID #6-#3995: Reserved for IETF consensus. - MT ID #3996-#4095: Reserved for development, experimental and proprietary features [RFC3692].
- MT ID#0：相当于“标准”拓扑MT ID#1：保留用于IPv4带内管理目的。-MT ID#2：为IPv6路由拓扑保留。-MT ID#3：为IPv4多播路由拓扑保留。-MT ID#4：为IPv6多播路由拓扑保留。-MT ID#5：保留用于IPv6带内管理目的。-MT ID#6-#3995：为IETF共识保留。-MT ID#3996-#4095：保留用于开发、实验和专有功能[RFC3692]。
Using MT extension for IS-IS routing can result in multiple RIBs on the system. In this section, we list some of the known considerations for IP forwarding in various MT scenarios. Certain deployment scenarios presented here imply different trade-offs in terms of deployment difficulties and advantages obtained.
使用MT扩展进行IS-IS布线可能会导致系统上出现多个加强筋。在本节中，我们列出了各种MT场景中IP转发的一些已知注意事项。这里介绍的某些部署场景意味着在部署困难和获得的优势方面有不同的权衡。
In this case, each MT related route is installed into a separate RIB. Multiple topologies can share the same IS-IS interface on detecting the incoming packet address family. As an example, IPv4 and IPv6 can share the same interface without any further considerations under MT ISIS.
在这种情况下，每个MT相关路线都安装在单独的肋中。在检测传入数据包地址族时，多个拓扑可以共享同一IS-IS接口。例如，IPv4和IPv6可以共享同一接口，而无需在MT ISIS下进一步考虑。
In this case, MTs can be used to forward packets from the same address family, even with overlapping addresses, since the MTs have their dedicated interfaces, and those interfaces can be associated with certain MT RIBs and FIBs.
在这种情况下，MTs可用于转发来自相同地址族的分组，即使具有重叠的地址，因为MTs具有其专用接口，并且这些接口可与某些MT肋骨和fib相关联。
Some additional mechanism is needed to select the correct RIBs for the incoming IP packets to determine the correct RIB to make a forwarding decision. For example, if the topologies are Quality of Service (QoS) partitioned, then the Differentiated Services Code Point (DSCP) bits in the IP packet header can be utilized to make the decision. Some IP headers, or even packet data information, MAY be checked to make the forwarding table selection, for example, the source IP address in the header can be used to determine the desired forwarding behavior.
需要一些额外的机制来为传入的IP数据包选择正确的RIB，以确定做出转发决策的正确RIB。例如，如果拓扑是服务质量（QoS）分区的，则可以利用IP分组报头中的区分服务码点（DSCP）位来做出决策。可以检查一些IP报头，甚至分组数据信息以进行转发表选择，例如，报头中的源IP地址可用于确定所需的转发行为。
This topic is not unique to IS-IS or even to Multi-topology, it is a local policy and configuration decision to make sure the inbound traffic uses the correct forwarding tables. For example, preferred customer packets are sent through a Layer 2 Tunneling Protocol (L2TP) towards the high-bandwidth upstream provider, and other packets are sent through a different L2TP to a normal-bandwidth provider. Those mechanisms are not part of the L2TP protocol specifications.
此主题不是is-is甚至多拓扑独有的，它是一个本地策略和配置决策，用于确保入站流量使用正确的转发表。例如，优选客户分组通过第2层隧道协议（L2TP）发送到高带宽上游提供商，其他分组通过不同的L2TP发送到正常带宽提供商。这些机制不是L2TP协议规范的一部分。
The generic approach of packet to multiple MT RIB mapping over the same inbound interface is outside the scope of this document.
在同一入站接口上进行数据包到多个MT RIB映射的通用方法不在本文档的范围内。
When there is no overlap in the address space among all the MTs, strictly speaking, the destination address space classifies the topology to which a packet belongs. It is possible to install routes from different MTs into a shared RIB. As an example of such a deployment, a special IS-IS topology can be set up for certain External Border Gateway Protocol (eBGP) nexthop addresses.
当所有mt之间的地址空间中没有重叠时，严格地说，目的地址空间将分组所属的拓扑分类。可以将来自不同MTs的路线安装到共享肋中。作为此类部署的示例，可以为某些外部边界网关协议（eBGP）nexthop地址设置特殊的IS-IS拓扑。
MT in IS-IS MAY be used even if the resulting RIB is not used for forwarding purposes. As an example, multicast Reverse Path Forwarding (RPF) check can be performed on a different RIB than the standard unicast RIB, albeit an entirely different RIB is used for the multicast forwarding. However, an incoming packet MUST still be clearly identified as belonging to a unique topology.
即使生成的肋骨不用于转发目的，也可以使用IS-IS中的MT。例如，多播反向路径转发（RPF）检查可以在不同于标准单播RIB的RIB上执行，尽管用于多播转发的RIB完全不同。然而，传入数据包仍然必须清楚地标识为属于唯一拓扑。
When multiple IS-IS topologies exist within a domain, some of the routers can be configured to participate in a subset of the MTs in the network. This section discusses some of the options we have to enable operations or the network management stations to access those routers.
当一个域中存在多个IS-IS拓扑时，可以将一些路由器配置为参与网络中MTs的子集。本节讨论我们必须启用操作或网络管理站来访问这些路由器的一些选项。
This approach is to set up a dedicated management topology or 'in-band' management topology. This 'mgmt' topology will include all the routers need to be managed. The computed routes in the topology will be installed into the 'mgmt' RIB. In the condition that the 'mgmt' topology uses a set of non-overlapping address space with the default topology, those 'mgmt' routes can also be optionally installed into the default RIB. The advantages of duplicate 'mgmt' routes in both RIBs include: the network management utilities on the system does not have to be modified to use a specific RIB other than the default RIB; the 'mgmt' topology can share the same link with the default topology if so designed.
此方法用于设置专用管理拓扑或“带内”管理拓扑。此“管理”拓扑将包括需要管理的所有路由器。拓扑中的计算路由将安装到“管理”肋骨中。在“mgmt”拓扑使用一组与默认拓扑不重叠的地址空间的情况下，这些“mgmt”路由也可以选择性地安装到默认RIB中。两个RIB中重复“管理”路由的优点包括：系统上的网络管理实用程序不必修改为使用默认RIB以外的特定RIB；“mgmt”拓扑可以与默认拓扑共享相同的链接（如果这样设计的话）。
Even in the case that default topology is not used on some of the nodes in the IP forwarding, we MAY want to extend the default topology to those nodes for the purpose of network management. Operators SHOULD set high costs on the links that belong to the extended portion of the default topology. This way, the IP data traffic will not be forwarded through those nodes during network topology changes.
即使在IP转发中的某些节点未使用默认拓扑的情况下，出于网络管理的目的，我们可能希望将默认拓扑扩展到这些节点。操作员应在属于默认拓扑扩展部分的链路上设置高成本。这样，在网络拓扑更改期间，IP数据流量将不会通过这些节点转发。
The authors would like to thank Andrew Partan, Dino Farinacci, Derek Yeung, Alex Zinin, Stefano Previdi, Heidi Ou, Steve Luong, Pekka Savola, Mike Shand, Shankar Vemulapalli, and Les Ginsberg for the discussion, their review, comments, and contributions to this document.
作者感谢Andrew Partan、Dino Farinaci、Derek Yang、Alex Zinin、Stefano Previdi、Heidi Ou、Steve Luong、Pekka Savola、Mike Shand、Shankar Vemulapalli和Les Ginsberg对本文件的讨论、评论和贡献。
IS-IS security applies to the work presented. No specific security issues with the proposed solutions are known. The authentication procedure for IS-IS PDUs is the same regardless of MT information inside the IS-IS PDUs.
IS-IS安全性适用于所展示的作品。目前还不知道拟议解决方案的具体安全问题。无论IS-IS PDU内的MT信息如何，IS-IS PDU的身份验证过程都是相同的。
Note that an authentication mechanism, such as the one defined in [RFC3567], SHOULD be applied if there is high risk resulting from modification of multi-topology information.
请注意，如果修改多拓扑信息导致高风险，则应采用[RFC3567]中定义的身份验证机制。
As described in Section 8.2.2, multiple topologies share an interface in the same address space, some mechanism beyond IS-IS needs to be used to select the right forwarding table for an inbound packet. A misconfiguration on the system or a packet with a spoofed source address, for example, can lead to packet loss or unauthorized use of premium network resource.
如第8.2.2节所述，多个拓扑在同一地址空间中共享一个接口，需要使用IS-IS之外的某种机制为入站数据包选择正确的转发表。例如，系统配置错误或具有伪造源地址的数据包可能导致数据包丢失或未经授权使用高级网络资源。
This document defines the following new IS-IS TLV types, which have already been reflected in the IANA IS-IS TLV code-point registry:
本文件定义了以下新的IS-IS TLV类型，这些类型已反映在IANA IS-IS TLV代码点注册表中：
Name Value
名称值
MT-ISN 222 M-Topologies 229 MT IP. Reach 235 MT IPv6 IP. Reach 237
MT-ISN 222 M-Topologys 229 MT IP。达到235 MT IPv6 IP。达到237
IANA has created a new registry, "IS-IS Multi-Topology Parameters", with the assignments listed in Section 7.5 of this document and registration policies [RFC2434] for future assignments. The MT ID values range 6-3995 are allocated through Expert Review; values in the range of 3996-4095 are reserved for Private Use. In all cases, assigned values are to be registered with IANA.
IANA已经创建了一个新的注册表“IS-IS多拓扑参数”，其分配在本文件第7.5节中列出，注册政策[RFC2434]用于将来的分配。MT ID值范围6-3995通过专家评审分配；3996-4095范围内的值保留供私人使用。在所有情况下，应向IANA注册指定值。
[ISO10589] ISO. Intermediate System to Intermediate System Routing Exchange Protocol for Use in Conjunction with the Protocol for Providing the Connectionless-Mode Network Service. ISO 10589, 1992.
[ISO10589]ISO。中间系统到中间系统路由交换协议，与提供无连接模式网络服务的协议一起使用。ISO 105891992。
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990.
[RFC1195]Callon，R.，“OSI IS-IS在TCP/IP和双环境中的路由使用”，RFC 11951990年12月。
[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。
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC3692]Narten，T.，“分配被认为有用的实验和测试数字”，BCP 82，RFC 3692，2004年1月。
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[RFC2434]Narten，T.和H.Alvestrand，“在RFCs中编写IANA注意事项部分的指南”，BCP 26，RFC 2434，1998年10月。
[RFC3567] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003.
[RFC3567]Li，T.和R.Atkinson，“中间系统到中间系统（IS-IS）加密认证”，RFC 3567，2003年7月。
[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate System (IS-IS) Extensions for Traffic Engineering (TE)", RFC 3784, June 2004.
[RFC3784]Smit，H.和T.Li，“交通工程（TE）的中间系统到中间系统（IS-IS）扩展”，RFC 37842004年6月。
[H01] C. Hopps, "Routing IPv6 with IS-IS", Work in Progress.
[H01]C.Hopps，“使用IS-IS路由IPv6”，工作正在进行中。
Authors' Addresses
作者地址
Tony Przygienda Z2 Sagl Via Rovello 32 CH-6942 Savosa EMail: prz@net4u.ch
Tony Przygienda Z2 Sagl通过Rovello 32 CH-6942 Savosa发送电子邮件：prz@net4u.ch
Naiming Shen Cisco Systems 225 West Tasman Drive San Jose, CA, 95134 USA EMail: naiming@cisco.com
沈乃明思科系统225西塔斯曼大道圣何塞，加利福尼亚州，95134美国电子邮件：naiming@cisco.com
Nischal Sheth Juniper Networks 1194 North Mathilda Avenue Sunnyvale, CA 94089 USA EMail: nsheth@juniper.net
Nischal Sheth Juniper Networks 1194 North Mathilda Avenue Sunnyvale，CA 94089美国电子邮件：nsheth@juniper.net
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