Network Working Group R. Balay
Request for Comments: 2973 CoSine Communications
Category: Informational D. Katz
Juniper Networks
J. Parker
Axiowave Networks
October 2000
Network Working Group R. Balay
Request for Comments: 2973 CoSine Communications
Category: Informational D. Katz
Juniper Networks
J. Parker
Axiowave Networks
October 2000
IS-IS Mesh Groups
IS-IS网格组
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
Abstract
摘要
This document describes a mechanism to reduce redundant packet transmissions for the Intermediate System to Intermediate System (IS-IS) Routing protocol, as described in ISO 10589. The described mechanism can be used to reduce the flooding of Link State PDUs (Protocol Data Units) (LSPs) in IS-IS topologies. The net effect is to engineer a flooding topology for LSPs which is a subset of the physical topology. This document serves to document the existing behavior in deployed implementations.
本文件描述了一种减少中间系统到中间系统（IS-IS）路由协议冗余数据包传输的机制，如ISO 10589所述。所述机制可用于减少IS-IS拓扑中链路状态PDU（协议数据单元）（LSP）的泛洪。最终的效果是为LSP设计一个泛洪拓扑，它是物理拓扑的一个子集。本文档用于记录已部署实现中的现有行为。
The document describes behaviors that are backwards compatible with implementations that do not support this feature.
该文档描述了与不支持此功能的实现向后兼容的行为。
Table of Contents
目录
1. Overview..................................................... 2
2. Definitions of Mesh Groups................................... 3
3. Drawbacks of Mesh Groups..................................... 5
4. Interoperation with Mesh Groups.............................. 6
5. Acknowledgments.............................................. 6
6. References................................................... 6
7. Security Considerations...................................... 6
8. Authors' Addresses........................................... 7
9. Full Copyright Statement..................................... 8
1. Overview..................................................... 2
2. Definitions of Mesh Groups................................... 3
3. Drawbacks of Mesh Groups..................................... 5
4. Interoperation with Mesh Groups.............................. 6
5. Acknowledgments.............................................. 6
6. References................................................... 6
7. Security Considerations...................................... 6
8. Authors' Addresses........................................... 7
9. Full Copyright Statement..................................... 8
In ATM or frame relay networks Intermediate Systems are inter-connected using virtual circuits (VCs) which are logical point-to-point links. Some organizations attach multiple Intermediate Systems to form a full "mesh" topology, where every pair of Intermediate Systems are connected by a point-to-point link. In such topologies, IS-IS protocol operation leads to redundant transmission of certain PDUs due to the flooding operation which is illustrated below.
在ATM或帧中继网络中，中间系统使用作为逻辑点到点链路的虚拟电路（VCs）相互连接。一些组织连接多个中间系统以形成完整的“网状”拓扑，其中每对中间系统通过点对点链接连接。在这样的拓扑中，IS-IS协议操作由于洪泛操作导致某些PDU的冗余传输，如下所示。
When an Intermediate System gets a new Link State Protocol Data Unit (LSP), it stores it, and prepares to flood it out every circuit except the source circuit. This is done by setting SRM (Send Routing Message) bits held in the local copy of the LSP: there is an SRM for each circuit.
当一个中间系统获得一个新的链路状态协议数据单元（LSP）时，它将其存储起来，并准备将其从除源电路外的所有电路中溢出。这是通过设置保存在LSP本地副本中的SRM（发送路由消息）位来实现的：每个电路都有一个SRM。
+----------+ +----------+
| | I12 I21 | |
| System 1 | --------------------------- | System 2 |
| | | |
+----------+ +----------+
I13 | \ I14 I23 / | I24
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| . |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
I31 | / I32 I41 \ | I42
+----------+ +----------+
| | | |
| System 3 | --------------------------- | System 4 |
| | I34 I43 | |
+----------+ +----------+
+----------+ +----------+
| | I12 I21 | |
| System 1 | --------------------------- | System 2 |
| | | |
+----------+ +----------+
I13 | \ I14 I23 / | I24
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| . |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
I31 | / I32 I41 \ | I42
+----------+ +----------+
| | | |
| System 3 | --------------------------- | System 4 |
| | I34 I43 | |
+----------+ +----------+
Figure 1. A four node full mesh topology
图1。四节点全网格拓扑
When System1 regenerates an LSP, it will flood the LSP through the network by marking the SRM bits for circuits I12, I14, and I13. In due course, it will send out the LSP on each circuit.
当System1重新生成LSP时，它将通过标记电路I12、I14和I13的SRM位使LSP通过网络。在适当的时候，它将在每个电路上发送LSP。
When System2 receives System1's LSP, it propagates the PDU according to section 7.2.14 of ISO 10589 [1]. It sets the SRM bits on circuits I23 and I24, to flood the LSP to System3 and System4. However, these Intermediate Systems will get the LSP directly from System1. In a full mesh of N Intermediate Systems, the standard protocol mechanism results in N-2 extra transmissions of each LSP, a waste of bandwidth and processing effort, with little gain in reliability.
当System2收到System1的LSP时，它根据ISO 10589[1]第7.2.14节传播PDU。它在电路I23和I24上设置SRM位，以将LSP洪泛到System3和System4。但是，这些中间系统将直接从System1获得LSP。在由N个中间系统组成的全网中，标准协议机制会导致每个LSP的N-2个额外传输，浪费带宽和处理工作量，可靠性几乎没有提高。
Mesh groups provide a mechanism to reduce the flooding of LSPs.
网格组提供了一种减少LSP泛滥的机制。
A mesh group is defined as a set of point-to-point circuits which provide full connectivity to a set of Intermediate Systems. Each circuit has two new attributes: meshGroupEnabled, which is in state {meshInactive, meshBlocked, or meshSet} and an integer variable meshGroup, which is valid only if the value of meshGroupEnabled attribute is 'meshSet'. Circuits that are in state 'meshSet' and that have the same value of meshGroup are said to be in the same mesh group.
网格组定义为一组点到点电路，这些电路提供与一组中间系统的完全连接。每个回路都有两个新属性：meshGroupEnabled（处于状态{meshInactive、meshBlocked或meshSet}）和整数变量meshGroup（仅当meshGroupEnabled属性的值为“meshSet”时才有效）。处于“网格集”状态且具有相同网格组值的电路称为处于同一网格组中。
LSPs are not flooded over circuits in 'meshBlocked' state, and an LSP received on a circuit C is not flooded out circuits that belong to C's mesh group.
LSP不会淹没在处于“网状阻塞”状态的电路上，并且在电路C上接收的LSP不会淹没属于C的网状组的电路。
Section 7.3.15.1 clause e.1.ii) of ISO 10589 [1] is modified as follows:
ISO 10589[1]第7.3.15.1节第e.1.ii）条修改如下：
e.1.ii) if the meshGroupEnabled attribute is 'meshSet' for the circuit C, set the SRMflag for that LSP for all circuits other than C whose meshGroupEnabled attribute is 'meshInactive'. Also set the SRMflag for all circuits in state 'meshSet' whose meshGroup attribute is not the same as C's.
e、 1.ii）如果电路C的meshGroupEnabled属性为“meshSet”，则为除C以外的所有电路（其meshGroupEnabled属性为“meshInactive”）的LSP设置SRMflag。同时，为状态为“meshSet”且meshGroup属性与C不相同的所有电路设置SRMflag。
if the meshGroupEnabled attribute is 'meshInactive' for circuit C, set the SRMflag for that LSP for all circuits other than C whose meshGroupEnabled attribute is not 'meshBlocked'.
如果电路C的meshGroupEnabled属性为“meshInactive”，则为除C以外的所有电路（其meshGroupEnabled属性不是“meshBlocked”）设置该LSP的SRMflag。
For robust database synchronization when using mesh groups, the Complete Sequence Number PDUs (CSNPs) are sent periodically on point-to-point links with a mesh group meshEnabled or meshBlocked. Section 7.3.15.3 clause b) of ISO 10589 [1] is modified as follows:
为了在使用网格组时实现强健的数据库同步，完整的序列号PDU（CSNPs）在网格组启用或阻止的点到点链路上定期发送。ISO 10589[1]第7.3.15.3节第b）条修改如下：
b) If C is a point-to-point circuit (including non-DA DED circuits and virtual links), then
b) 如果C是点对点电路（包括非数据电路和虚拟链路），则
1) If the circuit's attribute is 'meshSet' or 'meshBlocked', then for each valid level, the IS will send a complete set of CSNPs as described for a Designated IS in section 7.3.15.3 clause a).
1) 如果电路属性为“meshSet”或“MESHSBLOCKED”，则对于每个有效级别，is将发送一套完整的CSNP，如第7.3.15.3节第a条中指定is所述。
2) CSNPs are transmitted only at initialization on point-to-point links whose state is 'meshInactive'.
2) CSNP仅在初始化时在状态为“非活动”的点到点链路上传输。
Use of mesh groups at an Intermediate System also modifies the behavior in transmission of generated LSPs. These LSPs are not required to be transmitted over circuits in state 'meshBlocked' at system startup or when the LSP is regenerated. The second sentence of Section 7.3.12 is modified to read:
在中间系统中使用网格组也会修改生成的LSP的传输行为。在系统启动时或LSP重新生成时，这些LSP不需要通过处于“网状阻塞”状态的电路传输。第7.3.12节第二句修改为：
"For all the circuits whose meshGroupEnabled attribute is not 'meshBlocked', the IS shall set the SRMflags for that Link State PDU to propagate it on all these circuits. The IS shall clear the SRMflags for circuits whose meshGroupEnabled attribute is 'meshBlocked'."
“对于其meshGroupEnabled属性不是‘meshBlocked’的所有电路，is应为该链路状态PDU设置SRMflags，以将其传播到所有这些电路上。is应清除其meshGroupEnabled属性为‘meshBlocked’的电路的SRMflags。”
Some of the transient transmission overhead can be reduced by having an Intermediate System not transmit its copies of the LSPs in database on a circuit start-up/restart if the circuit is ' meshBlocked'. The clause a) in the last part of Section 7.3.17 of ISO 10589, which refers to the point-to-point circuits, is modified as follows:
如果电路“阻塞”，则在电路启动/重启时，中间系统不传输数据库中LSP的副本，可以减少一些瞬态传输开销。ISO 10589第7.3.17节最后一部分中的条款a）涉及点对点电路，修改如下：
a) set SRMflag for that circuit on all LSPs if the meshGroupEnabled attribute of the circuit is not 'meshBlocked', and
a) 如果电路的meshGroupEnabled属性不是“meshBlocked”，则在所有LSP上为该电路设置SRMflag，并且
Numbering of mesh groups provides the ability to divide a large full mesh topology into a smaller group of full mesh sub-topologies (mesh groups). These mesh groups are connected by "transit" circuits which are 'meshInactive', while the remaining circuits between the mesh groups are configured as 'meshBlocked' to reduce flooding redundancy. Use of numbering makes mesh groups more scalable.
网格组编号提供了将大型全网格拓扑划分为更小的全网格子拓扑组（网格组）的能力。这些网格组通过“非活动网格”的“传输”电路连接，而网格组之间的其余电路配置为“网格块”，以减少泛洪冗余。使用编号使网格组更具可伸缩性。
The mesh group feature described in this document is a simple mechanism to reduce flooding of LSPs in some IS-IS topologies. It relies on a correct user configuration. If a combination of user configuration and link failures result in a partitioned flooding topology, LSPs will not be sent in a timely fashion, which may lead to routing loops or black holes.
本文档中描述的网格组功能是一种简单的机制，用于减少某些is-is拓扑中LSP的泛滥。它依赖于正确的用户配置。如果用户配置和链路故障的组合导致分区泛洪拓扑，则不会及时发送LSP，这可能导致路由循环或黑洞。
The concept of using numbered mesh groups also suffers from the complexity and reliance on static configuration, making the topologies brittle. Loosing a transit link can partition LSP flooding in unpredictable ways, requiring the periodic flooding of CSNPs to synchronize databases. In large networks, CSNPs become large and also consume bandwidth.
使用编号网格组的概念还存在复杂性和对静态配置的依赖性，这使得拓扑结构变得脆弱。失去传输链路可能会以不可预测的方式划分LSP泛洪，需要定期泛洪CSNP以同步数据库。在大型网络中，CSNP变得很大，并且还消耗带宽。
The authors are not aware of any networks that have deployed numbered mesh groups: instead, administrators set links to state 'meshBlocked' to prune the flooding topology (also known as "poor man's mesh groups").
作者不知道有任何网络部署了编号的网格组：相反，管理员将链接设置为状态“meshBlocked”，以修剪泛洪拓扑（也称为“穷人的网格组”）。
Some improvements to mesh groups which have been suggested include:
已建议对网格组进行一些改进，包括：
a) To negotiate or check the mesh group attributes during initialization of an adjacency to verify that the two ends of every circuit hold identical values of the mesh state and mesh number.
a) 在邻接初始化期间协商或检查网格组属性，以验证每个回路的两端是否具有相同的网格状态和网格编号值。
b) Dynamic election of active transit links so that a topology could recover from failure of transit circuits.
b) 动态选择活动传输链路，以便拓扑能够从传输电路故障中恢复。
c) Reduce the flooding of CSNPs by sending them periodically on some meshGroup circuits rather than all circuits.
c) 通过在某些网络组电路而不是所有电路上定期发送CSNP，减少CSNP的泛滥。
d) Reduce the size of PDUs required by flooding of CSNPs by sending CSNP summaries: checksums or sequence numbers.
d) 通过发送CSNP摘要（校验和或序列号），减少CSNP泛滥所需的PDU大小。
e) A related problem is the unneeded multiple transmissions of LSPs to neighbors that are connected via multiple links. The protocol could use the remote system ID of each adjacency and attempt to send a single copy of each LSP to a neighbor.
e) 一个相关的问题是通过多个链路连接到邻居的LSP的不必要的多个传输。该协议可以使用每个邻接的远程系统ID，并尝试向邻居发送每个LSP的单个副本。
Any such improvements are outside the scope of this document, and may be the basis for future work.
任何此类改进均不在本文件范围内，可能是未来工作的基础。
Since mesh groups do not alter the content of packets, an Intermediate System that does not implement mesh groups will not see any different packets or new TLVs. The only impact will be that additional CSNPs will be seen on some point-to-point links. A conformant implementation can be expected to respond correctly to extra CSNPs.
由于网格组不会改变数据包的内容，因此不实现网格组的中间系统将不会看到任何不同的数据包或新的TLV。唯一的影响是在一些点到点链路上会看到额外的CSNPs。一致性实现可以正确响应额外的CSNP。
The original idea for mesh groups is due to Dave Katz. Thanks to Tony Li, Tony Przygienda, Peter Livesey, and Henk Smit for helpful comments.
网格组的最初想法是由Dave Katz提出的。感谢Tony Li、Tony Przygienda、Peter Livesey和Henk Smit提供的有用意见。
[1] ISO/IEC 10589, "Intermediate System to Intermediate System Intra-Domain Routing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", June 1992.
[1] ISO/IEC 10589，“与提供无连接模式网络服务的协议一起使用的中间系统到中间系统域内路由交换协议（ISO 8473）”，1992年6月。
This document raises no new security issues for IS-IS.
本文档没有为IS-IS提出新的安全问题。
Rajesh Balay CoSine Communications, Inc 1200 Bridge Parkway Redwood City, CA 94065
拉杰什·巴莱·科辛通信公司，加利福尼亚州红木市1200桥公园路，邮编94065
EMail: Rajesh.Balay@cosinecom.com
EMail: Rajesh.Balay@cosinecom.com
Dave Katz Juniper Networks 385 Ravendale Drive Mountain View, CA 94043
Dave Katz Juniper Networks加利福尼亚州山景城拉文代尔大道385号，邮编94043
EMail: dkatz@juniper.net
EMail: dkatz@juniper.net
Jeff Parker Axiowave Networks, 100 Nickerson Road, Marlborough, MA 01752
Jeff Parker Axiowave Networks，马萨诸塞州马尔伯勒尼克森路100号，邮编01752
EMail: jparker@axiowave.com
EMail: jparker@axiowave.com
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Acknowledgement
确认
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