Internet-Draft ISIS Mesh Groups Rajesh Balay Mesh Groups for IS-IS Torrent Networks, Inc. Jeff Parker Thu Jun 3 17:35:58 EDT 1999 Nexabit Networks, Inc. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Expires December 1999 [Page 1] Internet-Draft ISIS Mesh Groups June 1999 Copyright (C) The Internet Society (1997). All Rights Reserved. Expires December 1999 [Page 2] Internet-Draft ISIS Mesh Groups June 1999 Abstract This document describes a mechanism to reduce redundant packet transmissions for the IS-IS Routing protocol, as described in RFC 1142 [1], when it is used to construct routing tables for IP networks, as described in RFC 1195 [2]. The described mechanism can be used to reduce the flooding of Link State PDUs (LSPs) in IS-IS topologies with fully meshed routers. Table of Contents 1. Overview............................................. 4 2. Definitions.of.Mesh.Groups........................... 6 3. Other.ways.to.use.this.mechanism..................... 7 4. Potential.Problems.with.mesh.groups.................. 7 5. Acknowledgments...................................... 8 6. References........................................... 8 7. Security.Considerations.............................. 8 8. Authors'.Address..................................... 8 9. Full Copyright Statement............................. 9 Expires December 1999 [Page 3] Internet-Draft ISIS Mesh Groups June 1999 1. Overview This document is provided to the IETF working group on IS-IS. Some organizations attach multiple routers in an ATM mesh. Each router is connected to many others via point to point circuits. In the example below, assume that each of the four routers is connected to each of the other three with a point to point link, and assume we are running IS-IS over each link. When we get a new Link State Protocol Data Unit (LSP), we store it, and prepare to flood it out every port except the source port. 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. IS-IS then periodically selects a LSP to send out a port: this acts to space out the dispersal of LSPs. +----------+ +----------+ | | I12 I21 | | | Router 1 | ------------------------------ | Router 2 | | | | | +----------+ +----------+ I13 | \ I14 I23 / | I24 | \ / | | \ / | | \ / | | \ / | | \ / | | \ / | | . | | / \ | | / \ | | / \ | | / \ | | / \ | | / \ | I31 | / I32 I41 \ | I42 +----------+ +----------+ | | | | | Router 3 | ------------------------------ | Router 4 | | | I34 I43 | | +----------+ +----------+ Figure 1. Expires December 1999 [Page 4] Internet-Draft ISIS Mesh Groups June 1999 When Router1 regenerates an LSP, it will flood the LSP through the network by marking the SRM bits on the LSP for the interfaces I12, I14, and I13. In due course, it will send out the LSP on each interface. If Router2 runs the protocol described in [1]. when it receives Router1's LSP it should set the SRM bits on ports I23 and I24, and flood the LSP to Router3 and Router4. However, these routers will get the LSP directly from Router1. In a full mesh of N routers, the standard algorithm results in N-2 extra transmissions of each LSP, a waste of time and effort, with little gain in reliability. Mesh groups are used to reduce this unneeded traffic. A mesh group is defined as a collection of interfaces in a network. At an Intermediate System, an LSP received on an interface which belongs to a mesh group is not flooded out other interfaces that belong to the same mesh group. However, each LSP is available for transmission. In the figure above, the receipt of a PSNPacket from Router3 with an out-of date sequence number for Router1's LSP will force Router2 to set the SRM bit on interface I23 for the new version of the LSP. Expires December 1999 [Page 5] Internet-Draft ISIS Mesh Groups June 1999 2. Definitions of Mesh Groups Each interface has two new variables: meshGroupEnabled, which is in state {inactive, blocked, or set} and an integer variable meshGroup, which is examined if the value of meshGroupEnabled is 'set'. The original algorithm upon receipt of an LSP sets the SRMs for all circuits, as follows: RxLsp(port in, LinkStatePacket LSP) { for all ports 'out' if (in != out) set lsp.srm[level, out]; } When using mesh groups, this would be modified as follows: when a packet is received, set SRM bit on all ports that are not blocked and are not in the same (non-null) meshgroup. We use the SSN bits to mark circuits that will be notified about a new LSP via a PSNP (Partial Sequence Numbers PDU). RxLsp(port in, LinkStatePacket LSP) { for all ports 'out' { if ((in != out) && (out.meshGroupEnabled != blocked)) { if ((out.meshGroupEnabled == inactive) || (in.meshGroupEnabled == inactive) || (in.meshgroup != out.meshgroup)) { set lsp.srm[level, out]; } else { set lsp.ssn[level, out]; } } } } We only modify the our behavior on the receipt of LSPs. LSPs that we create are marked to go out all ports, whatever the Expires December 1999 [Page 6] Internet-Draft ISIS Mesh Groups June 1999 combination of mesh groups. Expires December 1999 [Page 7] Internet-Draft ISIS Mesh Groups June 1999 3. Other ways to use this mechanism One intermediate system in a fully meshed network could be used to distribute all routes. All interfaces not on the designated Intermediate System, or connected to the designated Intermediate System, are marked "blocked". As a result, all LSPs flow to the designated Intermediate System, which then paces the redistribution to other systems. Expires December 1999 [Page 8] Internet-Draft ISIS Mesh Groups June 1999 4. Potential Problems with mesh groups Mesh groups significantly reduce the redundant flooding of LSPs in a fully connected mesh of routers. However, some concerns which relate to the point-point protocol behavior exist. IS-IS protocol behavior is to send a Complete Sequence Number PDU (CSNP) over a point-point interface once an adjacency is established. A router on processing the received CSNP initiates Partial Sequence Number PDUs (PSNPs) [1, section 7.3.15.2] for all the LSPs which it is missing. This mechanism helps in synchronizing the database with the adjacent router. If these CSNPs are lost, routers may take longer time to synchronize their databases. However, the use of SSN and PSNPs produce synchronization in due time. If the configuration of a port does not match the underlying topology, then LSPs will not be sent in a timely fashion, which may lead to routing loops or black holes. Expires December 1999 [Page 9] Internet-Draft ISIS Mesh Groups June 1999 5. Acknowledgments XXX names, if any 6. References [1] Oran, D., Editor, "OSI IS-IS Intra-domain Routing Protocol", RFC 1142, February 1990 [2] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC 1195, December 1990 7. Security Considerations This proposal does not change any information that is exchanged on circuits. Inappropriate setings of mesh group variables, or "blocking" an interface will prevent routers from seeing the network. However, for intruders that can modify router settings, there are many other more direct ways to disable a router. This document raises no new security issues for IS-IS. 8. Authors' Address Jeff Parker Nexabit Networks, Inc. 200 Nickerson Road, Marlborough, MA 01752 email: jparker@nexabit.com Rajesh Balay Torrent Networking Technologies (An Ericsson Company) 3000 Aerial Center Pkwy, Suite 140 email: balay@torrentnet.com Expires December 1999 [Page 10] Internet-Draft ISIS Mesh Groups June 1999 9. Full Copyright Statement Copyright (C) The Internet Society (1997). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Expires December 1999 [Page 11]