Browse Prior Art Database

IS-IS Mesh Groups (RFC2973)

IP.com Disclosure Number: IPCOM000005166D
Original Publication Date: 2000-Oct-01
Included in the Prior Art Database: 2001-Aug-16
Document File: 9 page(s) / 15K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

R. Balay: AUTHOR [+3]

Abstract

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.

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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

Status of this Memo

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

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.

The document describes behaviors that are backwards compatible with implementations that do not support this feature.

Table of Contents

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

Balay, et al. Informational [Page 1]

RFC 2973 IS-IS Mesh Groups October 2000

1. Overview

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.

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.

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

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.

Balay, et al. Informational [Page 2]

RFC 2973 IS-IS Mesh Groups October 2000

When System2 receives System1's LSP, it propagates the PDU according to section 7.2.14 of ISO 10589 [1]. It s...