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Multicast Extensions to OSPF (RFC1584)

IP.com Disclosure Number: IPCOM000002418D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2001-Nov-09

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Moy: AUTHOR

Abstract

This memo documents enhancements to the OSPF protocol enabling the routing of IP multicast datagrams. In this proposal, an IP multicast packet is routed based both on the packet's source and its multicast destination (commonly referred to as source/destination routing). As it is routed, the multicast packet follows a shortest path to each multicast destination. During packet forwarding, any commonality of paths is exploited; when multiple hosts belong to a single multicast group, a multicast packet will be replicated only when the paths to the separate hosts diverge. (Download file contains alternative document formats.)

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Network Working Group                                             J. Moy

Request for Comments: 1584                                 Proteon, Inc.

Category: Standards Track                                     March 1994

                      Multicast Extensions to OSPF

Status of this Memo

    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.

Abstract

    This memo documents enhancements to the OSPF protocol enabling the

    routing of IP multicast datagrams. In this proposal, an IP multicast

    packet is routed based both on the packet's source and its multicast

    destination (commonly referred to as source/destination routing). As

    it is routed, the multicast packet follows a shortest path to each

    multicast destination. During packet forwarding, any commonality of

    paths is exploited; when multiple hosts belong to a single multicast

    group, a multicast packet will be replicated only when the paths to

    the separate hosts diverge.

    OSPF, a link-state routing protocol, provides a database describing

    the Autonomous System's topology. A new OSPF link state

    advertisement is added describing the location of multicast

    destinations. A multicast packet's path is then calculated by

    building a pruned shortest-path tree rooted at the packet's IP

    source. These trees are built on demand, and the results of the

    calculation are cached for use by subsequent packets.

    The multicast extensions are built on top of OSPF Version 2. The

    extensions have been implemented so that a multicast routing

    capability can be introduced piecemeal into an OSPF Version 2

    routing domain. Some of the OSPF Version 2 routers may run the

    multicast extensions, while others may continue to be restricted to

    the forwarding of regular IP traffic (unicasts).

    Please send comments to mospf@gated.cornell.edu.

Moy                                                             [Page 1]

RFC 1584              Multicast Extensions to OSPF            March 1994

Table of Contents

    1       Introduction ........................................... 4

    1.1     Terminology ............................................ 5

    1.2     Acknowledgments ........................................ 6

    2       Multicast routing in MOSPF ............................. 6

    2.1     Routing characteristics ................................ 6

    2.2     Sample path of a multicast datagram .................... 8

    2.3     MOSPF forwarding mechanism ............................ 10

    2.3.1   IGMP interface: the local group database .............. 10

    2.3.2   A datagram's shortest-path tree ....................... 14

    2.3.3   Support for Non-broadcast networks .................... 16

    2.3.4   Details concerning forwarding cache entries ........... 16

    3       Inter-area multicasting ............................... 18

    3.1     Extent of group-membership-LSAs ....................... 19

    3.2     Building inter-area datagram shortest-path trees ...... 22

    4       Inter-AS multicasting ................................. 27

    4.1     Building inter-AS datagram shortest-path trees ....