RFC 1584 (rfc1584) - Page 1 of 102

Multicast Extensions to OSPF

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