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Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")
RFC 4605

Document type: RFC - Proposed Standard (August 2006; Errata)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4605 (Proposed Standard)
Responsible AD: Margaret Wasserman
Send notices to: <kouvelas@cisco.com>, <brian@innovationslab.net>

Network Working Group                                          B. Fenner
Request for Comments: 4605                                 AT&T Research
Category: Standards Track                                          H. He
                                                                  Nortel
                                                             B. Haberman
                                                                 JHU-APL
                                                              H. Sandick
                                          Little River Elementary School
                                                             August 2006

              Internet Group Management Protocol (IGMP) /
     Multicast Listener Discovery (MLD)-Based Multicast Forwarding
                         ("IGMP/MLD Proxying")

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.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   In certain topologies, it is not necessary to run a multicast routing
   protocol.  It is sufficient for a device to learn and proxy group
   membership information and simply forward multicast packets based
   upon that information.  This document describes a mechanism for
   forwarding based solely upon Internet Group Management Protocol
   (IGMP) or Multicast Listener Discovery (MLD) membership information.

1.  Introduction

   This document applies spanning tree multicast routing [MCAST] to an
   Internet Group Management Protocol (IGMP) or Multicast Listener
   Discovery (MLD)-only environment.  The topology is limited to a tree,
   since we specify no protocol to build a spanning tree over a more
   complex topology.  The root of the tree is assumed to be connected to
   a wider multicast infrastructure.

Fenner, et al.              Standards Track                     [Page 1]
RFC 4605          IGMP/MLD-Based Multicast Forwarding        August 2006

1.1.  Motivation

   In a simple tree topology, it is not necessary to run a multicast
   routing protocol.  It is sufficient to learn and proxy group
   membership information and simply forward multicast packets based
   upon that information.  One typical example of such a tree topology
   can be found on an edge aggregation box such as a Digital Subscriber
   Line Access Multiplexer (DSLAM).  In most deployment scenarios, an
   edge box has only one connection to the core network side and has
   many connections to the customer side.

   Using IGMP/MLD-based forwarding to replicate multicast traffic on
   devices such as the edge boxes can greatly simplify the design and
   implementation of those devices.  By not supporting more complicated
   multicast routing protocols such as Protocol Independent Multicast
   (PIM) or Distance Vector Multicast Routing Protocol (DVMRP), it
   reduces not only the cost of the devices but also the operational
   overhead.  Another advantage is that it makes the proxy devices
   independent of the multicast routing protocol used by the core
   network routers.  Hence, proxy devices can be easily deployed in any
   multicast network.

   Robustness in an edge box is usually achieved by using a hot spare
   connection to the core network.  When the first connection fails, the
   edge box fails over to the second connection.  IGMP/MLD-based
   forwarding can benefit from such a mechanism and use the spare
   connection for its redundant or backup connection to multicast
   routers.  When an edge box fails over to the second connection, the
   proxy upstream connection can also be updated to the new connection.

1.2.  Applicability Statement

   The IGMP/MLD-based forwarding only works in a simple tree topology.
   The tree must be manually configured by designating upstream and
   downstream interfaces on each proxy device.  In addition, the IP
   addressing scheme applied to the proxying tree topology SHOULD be
   configured to ensure that a proxy device can win the IGMP/MLD Querier
   election to be able to forward multicast traffic.  There are no other
   multicast routers except the proxy devices within the tree, and the
   root of the tree is expected to be connected to a wider multicast
   infrastructure.  This protocol is limited to a single administrative
   domain.

   In more complicated scenarios where the topology is not a tree, a
   more robust failover mechanism is desired, or more than one
   administrative domain is involved, a multicast routing protocol

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