Cisco Systems Router-port Group Management Protocol (RGMP) (RFC3488)
Original Publication Date: 2003-Feb-01
Included in the Prior Art Database: 2003-Mar-04
Internet Society Requests For Comment (RFCs)
I. Wu: AUTHOR [+2]
This document describes the Router-port Group Management Protocol (RGMP). This protocol was developed by Cisco Systems and is used between multicast routers and switches to restrict multicast packet forwarding in switches to those routers where the packets may be needed.
Network Working Group I. Wu
Request for Comments: 3488 T. Eckert
Category: Informational Cisco Systems
Router-port Group Management Protocol (RGMP)
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 (C) The Internet Society (2003). All Rights Reserved.
This document describes the Router-port Group Management Protocol
(RGMP). This protocol was developed by Cisco Systems and is used
between multicast routers and switches to restrict multicast packet
forwarding in switches to those routers where the packets may be
RGMP is designed for backbone switched networks where multiple, high
speed routers are interconnected.
1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 .
IGMP Snooping is a popular, but not well documented mechanism to
restrict multicast traffic, in switched networks, to those ports that
want to receive the multicast traffic. It dynamically establishes
and terminates multicast group specific forwarding in switches that
support this feature.
Wu & Eckert Informational [Page 1]
RFC 3488 Cisco Systems RGMP February 2003
The main limitation of IGMP Snooping is that it can only restrict
multicast traffic onto switch ports where receiving hosts are
connected directly or indirectly via other switches. IGMP Snooping
can not restrict multicast traffic to ports where at least one
multicast router is connected. It must instead flood multicast
traffic to these ports. Snooping on IGMP messages alone is an
intrinsic limitation. Through it, a switch can only learn which
multicast flows are being requested by hosts. A switch can not learn
through IGMP which traffic flows need to be received by router ports
to be routed because routers do not report these flows via IGMP.
In situations where multiple multicast routers are connected to a
switched backbone, IGMP Snooping will not reduce multicast traffic
load. Nor will it assist in increasing internal bandwidth through