Igmp Snooping; Introduction; Overview - HP 445946-001 Application Manual

IGMP Snooping

Introduction

IGMP Snooping allows the switch to forward multicast traffic only to those ports that request it. IGMP
Snooping prevents multicast traffic from being flooded to all data ports. The switch learns which server
hosts are interested in receiving multicast traffic, and forwards it only to ports connected to those servers.
The following topics are discussed in this chapter:

Overview

IGMPv3
FastLeave
IGMP Filtering
Static Multicast Router
IGMP Snooping Configuration example
Overview
Internet Group Management Protocol (IGMP) is used by IP Multicast routers to learn about the existence of
host group members on their directly attached subnet (see RFC 2236). The IP Multicast routers get this
information by broadcasting IGMP Query Reports and listening for IP hosts reporting their host group
memberships. This process is used to set up a client/server relationship between an IP Multicast source
that provides the data streams and the clients that want to receive the data.
IGMP Snooping conserves bandwidth. With IGMP Snooping, the switch learns which ports are interested
in receiving multicast data, and forwards multicast data only to those ports. In this way, other ports are
not burdened with unwanted multicast traffic.
The switch currently supports snooping for IGMP version 1, version 2, and version 3.
The switch can sense IGMP Membership Reports from attached host servers and act as a proxy to set up a
dedicated path between the requesting host and a local IP Multicast router. After the pathway is
established, the switch blocks the IP Multicast stream from flowing through any port that does not connect
to a host member, thus conserving bandwidth.
The client-server path is set up as follows:
An IP Multicast Router (Mrouter) sends Membership Queries to the switch, which forwards them to all
ports in a given VLAN.
Hosts that want to receive the multicast data stream send Membership Reports to the switch, which
sends a proxy Membership Report to the Mrouter.
The switch sets up a path between the Mrouter and the host, and blocks all other ports from
receiving the multicast.
Periodically, the Mrouter sends Membership Queries to ensure that the host wants to continue
receiving the multicast. If the host fails to respond with a Membership Report, the Mrouter stops
sending the multicast to that path.
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