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46 Chapter 3 Configuring IGMP snooping

311208-A Rev 00

IGMP host membership reports

IP multicast routers use IGMP to learn about the existence of host group members

on their directly attached subnets. The IP multicast routers get this information by

broadcasting IGMP queries 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.

The client/server path is set up as follows:

The designated router sends out a host membership query to the subnet and

receives host membership reports from end stations on the subnet.

The designated routers set up a path between the IP multicast stream source

and the end stations.

Periodically, the router continues to query end stations on whether to continue

participation.

As long as any client continues to participate, all clients, including

nonparticipating end stations on that subnet, receive the IP multicast stream.

IGMP snooping

The IGMP snooping feature provides the same benefit as IP multicast routers, but

in the local area.

With IGMP snooping enabled, a switch senses IGMP host membership reports

from attached stations and uses this information to set up a dedicated path

between the requesting station and a local IP multicast router. After the path is

established, the switch blocks the IP multicast stream from exiting any other port

that does not connect to another host member, thus conserving bandwidth.

Note:

Even if nonparticipating end stations filter the IP multicast

stream, IP multicast traffic still consumes bandwidth on the subnet.

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Avaya Quick2Config User Manual Page 46