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Using the BayStack 410-24T 10BASE-T Switch

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309985-B Rev 00

IGMP Snooping

BayStack 410-24T switches can sense IGMP host membership reports from

attached stations and use this information to set up a dedicated path between the

requesting station and a local IP Multicast router. After the pathway is established,

the BayStack 410-24T switch blocks the IP Multicast stream from exiting any

other port that does not connect to another host member, thus conserving

bandwidth. The following discussion describes how BayStack 410-24T switches

provide the same benefit as IP Multicast routers, but in the local area.

Internet Group Management Protocol (IGMP), is used by IP Multicast routers to

learn about the existence of host group members on their directly attached subnets

(see RFC 2236). 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.

Figure 1-31

shows how IGMP is used to set up the path between the client and

server. As shown in this example, the IGMP host provides an IP Multicast stream

to designated routers which forward the IP Multicast stream on their local network

only if there is a recipient.

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 then 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.

IP Multicast can be optimized in a LAN by using IP Multicast filtering switches,

such as the BayStack 410-24T switch.

Note:

Although the nonparticipating end stations can filter the IP Multicast

traffic, the IP Multicast still exists on the subnet and consumes bandwidth.

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Nortel Networks 24T Bedienungsanleitung Seite 80