15.Multicast Configuration
Multicasting is used to support real-time applications such as video conferencing
or streaming audio. A multicast server does not have to establish a separate
connection with each client. It merely broadcasts its service to the network, and
any hosts that want to receive the multicast register with their local multicast
switch/router. Although this approach reduces the network overhead required by
a multicast server, the broadcast traffic must be carefully pruned at every multi-
cast switch/router it passes through to ensure that traffic is only passed on the
hosts which subscribed to this service.
This switch uses IGMP (Internet Group Management Protocol) to query for any
attached hosts that want to receive a specific multicast service. It identifies the
ports containing hosts requesting to join the service and sends data out to those
ports only. It then propagates the service request up to any neighboring multicast
switch/router to ensure that it will continue to receive the multicast service. This
procedure is called multicast filtering.
The purpose of IP multicast filtering is to optimize a switched network’s perform-
ance, so multicast packets will only be forwarded to those ports containing multi-
cast group hosts or multicast routers/switches, instead of flooding traffic to all
ports in the subnet (VLAN).
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