SMC Networks 8708L2, Management Manual

Page: 273 / 606

M
ULTICAST
F
ILTERING
3-221
Multicast Filtering
Multicasting is used to support real-time
applications such as videoconferencing
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 multicast switch/router it
passes through to ensure that traffic is
only passed on to 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
performance, so multicast packets will only be forwarded to those ports
containing multicast group hosts or multicast routers/switches, instead of
flooding traffic to all ports in the subnet (VLAN).
Unicast
Flow
Multicast
Flow