Igmp Snooping; Figure 50: Configuring Mvr - SMC Networks SMCGS10P-SMART Management Manual

| Configuring the Switch
C 4
HAPTER

IGMP Snooping

Figure 50: Configuring MVR

IGMP S
NOOPING
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 can use Internet Group Management Protocol (IGMP) to filter
multicast traffic. IGMP Snooping can be used to passively monitor or
"snoop" on exchanges between attached hosts and an IGMP-enabled
device, most commonly a multicast router. In this way, the switch can
discover the ports that want to join a multicast group, and set its filters
accordingly.
If there is no multicast router attached to the local subnet, multicast traffic
and query messages may not be received by the switch. In this case (Layer
2) IGMP Query can be used to actively ask the attached hosts if they want
to receive a specific multicast service. IGMP Query thereby 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.
The purpose of IP multicast filtering is to optimize a switched network's
performance, so multicast packets will only be forwarded to those ports
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