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ULTICAST
F
ILTERING
3-227
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).
Layer 2 IGMP (Snooping and Query)
IGMP Snooping and Query – If multicast routing is not supported on
other switches in your network, you can use IGMP Snooping and IGMP
Query (page 3-228) to monitor IGMP service requests passing between
multicast clients and servers, and dynamically configure the switch ports
which need to forward multicast traffic.
Static IGMP Router Interface – If IGMP snooping cannot locate the
IGMP querier, you can manually designate a known IGMP querier (i.e., a
multicast router/switch) connected over the network to an interface on
your switch (page 3-231). This interface will then join all the current
multicast groups supported by the attached router/switch to ensure that
multicast traffic is passed to all appropriate interfaces within the switch.
Static IGMP Host Interface – For multicast applications that you need to
control more carefully, you can manually assign a multicast service to
specific interfaces on the switch (page 3-233).