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ILTERING
15-2
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
containing multicast group hosts or multicast routers/switches, instead of
flooding traffic to all ports in the subnet (VLAN).
You can also configure a single network-wide multicast VLAN shared by
hosts residing in other standard or private VLAN groups, preserving
security and data isolation “Multicast VLAN Registration” on page 15-12.
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 15-4) to monitor IGMP service requests passing between
multicast clients and servers, and dynamically configure the switch ports
which need to forward multicast traffic.
When using IGMPv3 snooping, service requests from IGMP Version 1, 2
or 3 hosts are all forwarded to the upstream router as IGMPv3 reports.
The primary enhancement provided by IGMPv3 snooping is in keeping
track of information about the specific multicast sources which
downstream IGMPv3 hosts have requested or refused. The switch
maintains information about both multicast groups and channels, where a
group indicates a multicast flow for which the hosts have not requested a
specific source (the only option for IGMPv1 and v2 hosts unless statically
configured on the switch), and a channel indicates a flow for which the
hosts have requested service from a specific source.