Multicast Filtering And Your Switch - 3Com SuperStack 3C17300 Implementation Manual

Multicast Filtering 35
Figure 6 The effect of multicast filtering
Multicast Filtering Your Switch provides automatic multicast filtering support using IGMP
and Your Switch (Internet Group Management Protocol) Snooping. It also supports IGMP
query mode.
Snooping Mode
Snooping Mode allows your Switch to forward multicast packets only to
the appropriate ports. The Switch "snoops" on exchanges between
endstations and an IGMP device, typically a router, to find out the ports
that wish to join a multicast group and then sets its filters accordingly
Query Mode
Query mode allows the Switch to function as the Querier if it has the
lowest IP address in the subnetwork to which it belongs.
IGMP querying is disabled by default on the Switch 4200 Series. This
helps prevent interoperability issues with core products that may not
follow the lowest IP address election method.
You can enable or disable IGMP query mode for all Switch units in the
stack using the command on the command line interface
queryMode
IGMP menu.
You would enable query mode if you wish to run multicast sessions in a
network that does not contain any IGMP routers (or queriers). This