Configuring the Switch
IP Multicast (IGMP) Service
When IGMP is enabled on the switch, it examines the IGMP packets it receives:
■To learn which of its ports are linked to IGMP hosts and multicast routers/ queriers belonging to any multicast group
■To become a querier if a multicast router/querier is not discovered on the network
Once the switch learns the port location of the hosts belonging to any particular multicast group, it can direct group traffic to only those ports, resulting in bandwidth savings on ports where group members do not reside. The following example illustrates this operation.
Figure
■PCs 1 and 4, Switch #2, and all of the routers are members of an IP multicast group. (The routers operate as queriers.)
■Switch #1 ignores IGMP traffic and does not distinguish between IP multicast group members and
■Switch #2 is recognizing IGMP traffic and learns that PC #4 is in the IP multicast group receiving multicast data from the video server (PC X). Switch #2 then sends the multicast data only to the port for PC #4, thus avoiding unwanted multicast traffic on the ports for PCs #5 and #6.
Switch the Configuring