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CHAPTER 15: IGMP IGMP
MULTILINK ML2400 ETHERNET COMMUNICATIONS SWITCH – INSTRUCTION MANUAL 15–3
The figure below shows a network running IGMP.
FIGURE 15–1: Advantages of using IGMP
In the above diagram:
• 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 non-members. Thus, sends large amounts of unwanted multicast
traffic to PCs 2 and 3.
• 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 PC 4, thus avoiding unwanted multicast traffic on the ports
for PCs 5 and 6.
The next figure (below) shows a network running IP multicasting using IGMP without a
multicast router. In this case, the IGMP-configured switch runs as a querier. PCs 2, 5, and 6
are members of the same IP multicast group. IGMP is configured on switches 3 and 4.