554 CHAPTER 42: IGMP SNOOPING CONFIGURATION
Figure 170 Before and after IGMP Snooping is enabled on the Layer 2 device
Basic Concepts in IGMP
Snooping
IGMP Snooping related ports
As shown in Figure 171, Router A connects to the multicast source, IGMP
Snooping runs on Switch A and Switch B, Host A and Host C are receiver hosts
(namely, multicast group members).
Figure 171 IGMP Snooping related ports
Ports involved in IGMP Snooping, as shown in Figure 171, are described as
follows:
■ Router port: A router port is a port on the Ethernet switch that leads switch
towards the Layer 3 multicast device (DR or IGMP querier). In the figure,
Ethernet 1/0/1 of Switch A and Ethernet 1/0/1 of Switch B are router ports. The
Multicast packet transmission
without IGMP Snooping
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Multicast packets
Layer 2 switch
Multicast packet transmission
when IGMP Snooping runs
Source
Multicast route
Host A
Receiver
Host B
Host C
Receiver
Layer 2 switch
Router A Switch A
Switch B
Eth1/0/1 Eth1/0/2
Eth 1/0/3
Eth 1/0/1
Eth1/0/2
Receive
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
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