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Figure 3-1 Before and after IGMP Snooping is enabled on Layer 2 device
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 router
Host A
Receiver
Host B
Host C
Receiver
Layer 2 switch
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in Figure 3-2, 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 3-2 IGMP Snooping related ports
Router A Switch A
Switch B
Eth1/0/1 Eth1/0/2
Eth1/0/3
Eth1/0/1
Eth1/0/2
Receiver
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
Ports involved in IGMP Snooping, as shown in
Figure 3-2, are described as follows:
z Router port: A router port is a port on the Layer 3 multicast device (DR or IGMP querier) side of the
Ethernet switch. In the figure, Ethernet 1/0/1 of Switch A and Ethernet 1/0/1 of Switch B are router
ports. A switch registers all its local router ports in its router port list.
z Member port: A member port is a port on the multicast group member side of the Ethernet switch.
In the figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and Ethernet 1/0/2 of Switch B are