
29-2
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in Figure 29-2, 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 29-2 IGMP Snooping related ports
Ports involved in IGMP Snooping, as shown in
Figure 29-2, are described as follows:
z 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, GigabitEthernet 0/0/1 of Switch A and
GigabitEthernet 0/0/1 of Switch B are router ports. The switch registers all its local router ports
(including static and dynamic router ports) in its router port list.
z Member port: A member port is a port on the Ethernet switch that leads switch towards multicast
group members. In the figure, GigabitEthernet 0/0/2 and GigabitEthernet 0/0/3 of Switch A and
GigabitEthernet 0/0/2 of Switch B are member ports. The switch registers all the member ports
(including static and dynamic member ports) on the local device in its IGMP Snooping forwarding
table.
z Whenever mentioned in this document, a router port is a port on the switch that leads the switch to
a Layer 3 multicast device, rather than a port on a router.
z An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with the
source address other than 0.0.0.0 or PIM hello messages are received to be router ports.
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