15
Basic concepts in IGMP snooping
IGMP snooping related ports
In Figure 12, Router A connects to the multicast source, IGMP snooping runs on Switch A and Switch B,
and Host A and Host C are receiver hosts—also called “multicast group members.”
Figure 12 IGMP snooping related ports
Router A Switch A
Switch B
GE1/0/1 GE1/0/2
GE1/0/3
GE1/0/1
GE1/0/2
Receiver
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
IGMP snooping involves the following ports:
• Router port—A router port is a port on a Layer 2 switch that leads toward a Layer 3 multicast
device—DR or IGMP querier. In Figure 12, G
igabitEthernet 1/0/1 of Switch A and
GigabitEthernet 1/0/1 of Switch B are router ports. Each switch registers all its local router ports in
its router port list.
• Member port—A member port is a port on a Layer 2 switch that leads toward multicast group
members. In Figure 12, GigabitEthern
et 1/0/2 and GigabitEthernet 1/0/3 of Switch A and
GigabitEthernet 1/0/2 of Switch B are member ports. Each switch registers all the member ports
on the local device in its IGMP snooping forwarding table.
NOTE:
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.
Unless otherwise specified, router/member ports mentioned in this document include static and
dynamic ports.
An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with the
source IP address other than 0.0.0.0 or PIM hello messages are received are dynamic router ports.
For more information about PIM hello messages, see the chapter “PIM configuration.”
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