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2-2
Figure 2-2 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 2-2, 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
device. In the figure, Ethernet 1/0/1 of Switch A and Ethernet 1/0/1 of Switch B are router ports. A
device 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 device. In the
figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and Ethernet 1/0/2 of Switch B are member
ports. A device records all member ports on the local device in the IGMP Snooping forwarding
table.
Port aging timers in IGMP Snooping and related messages and actions
Table 2-1 Port aging timers in IGMP Snooping and related messages and actions
Timer Description
Message before
expiry
Action after expiry
Router port aging timer
For each router port,
the device sets a timer
initialized to the aging
time of the route port
IGMP general query or
PIM hello
The device removes
this port from its router
port list
Member port aging
timer
When a port joins a
multicast group, the
device sets a timer for
the port, which is
initialized to the
member port aging
time
IGMP membership
report
The device removes
this port from the
multicast group
forwarding table
Work Mechanism of IGMP Snooping
A device running IGMP Snooping performs different actions when it receives different IGMP messages,
as follows: