198 CHAPTER 16: IGMP SNOOPING CONFIGURATION
Figure 63 IGMP Snooping related ports
Ports involved in IGMP Snooping, as shown in Figure 63, are described as follows:
■ Router port: A router port is a port on the Layer 3 multicast device (DR or IGMP
querier) side of the Ethernet switch. In
Figure 63, 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.
■ Member port: A member port is a port on the multicast group member side of
the Ethernet switch. In
Figure 63, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch
A and Ethernet 1/0/2 of Switch B are member ports. The switch 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
Work Mechanism of
IGMP Snooping
A switch running IGMP Snooping performs different actions when it receives
different IGMP messages, as follows:
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers
on the local subnet to find out whether active multicast group members exist on
the subnet.
Tabl e 144 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
switch sets a timer
initialized to the aging time
of the route port
IGMP general query or
PIM hello
The switch removes
this port from its
router port list
Member port
aging timer
When a port joins a
multicast group, the switch
sets a timer for the port,
which is initialized to the
member port aging time
IGMP membership
report
The switch removes
this port from the
multicast group
forwarding table
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