3com 4210 PWR 9-Port 3CR17341-91-ME User Manual

C

HAPTER

 16: IGMP S

NOOPING

 C

ONFIGURATION

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. 

A switch running IGMP Snooping performs different actions when it receives 
different IGMP messages, as follows: 

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. 

Port aging timers in IGMP Snooping and related messages and actions

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