3Com WX3000 operation manual Work Mechanism of Igmp Snooping

Figure 2-2IGMP Snooping related ports

Router A		Switch A			Receiver
	Eth1/0/1		Eth1/0 /2
					Host A
		Eth 1/0/3
					Host B
		Eth 1/0/1		Receiver
Source			Eth1/0 /2
				Host C
		Switch B
	Router port
	Member port
	Multicast packets			Host D

Ports involved in IGMP Snooping, as shown in Figure 2-2, are described as follows:

z

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.

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 2-1Port aging timers in IGMP Snooping and related messages and actions

Timer	Description	Message before	Action after expiry
		expiry
	For each router port,	IGMP general query or	The device removes
Router port aging timer	the device sets a timer
			this port from its router
	initialized to the aging	PIM hello
			port list
	time of the route port
	When a port joins a
	multicast group, the		The device removes
	device sets a timer for
Member port aging		IGMP membership	this port from the
	the port, which is
timer		report	multicast group
	initialized to the
			forwarding table
	member port aging
	time

Work Mechanism of IGMP Snooping

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

2-2