H3C Technologies H3C WX3000 Series Unified Switches - Manual (Page 432)

44-2
Figure 44-2 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 44-2 , 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 44-1 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:
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.
Upon receiving an IGMP general query, the device forwards it through all ports in the VLAN except the
receiving port and performs the following to the receiving port: