252
a. IGMP snooping related ports
Router A Switch A
Switch B
GE1/0/1 GE1/0/2
GE1/0/3
GE1/0/1
GE1/0/2
Receiver
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
IGMP snooping related ports include:
Router port: A router port is a port on an Ethernet switch that leads the switch towards the Layer 3
multicast device (DR or IGMP querier). In the figure, GigabitEthernet 1/0/1 of Switch A and
GigabitEthernet 1/0/1 of Switch B are router ports. A switch registers all its local router ports in its
router port list.
Member port: On an Ethernet switch, a member port (also known as multicast group member port)
connects the switch to a multicast group member. In the figure, GigabitEthernet 1/0/2 and
GigabitEthernet 1/0/3 of Switch A and GigabitEthernet 1/0/2 of Switch B are member ports. A
switch registers all its member ports in the IGMP snooping forwarding table.
NOTE:
In this document, a router port is a port on the switch that leads the switch to a Layer 3 multicast device,
rather than a port on a router.
Unless otherwise specified, router ports and member ports in this document consist of dynamic and
static ports.
An IGMP snooping enabled switch deems that all its ports on which IGMP general queries with the
source address other than 0.0.0.0 or PIM hello messages are received to be router ports.
Work mechanism of IGMP snooping
A switch running IGMP snooping performs different actions when it receives different IGMP messages, as
follows:
CAUTION:
You can add or delete only dynamic ports rather than static ports.
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on the local
subnet to find out whether any active multicast group members exist on the subnet.
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