13
Figure 11 IGMP snooping related ports
The following describes the ports involved in IGMP snooping:
•
Router
port
—Layer 3 multicast device-side port. Layer 3 multicast devices include designated
routers (DRs) and IGMP queriers. In
, GigabitEthernet 1/0/1 of Switch A and
GigabitEthernet 1/0/1 of Switch B are the router ports. A Layer 2 device records all its router
ports in a router port list.
Do not confuse the "router port" in IGMP snooping with the "routed interface" commonly known
as the "Layer 3 interface." The router port in IGMP snooping is a Layer 2 interface.
•
Member
port
—Multicast receiver-side port. In
, GigabitEthernet 1/0/2 and
GigabitEthernet 1/0/3 of Switch A and GigabitEthernet 1/0/2 of Switch B are the member ports.
A Layer 2 device records all its member ports in the IGMP snooping forwarding table.
Unless otherwise specified, router ports and member ports in this document include both static and
dynamic router ports and member ports.
NOTE:
When IGMP snooping is enabled, all ports that receive PIM hello messages or IGMP general
queries with the source addresses other than 0.0.0.0 are considered dynamic router ports.
Aging timers for dynamic ports in IGMP snooping
The following are aging timers for dynamic ports in IGMP snooping:
•
Dynamic router port aging timer
—The Layer 2 device starts this timer for a port that receives
an IGMP general query with the source address other than 0.0.0.0 or a PIM hello message. If
the port does not receive either of these messages before the timer expires, the Layer 2 device
removes the port from its router port list.
•
Dynamic member port aging timer
—The Layer 2 device starts this timer for a port that
receives an IGMP report. If the port does not receive a report before the timer expires, the Layer
2 device removes the port from the IGMP snooping forwarding entries.
NOTE:
In IGMP snooping, only dynamic ports age out. Static ports never age out.
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
