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14.1.2 Implement IGMP Snooping
I. Related concepts of IGMP Snooping
To facilitate the description, this section first introduces some related switch concepts of
IGMP Snooping:
Router Port: The port of the switch, directly connected to the multicast router.
Multicast member port: The port connected to the multicast member. The multicast
member refers to a host joined a multicast group.
MAC multicast group: The multicast group is identified with MAC multicast address and
maintained by the Ethernet switch.
Router port aging time: Time set on the router port aging timer. If the switch has not
received any IGMP general query message before the timer times out, it considers the
port no longer as a router port.
Multicast group member port aging time: When a port joins an IP multicast group, the
aging timer of the port will begin timing. The multicast group member port aging time is
set on this aging timer. If the switch has not received any IGMP report message before
the timer times out, it transmits IGMP specific query message to the port.
Maximum response time: When the switch transmits IGMP specific query message to the
multicast member port, the Ethernet switch starts a response timer, which times before
the response to the query. If the switch has not received any IGMP report message
before the timer times out, it will remove the port from the multicast member ports
II. Implement Layer 2 multicast with IGMP Snooping
The Ethernet switch runs IGMP Snooping to listen to the IGMP messages and map the host
and its ports to the corresponding multicast group address. To implement IGMP Snooping,
the Layer 2 Ethernet switch processes different IGMP messages in the way illustrated in the
figure below:
