3com 8807 User Guide

C

HAPTER

 39: IGMP S

NOOPING

 C

ONFIGURATION

Figure 103   Multicast packet transmission when IGMP Snooping runs

To facilitate the description, this section first introduces some related switch 
concepts of IGMP Snooping.

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Router Port: The port of the switch, directly connected to the multicast router.

■

Multicast member port: The Ethernet switch 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 when the timer times out, it 
considers the port no longer as a router port.

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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 when 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

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:

Internet / Intranet

Video stream

VOD Server

Layer 2 Ethernet Switch

Video stream

Multicast group member

Non-multicast 
group member

Multicast router

Video stream

Video stream

Video stream

Non-multicast
group member