Igmp Snooping Overview - 3Com 8807 Configuration Manual

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IGMP Snooping
Overview
IGMP Snooping Principle
IGMP S
NOOPING
Running on the link layer, IGMP Snooping is a multicast control mechanism on the
Layer 2 Ethernet switch and it is used for multicast group management and
control.
When receiving the IGMP messages transmitted between the host and router, the
Layer 2 Ethernet switch uses IGMP Snooping to analyze the information carried in
the IGMP messages. If the switch hears IGMP host report message from an IGMP
host, it will add the host to the corresponding multicast table. If the switch hears
IGMP leave message from an IGMP host, it will remove the host from the
corresponding multicast table. The switch continuously listens to the IGMP
messages to create and maintain MAC multicast address table on Layer 2. And
then it can forward the multicast packets transmitted from the upstream router
according to the MAC multicast address table.
When IGMP Snooping is disabled, the packets are broadcasted on Layer 2. See the
following figure:
Figure 102 Multicast packet transmission without IGMP Snooping
Multicast router
Layer 2 Ethernet Switch
Video stream
Multicast group member Non-multicast
group member
When IGMP Snooping runs, the packets are multicast rather than broadcasted on
Layer 2. See the following figure:
C
ONFIGURATION
Internet / Intranet
Video stream
Video stream
Video stream
Non-multicast
group member
Video stream
VOD Server