3Com Switch 7750 Configuration Guide Guide

40
IGMP SNOOPING CONFIGURATION
Overview
IGMP Snooping
Fundamentals
Internet group management protocol snooping (IGMP Snooping) is a multicast
control mechanism running on Layer 2 switch. It is used to manage and control
multicast groups.
When the IGMP messages transferred from the hosts to the router pass through
the Layer 2 switch, the switch uses IGMP Snooping to analyze and process the
IGMP messages, as shown in
Table 303.
By listening to IGMP messages, the switch establishes and maintains MAC
multicast address tables at data link layer, and uses the tables to forward the
multicast packets delivered from the router.
As shown in Figure 91, multicast packets are broadcasted at Layer 2 when IGMP
Snooping is disabled and multicast at Layer 2 when IGMP Snooping is enabled.
Table 303 IGMP message processing on the switch
Received message
type
Sender Receiver Switch processing
IGMP host report
message
Host Switch
Add the host to the
corresponding
multicast group.
IGMP leave message Host Switch
Remove the host from
the multicast group.