Operation Manual – IGMP SnoopingH3C S9500 Series Routing Switches Chapter 1 IGMP Snooping Configuration1-1Chapter 1 IGMP Snooping ConfigurationWhen configuring IGMP Snooping, go to the following sections for the information youare interested in:z IGMP Snooping Overviewz IGMP Snooping Configuration Tasksz Displaying and Maintaining IGMP Snoopingz IGMP Snooping Configuration Examplez Troubleshooting IGMP Snooping1.1 IGMP Snooping Overview1.1.1 IGMP Snooping PrincipleRunning at the data link layer, IGMP Snooping is a multicast control mechanism on theLayer 2 Ethernet switch and it is used for multicast group management and control.When receiving IGMP messages transmitted between the host and router, the Layer 2Ethernet switch uses IGMP Snooping to analyze the information carried in the IGMPmessages. If the switch hears IGMP host report message from an IGMP host, it will addthe host to the corresponding multicast table. If the switch hears IGMP leave messagefrom an IGMP host, it will remove the host from the corresponding multicast table. Theswitch creates and maintains a MAC multicast address table at Layer 2 by continuouslylistening to IGMP messages. After that, the switch can forward the multicast packetstransmitted from the upstream router according to the MAC multicast address table.When IGMP Snooping is disabled, packets are broadcasted at Layer 2; with IGMPSnooping enabled, multicast packets are delivered to the receivers through multicastrather than being broadcast at Layer 2. See the following figure:
