User's Manual

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Chapter 42 IGMP Snooping Configuration
42.1 IGMP Snooping Configuration Task
The task of IGMP snooping is to maintain the relationships between VLAN and group address and to update
simultaneously with the multicast changes, enabling Layer 2 switches to forward data according to the topology
structure of the multicast group.
The main functions of IGMP snooping are shown as follows:
(4) Listening IGMP message;
(5) Maintaining the relationship table between VLAN and group address;
(6) Keeping the IGMP entity of host and the IGMP entity of router in the same state to prevent
flooding from occurring.
Note:
Because IGMP snooping realizes the above functions by listening the query message and report message of
IGMP, IGMP snooping can function properly only when it works on the multicast router, that is, the switch must
periodically receive the IGMP query information from the router. The router age timer of IGMP snooping must
be set to a time value that is bigger than the group query period of the multicast router connecting IGMP
snooping. You can check the multicast router information in each VLAN by running show ip igmp-snooping.
 Enabling/Disabling IGMP snooping of VLAN
 Adding/Deleting static multicast address of VLAN
 Configuring immediate-leave of VLAN
 Configuring the function to filter multicast message without registered destination address
 Configuring the
Router Age
timer of IGMP snooping
 Configuring the
Response Time
timer of IGMP snooping
 Configuring IGMP Querier of IGMP snooping
 Monitoring and maintaining IGMP snooping
 IGMP snooping configuration example
42.1.1 Enabling/Disabling IGMP Snooping of VLAN
Perform the following configurations in global configuration mode:
Command Description
ip igmp-snooping
[
vlan
vlan_id ] Enables IGMP-snooping of VLAN.
no ip igmp-snooping
[
vlan
vlan_id ] Resumes the default configuration.
If vlan is not specified, all vlans in the system, including vlans created later, can be enabled or disabled.
In the default configuration, IGMP snooping of all VLANs is enabled, just as the ip igmp-snooping command
is configured.
Note: IGMP snooping can run on up to 16 VLANs.
To enable IGMP snooping on VLAN3, you must first run no ip IGMP-snooping to disable IGMP
snooping of all VLANs, then configure ip IGMP-snooping VLAN 3 and save configuration.