Users Guide

Layer 2 Switching Commands 516
Enabling IGMP snooping on a VLAN in which L3 multicast is enabled is
recommended. If a multicast source is connected to a VLAN on which both
L3 multicast and IGMP/MLD snooping are enabled, the multicast source is
forwarded to the mrouter ports, including the internal mrouter port. If IGMP
snooping is disabled, multicast data plane packets are flooded in the VLAN.
IGMP snooping (and IGMP querier) validates IGMP packets. As part of the
validation, IGMP checks for the router alert option. If other devices in the
network do not send IGMP packets with the router alert option, IGMP
snooping (and snooping querier) will discard the packet. Use the no ip igmp
snooping router-alert-check command to disable checking for the router alert
option. IGMP packets are intended to be confined to the local link, IGMP
snooping validates that the IP TTL is 1 and discards packets with other
values.
Example
console(config)#ip igmp snooping
console(config)#no ip igmp snooping vlan 1
Command History
Revised in 6.3.5 release.
show ip igmp snooping
Use the show ip igmp snooping command to display the IGMP snooping
configuration and SSM statistics.
Syntax
show ip igmp snooping [vlan vlan-id]
• vlan-id —Specifies a VLAN ID value.
Default Configuration
This command has no default configuration.