Administrator Guide

Layer 2 Switching Commands 471
Command Mode
Global Configuration mode
User Guidelines
Use this command without parameters to globally enable IGMP snooping.
Use the no form of the command to disable IGMP snooping. Use the vlan
parameter to enable IGMP snooping on a specific VLAN. GMRP is
incompatible with IGMP snooping and should be disabled on any VLANs on
which IGMP snooping is enabled. It is recommended that MLD snooping
should be enabled whenever IGMP snooping is enabled to ensure that
unwanted pruning of multicast protocol packets used by other protocols does
not occur.
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 snoooping querier) will discard the packet. Use the no ip igmp
snooping router-alert-check command to disable checking for the router alert
option.
Example
console(config)#ip igmp snooping
console(config)#no ip igmp snooping vlan 1
show ip igmp snooping
Use the show ip igmp snooping command in Privileged Exec mode to display
the IGMP snooping configuration and SSM statistics.
Syntax
show ip igmp snooping [vlan vlan-id ]
• vlan-id —Specifies a VLAN ID value.
2CSNXXX_SWUM204.book Page 471 Monday, January 25, 2016 1:25 PM