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IGMP Snooping Commands 469
Parameter Description
Default Configuration
IGMP snooping is enabled globally and on all VLANs by default.
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.
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 that have been discovered when the multicast source is first
seen. If a new mrouter is later discovered on a different port, the multicast
source data is not forwarded to the new port. Likewise, if an existing mrouter
times out or stops querying, the multicast source data continues to be
forwarded to that port. If a host in the VLAN subsequently joins or leaves the
group, the list of mrouter ports is updated for the multicast source and the
forwarding of the multicast source is adjusted. The workaround to this
limitation is to statically configure mrouter ports when enabling IGMP/MLD
snooping in L3 multicast enabled VLANs.
Example
console(config)#ip igmp snooping
console(config)#no ip igmp snooping vlan 1
Parameter Description
vlan-id Specifies a VLAN ID value.
2CSPC4.X8100-SWUM102.book Page 469 Friday, March 15, 2013 8:56 AM