Dell Networking 2048, Reference Manual

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IGMP Snooping Commands
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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.
Enabling IGMP snooping on a VLAN in which L3 multicast is enabled is not
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 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 not updated for the multicast source
and the forwarding of the multicast source is not adjusted. The workaround
to this limitation is to avoid the use of multi-access VLANs in L3 multicast
routed topologies.
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
2CSNXXX_SWUM200.book Page 455 Tuesday, December 10, 2013 1:22 PM