Symptom
IGMP Snooping remains disabled in hardware. In some VPC setup, there could be duplicate traffic also.
Conditions
There are some IGMP snooping related commands for a vlan but the vlan itself is not present in the running config. ie the vlan is not created either through CLI or VTP. When such configs are present, it is possible that IGMP may pack updates for such vlans along with explicitly created vlans to m2rib module for hardware programming. But that message might be rejected by m2rib due to some vlans not explicitly created.
If the update contained snooping status info, then, we will end up with snooping status unchanged in the hardware.
Workaround
Deleting all unnecessary configs and restarting igmp will fix the problem.
