By default, IGMP snooping checks for the
presence of the router alert option in the IP packet header of an IGMP message. Packets
that do not include this option are dropped. When you disable the router alert, you also
disable the snooping check for the presence of the router alert option.
Enter global configuration mode.
device# configure terminal
Disable the router alert option.
device(config)# ip igmp router-alert-check-disable
