Dell Networking 7048 Reference Manual page 979

Default Value
The Router-Alert option is not required by default.
Command Mode
Global Configuration
Usage Guidelines
If the router alert check is enabled, IGMP frames without the router-alert
option in the IP header are discarded early in the processing of IGMP packets.
If all the multicast hosts in the network include the router alert option as
required by RFC 2236 and RFC 3376, then enabling this check can reduce
the load on the system.
Example
ip igmp router-alert-check
979
IGMP Commands