igmp require-router-alert
Function
The igmp require-router-alert command configures the device to accept only the IGMP messages with the Router-Alert option on an interface.
The undo igmp require-router-alert command disables the device from checking for the Router-Alert option in IGMP messages on an interface.
By default, the device does not check for the Router-Alert option in IGMP messages and processes all the IGMP messages received on an interface.
Usage Guidelines
Usage Scenario
Generally, a network device sends a packet to the routing protocol module for processing only when the destination address of the packet is the address of a local interface. Destination IP addresses of IGMP messages are multicast addresses but not interface addresses, so the IGMP messages are not sent to the routing protocol module. The Router-Alert option in the IP header of an IGMP message solves this problem. If an IGMP message contains the Router-Alert option, the device sends the message to the routing protocol module. You can configure the device to accept only IGMP messages with the Router-Alert option to improve IGMP security.
Prerequisites
Multicast routing has been enabled using the multicast routing-enable command.
Configuration Impact
After the igmp require-router-alert command is executed on an interface, the system checks whether an IGMP message received on the interface carries the Router-Alert option. If not, the system discards the IGMP message.
Precautions
This command has the same function as the require-router-alert command used in the IGMP view. The configuration in the IGMP view is globally valid in the instance, whereas the configuration in the interface view is valid only for the current interface. The configuration in the interface view takes precedence over the configuration in the IGMP view. The configuration in the IGMP view is used only when no configuration is performed in the interface view.
