The require-router-alert command configures the switch to discard IGMP messages without the Router-Alert option.
The undo require-router-alert command disables the switch from checking for the Router-Alert option in IGMP messages.
By default, the switch does not check whether the received IGMP messages contain the Router-Alert option in IP headers, and it accepts all the received IGMP messages.
Usage Scenario
Generally, a network device sends a packet to the corresponding protocol module for processing only when the destination address of the packet is a local interface address. Destination addresses of IGMP packets are multicast addresses but not interface addresses of multicast devices. Therefore, multicast devices do not send IGMP packets to the IGMP module, and the IGMP module cannot maintain group memberships.
The Router-Alert option in IP packet headers solves this problem. This option indicates that a packet needs to be sent to the protocol module.
You can configure the switch to accept only IGMP messages with the Router-Alert option. This configuration improves security of the IGMP service.
Prerequisites
IP multicast routing has been enabled using the multicast routing-enable command.
Precautions
This command has the same function as the igmp require-router-alert command used in the interface view. The configuration in the IGMP view is globally valid, whereas the configuration in the interface view takes effect only for the specified 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.