Configuring the Router-Alert Option
Context
Generally, a network device sends a message to the corresponding protocol stack for processing only when the destination address of the message is the address of a local interface. IGMP messages therefore cannot be sent to the IGMP stack because their destination addresses are multicast addresses but not a local interface address. As a result, the network device cannot maintain group memberships. The Router-Alert option was introduced to solve this problem. If a message contains the Router-Alert option in the IP header, devices that receive the message send the message to the corresponding protocol stack without checking its destination IP address.
By default, the industrial switch router sends received IGMP messages to the IGMP stack for processing regardless of whether the messages contain the Router-Alert option in their IP headers. This ensures compatibility between the industrial switch router and other devices. Configuring the industrial switch router to discard IGMP packets without the Router-Alert option can improve device performance, reduce transmission cost, and enhance protocol security.
You can also configure the industrial switch router to send IGMP messages with or without the Router-Alert option. By default, the industrial switch router sends IGMP messages with the Router-Alert option. If the industrial switch router needs to communicate with a device that does not support the Router-Alert option, configure the industrial switch router to send IGMP messages without the Router-Alert option.
The Router-Alert option can be configured in the IGMP view or interface view.
- Configuration in the IGMP view is valid globally, whereas configuration in the interface view is valid only for the specific interface.
- If the Router-Alert option is configured in both the interface view and IGMP view, configuration in the interface view takes precedence over configuration in the IGMP view. If the Router-Alert option is not configured on an interface, the interface uses the configuration in the IGMP view.
- If non-default configuration is made in the IGMP view, the default configuration in the interface view does not take effect.
