Configuring the Router-Alert Option
Context
An IPv6 network device sends received messages whose destination IPv6 addresses are local interface addresses to the routing protocol module. If the destination address of a message is not the local interface address, the message cannot be sent to the correct module. For example, the destination address of a Multicast Listener Discovery (MLD) message is a multicast address, the message cannot be sent to the MLD module and membership cannot be maintained. The Router-Alert option is introduced to solve this problem. If a message contains the Router-Alert option in the IPv6 header, devices that receive the message send the message to the corresponding protocol module without checking the destination IPv6 address of the message.
By default, the router sends received MLD messages to the MLD module for processing no matter whether the messages have the Router-Alert option in their IP headers. This ensures compatibility between the router and other devices. To improve device performance, reduce transmission cost, and enhance protocol security, configure the router to discard MLD messages without the Router-Alert option.
You can also configure the router to send MLD messages with or without the Router-Alert option. By default, the router sends MLD messages with the Router-Alert option. If the router needs to communicate with a device that does not support the Router-Alert option, configure the router to send MLD messages without the Router-Alert option
The Router-Alert option can be configured in the MLD view or interface view.
- The configuration in the MLD view is globally valid, whereas the configuration in the interface view takes effect only for the specified interface.
- If the Router-Alert option is configured in the interface view and the MLD view, the configuration in the interface view takes effect. If the Router-Alert option is not configured on an interface, the interface uses the configuration in the MLD view.
- If the non-default configuration is performed in the MLD view, the default configuration in the interface view does not take effect.