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 switch sends received MLD messages to the MLD module for processing regardless of whether the messages have the Router-Alert option in their IPv6 headers. This ensures compatibility between the switch and other devices. To improve device performance, reduce transmission cost, and enhance protocol security, configure the switch to discard MLD messages without the Router-Alert option.

You can also configure the switch to send MLD messages with or without the Router-Alert option. By default, the switch sends MLD messages with the Router-Alert option. If the switch needs to communicate with a device that does not support the Router-Alert option, configure the switch 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 non-default configuration is performed in the MLD view, the default configuration in the interface view does not take effect.

Procedure

Configuring the Router-Alert option globally
1. Run system-view
  The system view is displayed.
2. Run mld
  The MLD view is displayed.
3. Run require-router-alert
  The device is configured to check for the Router-Alert option in MLD messages and discard MLD messages without the Router-Alert option.
4. Run send-router-alert
  The switch is configured to send MLD messages with the Router-Alert option.
Configuring the Router-Alert option on an interface
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run mld require-router-alert
  The interface is configured to check for the Router-Alert option in MLD messages and discard MLD messages without the Router-Alert option.
5. Run mld send-router-alert
  The interface is configured to send MLD messages with the Router-Alert option.