Layer 2 Multicast Configuration Fails to Take Effect

Procedure

1. Check whether the MLD snooping version configured on the device is earlier than that running on user hosts.

   If the MLD snooping version configured on the device is earlier than that running on user hosts, the device only forward MLD Report messages to router ports and does not generate group member ports and forwarding entries.

   Run the display mld-snooping configuration command to check the MLD snooping configuration. If the MLD snooping version configured on the device is earlier than that running on user hosts, run the mld-snooping version version command to make the device run the same MLD version as user hosts.

2. Check whether the general query interval configured on the local device is the same as that configured on the upstream device.

   If the general query interval on the local device is smaller than the general query interval on the upstream MLD querier or MLD snooping device, the local device may mistakenly age out some MLD snooping entries that are still in use. As a result, multicast packets matching these entries cannot be forwarded.

   Run the display mld-snooping command to check MLD snooping parameters. If the general query interval on the local device is smaller than the general query interval on the upstream MLD querier or MLD snooping device, run the mld-snooping query-interval query-interval command to increase the MLD snooping general query interval. It is recommended that the upstream and downstream devices use the same general query interval.

3. Check whether fast leave for interfaces is configured.

   Prompt leave can be configured for an interface only when the interface is connected to one member host. If an interface is connected to multiple hosts and fast leave is configured in the VLAN to which the interface belongs, the router does not send Query message and immediately deletes the forwarding entries of the interface after receiving an MLD Done message from the member port. This causes traffic forwarding interruption.

   Run the display mld-snooping configuration command to check the configuration. If there is 'mld-snooping prompt-leave' in the command output, run the undo mld-snooping prompt-leave command in the VLAN view to disable the fast leave function.

4. Check whether Router-Alert option checking is configured.

   If the device is configured to check Router-Alert option, the router checks the Router-Alert option field in the MLD packets and discards packets without the option.

   Run the display mld-snooping configuration command to check the configuration. If there is "mld-snooping require-router-alert" in the command output, run the undo mld-snooping require-router-alert command in the VLAN view to delete corresponding configurations.

5. Check whether a multicast group policy is configured.

   The multicast group policy limits the multicast groups that the hosts in a VLAN can join. Run the display mld-snooping configuration command to verify the multicast group policy configuration. If IPv6 access control list (ACL6) rules are configured, run the display acl ipv6 command to check whether ACL6 rules are correct.