Layer 2 Multicast Packets Cannot Be Forwarded

Procedure

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

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

   Run the display igmp-snooping configuration command to check the IGMP snooping configuration. If the IGMP snooping version configured on the device is earlier than that running on user hosts, run the igmp-snooping version version command to make the device run the same IGMP 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 IGMP querier or IGMP snooping device, the local device may mistakenly age out some IGMP snooping entries that are still in use. As a result, multicast packets matching these entries cannot be forwarded.

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

3. Check whether router port dynamic learning is disabled.

   The router does not listen to IGMP Query messages in a VLAN after router port dynamic learning is disabled in the VLAN.

   Run the display igmp-snooping configuration command to check whether router port dynamic learning is disabled. If the command output contains "undo igmp-snooping router-learning", run the igmp-snooping router-learning command to enable dynamic learning of router ports in the VLAN.

4. Check whether fast leave for member ports is enabled.

   Configure fast leave in a VLAN only when each interface in the VLAN connects to only one host. If a member port is connected to multiple hosts and fast leave for member ports is enabled in the VLAN, the router immediately deletes the forwarding entry of the member port after receiving an IGMP Leave message from the member port, and does not send a Group-Specific Query message. Therefore, multicast packets cannot be forwarded.

   Run the display igmp-snooping configuration command to check whether fast leave for member ports is enabled. If the command output contains "igmp-snooping prompt-leave", run the undo igmp-snooping prompt-leave command in the VLAN view to disable the fast leave function.

5. Check whether the Router-Alert option is configured.

   If the Router-Alert option is configured, the router checks the Option field of IGMP messages to discard messages without the Router-Alert option.

   Run the display igmp-snooping configuration command to check whether the Router-Alert option is configured. If the command output contains "igmp-snooping require-router-alert", run the undo igmp-snooping require-router-alert command in the VLAN view to delete the related configuration.

6. 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 igmp-snooping configuration command to verify the configuration of multicast group policy. If an access control list (ACL) is configured, run the display acl command to verify the ACL configuration.