Troubleshooting multicast

Layer 2 multicast issues

Layer 2 multicast traffic forwarding failure

Symptom

A device fails to forward Layer 2 multicast traffic.

Common causes

The following are the common causes of this type of issue:

·     The device does not generate Layer 2 multicast forwarding entries.

·     The device does not receive Layer 2 multicast protocol packets

·     The IGMP protocol packet format is incorrect.

·     The version in IGMP protocol packets is different from the IGMP snooping version configured on the device.

·     Layer 3 multicast is configured.

Troubleshooting flow

Figure 1 shows the troubleshooting flowchart.

Figure 1 Flowchart for troubleshooting Layer 2 multicast traffic forwarding failure

Solution

1.     Identify whether the device generates Layer 2 multicast forwarding entries.

Execute the display l2-multicast ip forwarding command to check for Layer 2 multicast forwarding entries.

¡     If the device has generated Layer 2 multicast forwarding entries, contact the support.

¡     If the device has not generated Layer 2 multicast forwarding entries, proceed to step 2.

2.     Identify whether the device receives IGMP reports.

Execute the debugging igmp-snooping packet command to enable IGMP snooping packet debugging. If the following information is printed, the device has received IGMP reports:

*Sep 15 11:47:41:455 2011 Sysname MCS/7/PACKET: -MDC=1; Receive IGMPv2 report packet from port GE0/0/1 on VLAN 2. (G162625)

¡     If the device has not received IGMP reports, troubleshoot the downstream device and hosts.

¡     If the device has received IGMP reports, proceed to step 3.

3.     Verify that the IGMP protocol packet format is correct.

Configure mirroring, and use a packet capture tool (for example, Wireshark) to capture and analyze mirrored IGMP protocol packets under the guidance of the support.

¡     If the IGMP protocol packet format is incorrect, modify IGMP protocol packets.

¡     If the IGMP protocol packet format is correct, proceed to step 4.

4.     Verify that the version in IGMP protocol packets is the same as the IGMP snooping version configured on the device.

Execute the display igmp-snooping command, and check the Version field for the IGMP snooping version.

¡     If the version in IGMP protocol packets is different from the IGMP snooping version, perform one of the following tasks:

-     Modify the IGMP versions on the upstream and downstream devices so that they can be the same as the IGMP snooping version on the device.

-     Use the version command in IGMP-snooping view or the igmp-snooping version command in VLAN view to modify the IGMP snooping version so that it can be  the same as the IGMP versions on the upstream and downstream devices.

¡     If the version in IGMP protocol packets is the same as the IGMP snooping version, proceed to step 5.

5.     Verify that Layer 3 multicast is not configured.

¡     If Layer 3 multicast is configured, delete the Layer 3 multicast configuration.

¡     If Layer 3 multicast is not configured, proceed to step 6.

6.     If the issue persists, collect the following information and contact the support:

¡     Results of each step.

¡     The configuration file, log messages, and alarm messages.

Related alarm and log messages

Alarm messages

N/A

Log messages

N/A