Troubleshooting of Layer 2 Multicast Failure

Contents

Objective

Requirements

Introduction

Troubleshooting Steps

Conclusion

Objective

This article describes the troubleshooting steps for resolving issues with layer 2 multicast on switches, helping you quickly identify problems and address network faults.

Requirements

• Omada Smart / L2+ / L3 switches
• Omada Controller (Software Controller / Hardware Controller / Cloud-Based Controller, V5.9 and above)

Introduction

Multicast is commonly used in scenarios such as video conferencing and live streaming, allowing data packets to be received by multiple recipients simultaneously without the need to send individual packets to each receiver. Layer 2 multicast issues may be caused by various factors, and resolving these problems usually requires detailed diagnosis and configuration checks. This article introduces the general steps to troubleshoot multicast connectivity issues.

Troubleshooting Steps

Step 1. Check the state of the physical port and STP. Go to Devices, select the target switch to open the Properties window, and check if the port is linked up normally and if the port is in the STP Blocking state.

1. If the port is not linked up, change the network cable and try again, or try another available port on the switch.

2. If the port is in the STP Blocking state, eliminate network loops first.

Step 2. Check the state of multicast member ports. Go to Tools > Terminal, select Switch for Device Type, choose the target switch in the pop-up window of Sources and click Confirm. Click Open Terminal.

First enter enable in the Terminal, and then enter show ip igmp snooping groups vlan vlan-id to check if the Switch ports in the multicast group correspond to the user-side ports.

1. If the Switch ports correspond to the user-side ports, it indicates that the switch has received the IGMP Report requests from the user-side devices.

2. If the Switch ports do not correspond to the user-side ports correctly, the following are the possible causes, which may require packet capture for further diagnosis.

• The switch does not receive the Report message from the user or the message format does not meet the device’s requirements.
• The IGMP messages received by the switch do not conform to the IGMP standards. The destination MAC or IP address is not a multicast address.
• The version of the IGMP messages received by the switch is not compatible with the version configured on the device.

Step 3. Check the router port.

Enter show ip igmp snooping vlan vlan-id to check if the router port exists.

1. If the router port exists, it indicates that the uplink port has received the IGMP Query messages from the upstream querier, or that the static router port has sent the Query messages.

2. If the router port does not exist, it means that no static router port has been configured, and that the switch has not received any IGMP Query messages from the upstream layer 3 device. In this case, you need to debug and troubleshoot the upstream device.

Step 4. Check the multicast packets.

Enter show ip igmp snooping interface packet-stat to check the multicast packets received by the switch.

1. Check if the switch is receiving any Error messages. If so, you need to capture the packets on the corresponding port for further analysis.

2. Check the IGMP Report message counters on the member ports. If the Report message counters do not increase after a member port receives an IGMP Report request, it indicates that the port is not receiving the Report messages.

3. Check the IGMP Query message counters on the router port. If the Query message counters do not increase, it indicates that the port is not receiving the IGMP Query messages from the upstream device or the static router port.

Step 5. Collect information and seek technical support.

If the previous steps have not been able to resolve the issue, please collect the relevant information from the previous steps, and then seek technical support.

Conclusion

By taking the troubleshooting steps above, you now know how to fix the Layer 2 multicast failure.

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