Troubleshooting multicast video issues on Omada switches

Contents

Objective

Requirements

Introduction

Troubleshooting Steps

Conclusion

Objective

This article introduces common troubleshooting steps and targeted optimizations for multicast video problems, such as freeze and screen distortion, on Omada switches.

Requirements

• Omada smart / L2+ / L3 switches

Introduction

Internet Group Management Protocol Snooping (IGMP Snooping) is a fundamental feature of LAN multicast services. As a L2 multicast protocol, IGMP Snooping maintains the outbound interface information of multicast messages by listening to the multicast protocol messages exchanged between L3 multicast devices and user hosts. This process helps manage and control the forwarding of multicast data packets at the data link layer. In addition, if multicast routing is needed, features such as Protocol Independent Multicast (PIM) and Internet Group Management Protocol (IGMP) must be deployed. Any packet loss or malfunction in any part of the multicast service can result in screen distortion or freeze.

Two common reasons for such problems at the switch level are multicast data packet loss and unstable multicast group formation. When the switch functions properly and video bandwidth is not too high, these problems can be avoided through configuration and optimization. Common troubleshooting methods include checking the multicast group tables and monitoring packet loss and data stream forwarding.

Troubleshooting Steps

Step 1. Check the status of multicast group tables

Use the command show ip igmp snooping group {vlan}{vlan id} to check the status of L2 multicast group formation. When the multicast video is playing stably, multicast groups should not expire. The expiration of some multicast groups can be avoided by configuring static multicast groups. In multicast routing scenarios, IGMP needs to be configured at the junction of L2 and L3 networks. You can use the command show IP IGMP group interface {type+id}<detail> to check the formation of IGMP groups.

Step 2. Check the IGMP message transmission to pinpoint the cause

Use the command show ip igmp snooping interface {port type}{port id} packet-stat to check the sending and receiving of IGMP messages, which can help you determine whether there are any abnormal interactions between the IGMP querier and the client or among multiple clients.

Step 3. Check if there is congestion in the forwarding of multicast data streams

When multicast data streams from multiple channels are being forwarded simultaneously, fluctuations in the multicast data stream can cause peak traffic that exceeds network bandwidth. Sudden congestion can lead to multicast video packet loss, further causing video freezes and screen distortion. You can use the command show system info interface<port type><port id> to check the traffic usage of a port. It is recommended that some bandwidth headroom be reserved for the multicast data stream to cope with fluctuations. If congestion is detected, enable flow control on the port to reduce the forwarding rate of multicast data streams to avoid packet loss. To enable flow control, use the command flow-control on the port.

Step 4. Check the stability of multicast route table entries in the multicast route scenario

In the multicast route scenario, data streams sent from the multicast server need to go through multiple PIM routers for the multicast route before reaching the network where the client is located. If the multicast route table on the PIM router is unstable, video freezes, and screen distortion will occur. You can use the command show IP mroute to check the multicast route table: when a client is stably watching a specific multicast channel, the route table entries should remain unchanged; if there are abnormal changes, you need to further check the unicast routing, and PIM protocol status.

Step 5. Check the packet transmission on the port to confirm packet loss

Use the command show interface counter <port type><port id> to compare the receiving and forwarding ports to see if there is any packet loss. This command counts all messages, including multicast protocol messages, and forwards data streams. It is normal to see a small difference between the Tx and Rx message counts, so you will need to compare multiple times to confirm whether there is any packet loss.

Conclusion

This article briefs on the causes of multicast video freeze and screen distortion at the switch level and provides troubleshooting steps and corresponding optimization. If your problem persists, contact the TP-Link Support for technical assistance.

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