MediaMTX SRT Listener: Fix For Primary IP Response Only

Dec 3, 2025 by Alex Johnson 56 views

MediaMTX SRT Listener Only Responding on Primary IPv4/IPv6 Address: A Comprehensive Guide

If you're experiencing issues with your MediaMTX SRT listener only responding on the primary IPv4 or IPv6 address, you're not alone. This is a known issue that can occur when multiple IP addresses are configured on an interface. In this article, we'll explore the root cause of this problem, provide a step-by-step guide to replicating the issue, and offer solutions to ensure your SRT listener responds on all configured IP addresses.

Understanding the Issue: Why SRT Listener May Favor Primary IPs

When dealing with streaming media using SRT (Secure Reliable Transport) protocol within the MediaMTX environment, it's crucial to ensure that your listener responds across all available network interfaces. The core issue arises when MediaMTX, by default, may bind the SRT listener to only the primary IPv4 and IPv6 addresses of your system. This means if you have multiple IP addresses configured on a single interface, connections to the secondary addresses might fail, even though the service is intended to be accessible across all IPs.

The problem isn't immediately obvious, as the configuration seems straightforward. Typically, you set the srtAddress in your MediaMTX configuration file to **:port_number**, intending to listen on all interfaces. However, the underlying mechanism might be picking up only the primary addresses, leading to connection failures when clients attempt to connect via secondary IPs. This behavior can be particularly problematic in environments where you need to distribute traffic across multiple IPs for load balancing or network segmentation.

To further clarify, the desired behavior is for the MediaMTX SRT listener to respond on all configured IP addresses. This ensures that regardless of the IP address a client uses to connect, the stream is accessible. The frustration stems from the fact that while the configuration suggests this behavior, the actual outcome can be different, necessitating a deeper dive into the system's network settings and MediaMTX's configuration nuances.

Replicating the Issue: A Step-by-Step Guide

To effectively troubleshoot and resolve this issue, it's essential to replicate it in a controlled environment. This step-by-step guide will help you reproduce the problem and confirm that you're facing the same challenge.

Initial Setup with Primary IP: Start with a system configured with a single IP address. For example, if your system has the IP address 192.168.1.1/24, ensure your MediaMTX instance is running and configured to listen on the SRT port. A typical mediamtx.yml configuration would include:
```
srt: yes
srtAddress: :8890
```
Here, srtAddress: :8890 instructs MediaMTX to listen on port 8890 across all interfaces.
Verify Primary IP Connectivity: Connect to the SRT stream using the primary IP address. For instance, use an SRT client to connect to srt://192.168.1.1:8890?streamid=read:test. This connection should be successful, confirming that SRT is working on the primary IP.
Add a Secondary IP Address: Add a secondary IP address to the same interface. On a Linux system, you can use the ip command:
```
sudo ip address add 192.168.1.2/32 dev eth0
```
This command adds the IP address 192.168.1.2 to the eth0 interface.
Restart MediaMTX (Optional): While not always necessary, restarting the MediaMTX daemon ensures that the service recognizes the new IP address. You can restart using:
```
sudo systemctl restart mediamtx
```
Attempt Connection via Secondary IP: Try connecting to the SRT stream using the secondary IP address. Use the same SRT client but this time connect to srt://192.168.1.2:8890?streamid=read:test. This connection will likely fail, demonstrating the issue.
Explicitly Specify SRT Address: Modify the mediamtx.yml configuration to explicitly specify the secondary IP address:
```
srt: yes
srtAddress: 192.168.1.2:8890
```
Restart MediaMTX after making this change.
Verify Secondary IP Connectivity: Attempt to connect to the SRT stream again using srt://192.168.1.2:8890?streamid=read:test. This connection should now succeed, but connections to the primary IP address will likely fail, confirming that MediaMTX is only listening on the explicitly specified IP.

By following these steps, you can reliably replicate the issue and confirm that MediaMTX's SRT listener is not responding on all configured IP addresses when using the default srtAddress: :8890 setting.

Diagnosing the Root Cause: Network Configuration and MediaMTX Behavior

Understanding the underlying reasons for this behavior is crucial for implementing a sustainable solution. Several factors contribute to why MediaMTX's SRT listener might only respond on the primary IP address.

Binding Behavior: When srtAddress is set to **:port_number**, it instructs the application to listen on all interfaces. However, the underlying network stack and the specific implementation of the SRT library in Go (gosrt, in this case) might not handle multiple IP addresses on the same interface as expected. The system might default to the primary IP address when establishing the listening socket.
Network Stack Limitations: The network stack in the operating system might have limitations in how it handles connections to multiple IP addresses on the same interface. While the socket is bound to all interfaces, the routing and connection establishment might still favor the primary IP, especially if specific routing rules are not in place.
gosrt Library Behavior: The gosrt library, which MediaMTX uses for SRT functionality, might have its own nuances in handling multiple IP addresses. It's possible that the library's implementation does not fully account for scenarios where multiple IPs are configured on a single interface, leading to the observed behavior.
Configuration Overrides: Explicitly specifying an IP address in the srtAddress configuration overrides the default behavior. When you set srtAddress: 192.168.1.2:8890, you're telling MediaMTX to listen specifically on that IP, which works but defeats the purpose of listening on all interfaces.

To further diagnose the issue, you can use tools like tcpdump or Wireshark to capture network traffic. The provided network dump in the issue description shows that incoming UDP packets are observed on the secondary IP (192.168.1.2), but there are no responses. This indicates that MediaMTX is receiving the traffic but not processing it, likely because the SRT listener is not properly bound to that IP.

Additionally, checking the system's routing table and interface configurations can provide insights. Ensure that there are no conflicting routes or interface settings that might be directing traffic only to the primary IP address.

Solutions and Workarounds: Ensuring SRT Listener Responds on All IPs

Addressing this issue requires a multi-faceted approach, considering both MediaMTX configuration and potential network adjustments. Here are several solutions and workarounds to ensure your SRT listener responds on all configured IP addresses.

1. Explicitly Bind to All IP Addresses

One approach is to explicitly bind the SRT listener to each IP address individually in the MediaMTX configuration. This involves specifying multiple srtAddress entries, each with a specific IP address. While this is a workaround rather than a true solution, it can be effective in certain scenarios.

srt: yes
srtAddress:
  - 192.168.1.1:8890
  - 192.168.1.2:8890

This configuration tells MediaMTX to create separate listeners for each IP address. However, this method can become cumbersome if you have many IP addresses or if the IP addresses change frequently.

2. Modify the Application to Listen on All Interfaces Correctly

A more robust solution involves modifying the application code to ensure it correctly binds to all interfaces. This might require changes to how MediaMTX uses the gosrt library or how it handles socket binding. The goal is to ensure that the application listens on the wildcard address (0.0.0.0 for IPv4 and :: for IPv6) and properly handles incoming connections on all IP addresses.

This solution is more complex and requires a deeper understanding of the application's codebase and the SRT protocol. It might involve contributing changes to the MediaMTX project or creating a custom build with the necessary modifications.

3. Network Configuration Adjustments

In some cases, network configuration adjustments can help. Ensure that your routing table is correctly configured to route traffic to the appropriate interfaces. You might need to add specific routes to ensure that traffic destined for the secondary IP address is properly routed.

Additionally, check your firewall settings. Ensure that the firewall is not blocking traffic to the secondary IP address or the SRT port. Firewalls can sometimes interfere with connections to non-primary IP addresses if not configured correctly.

4. Using a Load Balancer

If you need to distribute traffic across multiple IP addresses for load balancing purposes, consider using a load balancer. A load balancer can distribute incoming connections across multiple backend servers, each listening on a different IP address. This approach adds complexity but provides a scalable and robust solution for handling high traffic loads.

5. Investigate and Update gosrt Library

Since MediaMTX uses the gosrt library for SRT functionality, investigating the library's behavior with multiple IP addresses can be beneficial. Check the gosrt library's documentation and issue tracker for any known issues or limitations related to multiple IP addresses. If necessary, consider contributing to the library to address the issue.

Conclusion: Ensuring Reliable SRT Streaming with MediaMTX

In conclusion, the issue of the MediaMTX SRT listener only responding on the primary IPv4/IPv6 address can be a significant challenge, especially in environments requiring robust and flexible streaming solutions. By understanding the root cause, replicating the issue, and implementing the appropriate solutions, you can ensure that your SRT listener responds on all configured IP addresses.

Whether it's explicitly binding to all IP addresses, modifying the application code, adjusting network configurations, or using a load balancer, there are several strategies to overcome this limitation. Each approach has its trade-offs, so choose the solution that best fits your specific needs and environment.

For further reading on SRT and MediaMTX, consider exploring resources like the SRT Alliance website (https://www.srtalliance.org/) and the MediaMTX GitHub repository. These resources can provide additional insights and help you stay up-to-date with the latest developments in SRT streaming.

By addressing this issue, you can enhance the reliability and scalability of your MediaMTX streaming setup, ensuring seamless delivery of content to your audience.