Describe the bug

Hey,

I am having issues setting up SITL with ROS2 with two seperate docker containers on an isolated network. I found a fix by modifying a config file and think it is a bug that PX4_PARAM_UXRCE_DDS_AG_IP is not respected.

What do I want?

Two docker containers

• offboard running ros2 and the xrce agent that is exactly the same as running on the drone
• px4_sim that simulates PX4 and the XRCE_DDS bridge to ROS2

running in an isolated network on docker defined with

networks:
  isolated_network:
    driver: bridge
    ipam:
      config:
        - subnet: 172.40.0.0/16
          gateway: 172.40.0.1

When using the host network, everything works.

To Reproduce

What should work but doesn't

Using that docker network, I

• set the IP of offboard to ipv4_address: 172.40.0.3
• configure px4_sim to have environment variable PX4_PARAM_UXRCE_DDS_AG_IP=-1406664701 (matching the IP Address in INT32)

I can see that environment variable being set correctly in Qgroundcontrol.

However, the bridge still does not work.

The fix

In this file
https://github.com/PX4/PX4-Autopilot/blob/14c0908082b8a9135895e1928e04b4775338ab54/ROMFS/px4fmu_common/init.d-posix/rcS#L322C1-L322C76

the uxrce_dds_client is started with a hardcoded IP address that overrides any environment variable.

uxrce_dds_client start -t udp -h 127.0.0.1 -p $uxrce_dds_port $uxrce_dds_ns

if I modify this line on my docker container to be

uxrce_dds_client start -t udp  -p $uxrce_dds_port $uxrce_dds_ns

and restart everything, the parameter is accepted, the correct IP is set and the bridge works.

Expected behavior

No response

Screenshot / Media

No response

Flight Log

No response

Software Version

I am not sure but saw that this line exists in all latest versions and main.

Flight controller

No response

Vehicle type

Multicopter

How are the different components wired up (including port information)

No response

Additional context

So I made it work for now by modifying that file in my docker build but it seems hacky to modify the config file and I think this is a bug and instead

• this config file should not start the client with a fixed IP
• to not break existing setups, one could set a default param to be 127.0.0.1

Thank you for your consideration. I am still new to PX4 so I hope I did not miss anything.

Also happy to make a PR :)