ROS 2 communication fails between computers

1. Symptoms

• ros2 topic list on one computer does not show the other’s topics.
• Topics appear and no data flows.
• Data flows on a wired link and not over Wi-Fi.

2. Possible causes

• Different ROS_DOMAIN_ID values (valid safe choices are 0 to 101).
• Discovery range limited (ROS_AUTOMATIC_DISCOVERY_RANGE) or localhost-only settings.
• Multicast blocked by the network or a firewall.
• Incompatible QoS between publisher and subscription.
• Large messages fragmented over a lossy link (see the DDS tuning guide).
• Different DDS implementations with incompatible settings, or clocks that differ.

3. Measurements to collect

• ROS_DOMAIN_ID and discovery variables on both computers.
• Network reachability and multicast.
• ros2 topic info --verbose for QoS.
• Packet loss and kernel buffers.

4. Diagnostic commands

Commands are not executed by the site’s automated tests (they need a ROS 2 Jazzy installation or the robot).

echo $ROS_DOMAIN_ID $ROS_AUTOMATIC_DISCOVERY_RANGE
ros2 topic list
ros2 topic info /scan --verbose
ping -c 3 <other-computer>

5. Step-by-step investigation

1. Compare the domain ID and discovery variables on both computers.
2. Check the network path and multicast; test with a simple talker and listener.
3. Check QoS compatibility with topic info --verbose.
4. Check message sizes and the link (Wi-Fi fragmentation, buffers).
5. Check the DDS implementation and the clocks.

6. Corrective actions

• Use the same domain ID and an appropriate discovery range.
• Allow multicast or configure static peers or a discovery server.
• Make QoS compatible.
• Reduce message size or use a wired link; tune buffers as in the DDS tuning guide.

7. Validation after the fix

• Topics list on both computers and data flows at the expected rate for an hour.

References

• ROS 2 Jazzy, The ROS_DOMAIN_ID: docs.ros.org, and Configuring your ROS 2 environment: docs.ros.org, read 2026-11-06.
• ROS 2 Jazzy, DDS tuning: docs.ros.org, read 2026-11-06.
• ROS 2 Jazzy, About Quality of Service settings: docs.ros.org, read 2026-11-06.