The canonical explanation is deeply buried in the RTPS spec (aka "DDS Interoperability Protocol"), section 9.6.1: http://www.omg.org/spec/DDSI-RTPS/2.2/PDF/ Four UDP ports are needed. The port numbers are a function of the DDS/RTPS domain ID, which in ROS 2 is populated with the ROS_DOMAIN_ID environment variable and defaults to zero. The expressions and magic numbers are on pages 190-191 of the PDF (document page numbers 178-179). Best regards, Morgan --- [Visit Topic](https://discourse.ros.org/t/ros2-behind-a-firewall/1178/2) or reply to this email to respond. If you do not want to receive messages from ros-users please use the unsubscribe link below. If you use the one above, you will stop all of ros-users from receiving updates. ______________________________________________________________________________ ros-users mailing list ros-users@lists.ros.org http://lists.ros.org/mailman/listinfo/ros-users Unsubscribe: