Switching from ROS2’s multicast default to unicast can be a bit tricky, especially if you’re testing. I came up with a way to get it working between to virtualbox virtual machine clones and wanted to share my strategy.

This tutorial assumes you have set up two clones of the same virtual machine according to this tutorial. If you would like to follow along, please complete that tutorial first.

Instructions

Follow these instructions for both virtual machine clones.

Start both the original and clone vms and obtain the ip addresses:

vm 1:

ip a

vm2:

ip a

Then install cyclone dds, which is not the default DDS middlewaer for humble.

sudo apt install -y ros-humble-rmw-cyclonedds-cpp

Then create a cyclonedds configuration file. Replace 192.168.xxx.yyy and 192.168.xxx.zzz with the two ip addresses for each of your vm clones.

cat <<EOT | sudo tee /etc/cyclonedds_pc.xml
<CycloneDDS>
    <Domain>
        <General>
            <DontRoute>true</DontRoute>        
            <AllowMulticast>false</AllowMulticast>
            <EnableMulticastLoopback>true</EnableMulticastLoopback>
        </General>
        <Discovery>
          <ParticipantIndex>auto</ParticipantIndex>
          <Peers>
            <Peer Address="192.168.xxx.yyy"/>
            <Peer Address="192.168.xxx.zzz"/>
          </Peers>
    </Discovery>
    </Domain>
</CycloneDDS>
EOT

Then modify .bashrc and source it.

echo "export CYCLONEDDS_URI=/etc/cyclonedds_pc.xml" >> ~/.bashrc
echo "export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp" >> ~/.bashrc
source ~/.bashrc

Close the terminal windows in each vm and opened new ones in each vm and ran:

vm1:

ros2 run demo_nodes_cpp talker

vm2:

ros2 run demo_nodes_cpp listener

Behavior

It seems that if you change the cyclone config xml file, those changes will not be seen until terminal windows on both machines are re-opened, or better yet, all machines are rebooted. it seems once the computers are linked, ros retains a memory of what it has connected to in the past.

It also seems that it is sufficient for either one or the other xml file to reflect the other machine’s ip address, regardless of which one is publishing and which one is subscribing.

I’m not sure if what I described is intended behavior