ROS Networking

Setting up a ROS network of computers is probably one of the hardest things to do, mostly because it is hard to troubleshoot networking errors.

There are a few environment variables you should know about:

• ROS_MASTER_URI - this is the http://network_hostname_or_ip_address:11311 address that ROS should look for a roscore master on
  • If developing locally this should be http://localhost:11311
  • If wanting to connect to Sawyer it should be http://sawyer.local:11311
  • If wanting to connect to Fetch it should be http://qiborg-wireless.cs.byu.edu:11311
• ROS_HOSTNAME - this should not be used
  • If it is set (check by running echo $ROS_HOSTNAME) then unset it like so unset ROS_HOSTNAME.
• ROS_IP - this should be set to your IP address that matches this pattern: 192.168.36.xxx

The reason you use ROS_HOSTNAME or ROS_IP is because the hostname reported by hostname does not always resolve to the correct IP address or can be found by other computers, so you have to explicitly tell ROS what IP or hostname that other computers should try to connect to when they want to set up a connection to a node running on your computer.

Symptoms of network problems:

• rostopic list does not work
  • Check to make sure that a roscore is running and your ROS_MASTER_URI is pointing to the machine that runs the roscore
• rostopic echo /some_topic does not work
  • Check to make sure the other computer can connect to yours.
    • Try pinging your computer
    • Make sure your ROS_IP is set properly
  • Check that your computer is getting the right hostname to connect to.
    • Run roswtf and see if you have errors around resolving hostnames
      • Make sure the computer running roscore is reporting it's hostname properly via ROS_HOSTNAME, ROS_IP, or hostname

The ./qiborg_wired.sh script in sawyer_ws typically sets up the environment variables on your machine in a new shell to connect to fetch. A common issue is that someone forgets to run the intera script, and then all the ros nodes fail to connect to the appropriate roscore on sawyer.