Troubleshooting

I don’t receive messages

For UDP Multicast (UDPm) to work properly, the kernel of your Operating System has to have a route for UDPm traffic. This means that a network interface has to be identified as the gateway for such traffic. When no explicit route exists, the default gateway is selected.

This can result in missing messages on computers where multiple network interfaces exist. For example, if you have a computer with two interfaces, say eth0 connected to a WAN and eth1 connected to a LAN, your default gateway will (most likely) be eth0, because it is the one with access to the internet.

If you create a Communication Group on such computer, the UDPm traffic will enter/leave your computer through the interface eth0. This means that any message incoming from a device within your LAN will not be received, and similarly, no messages leaving your computer will ever reach any device on your LAN.

This can be fixed by explicitly telling your kernel which interface should be responsible for Duckietown UDPm traffic. You can do so by running the command,

sudo route add -net 239.255.0.0 netmask 255.255.240.0 dev DEVICE

where you replace DEVICE with the network interface your LAN is connected to (e.g., eth1 in the example above).

Note

UDPm networks can take IP addresses from the range 224/4, which means any IP address between 224.0.0.0 and 239.255.255.255. Duckietown spans communication groups across the range 239.255.0/20 hence the route above only routes Duckietown UDPm traffic.