Ethernet Network with Nerves on RPiCM3+ over USB dongle

I flashed my Compute Module with Nerves and everything works except for the network connection. The CM does not connect to my router.

What is the best way to debug my problem?

The target is rpi3, which has an onboard Ethernet plug. The compute module does not, so I am using a USB to Eth dongle.
I suspect a missing driver or similar to prevent Linux from detecting the dongle as an Ethernet port.

Check what kind of device you got there on a linux PC using dmesg/lsusb.
Check if driver support is builtin to the kernel nerves is using.