@willn I think the OP tries to use the interface that is provided over the USB OTG port. I guess he has the same Setup as i Described in my Thread BeagleBone Black TTY over USB / FTDI. Just he wants to access the Ethernet port where i tried to access the serial port.
As i have some Intrest here aswell,
Is it possible to activate the Ethernet interface (i think on debian it is called usb0) ?