I suggest that, if you already installed Digi Embedded Linux (Digi ESP for Embedded Linux)on your development PC, please go through the help docs regarding USB0 and Ethernet. In the help docs mentioned that how to test the interfaces.
You can find the help docs under Digi EL-->Help-->Help Contents-->Expand Digi ESP for Embedded Linux, Section 9.11 Ethernet interface and 9.29 USB device interface.
Some more information on Development board, pls check HRM at the below link regarding jumpers related to Ethernet and USB.
Also I suggest that, use Digi's default images on the module to test the above interfaces.
I hope this helps you.