If it's a USB 3.0 dock (even if you're connecting it via USB 2.0) it's probably using ASIX drivers, not DisplayLink's. I don't think the DL drivers drive an Ethernet controller.
Try these.
http://plugable.com/products/USB3-E1000/drivers
If it's a USB 2.0 dock, don't bother with trying the drivers.
I don't know what to do in that case, unfortunately.