My ZT6688 (aka DM9601) usb-to-ethernet adapter wasn't working, so I emailed Davicom about it. Here's what they said:

DM9601 doesn't support AutoMDIX function. Please be sure your cable is
straight-through type to connect with Switch or your Switch supports
AutoMDIX function.

My problem is that it just hangs for some 30 seconds when I try to do a "dhcpcd eth0", then shuts down the interface.

My cable is connected, for all intents and purposes, straight to my wireless router. Could somebody please explain this to me/provide some help?