Ethernet cannot see RTA1025W modem (wi-fi can)

At home I have a Dynalink RTA1025W DSL modem.

• MBP can obtain IP via WiFI


• MBP cannot see modem or get IP via ethernet.


• Ubuntu/Win7/Win8 can get IP via the same ethernet cable & modem.

At work:

• MBP can see the LAN and obtain IP via ethernet using the same USB ethernet adapter.

When I'm at home and I attempt to get an IP address via ethernet, I open the network preferences | USB Ethernet | Advanced | Renew DHCP Lease. It thinks about it for a second, then puts focus in the box titled "DHCP Client ID", as if it expects me to type something.

The status remains "cable unplugged".

If I try to ping my router's address (192.168.1.1) no route is found.

I have tried many different cables, all otherwise known to be working.

Occasionally, the network config will decided to allocate a self-assigned IP, which is not helpful. It does this at random times without any prompting from me.

I have tried the following without success:

• deleting and re-adding the USB Ethernet interface


• creating a new network "location"


• removing the file com.apple.plf.plist


• assigning manually an IP from the valid range

Any other advice?