dual wired network connections when in dock?

I've got a T420 and the dock. I wanted to use both wired ethernet ports; the one on the side and the one back in the dock. But it disables the side port on the T420 when it's docked. Is this normal? Is it possible to configure it to allow both ports to be active at the same time?

The main reason for this is ease of setting up a couple of wired routers. I can leave my T420 in the dock and get to the internet through that port. I could then use the side port to deal with connecting the new routers. I happen to have a wifi network accessible, so I can 'work around' it (and have done just that). But I'd like to know if both ports could be active simultaneously.

And yes, I could also use a USB connected wired ethernet dongle. I have one lying around. I may go that route if the onboard and dock port can't be used at the same time.

 

What you are seeing is normal. Docking your T420 does not add an additional network adapter to your system.

 

Well, that's disappointing. Many other brands of docks I've used over the years have a dedicated port on the dock, in addition to the one in the laptop itself (several sony, compaq and dell models). Were the dock less expensive I could forgive the omission, but given the price paid I naively expected an actual, separate, network interface to be in there.

Anyone running linux care to confirm that there's not a separate NIC in the dock? I'd wonder whether they've got some Windows driver nonsense going on here. Or if they've, in fact, bothered to pull gigE signals out the docking port. Gotta be stuff of an EE's nightmares to deal with the amount of EMI noise that must cause...