I'm trying to use Ethernet through the Thunderbolt display. For some reason Network preferences say that the "Display Ethernet" is not connected, and indeed I get not signal if I turn WiFi off. What is wrong?
Do you have an Ethernet cable attached between the display and a switch/hub/router? I don't believe the interface will show as connected without a physical connection.
After a bit of playing around, unplugging and plugging in a couple of cables and what not, I went to Software Update, and found there was an App to download, to allow the firmware on the display to be updated.
Download the App via software update, it is them saved under Applications|Utilities, disconnect all external storage devices from the display, I had to physically unplug them, and run the firmware updater.
You need to have your MBP open for it to work too.
After the firmware update was complete, I restarted my MBP and now am using the Display Ethernet as my network connection.