How to force Thunderbolt-ethernet connection when switching networks without restarting computer? I have a thunderbolt to ethernet cable on a MacBookPro Retina on Lion. 

Sometimes the thunderbolt to ethernet connection does not work. It seems to occur when I switch network locations (e.g., I move from my home network to my work network). Restarting the computer fixes the problem, however, I don't want to have to restart my computer.

How can I force thunderbolt to ethernet to connect without restarting the computer? 

More details:

Under network settings, there is a red dot and not connected on "Thund...thernet".
It further says:

Status: Cable Unplugged
Either the cable for Thunderbolt Ethernet is 
not plugged in or the device at the other end 
is not responding.


Under system information - thunderbolt it states

Thunderbolt to Gigabit Ethernet Adapter:

  Vendor Name:  Apple, Inc.
  Device Name:  Thunderbolt to Gigabit Ethernet Adapter
  Vendor ID:    0x1
  Device ID:    0x8003
  Device Revision:  0x1
  Route String: 3
  Firmware Version: 5.5
  Port:
  Status:   Connected
  Link Status:  2
  Port Micro Firmware Version:  0.0.8


Under Network - Thunderbolt Ethernet it states:

Thunderbolt Ethernet:

  Type: Ethernet
  Hardware: Ethernet
  BSD Device Name:  en1
  IPv4:
  Configuration Method: DHCP
  IPv6:
  Configuration Method: Automatic
  Proxies:
  Exceptions List:  *.local, 169.254/16
  FTP Passive Mode: Yes
  Service Order:    0
I had this problem, too, and an Apple Support call and Genius Bar visit later, I had the answer: if you're using Network Locations that preexist your Thunderbolt display, it doesn't seem to auto-add the possibility of "Display Ethernet" to your available network ports. To solve this, either:

Create a new Location in your Network system preferences. It will finally detect the "Display Ethernet" and use it. It'll slowly change from disconnected to No IP to green-is-for-go. 

or

Fix an existing Location by clicking the + to add a port and choosing Display Ethernet. It'll slowly change from disconnected to No IP to green-is-for-go.