MacOS – Thunderbolt ethernet adapter ist not appearing in netwoks tab

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.

When an interface self-assigns an IP it generally means the interface isn't getting any response from your router or DHCP server. This is a feature of OS X to let the machines build an adhoc network when they cannot determine the actual network they're on -- you can put a bunch of Macs on a dumb hub and almost get them to self-organize and function with this feature.

Your router and DHCP server are going to see the MAC address listed for the device in the Network Preferences pane. Go to System Preferences -> Network and click on your Thunderbolt interface. Click on the Advanced... button and then on the Hardware tab:

That's the MAC address that your interface is broadcasting on the network when it's trying to acquire an IP on your network from your DHCP server.