What MAC address should I use for my Thunderbolt Ethernet on a MBPR?
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 -&gt; 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.