I have a thunderbolt to usb 3 adapter & it is plugged into the thunderbolt port. I also have an ac wifi adapter usb 3 plugged into the thunderbolt adapter. It works fine, but my question is, in Network in system preferences shows the ac wifi adapter as connected but the thunderbolt port shows inactive. Confused about this. MacBook Pro 17" early 2011 - Sierra. Thanks
That makes sense. The USB adapter has a driver and is active.
Thunderbolt isn't getting a network address since you don't have a direct network on that port. You would have an active connection if you went thunderbolt to thunderbolt on another Mac or PC or a direct thunderbolt to gigabit ethernet adapter.
Don't over think the network pane - as long as the end device is listed, you are good to go without worrying about what's between it and the CPU.
The Network Preferences Pane shows network location settings. If your Thunderbolt port isn't being used as a network location (connecting to other computers or the internet) then it's inactive. I have a Thunderbolt to ethernet adapter connected, so it says Thunderbolt Ethernet connected. If I had Thunderbolt to another computer connected the Thunderbolt Bridge location would show as connected.
The only time you really need to pay attention to this is if your Thunderbolt connection is not working. It's possible that the network location for that service is missing or misconfigured and needs to be recreated.
Thanks so much bmike & Aaron Paul for your answers & explanations. Now I understand why Thunderbolt port is showing "inactive", even though my Wifi adapter is functioning via the Thunderbolt adapter. Cheers