Yes, the connected light is green and showing “connected” for my display ethernet even though the display is unplugged. And even when it’s plugged in my computer only connects to the net via the backup wifi while in my office. The jack on the wall and the cable are OK, because they work with an older laptop with a direct connect ethernet jack.
Going to have to try this.
Update: that seems to have worked! Adding details so Google might find it for those with similar problems… it seems that something in the network configuration was corrupted. The info at the link suggested
- Remove Display Ethernet from the System Preferences from the gui
- Unplug the display
- delete /Library/Preferences/NetworkInterfaces.plist (using sudo… I used mv instead of rm to move it to my home directory, just in case
- plug the display back in.
- Add back the configs to the gui version of Network Preferences
I found that in doing this I had to reenter the info for my manual IP configuration and DNS servers. But now I can connect again via the ethernet from my office.