Oh, yes it is!
"Oh, no it isn't," says System Preferences.
Physically it is connected. The ethernet works fine when I try it with another laptop. But my MacBook Air has no network connection.
Not sure what causes this, but it seems to arise when moving from one network to another — work to home. Until Apple fix their bug, one workaround is as follows:
- Open System Preferences >> Network
- Select USB Ethernet in the ports list.
- Click the - sign at the bottom of the ports list to delete your existing USB Ethernet port
- Click the + sign, to add a new one; select the new one click Apply.
If you're lucky (it's worked for me a couple of times already) you will find that, after a short pause, the USB Ethernet n port you just created now works as normal.
If the option to create a USB Ethernet port doesn't appear, check that you have the ethernet adapter dongle plugged in. This seems to be neccessary.
If it still doesn't appear (sometimes it doesn't), restart and try again. This has always worked for me (so far).