Q: Ethernet connection not found

If you are using 10.11.x:

Try this:

Boot the computer into Safe Mode, then restart normally. This will be slower than a normal startup.

Intel-based Macs: Resetting the System Management Controller (SMC)

Resetting your Mac's PRAM and NVRAM

Repair the Hard Drive and Permissions - El Capitan

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.

Repair

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the indented Macintosh HD entry from the the left side list.  Click on the First Aid tab in the toolbar.. If Disk Utility reports any errors that have been fixed, then re-run First Aid until no errors are reported. Wait until the operation completes, then quit Disk Utility and return to the main menu. Select Restart from the Apple menu.

Now, Download and Reinstall OS X El Capitan 10.11.3 Combo Update.

If the problem persists then view this: Re- Built-in ethernet vanished.

Just shutting down and restarting should allow the ethernet port to display again.

The problem is caused by a bug in an automatic software update that was pushed out last night.

If you don't already have a current backup, please back up all data, then reinstall the OS.* You don't need to erase the startup volume, and you won't need the backup unless something goes wrong. If the system was upgraded from an older version of OS X, you may need the Apple ID and password you used.

There are ways to back up a computer that isn't fully functional. Ask if you need guidance.

If you installed the Java runtime distributed by Apple and still need it, you'll have to reinstall it. The same goes for Xcode. All other data will be preserved.

*The linked support article refers to OS X 10.11 ("El Capitan"), but the procedure is the same for OS X 10.7 ("Lion") and later.

Then go ahead and just reinstall the OS (make sure your WiFi is connecting) as per...

Just reboot, hold down the Comand & R keys, do a First Aid (as a safety measure) from the Disk Utility menu, then do a Reinstall OS (of course you have to be online somehow to do this. My WiFi worked, so I used that).  Once you've reinstalled the OS, your Ethernet port should work again.  It did for me!  (That's the quick way to do it - from Apple Tech Support)

Perhaps now you will review what i first posted 3 hours ago.

Same problem, no Ethernet. Wi-Fi is fine.

read all about it here.....

http://www.macrumors.com/2016/02/27/ethernet-not-working-imac-macbook-pro/

Thank you Linc Davies.  This has solved my Ethernet problem.

Apple seems to have released a fix.

Go to About This Mac > System Report > Software > Installations. Sort by Install Date and check to see if you haveIncompatible Kernel Extension Configuration Data version 3.28.2 installed. 3.28.1 is the version that caused problems.

If you haven't gotten 3.28.2 yet, try going into terminal and typing:

sudo softwareupdate --background

Enter your password when prompted. Should update in a bit. Keep checking System Report until you get it. Reboot and all should be well.

I had the ethernet suddenly not working after reboot problem. When I checked I could not see any recent Incompatible Kernel Extension Configuration Data versions. But I applied this  fix and the ethernet port is back. And now I can see the data versions and I now have 3.28.2 installed

Angel's solution works. Thank you

Angle_Swat, excellent post.