Ethernet says "cable unplugged"

Thanks for the additional information.

Please try the following steps, in order, or until resolved:

Step 1

• Open a Terminal session. The Terminal application is located in /Applications/Utilities.
• At the command prompt, enter: ifconfig -a
• Locate the network interface that is giving you trouble. (Note: en0 = Ethernet)
• Look to see if Terminal indicates the problematic interface is not enabled. (Note: Enabled = flags: UP, status: active)

• If not enabled, enter: sudo ifconfig en0 inet up
• At the command prompt, enter: ifconfig -a
• Verify that the problematic interface is now active and various network interface related data should now be listed.

Step 2

• In Finder, go to /Macintosh HD/Library/Preferences/SystemConfiguration
• Move (not copy) the entire SystemConfiguration folder to the OS X desktop.
• Restart the computer.
• Verify that you now have connectivity.

mikesgym wrote:

Ethernet says "cable unplugged"

Have you tried changing ethernet cables? What is the other end of the ethernet cable connected to besides your iMac?

Describe in detail your network setup.

I suspect that a setting is incorrect in your router or the ethernet cable is set up incorrectly.

Other end of cable is connected to a new router that is connected to a new Modem from my cable company.

Make sure the modem ethernet cable is connect to the the LAN port on the router. Your second ethernet cable should be connected to your Mac into an ethernet port on your router.

Go into airport utility or whatever app your 3rd party router uses. Go into the Network tab and make sure router mode is set to DHCP & NAT.

When done, restart your modem and your computer. If all else fails, you are still under warranty for your router. If the user manual is of no help in the troubleshooting section, call them and explain your issue. Ask them to provide step by step instructions and write them down. Keep the instructions in a safe place.

Ok, so the article stated that you would need to update the Kernel Extension Configuration from 3.28.1. It also references an Apple Support article that lets you know that you would need 3.28.2 to resolve the Ethernet port issue. That article was dated 4/15/2016.

In your initial post, you stated that you already have 3.30.1. Are you sure that this is the Kernel Extension Configuration data file mentioned in the Apple Support article?

Basically it comes down to one of two things: 1) The file is the wrong version, or 2) The Ethernet port on your iMac has failed.

What are you referring to by updating to 3.28.2? Where are you getting this error message? Is your iMac still running OS X Mountain Lion 10.8.1? Which exact model is your iMac?

Take a look at the following 9to5Mac article to see if it can help.