Ethernet not working on MacBook pro retina 13
If this is recent, you may be the victim of a bad malware protection update from Apple. They have posted a support article explaining how to check if this was the cause, and how to fix it.


  First, check your version number
  
  
  While pressing the Option key, choose System Information from the
  Apple menu.  
  Expand the Software section and select Installations.
  Click the Software Name column header to sort the list
  alphabetically.
  Look for “Incompatible Kernel Extension
  Configuration Data.” If the most recent version installed is 3.28.1,
  follow the steps below.
  
  
  If you can connect to Wi-Fi, follow these steps to update to version 3.28.2
  
  
  Open the Terminal app.
  Enter this command to update to the current version of the “Incompatible Kernel Extension Configuration Data” kernel extension: 
  sudo softwareupdate --background
  Quit Terminal and restart your Mac. 
  
  
  If you can't connect to Wi-Fi, follow these steps to update to version 3.28.2
  
  
  Restart from OS X Recovery by holding down Command-R while your Mac starts up.
  Select Disk Utility from the list of OS X Utilities.
  Select your drive from the list of internal drives in the sidebar. The default name is “Macintosh HD.” Your drive might have a different name or location, if you renamed or moved it.
  If the drive name is dimmed, your drive might be protected by FileVault. Choose File > Unlock from the Disk Utility menu, then enter your FileVault password. 
  Choose File > Mount in Disk Utility to mount your drive, if it's not already mounted. 
  Quit Disk Utility. 
  To make it easier to enter the command shown in step 9, you might want to copy it from Safari:
  
  
  Choose Get Help Online from the OS X Utilities list, then go to support.apple.com/kb/HT205956.
  Select the command in step 9, copy it, then quit Safari before you continue to the next step. 
  
  Choose Utilities > Terminal to open the Terminal app.
  Type or paste the following command as one line in Terminal, then press Return. Replace Macintosh HD with the name of your hard drive, if different: rm -rf "/Volumes/Macintosh HD/System/Library/Extensions/AppleKextExcludeList.kext"
  
  
  Now complete these steps to update to the current version of the “Incompatible Kernel Extension Configuration Data” kernel extension:
  
  
  Quit Terminal.
  Choose Restart from the Apple menu. After your Mac restarts, your Ethernet connection should work. 
  Open Terminal and enter this command: sudo softwareupdate --background
  Quit Terminal
  Choose Restart from the Apple menu.
  
  
  Alternatively, if you confirmed that your Mac has Incompatible Kernel Extension Configuration Data version 3.28.1, you can also restart your Mac into OS X Recovery mode, then select Reinstall OS X. You can reinstall OS X on your drive without reformatting it.