How to Turn Off the Internet with iMac Ethernetby Micah McDunnigan
You can turn off the wireless Internet connection on your iMac through the Wireless menu that is always on the top of your screen, but the option to turn off your Ethernet connection isn't quite as prominent. While unplugging the Ethernet cord technically works, there is also a software-based method for turning off the Internet through your Ethernet port. The Network section of your iMac's System Preferences has a list of all your computer's network connections and the interface for deactivating them.
Click on the Apple icon in the upper left corner of your screen, then select "System Preferences" from the drop-down menu.
Click the "Network" icon in the System Preferences window, then click on the "Ethernet" entry from the list of connections along the left side of the window.
Click on the gear-shaped icon below the list of connections, then select "Make Service Inactive" from the menu that appears. The Ethernet entry in the list of connections should now have the word "Inactive" below it. This confirms that you have disabled your iMac's Ethernet connection.
- You can reactivate your Ethernet connection by returning the the Network section of System Preferences, selecting the Ethernet connection and selecting "Make Service Active" from the menu that appears when you click the gear-shaped icon.