There is a number of other problems that could prevent your network connection from functioning but the above are the most common ones. You should be able to go through the troubleshooting process pretty quickly. Setting up the network in this course is never a primary task, but it's almost always a prerequisite for anything else we're going to do. You can't have a working web server (or any other kind of server) if you don't have a working network connection.

The default (and often the only) way to administer a linux server is via SSH. Even in your case where you have a direct console to all your VM screens you may find it helpful to connect to your virtual machines using SSH (if nothing else - you can resize the terminal window).