Nowadays, it's not uncommon for a computer to have multiple network interfaces. For example, if you're using a laptop (other than an Ultrabook), it's likely that you have a wired, as well as a wireless, network interface. Each network interface will have its own IP address and they operate independently of each other. In fact, you can even route traffic between multiple interfaces, though this is typically disabled by default in most Linux distributions. Just like each interface has its own IP address, each will also be identified by the system by its own device name. Before we discuss this further, go ahead and take a look at the device names on your system. Open up a terminal and type the following command:

ip addr show

Your output will look like this:

The output of the ip command, showing network interfaces and address assignments

In this example, we see three network interfaces listed. The first, lo, is the local loopback adapter. The second listing, eth0, is the...