You can find out what IP addresses have been assigned to your computer by running ip addr or ipconfig all on Windows systems, or on a Terminal.

If we run one of these commands, we will see that the IP addresses are assigned to our device's network interfaces. On Linux, these will have names, such as eth0; on Windows, these will have phrases, such as Ethernet adapter Local Area Connection.

You will get the following output when you run the ip addr command on Linux:

You will get the following options when you run the ipconfig command on Windows:

You will get IP addresses for the interfaces in your local machine when you run the ip addr command:

Every device has a virtual interface called the loopback interface, which you can see in the preceding listing as interface 1. This interface doesn't actually connect to anything outside the device, and only the device itself can communicate with it. While this may sound a little redundant, it's actually very useful when it comes to local network application testing, and it can also be used as a means of inter-process communication. The loopback interface is often referred to as localhost, and it is almost always assigned the IP address 127.0.0.1.