The loopback device is sometimes explained as purely a diagnostic tool. This is important for troubleshooting (it can be compared to looking in a mirror). The loopback interface does not represent any actual hardware, but exists so applications running on your computer can always connect to servers on the same machine. When a network interface is disconnected-for example, when an Ethernet port is unplugged or Wi-Fi is turned off or not associated with an access point-no communication on that interface is possible, not even communication between your computer and itself. It is used mainly for diagnostics and troubleshooting, and to connect to servers running on the local machine.
The loopback device is a special, virtual network interface that your computer uses to communicate with itself.
