The loopback IP range starts at and reaches to The IP stack automatically short-circuits any packets that are sent to a loopback IP, and never puts them onto a real network. Instead, the packets get routed to the localhost, the network interface that the packets were sent from.

The loopback IP exists independently of any of the interfaces contactable IP addresses, and is always available, even if the interface is down (this is due to the fact that the packets sent to a loopback IP are intercepted in the software TCP/IP stack, and never makes it to the hardware interface).