In TCP/IP networking, the special IP address 127.0.0.1. The loopback address is used to route outgoing IP packets to the TCP/IP protocol stack bound to the network interface card (NIC) and back to the source application without actually placing the packets on the network.
To test whether TCP/IP is installed correctly on a machine running Microsoft Windows, type ping 127.0.0.1 at the command prompt. You can also type the command ping localhost to achieve the same result, or you can even ping any other legal IP address with the form 127.x.y.z. If this test produces an error, your NIC is incorrectly configured or your TCP/IP stack is corrupt. Try removing and reinstalling TCP/IP on your machine. If that fails, try reinstalling the driver for your NIC or replacing the NIC.