loopback(1) In telecommunications, loopback is a method used to perform transmission tests of the lines at the switching center.
(2) Loopback is a communication channel with only one endpoint. TCP/IP networks specify a loopback that allows client software to communicate with server software on the same computer. users can specify an IP address, usually 127.0.0.1, which will point back to the computer's TCP/IP network configuration. The range of addresses for loopback functionality is the range of 127.0.0.0 to 127.255.255.255. Similar to ping, loopback enables a user to test one's own network to ensure the IP stack is functioning properly.