loopback address

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In Internet Protocol (IP), a type of unicast address used when a host needs to send a packet back to itself for test purposes. An address that sends outgoing signals back to the same computer for testing. In a TCP/IP network, the loopback IP address is 127.0.0.1, and pinging it will always return a reply. The loopback address allows a network administrator to treat the local machine as if it were a remote machine.
Loopback address is a special IP number (127.0.0.1) that is designated for the software loopback interface of a machine. The loopback interface has no hardware associated with it, and it is not physically connected to a network. The loopback interface allows IT professionals to test IP software without worrying about broken or corrupted drivers or hardware.
127.0.0.1 is is a special purpose IP address conventionally used as a computer's loopback address. Messages sent to loopback IP addresses like 127.0.0.1 do not reach outside to the local area network (LAN) but instead are automatically re-routed by the computer's own network adapter back to the receiving end of the TCP/IP stack.
The term loopback (sometimes spelled loop-back) is generally used to describe methods or procedures of routing electronic signals, digital data streams, or other flows of items, from their originating facility quickly back to the same source entity without intentional processing or modification. This is primarily intended as a means of testing the transmission or transportation infrastructure.
Examples of applications include the following:
• A method of performing transmission tests of access lines from the serving switching center, which usually does not require the assistance of personnel at the served terminal.
• A method of testing between stations (not necessarily adjacent) where in two lines are used, with the test being done at one station and the two lines interconnected at the distant station. Commonly called loop around when the interconnecting circuit is accessed by dialing.
• A patch cable, applied manually or automatically, remotely or locally, that facilitates a loop-back test.
• A communication channel with only one endpoint. Any message transmitted through such a channel is immediately received by the same channel
a special IP number (127.0.0.1) that is designated for the software loopback interface of a machine. 127.0.0.0 through 127.255.255.255 is also reserved for loopback and is used for internal testing on local machines.