Classnotes | UNIX01 | RecentChanges | Preferences We've just looked at a couple of common networking interfaces, /dev/eth# and /dev/ppp#, however there is one networking interface that is the most important one of all.
The Loopback Interface
The loopback interface is a special kind of interface that allows applications and servers on your Linux machine to make connections back to the Linux machine. There are a variety of reasons why you would want to do something like this; you could be testing something out and not wish to disturb anyone on your local network, you could be running a server locally which will not have an external interface, or you could have specific encrypted tunnelling you wish to do with an application that cannot natively support it. For the vast majority of Linux networking applications to work, you must have a loopback device.
Traditionally, the loopback interface is defined the IP address of 127.0.0.1, thus, when you sit down at any Linux (or even UNIX) machine and connect to 127.0.0.1 you are connecting to the local machine. The loopback interface is also tradionally called 'lo'.
