I figured it was worth mentioning that this is not a *nix concept only, but rather specified on a more global scale in the context of the IPv4 specification (see http://ietf.org/rfc/rfc3330).
127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host. This is ordinarily implemented using only 127.0.0.1/32 for loopback, but no addresses within this block should ever appear on any network anywhere [RFC1700, page 5]. So the behavior should be dependable and predictble in just about any situtation. -Tom On 4/22/05, Rick Carlson <[EMAIL PROTECTED]> wrote: > John H. Robinson, IV wrote: > > [EMAIL PROTECTED] wrote: > > > >>I'm trying to understand what loopback interface is used for > >>and /how/ it is works. > > > > > > I'm not exactly sure how it works. But it looks like a network > > interface, except it never leaves the box. This means that a Linux(UNIX) > > box with no network interfaces (no ethernet, no phone line, no ISDN, no > > toekn ring,no nothing) can still do all those neat networking protocol > > stuff. > > > > > >>Anyone got any examples of how an app uses loopback interface > >>effectively?? > > > > > > Start a webserver. > > http://127.0.0.1/ > > > > Start an ftp server, > > ncftp 127.0.0.1 > > > > Start an X server > > DISPLAY=127.0.0.1:0; export DISPLAY > > (or setenv DISPLAY 127.0.0.1:0 for you *csh'rs) > > > > > >>I vaguely know it acts like a remote node without > >>actually being one. I'd like the details. > > > > > > Not sure what details you need. > > > > -john > > Quoted from: > > http://www.geekcomix.com/cgi-bin/classnotes/wiki.pl?UNIX01/The_Loopback_Interface > > Despite it coming from geekcomix the info is for real. It appeared in a > series of tutorials called Unix01 written by Sam Hart who was/is > affiliated with the Physics Department at the University of Arizona. > > /begin quote > 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 tunneling 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 with 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 traditionally called 'lo'. > > /end quote > > Rick > [EMAIL PROTECTED] > -- > [email protected] > http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list > -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
