4.4BSD/usr/share/man/cat4/lo.0

LO(4)                       BSD Programmer's Manual                      LO(4)

NNAAMMEE
     lloo - software loopback network interface

SSYYNNOOPPSSIISS
     ppsseeuuddoo--ddeevviiccee
     lloooopp

DDEESSCCRRIIPPTTIIOONN
     The lloooopp interface is a software loopback mechanism which may be used for
     performance analysis, software testing, and/or local communication.  As
     with other network interfaces, the loopback interface must have network
     addresses assigned for each address family with which it is to be used.
     These addresses may be set or changed with the SIOCSIFADDR ioctl(2).  The
     loopback interface should be the last interface configured, as protocols
     may use the order of configuration as an indication of priority.  The
     loopback should _n_e_v_e_r be configured first unless no hardware interfaces
     exist.

DDIIAAGGNNOOSSTTIICCSS
     lloo%%dd:: ccaann''tt hhaannddllee aaff%%dd..  The interface was handed a message with ad-
     dresses formatted in an unsuitable address family; the packet was
     dropped.

SSEEEE AALLSSOO
     intro(4),  inet(4),  ns(4)

HHIISSTTOORRYY
     The lloo device appeared in 4.2BSD.

BBUUGGSS
     Previous versions of the system enabled the loopback interface automati-
     cally, using a nonstandard Internet address (127.1).  Use of that address
     is now discouraged; a reserved host address for the local network should
     be used instead.

4.2 Berkeley Distribution        June 5, 1993                                1