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LO(4)                    BSD Kernel Interfaces Manual                    LO(4)

NAME
     lo -- software loopback network interface

SYNOPSIS
     pseudo-device
     loop

DESCRIPTION
     The loop 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 never be configured first unless no hardware interfaces
     exist.

DIAGNOSTICS
     lo%d: can't handle af%d.  The interface was handed a message with
     addresses formatted in an unsuitable address family; the packet was
     dropped.

SEE ALSO
     intro(4), inet(4), ns(4)

HISTORY
     The lo device appeared in 4.2BSD.

BUGS
     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        4.2 Berkeley Distribution