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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, soft-ware software
     ware 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 prior-ity. priority.
     ity.  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
     inet(4), intro(4), ns(4)

HISTORY
     The lo device appeared in 4.2BSD.

BUGS
     Previous versions of the system enabled the loopback interface automatically, 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