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NAME

     lo - software loopback network interface

SYNOPSIS

     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: cant 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)

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.