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

NAME
     lo - software loopback network interface

SYNOPSIS
     pseudo-device loop <number>

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.

     Configuring a loopback interface for inet(4) with the link1 flag set will
     make the interface answer to the whole set of addresses identified as be-
     ing in super-net which is specified by the address and netmask.  Obvious-
     ly you should not set the link1 flag on interface lo0, but instead use
     another interface like lo1.

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

EXAMPLES
     ifconfig lo1 inet 192.168.1.1 netmask 255.255.255.0 link1

     is equivalent to:

     awk 'BEGIN {for(i=1;i<255;i++) print "ifconfig lo1 inet 192.168.1."i"
     netmask 255.255.255.255 alias"}'|sh

SEE ALSO
     inet(4), inet6(4), netintro(4), ns(4), ifconfig(8)

HISTORY
     The lo device appeared in 4.2BSD.

     The wildcard functionality first appeared in OpenBSD 2.3.

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.

     Care should be taken when using NAT with interfaces that have the link1
     flag set, because it may believe the packets are coming from a loopback
     address.

OpenBSD 3.0                      June 5, 1993                                1
