NAME    [Toc]    [Back]

     lo - software loopback network interface

SYNOPSIS    [Toc]    [Back]

     pseudo-device loop [count]

DESCRIPTION    [Toc]    [Back]

     The loop interface is a software  loopback  mechanism  which
may be used for
     performance  analysis, software testing, and/or local communication.

     A loop  interface  can  be  created  at  runtime  using  the
ifconfig loN create
     command or by setting up a hostname.if(5) configuration file
for
     netstart(8).  The lo0 interface will always exist and cannot
be destroyed
     using ifconfig(8).

     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 being
  in super-net which is specified by the address and netmask.  Obviously
 you should not set the link1 flag on interface  lo0,  but
instead use
     another interface like lo1.

EXAMPLES    [Toc]    [Back]

     # ifconfig lo1 create
     # ifconfig lo1 inet 192.168.1.1 netmask 255.255.255.0 link1

     is equivalent to:

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

DIAGNOSTICS    [Toc]    [Back]

     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    [Toc]    [Back]

     inet(4),  inet6(4),  netintro(4), ns(4), hostname.if(5), ifconfig(8),
     netstart(8)

HISTORY    [Toc]    [Back]

     The lo device appeared in 4.2BSD.

     The wildcard functionality first appeared in OpenBSD 2.3.

BUGS    [Toc]    [Back]

     Previous versions of the system enabled the loopback  interface automatically,
  using  a non-standard 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      3.6                           June      5,      1993