LO(4) OpenBSD Programmer's Manual LO(4)NAMElo - 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.
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
# 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
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 ALSOinet(4), inet6(4), netintro(4), hostname.if(5), ifconfig(8), netstart(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
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 4.9 May 31, 2007 OpenBSD 4.9