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	1	.\" $NetBSD: lo.4,v 1.3 1994/11/30 16:22:23 jtc Exp $
	2	.\"
	3	.\" Copyright (c) 1983, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)lo.4 8.1 (Berkeley) 6/5/93
	35	.\"
	36	.Dd June 5, 1993
	37	.Dt LO 4
	38	.Os BSD 4.2
	39	.Sh NAME
	40	.Nm lo
	41	.Nd software loopback network interface
	42	.Sh SYNOPSIS
	43	.Sy pseudo-device
	44	.Nm loop
	45	.Sh DESCRIPTION
	46	The
	47	.Nm loop
	48	interface is a software loopback mechanism which may be
	49	used for performance analysis, software testing, and/or local
	50	communication.
	51	As with other network interfaces, the loopback interface must have
	52	network addresses assigned for each address family with which it is to be used.
	53	These addresses
	54	may be set or changed with the
	55	.Dv SIOCSIFADDR
	56	.Xr ioctl 2 .
	57	The loopback interface should be the last interface configured,
	58	as protocols may use the order of configuration as an indication of priority.
	59	The loopback should
	60	.Em never
	61	be configured first unless no hardware
	62	interfaces exist.
	63	.Sh DIAGNOSTICS
	64	.Bl -diag
	65	.It lo%d: can't handle af%d.
	66	The interface was handed
	67	a message with addresses formatted in an unsuitable address
	68	family; the packet was dropped.
	69	.El
	70	.Sh SEE ALSO
	71	.Xr inet 4 ,
	72	.Xr intro 4 ,
	73	.Xr ns 4
	74	.Sh HISTORY
	75	The
	76	.Nm
	77	device appeared in
	78	.Bx 4.2 .
	79	.Sh BUGS
	80	Previous versions of the system enabled the loopback interface
	81	automatically, using a nonstandard Internet address (127.1).
	82	Use of that address is now discouraged; a reserved host address
	83	for the local network should be used instead.