91 lines
3.5 KiB
Groff
91 lines
3.5 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California.
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.\" Copyright (c) 2009 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)lo.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd January 25, 2012
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.Dt LO 4
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.Os
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.Sh NAME
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.Nm lo
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.Nd software loopback network interface
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.Sh SYNOPSIS
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.Cd "device loop"
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.Sh DESCRIPTION
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The
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.Nm loop
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interface is a software loopback mechanism which may be
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used for performance analysis, software testing, and/or local
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communication.
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As with other network interfaces, the loopback interface must have
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network addresses assigned for each address family with which it is to be used.
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These addresses
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may be set with the appropriate
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.Xr ioctl 2
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commands for corresponding address families.
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The loopback interface should be the last interface configured,
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as protocols may use the order of configuration as an indication of priority.
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The loopback should
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.Em never
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be configured first unless no hardware
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interfaces exist.
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.Pp
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If the transmit checksum offload capability flag is enabled on a loopback
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interface, checksums will not be generated by IP, UDP, or TCP for packets
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sent on the interface.
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.Pp
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If the receive checksum offload capability flag is enabled on a loopback
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interface, checksums will not be validated by IP, UDP, or TCP for packets
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received on the interface.
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.Pp
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By default, both receive and transmit checksum flags will be enabled, in
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order to avoid the overhead of checksumming for local communication where
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data corruption is unlikely.
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If transmit checksum generation is disabled, then validation should also be
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disabled in order to avoid packets being dropped due to invalid checksums.
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.Sh DIAGNOSTICS
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.Bl -diag
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.It lo%d: can't handle af%d.
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The interface was handed
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a message with addresses formatted in an unsuitable address
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family; the packet was dropped.
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.El
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.Sh SEE ALSO
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.Xr inet 4 ,
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.Xr intro 4
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.\" .Xr ns 4
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.Sh HISTORY
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The
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.Nm
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device appeared in
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.Bx 4.2 .
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The current checksum generation and validation avoidance policy appeared in
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.Fx 8.0 .
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