mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-22 11:17:19 +00:00
91 lines
3.5 KiB
Groff
91 lines
3.5 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California.
|
|
.\" Copyright (c) 2009 Robert N. M. Watson
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)lo.4 8.1 (Berkeley) 6/5/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd January 25, 2012
|
|
.Dt LO 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm lo
|
|
.Nd software loopback network interface
|
|
.Sh SYNOPSIS
|
|
.Cd "device loop"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm 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 with the appropriate
|
|
.Xr ioctl 2
|
|
commands for corresponding address families.
|
|
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
|
|
.Em never
|
|
be configured first unless no hardware
|
|
interfaces exist.
|
|
.Pp
|
|
If the transmit checksum offload capability flag is enabled on a loopback
|
|
interface, checksums will not be generated by IP, UDP, or TCP for packets
|
|
sent on the interface.
|
|
.Pp
|
|
If the receive checksum offload capability flag is enabled on a loopback
|
|
interface, checksums will not be validated by IP, UDP, or TCP for packets
|
|
received on the interface.
|
|
.Pp
|
|
By default, both receive and transmit checksum flags will be enabled, in
|
|
order to avoid the overhead of checksumming for local communication where
|
|
data corruption is unlikely.
|
|
If transmit checksum generation is disabled, then validation should also be
|
|
disabled in order to avoid packets being dropped due to invalid checksums.
|
|
.Sh DIAGNOSTICS
|
|
.Bl -diag
|
|
.It 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.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr inet 4 ,
|
|
.Xr intro 4
|
|
.\" .Xr ns 4
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
device appeared in
|
|
.Bx 4.2 .
|
|
The current checksum generation and validation avoidance policy appeared in
|
|
.Fx 8.0 .
|