.\"-
.\" Copyright (c) 2008 The FreeBSD Foundation
.\" All rights reserved.
.\"
.\" This software was developed by CK Software GmbH under sponsorship
.\" from the FreeBSD Foundation.
.\"
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.\" $FreeBSD: releng/10.1/share/man/man4/epair.4 235317 2012-05-12 03:25:46Z gjb $
.\"
.Dd July 26, 2009
.Dt EPAIR 4
.Os
.Sh NAME
.Nm epair
.Nd A pair of virtual back-to-back connected Ethernet interfaces
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device epair"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
if_epair_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
is a pair of Ethernet-like software interfaces,
which are connected back-to-back with a virtual cross-over cable.
.Pp
Each
.Nm
interface pair is created at runtime using interface cloning.
This is most easily done with the
.Xr ifconfig 8
.Cm create
command or using the
.Va cloned_interfaces
variable in
.Xr rc.conf 5 .
While for cloning you only give either
.Pa epair
or
.Pa epair<n>
the
.Nm
pair will be named like
.Pa epair<n>[ab] .
This means the names of the first
.Nm
interfaces will be
.Pa epair0a
and
.Pa epair0b .
.Pp
Like any other Ethernet interface, an
.Nm
needs to have a network address.
Each
.Nm
will be assigned a locally administered address by default,
that is only guaranteed to be unique within one network stack.
To change the default addresses one may use the SIOCSIFADDR ioctl(2) or
ifconfig(8) utility.
.Pp
The basic intend is to provide connectivity between two virtual
network stack instances.
When connected to a
.Xr if_bridge 4
one end of the interface pair can also be part of another (virtual) LAN.
As with any other Ethernet interface one can configure
.Xr vlan 4
support on top of it.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr altq 4 ,
.Xr bpf 4 ,
.Xr if_bridge 4 ,
.Xr vlan 4 ,
.Xr loader.conf 5 ,
.Xr rc.conf 5 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
interface first appeared in
.Fx 8.0 .
.Sh AUTHORS
The
.Nm
interface was written by
.An Bjoern A. Zeeb, CK Software GmbH,
under sponsorship from the FreeBSD Foundation.