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.\" $OpenBSD: gif.4,v 1.29 2016/06/07 20:25:48 sthen Exp $
.\" $KAME: gif.4,v 1.15 2000/04/19 09:39:42 itojun Exp $
.\"
.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" notice, this list of conditions and the following disclaimer.
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.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the project 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 PROJECT 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 PROJECT OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" 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.
.\"
.Dd $Mdocdate: June 7 2016 $
.Dt GIF 4
.Os
.Sh NAME
.Nm gif
.Nd generic tunnel interface
.Sh SYNOPSIS
.Cd "pseudo-device gif"
.Sh DESCRIPTION
The
.Nm
interface is a generic tunnelling pseudo-device for IPv4 and IPv6.
It can tunnel IPv[46] over IPv[46] with behavior mainly based on
RFC 4213 IPv6-over-IPv4, for a total of four possible combinations.
.Pp
A
.Nm
interface can be created at runtime using the
.Ic ifconfig gif Ns Ar N Ic create
command or by setting up a
.Xr hostname.if 5
configuration file for
.Xr netstart 8 .
.Pp
The
.Nm
interface must be configured with the
addresses used for the outer header.
This can be done by using
.Xr ifconfig 8 Ns 's
.Ic tunnel
command (which uses the
.Dv SIOCSIFPHYADDR
ioctl).
.Pp
The addresses of the inner header must be configured by using
.Xr ifconfig 8
in the normal way.
The routing table can be used to direct packets toward the
.Nm
interface.
.Sh SEE ALSO
.Xr sysctl 3 ,
.Xr etherip 4 ,
.Xr inet 4 ,
.Xr inet6 4 ,
.Xr ipsec 4 ,
.Xr hostname.if 5 ,
.Xr ifconfig 8 ,
.Xr netstart 8
.Sh STANDARDS
.Rs
.%A E. Nordmark
.%A R. Gilligan
.%D October 2005
.%R RFC 4213
.%T Basic Transition Mechanisms for IPv6 Hosts and Routers
.Re
.Sh HISTORY
The
.Nm
device first appeared in WIDE hydrangea IPv6 kit.
.Pp
Previously,
.Nm
supported RFC 3378 EtherIP tunnels over
.Xr bridge 4
interfaces.
This is now handled by
.Xr etherip 4 .
.Sh BUGS
There are many tunnelling protocol specifications,
defined differently from each other.
.Nm
may not interoperate with peers which are based on different specifications,
and are picky about outer header fields.
For example, you cannot usually use
.Nm
to talk with IPsec devices that use IPsec tunnel mode.
.Pp
The current code does not check if the ingress address
.Pq outer source address
configured to
.Nm
makes sense.
Make sure to configure an address which belongs to your node.
Otherwise, your node will not be able to receive packets from the peer,
and your node will generate packets with a spoofed source address.
.Pp
If the outer protocol is IPv6, path MTU discovery for encapsulated packet
may affect communication over the interface.
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