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Manpage for gre network interface.

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hwr 1998-09-13 20:39:35 +00:00
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share/man/man4/Makefile
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# $NetBSD: Makefile,v 1.73 1998/08/18 08:16:56 augustss Exp $
# $NetBSD: Makefile,v 1.74 1998/09/13 20:39:35 hwr Exp $
# @(#)Makefile 8.1 (Berkeley) 6/18/93
MAN= ahb.4 ahc.4 aria.4 atalk.4 audio.4 bha.4 bpf.4 ccd.4 cd.4 ch.4 clnp.4 \
cltp.4 ddb.4 drum.4 eap.4 eisa.4 en.4 ep.4 esh.4 esis.4 fd.4 fpa.4 \
cltp.4 ddb.4 drum.4 eap.4 eisa.4 en.4 ep.4 esh.4 esis.4 fd.4 fpa.4 gre.4 \
icmp.4 idp.4 ifmedia.4 inet.4 ip.4 iso.4 isp.4 lc.4 lkm.4 lo.4 md.4 \
midi.4 ncr.4 ne.4 netintro.4 ns.4 nsip.4 null.4 opl.4 options.4 ppp.4 \
pty.4 puc.4 rnd.4 route.4 scsi.4 sd.4 sl.4 sm.4 spp.4 ss.4 st.4 \

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.\" $NetBSD: gre.4,v 1.1 1998/09/13 20:39:36 hwr Exp $
.\"
.\" Copyright 1998 (c) The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Heiko W.Rupp <hwr@pilhuhn.de>
.\"
.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the NetBSD
.\" Foundation, Inc. and its contributors.
.\" 4. Neither the name of the The NetBSD Foundation 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
.\"
.Dd 13 September 1998
.Dt GRE 4
.Os NetBSD
.Sh NAME
.Nm gre
.Nd encapsulating network device
.Sh SYNOPSIS
.Cd pseudo-device gre Op Ar count
.Sh DESCRIPTION
The
.Nm tun
network interface is a pseudo device that allows to encapsulate datagrams
into IP. These encapsulated datagrams are routed to a destination host,
where they are decapsulated and further routed to their final destination.
The so called ``tunnel'' appears to the inner datagrams like one hop.
.Pp
This driver currently supports two modes of operation:
.Bl -tag -width abc
.It IPIP encapsulation (IP protocol number 4). Here packets are
directly encapsulated into IP packets
and sent to the tunnel destionation. This mode allows only for IP in IP
tunneling.
.It GRE encapsulation (IP protocol number 47). Encapsulated datagrams are
prepended by a outer datagram and a GRE header. The GRE header specifies
the type of the encapsulated datagram and thus allows for tunneling other
protocols than IP like e.g. AppleTalk (not yet supported). GRE mode is
also the default tunnel mode on Cisco routers.
.El
.Pp
GRE mode is the default mode of operation.
.Pp
The network interfaces are named
.Sy gre Ns Ar 0 ,
.Sy gre Ns Ar 1
and so on, as many as have given on the
.Sy pseudo-device
line in the system config file. Each interface supports a number of
.Xr ioctl 2 Ns s,
such as:
.Bl -tag -width aaa
.It GRESADDRS:
Set the IP address of the local tunnel end.
.It GRESADDRD:
Set the IP address of the remote tunnel end.
.It GREGADDRS:
Query the the IP address that is set for the local tunnel end.
.It GREGADDRD:
Query the the IP address that is set for the remote tunnel end.
.It GRESPROTO:
Set the operation mode. The operation mode can (in a limited manner) also
be given as ``-link0'' (gre) or ``link0'' (ipip) flag on the command line
of
.Xr ifconfig .
.It GREGPROTO:
Query operation mode.
.El
.Pp
Note that the IP adresses of the tunnel endpoints may be the same as the
ones defined with
.Xr ifconfig
for the interface (as if IP is encapsulated), but need not be, as e.g. when
encapsulating AppleTalk.
.Pp
.Sh EXAMPLE
Configuration example:
Host X-- Host A ----------------tunnel---------- cisco D------Host E
\\ |
\\ /
+------Host B----------Host C----------+
On host A (NetBSD):
# route add default B
# ifconfig greN A D
# greconfig -i greN -s A -d D
# route add E D
On Host D (Cisco):
Interface TunnelX
ip unnumbered D ! e.g. address from ethernet interface
tunnel source D ! e.g. address from ethernet interface
tunnel destination A
ip route C <some interface and mask>
ip route A mask C
ip route X mask tunnelX
OR
On Host D (NetBSD):
# route add default C
# ifconfig greN D A
.Pp
If all goes well, you should see packets flowing ;-)
.Pp
If you want to reach Host A over the tunnel (from the Cisco D), then
you have to have an alias on Host A for e.g. the ethernet interface like:
ifconfig <etherif> alias Y
and on the cisco
ip route Y mask tunnelX
.Sh NOTE
For correct operation, the
.Nm
device needs a route to the destination, that is less specific than the
one over the tunnel.
(Basically, there needs to be a route to the decapsulating host that
does not run over the tunnel, as this would be a loop ..)
.Sh SEE ALSO
.Xr netintro 4 ,
.Xr ip 4 ,
.Xr atalk 4 ,
.Xr inet 4 ,
.Xr ifconfig 8 ,
.Xr greconfig 8 ,
.Xr protocols 5
.Pp
A description of GRE encapsulation can be found in RFC 1701, RFC 1702.
.Pp
A description of IPIP encapsulation can be found in RFC 2003.
.Sh BUGS
The compute_route() code in if_gre.c toggles the last bit of the
IP-address to provoke the search for a less specific route than the
one directly over the tunnel to prevent loops. This is possibly not
the best solution.
.Pp
GRE RFC not yet fully implemented (no GRE options), no other protocols
yet than IP over IP.
RFC 2003 also not yet fully supportet wrt. options etc.
.Pp
Code quality is surely not best and possibly not near anything like KNF
.Pp
Traceroute does not work yet over the tunnel :(
.Pp
BPF does probably not yet work (it might, but last time I looked,
it bombed, so I #if 0'd it out).
.Pp
.Sh AUTHOR
Heiko W.Rupp <hwr@pilhuhn.de>