217 lines
7.2 KiB
Groff
217 lines
7.2 KiB
Groff
.\" $NetBSD: gre.4,v 1.12 2000/07/05 18:14:40 thorpej Exp $
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.\"
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.\" Copyright 1998 (c) The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Heiko W.Rupp <hwr@pilhuhn.de>
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of the The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd 13 September 1998
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.Dt GRE 4
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.Os
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.Sh NAME
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.Nm gre
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.Nd encapsulating network device
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.Sh SYNOPSIS
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.Cd pseudo-device gre
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.Sh DESCRIPTION
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The
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.Nm gre
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network interface is a pseudo device that allows to encapsulate datagrams
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into IP. These encapsulated datagrams are routed to a destination host,
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where they are decapsulated and further routed to their final destination.
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The so called ``tunnel'' appears to the inner datagrams like one hop.
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.Pp
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.Nm
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interfaces are dynamically created and destroyed with the
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.Xr ifconfig 8
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.Cm create
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and
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.Cm destroy
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subcommands.
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.Pp
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This driver currently supports the following modes of operation:
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.Bl -tag -width abc
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.It GRE encapsulation (IP protocol number 47).
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Encapsulated datagrams are
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prepended by a outer datagram and a GRE header. The GRE header specifies
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the type of the encapsulated datagram and thus allows for tunneling other
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protocols than IP like e.g. AppleTalk (not yet supported). GRE mode is
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also the default tunnel mode on Cisco routers. This is also the default
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mode of operation of the
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.Sy gre Ns Ar X
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interfaces.
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.It MOBILE encapsulation (IP protocol number 55).
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Datagrams are
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encapsulated into IP, but with a shorter encapsulation. The original
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IP header is modified and the modifications are inserted between the
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so modified header and the original payload. Like IPIP only for IP in IP
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encapsulation.
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.El
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.Pp
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The network interfaces are named
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.Sy gre Ns Ar 0 ,
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.Sy gre Ns Ar 1
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and so on, as many as have given on the
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.Sy pseudo-device
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line in the system config file. Each interface supports a number of
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.Xr ioctl 2 Ns s,
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such as:
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.Bl -tag -width aaa
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.It GRESADDRS:
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Set the IP address of the local tunnel end.
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.It GRESADDRD:
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Set the IP address of the remote tunnel end.
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.It GREGADDRS:
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Query the IP address that is set for the local tunnel end.
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.It GREGADDRD:
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Query the IP address that is set for the remote tunnel end.
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.It GRESPROTO:
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Set the operation mode to the specified IP protocol value. The
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protocol is passed to the interface in (struct ifreq)->ifr_flags.
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The operation mode can also
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be given as
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.Bl -tag -width bbb
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.It link0
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IPPROTO_GRE
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.It link2
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IPPROTO_MOBILE
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.El
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to
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.Xr ifconfig .
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As the linkN flags are not mutually exclusive, modes must be set by applying
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positive and negative flags as e.g.
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.Xr ifconfig
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link0 -link1 -link2
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.It GREGPROTO:
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Query operation mode.
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.El
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.Pp
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Note that the IP addresses of the tunnel endpoints may be the same as the
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ones defined with
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.Xr ifconfig
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for the interface (as if IP is encapsulated), but need not be, as e.g. when
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encapsulating AppleTalk.
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.Pp
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.Sh EXAMPLE
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Configuration example:
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.Bd -literal
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Host X-- Host A ----------------tunnel---------- cisco D------Host E
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\\ |
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\\ /
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+------Host B----------Host C----------+
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.Ed
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On host A (NetBSD):
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# route add default B
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# ifconfig greN A D netmask 0xffffffff linkX up
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# greconfig -i greN -s A -d D
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# route add E D
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On Host D (Cisco):
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Interface TunnelX
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ip unnumbered D ! e.g. address from Ethernet interface
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tunnel source D ! e.g. address from Ethernet interface
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tunnel destination A
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ip route C <some interface and mask>
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ip route A mask C
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ip route X mask tunnelX
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OR
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On Host D (NetBSD):
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# route add default C
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# ifconfig greN D A
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.Pp
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If all goes well, you should see packets flowing ;-)
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.Pp
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If you want to reach Host A over the tunnel (from the Cisco D), then
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you have to have an alias on Host A for e.g. the Ethernet interface like:
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ifconfig <etherif> alias Y
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and on the cisco
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ip route Y mask tunnelX
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.Sh NOTE
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For correct operation, the
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.Nm
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device needs a route to the destination, that is less specific than the
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one over the tunnel.
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(Basically, there needs to be a route to the decapsulating host that
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does not run over the tunnel, as this would be a loop ..)
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.Pp
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In order to
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.Xr ifconfig
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to actually mark the interface as up, the keyword ``up'' must be given
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last on its command line.
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.Pp
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The kernel must be set to forward datagrams by either option
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``GATEWAY'' in the kernel config file or by issuing the appropriate
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option to
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.Xr sysctl .
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.Sh SEE ALSO
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.Xr netintro 4 ,
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.Xr ip 4 ,
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.Xr atalk 4 ,
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.Xr inet 4 ,
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.Xr ifconfig 8 ,
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.Xr greconfig 8 ,
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.Xr options 4 ,
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.Xr protocols 5 ,
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.Xr sysctl 8
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.Pp
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A description of GRE encapsulation can be found in RFC 1701, RFC 1702.
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.Pp
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A description of MOBILE encapsulation can be found in RFC 2004.
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.Sh BUGS
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The compute_route() code in if_gre.c toggles the last bit of the
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IP-address to provoke the search for a less specific route than the
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one directly over the tunnel to prevent loops. This is possibly not
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the best solution.
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.Pp
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To avoid the address munging described above, turn on the link1 flag
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on the ifconfig command line. This implies that the GRE packet
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destination (set via greconfig -d) and the ifconfig remote host are
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not the same IP addresses, and that the GRE destination does not route
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over the greX interface itself.
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.Pp
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GRE RFC not yet fully implemented (no GRE options), no other protocols
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yet than IP over IP.
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.Pp
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Traceroute does not work yet over the tunnel :(
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.Pp
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BPF does probably not yet work (it might, but last time I looked,
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it bombed, so I #if 0'd it out).
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.Pp
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.Sh AUTHOR
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Heiko W.Rupp <hwr@pilhuhn.de>
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