.\" $NetBSD: gre.4,v 1.16 2001/09/19 01:03:44 wiz 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 .\" .\" 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 September 13, 1998 .Dt GRE 4 .Os .Sh NAME .Nm gre .Nd encapsulating network device .Sh SYNOPSIS .Cd pseudo-device gre .Sh DESCRIPTION The .Nm gre 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 .Nm interfaces are dynamically created and destroyed with the .Xr ifconfig 8 .Cm create and .Cm destroy subcommands. .Pp This driver currently supports the following modes of operation: .Bl -tag -width abc .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. This is also the default mode of operation of the .Sy gre Ns Ar X interfaces. .It MOBILE encapsulation (IP protocol number 55) . Datagrams are encapsulated into IP, but with a shorter encapsulation. The original IP header is modified and the modifications are inserted between the so modified header and the original payload. Like IPIP only for IP in IP encapsulation. .El .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 IP address that is set for the local tunnel end. .It GREGADDRD : Query the IP address that is set for the remote tunnel end. .It GRESPROTO : Set the operation mode to the specified IP protocol value. The protocol is passed to the interface in (struct ifreq)->ifr_flags. The operation mode can also be given as .Bl -tag -width bbb .It link0 IPPROTO_GRE .It link2 IPPROTO_MOBILE .El to .Ic ifconfig . As the linkN flags are not mutually exclusive, modes must be set by applying positive and negative flags as e.g. .Ic ifconfig link0 -link1 -link2 .It GREGPROTO : Query operation mode. .El .Pp Note that the IP addresses of the tunnel endpoints may be the same as the ones defined with .Ic ifconfig for the interface (as if IP is encapsulated), but need not be, as e.g. when encapsulating AppleTalk. .Sh EXAMPLES Configuration example: .Bd -literal Host X-- Host A ----------------tunnel---------- cisco D------Host E \\ | \\ / +------Host B----------Host C----------+ .Ed On host A .Ns ( Nx ) : .Bd -literal # route add default B # ifconfig greN A D netmask 0xffffffff linkX up # greconfig -i greN -s A -d D # route add E D .Ed On Host D (Cisco): .Bd -literal 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 ip route A mask C ip route X mask tunnelX .Ed OR On Host D .Ns ( Nx ) : .Bd -literal # route add default C # ifconfig greN D A .Ed .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: .Bd -literal ifconfig alias Y .Ed and on the cisco .Bd -literal ip route Y mask tunnelX .Ed .Sh NOTES 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 ..) .Pp In order to .Ic ifconfig to actually mark the interface as up, the keyword .Dq up must be given last on its command line. .Pp The kernel must be set to forward datagrams by either option .Dq GATEWAY in the kernel config file or by issuing the appropriate option to .Xr sysctl 8 . .Sh SEE ALSO .Xr atalk 4 , .Xr inet 4 , .Xr ip 4 , .Xr netintro 4 , .Xr options 4 , .Xr protocols 5 , .Xr greconfig 8 , .Xr ifconfig 8 , .Xr sysctl 8 .Pp A description of GRE encapsulation can be found in RFC 1701, RFC 1702. .Pp A description of MOBILE encapsulation can be found in RFC 2004. .Sh AUTHORS .An Heiko W.Rupp Aq hwr@pilhuhn.de .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 To avoid the address munging described above, turn on the link1 flag on the ifconfig command line. This implies that the GRE packet destination (set via greconfig -d) and the ifconfig remote host are not the same IP addresses, and that the GRE destination does not route over the greX interface itself. .Pp GRE RFC not yet fully implemented (no GRE options), no other protocols yet than IP over IP. .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).