121294362f
- Remove superfluous paragraph macros. - Remove/fix empty or incorrect macros. - Sort sections into conventional order. - Terminate quoted strings properly. - Remove EOL whitespace.
158 lines
5.0 KiB
Groff
158 lines
5.0 KiB
Groff
.\" $NetBSD: gre.4,v 1.28 2002/06/10 02:49:35 itojun 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.
|
|
.\"
|
|
.\" 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd November 7, 2014
|
|
.Dt GRE 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm gre
|
|
.Nd encapsulating network device
|
|
.Sh SYNOPSIS
|
|
To compile the
|
|
driver into the kernel, place the following line in the kernel
|
|
configuration file:
|
|
.Bd -ragged -offset indent
|
|
.Cd "device gre"
|
|
.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_gre_load="YES"
|
|
.Ed
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
network interface pseudo device encapsulates datagrams
|
|
into IP.
|
|
These encapsulated datagrams are routed to a destination host,
|
|
where they are decapsulated and further routed to their final destination.
|
|
The
|
|
.Dq tunnel
|
|
appears to the inner datagrams as one hop.
|
|
.Pp
|
|
.Nm
|
|
interfaces are dynamically created and destroyed with the
|
|
.Xr ifconfig 8
|
|
.Cm create
|
|
and
|
|
.Cm destroy
|
|
subcommands.
|
|
.Pp
|
|
This driver corresponds to RFC 2784.
|
|
Encapsulated datagrams are prepended an 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.
|
|
GRE mode is also the default tunnel mode on Cisco routers.
|
|
.Nm
|
|
also supports Cisco WCCP protocol, both version 1 and version 2.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
interfaces support a number of additional parameters to the
|
|
.Xr ifconfig 8 :
|
|
.Bl -tag -width "enable_csum"
|
|
.It Ar grekey
|
|
Set the GRE key used for outgoing packets.
|
|
A value of 0 disables the key option.
|
|
.It Ar enable_csum
|
|
Enables checksum calculation for outgoing packets.
|
|
.It Ar enable_seq
|
|
Enables use of sequence number field in the GRE header for outgoing packets.
|
|
.El
|
|
.Sh EXAMPLES
|
|
.Bd -literal
|
|
192.168.1.* --- Router A -------tunnel-------- Router B --- 192.168.2.*
|
|
\\ /
|
|
\\ /
|
|
+------ the Internet ------+
|
|
.Ed
|
|
.Pp
|
|
Assuming router A has the (external) IP address A and the internal address
|
|
192.168.1.1, while router B has external address B and internal address
|
|
192.168.2.1, the following commands will configure the tunnel:
|
|
.Pp
|
|
On router A:
|
|
.Bd -literal -offset indent
|
|
ifconfig greN create
|
|
ifconfig greN inet 192.168.1.1 192.168.2.1
|
|
ifconfig greN inet tunnel A B
|
|
route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
|
|
.Ed
|
|
.Pp
|
|
On router B:
|
|
.Bd -literal -offset indent
|
|
ifconfig greN create
|
|
ifconfig greN inet 192.168.2.1 192.168.1.1
|
|
ifconfig greN inet tunnel B A
|
|
route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
|
|
.Ed
|
|
.Sh NOTES
|
|
The MTU of
|
|
.Nm
|
|
interfaces is set to 1476 by default, to match the value used by Cisco routers.
|
|
This may not be an optimal value, depending on the link between the two tunnel
|
|
endpoints.
|
|
It can be adjusted via
|
|
.Xr ifconfig 8 .
|
|
.Pp
|
|
For correct operation, the
|
|
.Nm
|
|
device needs a route to the decapsulating host that does not run over the tunnel,
|
|
as this would be a loop.
|
|
.Pp
|
|
The kernel must be set to forward datagrams by setting the
|
|
.Va net.inet.ip.forwarding
|
|
.Xr sysctl 8
|
|
variable to non-zero.
|
|
.Sh SEE ALSO
|
|
.Xr gif 4 ,
|
|
.Xr inet 4 ,
|
|
.Xr ip 4 ,
|
|
.Xr me 4 ,
|
|
.Xr netintro 4 ,
|
|
.Xr protocols 5 ,
|
|
.Xr ifconfig 8 ,
|
|
.Xr sysctl 8
|
|
.Pp
|
|
A description of GRE encapsulation can be found in RFC 2784 and RFC 2890.
|
|
.Sh AUTHORS
|
|
.An Andrey V. Elsukov Aq Mt ae@FreeBSD.org
|
|
.An Heiko W.Rupp Aq Mt hwr@pilhuhn.de
|
|
.Sh BUGS
|
|
The current implementation uses the key only for outgoing packets.
|
|
Incoming packets with a different key or without a key will be treated as if they
|
|
would belong to this interface.
|
|
.Pp
|
|
The sequence number field also used only for outgoing packets.
|