360 lines
11 KiB
Groff
360 lines
11 KiB
Groff
.\" $NetBSD: gre.4,v 1.44 2014/03/18 18:20:39 riastradh Exp $
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.\"
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.\" Copyright (c) 1998 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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.\"
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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 January 4, 2009
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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 pseudo device encapsulates datagrams
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into IP.
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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
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.Dq tunnel
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appears to the inner datagrams as 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 an outer datagram and a GRE header.
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The GRE header specifies the type of the encapsulated datagram and
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thus allows for tunneling other protocols than IP like e.g. AppleTalk.
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GRE mode is also the default tunnel mode on Cisco routers.
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This is also the default mode of operation of the
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.Sy gre Ns Ar X
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interfaces.
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.It GRE in UDP encapsulation
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Encapsulated datagrams are prepended a GRE header, and then they
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are sent over a UDP socket.
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Userland may create the socket and
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.Dq delegate
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it to the kernel using the
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.Dv GRESSOCK
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.Xr ioctl 2 .
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If userland does not supply a socket, then the kernel will create
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one using the addresses and ports supplied by
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.Xr ioctl 2 Ns s
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.Dv SIOCSLIFPHYADDR ,
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.Dv GRESADDRD ,
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and/or
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.Dv GRESADDRS .
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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.
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The original IP header is modified and the modifications are inserted
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between the so modified header and the original payload.
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Like
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.Xr gif 4 ,
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only for IP in IP encapsulation.
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.El
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.Pp
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The
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.Sy gre Ns Ar X
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interfaces support 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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This is the source address set by or displayed by ifconfig for the
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.Sy gre Ns Ar X
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interface.
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.It GRESADDRD :
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Set the IP address of the remote tunnel end.
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This is the destination address set by or displayed by ifconfig for the
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.Sy gre Ns Ar X
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interface.
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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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This is the address the encapsulation header carries as local
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address (i.e. the real address of the tunnel start point.)
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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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This is the address the encapsulated packets are sent to (i.e. the
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real address of the remote tunnel endpoint.)
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.It GRESPROTO :
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Set the operation mode to the specified IP protocol value.
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The protocol is passed to the interface in (struct ifreq)-\*[Gt]ifr_flags.
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The operation mode can also be given as
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.Bl -tag -width link0xxx
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.It link0 link2
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IPPROTO_UDP
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.It link0 -link2
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IPPROTO_GRE
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.It -link0 -link2
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IPPROTO_MOBILE
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.El
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.Pp
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to
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.Xr ifconfig 8 .
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.It GREGPROTO :
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Query operation mode.
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.It GRESSOCK :
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Delegate a socket from userland to a tunnel interface in UDP
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encapsulation mode.
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The file descriptor for the socket is passed in
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(struct ifreq)-\*[Gt]ifr_value.
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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 8
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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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.Sh EXAMPLES
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.Ss Example 1: Basic GRE tunneling
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Configuration example:
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.Bd -literal
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Host X-- Router A --------------tunnel---------- Router D ----Host E
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\\ /
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+----- Router B ----- Router C --------+
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.Ed
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.Pp
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On Router A
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.Pq Nx :
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.Bd -literal
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# route add default B
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# ifconfig greN create
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# ifconfig greN A D netmask 0xffffffff linkX up
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# ifconfig greN tunnel A D
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# route add E D
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.Ed
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.Pp
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On Router D (Cisco):
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.Bd -literal
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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 \*[Lt]some interface and mask\*[Gt]
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ip route A mask C
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ip route X mask tunnelX
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.Ed
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.Pp
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or on Router D
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.Pq Nx :
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.Bd -literal
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# route add default C
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# ifconfig greN create
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# ifconfig greN D A
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# ifconfig tunnel greN D A
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.Ed
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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 Router A over the tunnel (from Router D (Cisco)), then
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you have to have an alias on Router A for e.g. the Ethernet interface like:
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.Bd -literal
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ifconfig \*[Lt]etherif\*[Gt] alias Y
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.Ed
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.Pp
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and on the Cisco
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.Bd -literal
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ip route Y mask tunnelX
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.Ed
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.Ss Example 2: Linking private subnets
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A similar setup can be used to create a link between two private networks
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(for example in the 192.168 subnet) over the Internet:
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.Bd -literal
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192.168.1.* --- Router A -------tunnel-------- Router B --- 192.168.2.*
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\\ /
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\\ /
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+----- the Internet ------+
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.Ed
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.Pp
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Assuming Router A has the (external) IP address A and the internal address
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192.168.1.1, while Router B has external address B and internal address
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192.168.2.1, the following commands will configure the tunnel:
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.Pp
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On Router A:
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.Bd -literal
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# ifconfig greN create
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# ifconfig greN 192.168.1.1 192.168.2.1
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# ifconfig greN tunnel A B
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# route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
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.Ed
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.Pp
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On Router B:
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.Bd -literal
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# ifconfig greN create
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# ifconfig greN 192.168.2.1 192.168.1.1
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# ifconfig greN tunnel B A
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# route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
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.Ed
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.Ss Example 3: Encapsulating GRE in UDP
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To setup the same tunnel as above, but using GRE in UDP encapsulation
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instead of GRE encapsulation, set flags
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.Ar link0
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and
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.Ar link2 ,
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and specify source and destination UDP ports.
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.Pp
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On Router A:
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.Bd -literal
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# ifconfig greN create
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# ifconfig greN link0 link2
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# ifconfig greN 192.168.1.1 192.168.2.1
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# ifconfig greN tunnel A,port-A B,port-B
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# route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
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.Ed
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.Pp
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On Router B:
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.Bd -literal
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# ifconfig greN create
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# ifconfig greN link0 link2
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# ifconfig greN 192.168.2.1 192.168.1.1
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# ifconfig greN tunnel B,port-B A,port-A
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# route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
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.Ed
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.Ss Example 4: Realizing IPv6 connectivity
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Along these lines, you can use GRE tunnels to interconnect two IPv6
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networks over an IPv4 infrastructure, or to hook up to the IPv6 internet
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via an IPv4 tunnel to a Cisco router.
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.Bd -literal
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2001:db8:1::/64 -- NetBSD A ---- Tunnel ---- Cisco B --- IPv6 Internet
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\\ /
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\\ /
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+------ the Internet ------+
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.Ed
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.Pp
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The example will use the following addressing:
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.Bl -hang
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.It Nx
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A has the IPv4 address A and the IPv6 address 2001:db8:1::1 (connects
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to internal network 2001:db8:1::/64).
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.It Cisco B
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has external IPv4 address B.
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.It All the IPv6 internet world
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is behind B, so A wants to route 0::0/0
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(the IPv6 default route) into the tunnel.
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.It The GRE tunnel
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will use a transit network: 2001:db8:ffff::1/64 on
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the
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.Nx
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side, and ::2/64 on the Cisco side.
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.El
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.Pp
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Then the following commands will configure the tunnel:
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.Pp
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On Router A
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.Pq Nx :
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.Bd -literal
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# ifconfig greN create
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# ifconfig greN inet6 2001:db8:ffff::1/64
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# ifconfig greN tunnel A B
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# route add -inet6 2001:db8:ffff::/64 2001:db8:ffff::2 -ifp greN
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# route add -inet6 0::0/0 2001:db8:ffff::2 -ifp greN
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.Ed
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.Pp
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On Router B (Cisco):
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.Bd -literal
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Interface TunnelX
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tunnel mode gre ip
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ipv6 address 2001:db8:ffff::2/64 ! transfer network
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tunnel source B ! e.g. address from LAN interface
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tunnel destination A ! where the tunnel is connected to
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ipv6 route 2001:db8::/64 TunnelX ! route this network through tunnel
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.Ed
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.Sh NOTES
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The MTU of
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.Sy gre Ns Ar X
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interfaces is set to 1476 by default to match the value used by Cisco routers.
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This may not be an optimal value, depending on the link between the two tunnel
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endpoints.
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It can be adjusted via
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.Xr ifconfig 8 .
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.Pp
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There needs to be a route to the decapsulating host that does not
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run over the tunnel, as this would be a loop.
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(This is not relevant for IPv6-over-IPv4 tunnels, of course.)
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.Pp
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In order to tell
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.Xr ifconfig 8
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to actually mark the interface as up, the keyword
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.Dq up
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must be given 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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.Em GATEWAY
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in the kernel config file or by issuing the appropriate option to
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.Xr sysctl 8 .
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.Sh SEE ALSO
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.Xr atalk 4 ,
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.Xr gif 4 ,
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.Xr inet 4 ,
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.Xr ip 4 ,
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.Xr netintro 4 ,
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.Xr options 4 ,
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.Xr protocols 5 ,
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.Xr ifconfig 8 ,
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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 and 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 AUTHORS
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.An Heiko W.Rupp Aq Mt hwr@pilhuhn.de
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.An David Young Aq Mt dyoung@NetBSD.org
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.Pq GRE in UDP encapsulation, bug fixes
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.Sh BUGS
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The GRE RFCs are not yet fully implemented (no GRE options).
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.Pp
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The MOBILE encapsulation appears to have been broken since
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it was first added to
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.Nx ,
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until August 2006.
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It is known to interoperate with another
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.Nm
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in MOBILE mode, however, it has not been tested for interoperability
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with any other implementation of RFC 2004.
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.Pp
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The
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.Nx
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base system does not
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.Pq yet
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contain a daemon for automatically establishing a UDP tunnel between
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a host behind a NAT router and a host on the Internet.
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