NetBSD/share/man/man4/ipip.4

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.\" $NetBSD: ipip.4,v 1.6 2001/04/11 18:31:53 wiz Exp $
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Heiko W.Rupp <hwr@pilhuhn.de>
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.Dd March 28, 1999
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.Dt IPIP 4
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.Os
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.Sh NAME
.Nm ipip
.Nd encapsulating network device
.Sh SYNOPSIS
.Cd pseudo-device ipip Op Ar count
.Sh DESCRIPTION
The
.Nm ipip
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.
Encapsulation is according to RFC 2003. The outer datagram header is of
IP type 4 (IPIP).
.Pp
The network interfaces are named
.Sy ipip Ns Ar 0 ,
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.Sy ipip Ns Ar 1
and so on, as many as have given on the
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.Sy pseudo-device
line in the system config file.
.Pp
Note that the IP addresses of the tunnel endpoints may be the same as the
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ones defined with
.Ic ifconfig
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for the interface (as if IP is encapsulated), but need not be.
.Pp
.Sh EXAMPLE
Configuration example:
.Bd -literal
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Host X-- Host A ----------------tunnel---------- cisco D------Host E
\\ |
\\ /
+------Host B----------Host C----------+
.Ed
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On host A (NetBSD):
# route add default B
# ifconfig ipipN A D netmask 0xffffffff up
# route add E D
On Host D (Cisco):
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Interface TunnelX
ip unnumbered D ! e.g. address from Ethernet interface
tunnel source D ! e.g. address from Ethernet interface
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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
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# ifconfig ipipN D A
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.Pp
If all goes well, you should see packets flowing ;-)
.Pp
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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:
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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 ..)
.Pp
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In order to get
.Ic ifconfig
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to actually mark the interface as up, the keyword ``up'' must be given
last on its command line.
.Pp
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 8 .
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.Sh SEE ALSO
.Xr atalk 4 ,
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.Xr gre 4 ,
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.Xr inet 4 ,
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.Xr ip 4 ,
.Xr netintro 4 ,
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.Xr options 4 ,
.Xr protocols 5 ,
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.Xr ifconfig 8 ,
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.Xr sysctl 8
.Pp
A description of IPIP encapsulation can be found in RFC 2003.
.Sh BUGS
The ipip_compute_route() code in ip_ipip.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
Traceroute does not work yet over the tunnel :(