259 lines
7.1 KiB
Groff
259 lines
7.1 KiB
Groff
.\" $KAME: gif.4,v 1.28 2001/05/18 13:15:56 itojun Exp $
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.\"
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.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
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.\" All rights reserved.
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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. Neither the name of the project nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 10, 1999
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.Dt GIF 4
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.Os
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.Sh NAME
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.Nm gif
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.Nd generic tunnel interface
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.Sh SYNOPSIS
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.Cd "device gif"
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.Sh DESCRIPTION
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The
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.Nm
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interface is a generic tunnelling device for IPv4 and IPv6.
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It can tunnel IPv[46] traffic over IPv[46].
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Therefore, there can be four possible configurations.
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The behavior of
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.Nm
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is mainly based on RFC2893 IPv6-over-IPv4 configured tunnel.
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On
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.Nx ,
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.Nm
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can also tunnel ISO traffic over IPv[46] using EON encapsulation.
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Note that
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.Nm
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does not perform GRE encapsulation; use
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.Xr gre 4
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for GRE encapsulation.
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.Pp
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Each
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.Nm
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interface is created at runtime using interface cloning.
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This is
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most easily done with the
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.Dq Nm ifconfig Cm create
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command or using the
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.Va gifconfig_ Ns Aq Ar interface
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variable in
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.Xr rc.conf 5 .
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.Pp
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To use
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.Nm ,
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the administrator needs to configure the protocol and addresses used for the outer
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header.
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This can be done by using
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.Xr ifconfig 8
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.Cm tunnel ,
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or
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.Dv SIOCSIFPHYADDR
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ioctl.
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The administrator also needs to configure the protocol and addresses for the
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inner header, with
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.Xr ifconfig 8 .
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Note that IPv6 link-local addresses
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(those that start with
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.Li fe80:: )
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will be automatically configured whenever possible.
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You may need to remove IPv6 link-local addresses manually using
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.Xr ifconfig 8 ,
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if you want to disable the use of IPv6 as the inner header
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(for example, if you need a pure IPv4-over-IPv6 tunnel).
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Finally, you must modify the routing table to route the packets through the
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.Nm
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interface.
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.Pp
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The
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.Nm
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device can be configured to be ECN friendly.
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This can be configured by
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.Dv IFF_LINK1 .
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.Ss ECN friendly behavior
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The
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.Nm
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device can be configured to be ECN friendly, as described in
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.Dv draft-ietf-ipsec-ecn-02.txt .
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This is turned off by default, and can be turned on by the
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.Dv IFF_LINK1
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interface flag.
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.Pp
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Without
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.Dv IFF_LINK1 ,
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.Nm
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will show normal behavior, as described in RFC2893.
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This can be summarized as follows:
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.Bl -tag -width "Ingress" -offset indent
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.It Ingress
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Set outer TOS bit to
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.Dv 0 .
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.It Egress
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Drop outer TOS bit.
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.El
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.Pp
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With
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.Dv IFF_LINK1 ,
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.Nm
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will copy ECN bits
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.Dv ( 0x02
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and
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.Dv 0x01
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on IPv4 TOS byte or IPv6 traffic class byte)
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on egress and ingress, as follows:
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.Bl -tag -width "Ingress" -offset indent
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.It Ingress
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Copy TOS bits except for ECN CE
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(masked with
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.Dv 0xfe )
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from
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inner to outer.
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Set ECN CE bit to
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.Dv 0 .
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.It Egress
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Use inner TOS bits with some change.
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If outer ECN CE bit is
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.Dv 1 ,
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enable ECN CE bit on the inner.
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.El
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.Pp
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Note that the ECN friendly behavior violates RFC2893.
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This should be used in mutual agreement with the peer.
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.Ss Security
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A malicious party may try to circumvent security filters by using
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tunnelled packets.
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For better protection,
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.Nm
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performs both martian and ingress filtering against the outer source address
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on egress.
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Note that martian/ingress filters are in no way complete.
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You may want to secure your node by using packet filters.
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Ingress filtering can break tunnel operation in an asymmetrically
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routed network.
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It can be turned off by
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.Dv IFF_LINK2
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bit.
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.Ss Route caching
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Processing each packet requires two route lookups: first on the
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packet itself, and second on the tunnel destination.
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This second route can be cached, increasing tunnel performance.
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However, in a dynamically routed network, the tunnel will stick
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to the cached route, ignoring routing table updates.
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Route caching can be enabled with the
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.Dv IFF_LINK0
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flag.
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.\"
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.Ss Miscellaneous
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By default,
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.Nm
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tunnels may not be nested.
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This behavior may be modified at runtime by setting the
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.Xr sysctl 8
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variable
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.Va net.link.gif.max_nesting
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to the desired level of nesting.
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Additionally,
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.Nm
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tunnels are restricted to one per pair of end points.
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Parallel tunnels may be enabled by setting the
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.Xr sysctl 8
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variable
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.Va net.link.gif.parallel_tunnels
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to 1.
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.Sh SEE ALSO
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.Xr gre 4 ,
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.Xr inet 4 ,
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.Xr inet6 4 ,
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.Xr ifconfig 8
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.Rs
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.%A R. Gilligan
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.%A E. Nordmark
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.%B RFC2893
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.%T Transition Mechanisms for IPv6 Hosts and Routers
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.%D August 2000
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.%O ftp://ftp.isi.edu/in-notes/rfc2893.txt
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.Re
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.Rs
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.%A Sally Floyd
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.%A David L. Black
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.%A K. K. Ramakrishnan
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.%T "IPsec Interactions with ECN"
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.%D December 1999
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.%O draft-ietf-ipsec-ecn-02.txt
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.Re
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.\"
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.Sh HISTORY
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The
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.Nm
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device first appeared in the WIDE hydrangea IPv6 kit.
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.\"
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.Sh BUGS
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There are many tunnelling protocol specifications, all
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defined differently from each other.
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The
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.Nm
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device may not interoperate with peers which are based on different specifications,
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and are picky about outer header fields.
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For example, you cannot usually use
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.Nm
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to talk with IPsec devices that use IPsec tunnel mode.
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.Pp
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The current code does not check if the ingress address
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(outer source address)
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configured in the
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.Nm
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interface makes sense.
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Make sure to specify an address which belongs to your node.
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Otherwise, your node will not be able to receive packets from the peer,
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and it will generate packets with a spoofed source address.
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.Pp
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If the outer protocol is IPv4,
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.Nm
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does not try to perform path MTU discovery for the encapsulated packet
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(DF bit is set to 0).
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.Pp
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If the outer protocol is IPv6, path MTU discovery for encapsulated packets
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may affect communication over the interface.
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The first bigger-than-pmtu packet may be lost.
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To avoid the problem, you may want to set the interface MTU for
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.Nm
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to 1240 or smaller, when the outer header is IPv6 and the inner header is IPv4.
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.Pp
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The
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.Nm
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device does not translate ICMP messages for the outer header into the inner header.
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.Pp
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In the past,
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.Nm
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had a multi-destination behavior, configurable via
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.Dv IFF_LINK0
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flag.
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The behavior is obsolete and is no longer supported.
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