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267 lines
7.8 KiB
Groff
267 lines
7.8 KiB
Groff
.\" $FreeBSD$
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.\" $KAME: stf.4,v 1.35 2001/05/02 06:24:49 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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.Dd April 27, 2001
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.Dt STF 4
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.Os
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.Sh NAME
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.Nm stf
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.Nd
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.Tn 6to4
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tunnel interface
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.Sh SYNOPSIS
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.Cd "device stf"
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.Sh DESCRIPTION
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The
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.Nm
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interface supports
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.Dq 6to4
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IPv6 in IPv4 encapsulation.
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It can tunnel IPv6 traffic over IPv4, as specified in
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.Li RFC3056 .
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.Pp
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For ordinary nodes in 6to4 site, you do not need
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.Nm
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interface.
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The
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.Nm
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interface is necessary for site border router
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(called
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.Dq 6to4 router
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in the specification).
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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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.Xr ifconfig 8
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.Cm create
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command or using the
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.Va cloned_interfaces
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variable in
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.Xr rc.conf 5 .
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.Pp
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Due to the way 6to4 protocol is specified,
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.Nm
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interface requires certain configuration to work properly.
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Single
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(no more than 1)
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valid 6to4 address needs to be configured to the interface.
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.Dq A valid 6to4 address
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is an address which has the following properties.
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If any of the following properties are not satisfied,
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.Nm
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raises runtime error on packet transmission.
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Read the specification for more details.
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.Bl -bullet
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.It
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matches
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.Li 2002:xxyy:zzuu::/48
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where
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.Li xxyy:zzuu
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is a hexadecimal notation of an IPv4 address for the node.
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IPv4 address can be taken from any of interfaces your node has.
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Since the specification forbids the use of IPv4 private address,
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the address needs to be a global IPv4 address.
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.It
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Subnet identifier portion
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(48th to 63rd bit)
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and interface identifier portion
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(lower 64 bits)
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are properly filled to avoid address collisions.
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.El
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.Pp
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If you would like the node to behave as a relay router,
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the prefix length for the IPv6 interface address needs to be 16 so that
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the node would consider any 6to4 destination as
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.Dq on-link .
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If you would like to restrict 6to4 peers to be inside certain IPv4 prefix,
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you may want to configure IPv6 prefix length as
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.Dq 16 + IPv4 prefix length .
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.Nm
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interface will check the IPv4 source address on packets,
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if the IPv6 prefix length is larger than 16.
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.Pp
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.Nm
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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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See
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.Xr gif 4
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for details.
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.Pp
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Please note that 6to4 specification is written as
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.Dq accept tunnelled packet from everyone
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tunnelling device.
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By enabling
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.Nm
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device, you are making it much easier for malicious parties to inject
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fabricated IPv6 packet to your node.
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Also, malicious party can inject an IPv6 packet with fabricated source address
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to make your node generate improper tunnelled packet.
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Administrators must take caution when enabling the interface.
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To prevent possible attacks,
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.Nm
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interface filters out the following packets.
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Note that the checks are no way complete:
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.Bl -bullet
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.It
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Packets with IPv4 unspecified address as outer IPv4 source/destination
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.Pq Li 0.0.0.0/8
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.It
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Packets with loopback address as outer IPv4 source/destination
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.Pq Li 127.0.0.0/8
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.It
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Packets with IPv4 multicast address as outer IPv4 source/destination
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.Pq Li 224.0.0.0/4
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.It
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Packets with limited broadcast address as outer IPv4 source/destination
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.Pq Li 255.0.0.0/8
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.It
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Packets with private address as outer IPv4 source/destination
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.Pq Li 10.0.0.0/8 , 172.16.0.0/12 , 192.168.0.0/16
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.It
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Packets with subnet broadcast address as outer IPv4 source/destination.
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The check is made against subnet broadcast addresses for
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all of the directly connected subnets.
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.It
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Packets that does not pass ingress filtering.
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Outer IPv4 source address must meet the IPv4 topology on the routing table.
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Ingress filter can be turned off by
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.Dv IFF_LINK2
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bit.
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.It
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The same set of rules are applied against the IPv4 address embedded into
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inner IPv6 address, if the IPv6 address matches 6to4 prefix.
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.El
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.Pp
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It is recommended to filter/audit
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incoming IPv4 packet with IP protocol number 41, as necessary.
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It is also recommended to filter/audit encapsulated IPv6 packets as well.
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You may also want to run normal ingress filter against inner IPv6 address
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to avoid spoofing.
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.Pp
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By setting the
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.Dv IFF_LINK0
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flag on the
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.Nm
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interface, it is possible to disable the input path,
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making the direct attacks from the outside impossible.
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Note, however, there are other security risks exist.
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If you wish to use the configuration,
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you must not advertise your 6to4 address to others.
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.\"
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.Sh EXAMPLES
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Note that
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.Li 8504:0506
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is equal to
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.Li 133.4.5.6 ,
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written in hexadecimals.
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.Bd -literal
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# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
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# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\
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prefixlen 16 alias
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.Ed
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.Pp
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The following configuration accepts packets from IPv4 source
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.Li 9.1.0.0/16
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only.
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It emits 6to4 packet only for IPv6 destination 2002:0901::/32
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(IPv4 destination will match
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.Li 9.1.0.0/16 ) .
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.Bd -literal
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# ifconfig ne0 inet 9.1.2.3 netmask 0xffff0000
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# ifconfig stf0 inet6 2002:0901:0203:0000:a00:5aff:fe38:6f86 \\
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prefixlen 32 alias
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.Ed
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.Pp
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The following configuration uses the
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.Nm
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interface as an output-only device.
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You need to have alternative IPv6 connectivity
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(other than 6to4)
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to use this configuration.
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For outbound traffic, you can reach other 6to4 networks efficiently via
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.Nm stf .
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For inbound traffic, you will not receive any 6to4-tunneled packets
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(less security drawbacks).
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Be careful not to advertise your 6to4 prefix to others
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.Pq Li 2002:8504:0506::/48 ,
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and not to use your 6to4 prefix as a source.
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.Bd -literal
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# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
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# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\
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prefixlen 16 alias deprecated link0
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# route add -inet6 2002:: -prefixlen 16 ::1
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# route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0
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.Ed
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.\"
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.Sh SEE ALSO
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.Xr gif 4 ,
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.Xr inet 4 ,
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.Xr inet6 4
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.Pp
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.Pa http://www.6bone.net/6bone_6to4.html
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.Rs
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.%A Brian Carpenter
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.%A Keith Moore
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.%T "Connection of IPv6 Domains via IPv4 Clouds"
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.%D February 2001
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.%R RFC
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.%N 3056
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.Re
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.Rs
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.%A Jun-ichiro itojun Hagino
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.%T "Possible abuse against IPv6 transition technologies"
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.%D July 2000
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.%N draft-itojun-ipv6-transition-abuse-01.txt
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.%O work in progress
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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 WIDE/KAME IPv6 stack.
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.\"
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.Sh BUGS
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No more than one
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.Nm
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interface is allowed for a node,
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and no more than one IPv6 interface address is allowed for an
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.Nm
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interface.
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It is to avoid source address selection conflicts
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between IPv6 layer and IPv4 layer,
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and to cope with ingress filtering rule on the other side.
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This is a feature to make
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.Nm
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work right for all occasions.
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