1.\" $KAME: stf.4,v 1.35 2001/05/02 06:24:49 itojun Exp $ 2.\" 3.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the project nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" $FreeBSD$ 31.\" 32.Dd April 27, 2001 33.Dt STF 4 34.Os 35.Sh NAME 36.Nm stf 37.Nd 38.Tn 6to4 39tunnel interface 40.Sh SYNOPSIS 41.Cd "device stf" 42.Sh DESCRIPTION 43The 44.Nm 45interface supports 46.Dq 6to4 47IPv6 in IPv4 encapsulation. 48It can tunnel IPv6 traffic over IPv4, as specified in 49.Li RFC3056 . 50.Pp 51For ordinary nodes in 6to4 site, you do not need 52.Nm 53interface. 54The 55.Nm 56interface is necessary for site border router 57(called 58.Dq 6to4 router 59in the specification). 60.Pp 61Each 62.Nm 63interface is created at runtime using interface cloning. 64This is 65most easily done with the 66.Xr ifconfig 8 67.Cm create 68command or using the 69.Va cloned_interfaces 70variable in 71.Xr rc.conf 5 . 72.Pp 73Due to the way 6to4 protocol is specified, 74.Nm 75interface requires certain configuration to work properly. 76Single 77(no more than 1) 78valid 6to4 address needs to be configured to the interface. 79.Dq A valid 6to4 address 80is an address which has the following properties. 81If any of the following properties are not satisfied, 82.Nm 83raises runtime error on packet transmission. 84Read the specification for more details. 85.Bl -bullet 86.It 87matches 88.Li 2002:xxyy:zzuu::/48 89where 90.Li xxyy:zzuu 91is a hexadecimal notation of an IPv4 address for the node. 92IPv4 address can be taken from any of interfaces your node has. 93Since the specification forbids the use of IPv4 private address, 94the address needs to be a global IPv4 address. 95.It 96Subnet identifier portion 97(48th to 63rd bit) 98and interface identifier portion 99(lower 64 bits) 100are properly filled to avoid address collisions. 101.El 102.Pp 103If you would like the node to behave as a relay router, 104the prefix length for the IPv6 interface address needs to be 16 so that 105the node would consider any 6to4 destination as 106.Dq on-link . 107If you would like to restrict 6to4 peers to be inside certain IPv4 prefix, 108you may want to configure IPv6 prefix length as 109.Dq 16 + IPv4 prefix length . 110.Nm 111interface will check the IPv4 source address on packets, 112if the IPv6 prefix length is larger than 16. 113.Pp 114.Nm 115can be configured to be ECN friendly. 116This can be configured by 117.Dv IFF_LINK1 . 118See 119.Xr gif 4 120for details. 121.Pp 122Please note that 6to4 specification is written as 123.Dq accept tunnelled packet from everyone 124tunnelling device. 125By enabling 126.Nm 127device, you are making it much easier for malicious parties to inject 128fabricated IPv6 packet to your node. 129Also, malicious party can inject an IPv6 packet with fabricated source address 130to make your node generate improper tunnelled packet. 131Administrators must take caution when enabling the interface. 132To prevent possible attacks, 133.Nm 134interface filters out the following packets. 135Note that the checks are no way complete: 136.Bl -bullet 137.It 138Packets with IPv4 unspecified address as outer IPv4 source/destination 139.Pq Li 0.0.0.0/8 140.It 141Packets with loopback address as outer IPv4 source/destination 142.Pq Li 127.0.0.0/8 143.It 144Packets with IPv4 multicast address as outer IPv4 source/destination 145.Pq Li 224.0.0.0/4 146.It 147Packets with limited broadcast address as outer IPv4 source/destination 148.Pq Li 255.0.0.0/8 149.It 150Packets with private address as outer IPv4 source/destination 151.Pq Li 10.0.0.0/8 , 172.16.0.0/12 , 192.168.0.0/16 152.It 153Packets with subnet broadcast address as outer IPv4 source/destination. 154The check is made against subnet broadcast addresses for 155all of the directly connected subnets. 156.It 157Packets that does not pass ingress filtering. 158Outer IPv4 source address must meet the IPv4 topology on the routing table. 159Ingress filter can be turned off by 160.Dv IFF_LINK2 161bit. 162.It 163The same set of rules are applied against the IPv4 address embedded into 164inner IPv6 address, if the IPv6 address matches 6to4 prefix. 165.El 166.Pp 167It is recommended to filter/audit 168incoming IPv4 packet with IP protocol number 41, as necessary. 169It is also recommended to filter/audit encapsulated IPv6 packets as well. 170You may also want to run normal ingress filter against inner IPv6 address 171to avoid spoofing. 172.Pp 173By setting the 174.Dv IFF_LINK0 175flag on the 176.Nm 177interface, it is possible to disable the input path, 178making the direct attacks from the outside impossible. 179Note, however, there are other security risks exist. 180If you wish to use the configuration, 181you must not advertise your 6to4 address to others. 182.\" 183.Sh EXAMPLES 184Note that 185.Li 8504:0506 186is equal to 187.Li 133.4.5.6 , 188written in hexadecimals. 189.Bd -literal 190# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00 191# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\ 192 prefixlen 16 alias 193.Ed 194.Pp 195The following configuration accepts packets from IPv4 source 196.Li 9.1.0.0/16 197only. 198It emits 6to4 packet only for IPv6 destination 2002:0901::/32 199(IPv4 destination will match 200.Li 9.1.0.0/16 ) . 201.Bd -literal 202# ifconfig ne0 inet 9.1.2.3 netmask 0xffff0000 203# ifconfig stf0 inet6 2002:0901:0203:0000:a00:5aff:fe38:6f86 \\ 204 prefixlen 32 alias 205.Ed 206.Pp 207The following configuration uses the 208.Nm 209interface as an output-only device. 210You need to have alternative IPv6 connectivity 211(other than 6to4) 212to use this configuration. 213For outbound traffic, you can reach other 6to4 networks efficiently via 214.Nm stf . 215For inbound traffic, you will not receive any 6to4-tunneled packets 216(less security drawbacks). 217Be careful not to advertise your 6to4 prefix to others 218.Pq Li 2002:8504:0506::/48 , 219and not to use your 6to4 prefix as a source. 220.Bd -literal 221# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00 222# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\ 223 prefixlen 16 alias deprecated link0 224# route add -inet6 2002:: -prefixlen 16 ::1 225# route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0 226.Ed 227.\" 228.Sh SEE ALSO 229.Xr gif 4 , 230.Xr inet 4 , 231.Xr inet6 4 232.Pp 233.Pa http://www.6bone.net/6bone_6to4.html 234.Rs 235.%A Brian Carpenter 236.%A Keith Moore 237.%T "Connection of IPv6 Domains via IPv4 Clouds" 238.%D February 2001 239.%R RFC 240.%N 3056 241.Re 242.Rs 243.%A Jun-ichiro itojun Hagino 244.%T "Possible abuse against IPv6 transition technologies" 245.%D July 2000 246.%N draft-itojun-ipv6-transition-abuse-01.txt 247.%O work in progress 248.Re 249.\" 250.Sh HISTORY 251The 252.Nm 253device first appeared in WIDE/KAME IPv6 stack. 254.\" 255.Sh BUGS 256No more than one 257.Nm 258interface is allowed for a node, 259and no more than one IPv6 interface address is allowed for an 260.Nm 261interface. 262It is to avoid source address selection conflicts 263between IPv6 layer and IPv4 layer, 264and to cope with ingress filtering rule on the other side. 265This is a feature to make 266.Nm 267work right for all occasions. 268