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