1.\" $FreeBSD$ 2.\" $KAME: stf.4,v 1.24 2000/06/07 23:35:18 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 March 6, 2000 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 draft-ietf-ngtrans-6to4-06.txt . 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.Po 57called 58.Dq 6to4 router 59in the specification 60.Pc . 61.Pp 62Due to the way 6to4 protocol is specified, 63.Nm 64interface requires certain configuration to work properly. 65Single 66.Pq no more than 1 67valid 6to4 address needs to be configured to the interface. 68.Dq A valid 6to4 address 69is an address which has the following properties. 70If any of the following properties are not satisfied, 71.Nm 72raises runtime error on packet transmission. 73Read the specification for more details. 74.Bl -bullet 75.It 76matches 77.Li 2002:xxyy:zzuu::/48 78where 79.Li xxyy:zzuu 80is a hexadecimal notation of an IPv4 address for the node. 81IPv4 address can be taken from any of interfaces your node has. 82Since the specification forbids the use of IPv4 private address, 83the address needs to be a global IPv4 address. 84.It 85Subnet identifier portion 86.Pq 48th to 63rd bit 87and interface identifier portion 88.Pq lower 64 bits 89are properly filled to avoid address collisions. 90.El 91.Pp 92If you would like the node to behave as a relay router, 93the prefix length for the IPv6 interface address needs to be 16 so that 94the node would consider any 6to4 destination as 95.Dq on-link . 96If you would like to restrict 6to4 peers to be inside certain IPv4 prefix, 97you may want to configure IPv6 prefix length as 98.Dq 16 + IPv4 prefix length . 99.Nm 100interface will check the IPv4 source address on packets, 101if the IPv6 prefix length is larger than 16. 102.Pp 103.Nm 104can be configured to be ECN friendly. 105This can be configured by 106.Dv IFF_LINK1 . 107See 108.Xr gif 4 109for details. 110.Pp 111Please note that 6to4 specification is written as 112.Dq accept tunnelled packet from everyone 113tunnelling device. 114By enabling 115.Nm 116device, you are making it much easier for malicious parties to inject 117fabricated IPv6 packet to your node. 118Also, malicious party can inject an IPv6 packet with fabricated source address 119to make your node generate improper tunnelled packet. 120Administrators must take caution when enabling the interface. 121To prevent possible attacks, 122.Nm 123interface filters out the following packets. 124Note that the checks are no way complete: 125.Bl -bullet 126.It 127Packets with IPv4 unspecified addrss as outer IPv4 source/destination 128.Pq Li 0.0.0.0/8 129.It 130Packets with loopback address as outer IPv4 source/destination 131.Pq Li 127.0.0.0/8 132.It 133Packets with IPv4 multicast address as outer IPv4 source/destination 134.Pq Li 224.0.0.0/4 135.It 136Packets with limited broadcast address as outer IPv4 source/destination 137.Pq Li 255.0.0.0/8 138.It 139Packets with subnet broadcast address as outer IPv4 source/destination. 140The check is made against subnet broadcast addresses for 141all of the directly connected subnets. 142.It 143Packets that does not pass ingress filtering. 144Outer IPv4 source address must meet the IPv4 topology on the routing table. 145.It 146The same set of rules are appplied against the IPv4 address embedded into 147inner IPv6 address, if the IPv6 address matches 6to4 prefix. 148.El 149.Pp 150It is recommended to filter/audit 151incoming IPv4 packet with IP protocol number 41, as necessary. 152It is also recommended to filter/audit encapsulated IPv6 packets as well. 153You may also want to run normal ingress filter against inner IPv6 address 154to avoid spoofing. 155.\" 156.Sh EXAMPLES 157Note that 158.Li 8504:0506 159is equal to 160.Li 133.4.5.6 , 161written in hexadecimals. 162.Bd -literal 163# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00 164# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\ 165 prefixlen 16 alias 166.Ed 167.Pp 168The following configuration accepts packets from IPv4 source 169.Li 9.1.0.0/16 170only. 171It emits 6to4 packet only for IPv6 destination 2002:0901::/32 172.Pq IPv4 destination will match Li 9.1.0.0/16 . 173.Bd -literal 174# ifconfig ne0 inet 9.1.2.3 netmask 0xffff0000 175# ifconfig stf0 inet6 2002:0901:0203:0000:a00:5aff:fe38:6f86 \\ 176 prefixlen 32 alias 177.Ed 178.\" 179.Sh SEE ALSO 180.Xr gif 4 , 181.Xr inet 4 , 182.Xr inet6 4 183.Rs 184.%A Brian Carpenter 185.%A Keith Moore 186.%T "Connection of IPv6 Domains via IPv4 Clouds without Explicit Tunnels" 187.%D June 2000 188.%N draft-ietf-ngtrans-6to4-06.txt 189.%O work in progress 190.Re 191.Rs 192.%A Jun-ichiro itojun Hagino 193.%T "Possible abuse against IPv6 transition technologies" 194.%D March 2000 195.%N draft-itojun-ipv6-transition-abuse-00.txt 196.%O work in progress, http://playground.iijlab.net/i-d/draft-itojun-ipv6-transition-abuse-00.txt 197.Re 198.\" 199.Sh HISTORY 200The 201.Nm 202device first appeared in WIDE/KAME IPv6 stack. 203