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1.\" $FreeBSD: src/share/man/man4/stf.4,v 1.3.2.4 2001/08/17 13:08:39 ru Exp $
2.\" $KAME: stf.4,v 1.35 2001/05/02 06:24:49 itojun Exp $
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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 "pseudo-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
60Due to the way 6to4 protocol is specified,
61.Nm
62interface requires certain configuration to work properly.
63Single
64(no more than 1)
65valid 6to4 address needs to be configured to the interface.
66.Dq A valid 6to4 address
67is an address which has the following properties.
68If any of the following properties are not satisfied,
69.Nm
70raises runtime error on packet transmission.
71Read the specification for more details.
72.Bl -bullet
73.It
74matches
75.Li 2002:xxyy:zzuu::/48
76where
77.Li xxyy:zzuu
78is a hexadecimal notation of an IPv4 address for the node.
79IPv4 address can be taken from any of interfaces your node has.
80Since the specification forbids the use of IPv4 private address,
81the address needs to be a global IPv4 address.
82.It
83Subnet identifier portion
84(48th to 63rd bit)
85and interface identifier portion
86(lower 64 bits)
87are properly filled to avoid address collisions.
88.El
89.Pp
90If you would like the node to behave as a relay router,
91the prefix length for the IPv6 interface address needs to be 16 so that
92the node would consider any 6to4 destination as
93.Dq on-link .
94If you would like to restrict 6to4 peers to be inside certain IPv4 prefix,
95you may want to configure IPv6 prefix length as
96.Dq 16 + IPv4 prefix length .
97.Nm
98interface will check the IPv4 source address on packets,
99if the IPv6 prefix length is larger than 16.
100.Pp
101.Nm
102can be configured to be ECN friendly.
103This can be configured by
104.Dv IFF_LINK1 .
105See
106.Xr gif 4
107for details.
108.Pp
109Please note that 6to4 specification is written as
110.Dq accept tunnelled packet from everyone
111tunnelling device.
112By enabling
113.Nm
114device, you are making it much easier for malicious parties to inject
115fabricated IPv6 packet to your node.
116Also, malicious party can inject an IPv6 packet with fabricated source address
117to make your node generate improper tunnelled packet.
118Administrators must take caution when enabling the interface.
119To prevent possible attacks,
120.Nm
121interface filters out the following packets.
122Note that the checks are no way complete:
123.Bl -bullet
124.It
125Packets with IPv4 unspecified addrss as outer IPv4 source/destination
126.Pq Li 0.0.0.0/8
127.It
128Packets with loopback address as outer IPv4 source/destination
129.Pq Li 127.0.0.0/8
130.It
131Packets with IPv4 multicast address as outer IPv4 source/destination
132.Pq Li 224.0.0.0/4
133.It
134Packets with limited broadcast address as outer IPv4 source/destination
135.Pq Li 255.0.0.0/8
136.It
137Packets with subnet broadcast address as outer IPv4 source/destination.
138The check is made against subnet broadcast addresses for
139all of the directly connected subnets.
140.It
141Packets that does not pass ingress filtering.
142Outer IPv4 source address must meet the IPv4 topology on the routing table.
143Ingress filter can be turned off by
144.Dv IFF_LINK2
145bit.
146.It
147The same set of rules are appplied against the IPv4 address embedded into
148inner IPv6 address, if the IPv6 address matches 6to4 prefix.
149.El
150.Pp
151It is recommended to filter/audit
152incoming IPv4 packet with IP protocol number 41, as necessary.
153It is also recommended to filter/audit encapsulated IPv6 packets as well.
154You may also want to run normal ingress filter against inner IPv6 address
155to avoid spoofing.
156.Pp
157By setting the
158.Dv IFF_LINK0
159flag on the
160.Nm
161interface, it is possible to disable the input path,
162making the direct attacks from the outside impossible.
163Note, however, there are other security risks exist.
164If you wish to use the configuration,
165you must not advertise your 6to4 address to others.
166.\"
167.Sh EXAMPLES
168Note that
169.Li 8504:0506
170is equal to
171.Li 133.4.5.6 ,
172written in hexadecimals.
173.Bd -literal
174# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
175# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\
176 prefixlen 16 alias
177.Ed
178.Pp
179The following configuration accepts packets from IPv4 source
180.Li 9.1.0.0/16
181only.
182It emits 6to4 packet only for IPv6 destination 2002:0901::/32
183(IPv4 destination will match
184.Li 9.1.0.0/16 ) .
185.Bd -literal
186# ifconfig ne0 inet 9.1.2.3 netmask 0xffff0000
187# ifconfig stf0 inet6 2002:0901:0203:0000:a00:5aff:fe38:6f86 \\
188 prefixlen 32 alias
189.Ed
190.Pp
191The following configuration uses the
192.Nm
193interface as an output-only device.
194You need to have alternative IPv6 connectivity
195(other than 6to4)
196to use this configuration.
197For outbound traffic, you can reach other 6to4 networks efficiently via
198.Nm stf .
199For inbound traffic, you will not receive any 6to4-tunneled packets
200(less security drawbacks).
201Be careful not to advertise your 6to4 prefix to others
202.Pq Li 2002:8504:0506::/48 ,
203and not to use your 6to4 prefix as a source.
204.Bd -literal
205# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00
206# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\
207 prefixlen 16 alias deprecated link0
208# route add -inet6 2002:: -prefixlen 16 ::1
209# route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0
210.Ed
211.\"
212.Sh SEE ALSO
213.Xr gif 4 ,
214.Xr inet 4 ,
215.Xr inet6 4
216.Pp
217.Pa http://www.6bone.net/6bone_6to4.html
218.Rs
219.%A Brian Carpenter
220.%A Keith Moore
221.%T "Connection of IPv6 Domains via IPv4 Clouds"
222.%D February 2001
223.%R RFC
224.%N 3056
225.Re
226.Rs
227.%A Jun-ichiro itojun Hagino
228.%T "Possible abuse against IPv6 transition technologies"
229.%D July 2000
230.%N draft-itojun-ipv6-transition-abuse-01.txt
231.%O work in progress
232.Re
233.\"
234.Sh HISTORY
235The
236.Nm
237device first appeared in WIDE/KAME IPv6 stack.
238.\"
239.Sh BUGS
240No more than one
241.Nm
242interface is allowed for a node,
243and no more than one IPv6 interface address is allowed for an
244.Nm
245interface.
246It is to avoid source address selection conflicts
247between IPv6 layer and IPv4 layer,
248and to cope with ingress filtering rule on the other side.
249This is a feature to make
250.Nm
251work right for all occasions.