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1 .\" $FreeBSD: src/share/man/man4/ipsec.4,v 1.3.2.10 2001/12/17 11:30:12 ru Exp $
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31 .Dd January 29, 1999
32 .Dt IPSEC 4
33 .Os
34 .Sh NAME
35 .Nm ipsec
36 .Nd IP security protocol
37 .Sh SYNOPSIS
38 .In sys/types.h
39 .In netinet/in.h
40 .In netinet6/ipsec.h
41 .Sh DESCRIPTION
42 .Nm
43 is a security protocol in Internet Protocol layer.
44 .Nm
45 is defined for both IPv4 and IPv6
46 .Xr ( inet 4
47 and
48 .Xr inet6 4 ) .
49 .Nm
50 consists of two sub-protocols, namely
51 ESP
52 (encapsulated security payload)
53 and AH
54 (authentication header).
55 ESP protects IP payload from wire-tapping by encrypting it by
56 secret key cryptography algorithms.
57 AH guarantees integrity of IP packet
58 and protects it from intermediate alteration or impersonation,
59 by attaching cryptographic checksum computed by one-way hash functions.
60 .Nm
61 has two operation modes: transport mode and tunnel mode.
62 Transport mode is for protecting peer-to-peer communication between end nodes.
63 Tunnel mode includes IP-in-IP encapsulation operation
64 and is designed for security gateways, like VPN configurations.
65 .\"
66 .Ss Kernel interface
67 .Nm
68 is controlled by key management engine and policy engine,
69 in the operating system kernel.
70 .Pp
71 Key management engine can be accessed from the userland by using
72 .Dv PF_KEY
73 sockets.
74 The
75 .Dv PF_KEY
76 socket API is defined in RFC2367.
77 .Pp
78 Policy engine can be controlled by extended part of
79 .Dv PF_KEY
80 API,
81 .Xr setsockopt 2
82 operations, and
83 .Xr sysctl 3
84 interface.
85 The kernel implements
86 extended version of
87 .Dv PF_KEY
88 interface, and allows you to define IPsec policy like per-packet filters.
89 .Xr setsockopt 2
90 interface is used to define per-socket behavior, and
91 .Xr sysctl 3
92 interface is used to define host-wide default behavior.
93 .Pp
94 The kernel code does not implement dynamic encryption key exchange protocol
95 like IKE
96 (Internet Key Exchange).
97 That should be implemented as userland programs
98 (usually as daemons),
99 by using the above described APIs.
100 .\"
101 .Ss Policy management
102 The kernel implements experimental policy management code.
103 You can manage the IPsec policy in two ways.
104 One is to configure per-socket policy using
105 .Xr setsockopt 2 .
106 The other is to configure kernel packet filter-based policy using
107 .Dv PF_KEY
108 interface, via
109 .Xr setkey 8 .
110 In both cases, IPsec policy must be specified with syntax described in
111 .Xr ipsec_set_policy 3 .
112 .Pp
113 With
114 .Xr setsockopt 2 ,
115 you can define IPsec policy in per-socket basis.
116 You can enforce particular IPsec policy onto packets that go through
117 particular socket.
118 .Pp
119 With
120 .Xr setkey 8
121 you can define IPsec policy against packets,
122 using sort of packet filtering rule.
123 Refer to
124 .Xr setkey 8
125 on how to use it.
126 .Pp
127 In the latter case,
128 .Dq Li default
129 policy is allowed for use with
130 .Xr setkey 8 .
131 By configuring policy to
132 .Li default ,
133 you can refer system-wide
134 .Xr sysctl 8
135 variable for default settings.
136 The following variables are available.
137 .Li 1
138 means
139 .Dq Li use ,
140 and
141 .Li 2
142 means
143 .Dq Li require
144 in the syntax.
145 .Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx
146 .It Sy "Name Type Changeable"
147 .It "net.inet.ipsec.esp_trans_deflev integer yes"
148 .It "net.inet.ipsec.esp_net_deflev integer yes"
149 .It "net.inet.ipsec.ah_trans_deflev integer yes"
150 .It "net.inet.ipsec.ah_net_deflev integer yes"
151 .It "net.inet6.ipsec6.esp_trans_deflev integer yes"
152 .It "net.inet6.ipsec6.esp_net_deflev integer yes"
153 .It "net.inet6.ipsec6.ah_trans_deflev integer yes"
154 .It "net.inet6.ipsec6.ah_net_deflev integer yes"
155 .El
156 .Pp
157 If kernel finds no matching policy system wide default value is applied.
158 System wide default is specified by the following
159 .Xr sysctl 8
160 variables.
161 .Li 0
162 means
163 .Dq Li discard
164 which asks the kernel to drop the packet.
165 .Li 1
166 means
167 .Dq Li none .
168 .Bl -column net.inet6.ipsec6.def_policy integerxxx
169 .It Sy "Name Type Changeable"
170 .It "net.inet.ipsec.def_policy integer yes"
171 .It "net.inet6.ipsec6.def_policy integer yes"
172 .El
173 .\"
174 .Ss Miscellaneous sysctl variables
175 The following variables are accessible via
176 .Xr sysctl 8 ,
177 for tweaking kernel IPsec behavior:
178 .Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx
179 .It Sy "Name Type Changeable"
180 .It "net.inet.ipsec.ah_cleartos integer yes"
181 .It "net.inet.ipsec.ah_offsetmask integer yes"
182 .It "net.inet.ipsec.dfbit integer yes"
183 .It "net.inet.ipsec.ecn integer yes"
184 .It "net.inet.ipsec.debug integer yes"
185 .It "net.inet6.ipsec6.ecn integer yes"
186 .It "net.inet6.ipsec6.debug integer yes"
187 .El
188 .Pp
189 The variables are interpreted as follows:
190 .Bl -tag -width 6n
191 .It Li ipsec.ah_cleartos
192 If set to non-zero, the kernel clears type-of-service field in the IPv4 header
193 during AH authentication data computation.
194 The variable is for tweaking AH behavior to interoperate with devices that
195 implement RFC1826 AH.
196 It should be set to non-zero
197 (clear the type-of-service field)
198 for RFC2402 conformance.
199 .It Li ipsec.ah_offsetmask
200 During AH authentication data computation, the kernel will include
201 16bit fragment offset field
202 (including flag bits)
203 in IPv4 header, after computing logical AND with the variable.
204 The variable is for tweaking AH behavior to interoperate with devices that
205 implement RFC1826 AH.
206 It should be set to zero
207 (clear the fragment offset field during computation)
208 for RFC2402 conformance.
209 .It Li ipsec.dfbit
210 The variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation.
211 If set to 0, DF bit on the outer IPv4 header will be cleared.
212 1 means that the outer DF bit is set regardless from the inner DF bit.
213 2 means that the DF bit is copied from the inner header to the outer.
214 The variable is supplied to conform to RFC2401 chapter 6.1.
215 .It Li ipsec.ecn
216 If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will
217 be friendly to ECN
218 (explicit congestion notification),
219 as documented in
220 .Li draft-ietf-ipsec-ecn-02.txt .
221 .Xr gif 4
222 talks more about the behavior.
223 .It Li ipsec.debug
224 If set to non-zero, debug messages will be generated via
225 .Xr syslog 3 .
226 .El
227 .Pp
228 Variables under
229 .Li net.inet6.ipsec6
230 tree has similar meaning as the
231 .Li net.inet.ipsec
232 counterpart.
233 .\"
234 .Sh PROTOCOLS
235 The
236 .Nm
237 protocol works like plug-in to
238 .Xr inet 4
239 and
240 .Xr inet6 4
241 protocols.
242 Therefore,
243 .Nm
244 supports most of the protocols defined upon those IP-layer protocols.
245 Some of the protocols, like
246 .Xr icmp 4
247 or
248 .Xr icmp6 4 ,
249 may behave differently with
250 .Nm .
251 This is because
252 .Nm
253 can prevent
254 .Xr icmp 4
255 or
256 .Xr icmp6 4
257 routines from looking into IP payload.
258 .\"
259 .Sh SEE ALSO
260 .Xr ioctl 2 ,
261 .Xr socket 2 ,
262 .Xr ipsec_set_policy 3 ,
263 .Xr icmp6 4 ,
264 .Xr intro 4 ,
265 .Xr ip6 4 ,
266 .Xr setkey 8 ,
267 .Xr sysctl 8
268 .\".Xr racoon 8
269 .Sh STANDARDS
270 .Rs
271 .%A Daniel L. McDonald
272 .%A Craig Metz
273 .%A Bao G. Phan
274 .%T "PF_KEY Key Management API, Version 2"
275 .%R RFC
276 .%N 2367
277 .Re
278 .Pp
279 .Rs
280 .%A "D. L. McDonald"
281 .%T "A Simple IP Security API Extension to BSD Sockets"
282 .%R internet draft
283 .%N "draft-mcdonald-simple-ipsec-api-03.txt"
284 .%O work in progress material
285 .Re
286 .Sh HISTORY
287 The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack.
288 .Sh BUGS
289 The IPsec support is subject to change as the IPsec protocols develop.
290 .Pp
291 There is no single standard for policy engine API,
292 so the policy engine API described herein is just for KAME implementation.
293 .Pp
294 AH and tunnel mode encapsulation may not work as you might expect.
295 If you configure inbound
296 .Dq require
297 policy against AH tunnel or any IPsec encapsulating policy with AH
298 (like
299 .Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) ,
300 tunnelled packets will be rejected.
301 This is because we enforce policy check on inner packet on reception,
302 and AH authenticates encapsulating
303 (outer)
304 packet, not the encapsulated
305 (inner)
306 packet
307 (so for the receiving kernel there's no sign of authenticity).
308 The issue will be solved when we revamp our policy engine to keep all the
309 packet decapsulation history.
310 .Pp
311 Under certain condition,
312 truncated result may be raised from the kernel
313 against
314 .Dv SADB_DUMP
315 and
316 .Dv SADB_SPDDUMP
317 operation on
318 .Dv PF_KEY
319 socket.
320 This occurs if there are too many database entries in the kernel
321 and socket buffer for the
322 .Dv PF_KEY
323 socket is insufficient.
324 If you manipulate many IPsec key/policy database entries,
325 increase the size of socket buffer.