1.\" $KAME: ipsec.4,v 1.17 2001/06/27 15:25:10 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 January 11, 2005 33.Dt IPSEC 4 34.Os 35.Sh NAME 36.Nm ipsec 37.Nd IP security protocol 38.Sh SYNOPSIS 39.In sys/types.h 40.In netinet/in.h 41.In netinet6/ipsec.h 42.Sh DESCRIPTION 43.Nm 44is a security protocol in Internet Protocol layer. 45.Nm 46is defined for both IPv4 and IPv6 47.Xr ( inet 4 48and 49.Xr inet6 4 ) . 50.Nm 51consists of two sub-protocols, namely 52ESP 53(encapsulated security payload) 54and AH 55(authentication header). 56ESP protects IP payload from wire-tapping by encrypting it by 57secret key cryptography algorithms. 58AH guarantees integrity of IP packet 59and protects it from intermediate alteration or impersonation, 60by attaching cryptographic checksum computed by one-way hash functions. 61.Nm 62has two operation modes: transport mode and tunnel mode. 63Transport mode is for protecting peer-to-peer communication between end nodes. 64Tunnel mode includes IP-in-IP encapsulation operation 65and is designed for security gateways, like VPN configurations. 66.\" 67.Ss Kernel interface 68.Nm 69is controlled by key management engine and policy engine, 70in the operating system kernel. 71.Pp 72Key management engine can be accessed from the userland by using 73.Dv PF_KEY 74sockets. 75The 76.Dv PF_KEY 77socket API is defined in RFC2367. 78.Pp 79Policy engine can be controlled by extended part of 80.Dv PF_KEY 81API, 82.Xr setsockopt 2 83operations, and 84.Xr sysctl 3 85interface. 86The kernel implements 87extended version of 88.Dv PF_KEY 89interface, and allows you to define IPsec policy like per-packet filters. 90.Xr setsockopt 2 91interface is used to define per-socket behavior, and 92.Xr sysctl 3 93interface is used to define host-wide default behavior. 94.Pp 95The kernel code does not implement dynamic encryption key exchange protocol 96like IKE 97(Internet Key Exchange). 98That should be implemented as userland programs 99(usually as daemons), 100by using the above described APIs. 101.\" 102.Ss Policy management 103The kernel implements experimental policy management code. 104You can manage the IPsec policy in two ways. 105One is to configure per-socket policy using 106.Xr setsockopt 2 . 107The other is to configure kernel packet filter-based policy using 108.Dv PF_KEY 109interface, via 110.Xr setkey 8 . 111In both cases, IPsec policy must be specified with syntax described in 112.Xr ipsec_set_policy 3 . 113.Pp 114With 115.Xr setsockopt 2 , 116you can define IPsec policy in per-socket basis. 117You can enforce particular IPsec policy onto packets that go through 118particular socket. 119.Pp 120With 121.Xr setkey 8 122you can define IPsec policy against packets, 123using sort of packet filtering rule. 124Refer to 125.Xr setkey 8 126on how to use it. 127.Pp 128In the latter case, 129.Dq Li default 130policy is allowed for use with 131.Xr setkey 8 . 132By configuring policy to 133.Li default , 134you can refer system-wide 135.Xr sysctl 8 136variable for default settings. 137The following variables are available. 138.Li 1 139means 140.Dq Li use , 141and 142.Li 2 143means 144.Dq Li require 145in the syntax. 146.Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx 147.It Sy "Name Type Changeable" 148.It "net.inet.ipsec.esp_trans_deflev integer yes" 149.It "net.inet.ipsec.esp_net_deflev integer yes" 150.It "net.inet.ipsec.ah_trans_deflev integer yes" 151.It "net.inet.ipsec.ah_net_deflev integer yes" 152.It "net.inet6.ipsec6.esp_trans_deflev integer yes" 153.It "net.inet6.ipsec6.esp_net_deflev integer yes" 154.It "net.inet6.ipsec6.ah_trans_deflev integer yes" 155.It "net.inet6.ipsec6.ah_net_deflev integer yes" 156.El 157.Pp 158If kernel finds no matching policy system wide default value is applied. 159System wide default is specified by the following 160.Xr sysctl 8 161variables. 162.Li 0 163means 164.Dq Li discard 165which asks the kernel to drop the packet. 166.Li 1 167means 168.Dq Li none . 169.Bl -column net.inet6.ipsec6.def_policy integerxxx 170.It Sy "Name Type Changeable" 171.It "net.inet.ipsec.def_policy integer yes" 172.It "net.inet6.ipsec6.def_policy integer yes" 173.El 174.\" 175.Ss Miscellaneous sysctl variables 176The following variables are accessible via 177.Xr sysctl 8 , 178for tweaking kernel IPsec behavior: 179.Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx 180.It Sy "Name Type Changeable" 181.It "net.inet.ipsec.ah_cleartos integer yes" 182.It "net.inet.ipsec.ah_offsetmask integer yes" 183.It "net.inet.ipsec.dfbit integer yes" 184.It "net.inet.ipsec.ecn integer yes" 185.It "net.inet.ipsec.debug integer yes" 186.It "net.inet6.ipsec6.ecn integer yes" 187.It "net.inet6.ipsec6.debug integer yes" 188.El 189.Pp 190The variables are interpreted as follows: 191.Bl -tag -width 6n 192.It Li ipsec.ah_cleartos 193If set to non-zero, the kernel clears type-of-service field in the IPv4 header 194during AH authentication data computation. 195The variable is for tweaking AH behavior to interoperate with devices that 196implement RFC1826 AH. 197It should be set to non-zero 198(clear the type-of-service field) 199for RFC2402 conformance. 200.It Li ipsec.ah_offsetmask 201During AH authentication data computation, the kernel will include 20216bit fragment offset field 203(including flag bits) 204in IPv4 header, after computing logical AND with the variable. 205The variable is for tweaking AH behavior to interoperate with devices that 206implement RFC1826 AH. 207It should be set to zero 208(clear the fragment offset field during computation) 209for RFC2402 conformance. 210.It Li ipsec.dfbit 211The variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. 212If set to 0, DF bit on the outer IPv4 header will be cleared. 2131 means that the outer DF bit is set regardless from the inner DF bit. 2142 means that the DF bit is copied from the inner header to the outer. 215The variable is supplied to conform to RFC2401 chapter 6.1. 216.It Li ipsec.ecn 217If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will 218be friendly to ECN 219(explicit congestion notification), 220as documented in 221.Li draft-ietf-ipsec-ecn-02.txt . 222.Xr gif 4 223talks more about the behavior. 224.It Li ipsec.debug 225If set to non-zero, debug messages will be generated via 226.Xr syslog 3 . 227.El 228.Pp 229Variables under 230.Li net.inet6.ipsec6 231tree has similar meaning as the 232.Li net.inet.ipsec 233counterpart. 234.\" 235.Sh PROTOCOLS 236The 237.Nm 238protocol works like plug-in to 239.Xr inet 4 240and 241.Xr inet6 4 242protocols. 243Therefore, 244.Nm 245supports most of the protocols defined upon those IP-layer protocols. 246Some of the protocols, like 247.Xr icmp 4 248or 249.Xr icmp6 4 , 250may behave differently with 251.Nm . 252This is because 253.Nm 254can prevent 255.Xr icmp 4 256or 257.Xr icmp6 4 258routines from looking into IP payload. 259.\" 260.Sh SEE ALSO 261.Xr ioctl 2 , 262.Xr socket 2 , 263.Xr ipsec_set_policy 3 , 264.Xr icmp6 4 , 265.Xr intro 4 , 266.Xr ip6 4 , 267.Xr setkey 8 , 268.Xr sysctl 8 269.\".Xr racoon 8 270.Rs 271.%A "S. Kent" 272.%A "R. Atkinson" 273.%T "IP Authentication Header" 274.%O "RFC 2404" 275.Re 276.Rs 277.%A "S. Kent" 278.%A "R. Atkinson" 279.%T "IP Encapsulating Security Payload (ESP)" 280.%O "RFC 2406" 281.Re 282.Sh STANDARDS 283.Rs 284.%A Daniel L. McDonald 285.%A Craig Metz 286.%A Bao G. Phan 287.%T "PF_KEY Key Management API, Version 2" 288.%R RFC 289.%N 2367 290.Re 291.Pp 292.Rs 293.%A "D. L. McDonald" 294.%T "A Simple IP Security API Extension to BSD Sockets" 295.%R internet draft 296.%N "draft-mcdonald-simple-ipsec-api-03.txt" 297.%O work in progress material 298.Re 299.Sh HISTORY 300The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack. 301.Sh BUGS 302The IPsec support is subject to change as the IPsec protocols develop. 303.Pp 304There is no single standard for policy engine API, 305so the policy engine API described herein is just for KAME implementation. 306.Pp 307AH and tunnel mode encapsulation may not work as you might expect. 308If you configure inbound 309.Dq require 310policy against AH tunnel or any IPsec encapsulating policy with AH 311(like 312.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) , 313tunnelled packets will be rejected. 314This is because we enforce policy check on inner packet on reception, 315and AH authenticates encapsulating 316(outer) 317packet, not the encapsulated 318(inner) 319packet 320(so for the receiving kernel there is no sign of authenticity). 321The issue will be solved when we revamp our policy engine to keep all the 322packet decapsulation history. 323.Pp 324Under certain condition, 325truncated result may be raised from the kernel 326against 327.Dv SADB_DUMP 328and 329.Dv SADB_SPDDUMP 330operation on 331.Dv PF_KEY 332socket. 333This occurs if there are too many database entries in the kernel 334and socket buffer for the 335.Dv PF_KEY 336socket is insufficient. 337If you manipulate many IPsec key/policy database entries, 338increase the size of socket buffer. 339