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 August 24, 2006 33.Dt IPSEC 4 34.Os 35.Sh NAME 36.Nm ipsec 37.Nd IP security protocol 38.Sh SYNOPSIS 39.Cd "options IPSEC" 40.Cd "options IPSEC_DEBUG" 41.Cd "options IPSEC_ESP" 42.Cd "options IPSEC_FILTERGIF" 43.Pp 44.In sys/types.h 45.In netinet/in.h 46.In netinet6/ipsec.h 47.Sh DESCRIPTION 48.Nm 49is a security protocol implemented within the Internet Protocol layer 50of the TCP/IP stack. 51.Nm 52is defined for both IPv4 and IPv6 53.Xr ( inet 4 54and 55.Xr inet6 4 ) . 56.Nm 57contains two protocols, 58ESP, the encapsulated security payload protocol and 59AH, the authentication header protocol. 60ESP prevents unauthorized parties from reading the payload of an IP packet 61by encrypting it using 62secret key cryptography algorithms. 63AH both authenticates guarantees the integrity of an IP packet 64by attaching a cryptographic checksum computed using one-way hash functions. 65.Nm 66has operates in one of two modes: transport mode or tunnel mode. 67Transport mode is used to protect peer-to-peer communication between end nodes. 68Tunnel mode encapsulates IP packets within other IP packets 69and is designed for security gateways such as VPN endpoints. 70.\" 71.Ss Kernel interface 72.Nm 73is controlled by a key management and policy engine, 74that reside in the operating system kernel. 75Key management 76is the process of associating keys with security associations, also 77know as SAs. 78Policy management dictates when new security 79associations created or destroyed. 80.Pp 81The key management engine can be accessed from userland by using 82.Dv PF_KEY 83sockets. 84The 85.Dv PF_KEY 86socket API is defined in RFC2367. 87.Pp 88The policy engine is controlled by an extension to the 89.Dv PF_KEY 90API, 91.Xr setsockopt 2 92operations, and 93.Xr sysctl 3 94interface. 95The kernel implements 96an extended version of the 97.Dv PF_KEY 98interface, and allows the programmer to define IPsec policies 99which are similar to the per-packet filters. 100The 101.Xr setsockopt 2 102interface is used to define per-socket behavior, and 103.Xr sysctl 3 104interface is used to define host-wide default behavior. 105.Pp 106The kernel code does not implement a dynamic encryption key exchange protocol 107such as IKE 108(Internet Key Exchange). 109Key exchange protocols are beyond what is necessary in the kernel and 110should be implemented as daemon processes which call the 111.Nm APIs. 112.\" 113.Ss Policy management 114IPsec policies can be managed in one of two ways, either by 115configuring per-socket policies using the 116.Xr setsockopt 2 117system calls, or by configuring kernel level packet filter-based 118policies using the 119.Dv PF_KEY 120interface, via the 121.Xr setkey 8 122command. 123In either case, IPsec policies must be specified using the syntax described in 124.Xr ipsec_set_policy 3 . 125Please refer to the 126.Xr setkey 8 127man page for instructions on its use. 128.Pp 129When setting policies using the 130.Xr setkey 8 131command the 132.Dq Li default 133option you can have the system use its default policy, explained 134below, for processing packets. 135The following sysctl variables are available for configuring the 136system's IPsec behavior. 137The variables can have one of two values. 138A 139.Li 1 140means 141.Dq Li use , 142which means that if there is a security association then use it but if 143there is not then the packets are not processed by IPsec. 144The value 145.Li 2 146is synonymous with 147.Dq Li require , 148which requires that a security association must exist for the packets 149to move, and not be dropped. 150These terms are defined in 151.Xr ipsec_set_policy 8 . 152.Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx 153.It Sy "Name Type Changeable" 154.It "net.inet.ipsec.esp_trans_deflev integer yes" 155.It "net.inet.ipsec.esp_net_deflev integer yes" 156.It "net.inet.ipsec.ah_trans_deflev integer yes" 157.It "net.inet.ipsec.ah_net_deflev integer yes" 158.It "net.inet6.ipsec6.esp_trans_deflev integer yes" 159.It "net.inet6.ipsec6.esp_net_deflev integer yes" 160.It "net.inet6.ipsec6.ah_trans_deflev integer yes" 161.It "net.inet6.ipsec6.ah_net_deflev integer yes" 162.El 163.Pp 164If the kernel does not find a matching, system wide, policy then the 165default value is applied. 166The system wide default policy is specified 167by the following 168.Xr sysctl 8 169variables. 170.Li 0 171means 172.Dq Li discard 173which asks the kernel to drop the packet. 174.Li 1 175means 176.Dq Li none . 177.Bl -column net.inet6.ipsec6.def_policy integerxxx 178.It Sy "Name Type Changeable" 179.It "net.inet.ipsec.def_policy integer yes" 180.It "net.inet6.ipsec6.def_policy integer yes" 181.El 182.\" 183.Ss Miscellaneous sysctl variables 184The following variables are accessible via 185.Xr sysctl 8 , 186for tweaking the kernel's IPsec behavior: 187.Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx 188.It Sy "Name Type Changeable" 189.It "net.inet.ipsec.ah_cleartos integer yes" 190.It "net.inet.ipsec.ah_offsetmask integer yes" 191.It "net.inet.ipsec.dfbit integer yes" 192.It "net.inet.ipsec.ecn integer yes" 193.It "net.inet.ipsec.debug integer yes" 194.It "net.inet6.ipsec6.ecn integer yes" 195.It "net.inet6.ipsec6.debug integer yes" 196.El 197.Pp 198The variables are interpreted as follows: 199.Bl -tag -width 6n 200.It Li ipsec.ah_cleartos 201If set to non-zero, the kernel clears the type-of-service field in the IPv4 header 202during AH authentication data computation. 203This variable is used to get current systems to inter-operate with devices that 204implement RFC1826 AH. 205It should be set to non-zero 206(clear the type-of-service field) 207for RFC2402 conformance. 208.It Li ipsec.ah_offsetmask 209During AH authentication data computation, the kernel will include a 21016bit fragment offset field 211(including flag bits) 212in the IPv4 header, after computing logical AND with the variable. 213The variable is used for inter-operating with devices that 214implement RFC1826 AH. 215It should be set to zero 216(clear the fragment offset field during computation) 217for RFC2402 conformance. 218.It Li ipsec.dfbit 219This variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. 220If set to 0, the DF bit on the outer IPv4 header will be cleared while 2211 means that the outer DF bit is set regardless from the inner DF bit and 2222 indicates that the DF bit is copied from the inner header to the 223outer one. 224The variable is supplied to conform to RFC2401 chapter 6.1. 225.It Li ipsec.ecn 226If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will 227be friendly to ECN 228(explicit congestion notification), 229as documented in 230.Li draft-ietf-ipsec-ecn-02.txt . 231.Xr gif 4 232talks more about the behavior. 233.It Li ipsec.debug 234If set to non-zero, debug messages will be generated via 235.Xr syslog 3 . 236.El 237.Pp 238Variables under the 239.Li net.inet6.ipsec6 240tree have similar meanings to those described above. 241.\" 242.Sh PROTOCOLS 243The 244.Nm 245protocol acts as a plug-in to the 246.Xr inet 4 247and 248.Xr inet6 4 249protocols and therefore supports most of the protocols defined upon 250those IP-layer protocols. 251The 252.Xr icmp 4 253and 254.Xr icmp6 4 255protocols may behave differently with 256.Nm 257because 258.Nm 259can prevent 260.Xr icmp 4 261or 262.Xr icmp6 4 263routines from looking into the IP payload. 264.\" 265.Sh SEE ALSO 266.Xr ioctl 2 , 267.Xr socket 2 , 268.Xr ipsec_set_policy 3 , 269.Xr fast_ipsec 4 , 270.Xr icmp6 4 , 271.Xr intro 4 , 272.Xr ip6 4 , 273.Xr setkey 8 , 274.Xr sysctl 8 275.\".Xr racoon 8 276.Rs 277.%A "S. Kent" 278.%A "R. Atkinson" 279.%T "IP Authentication Header" 280.%O "RFC 2404" 281.Re 282.Rs 283.%A "S. Kent" 284.%A "R. Atkinson" 285.%T "IP Encapsulating Security Payload (ESP)" 286.%O "RFC 2406" 287.Re 288.Sh STANDARDS 289.Rs 290.%A Daniel L. McDonald 291.%A Craig Metz 292.%A Bao G. Phan 293.%T "PF_KEY Key Management API, Version 2" 294.%R RFC 295.%N 2367 296.Re 297.Pp 298.Rs 299.%A "D. L. McDonald" 300.%T "A Simple IP Security API Extension to BSD Sockets" 301.%R internet draft 302.%N "draft-mcdonald-simple-ipsec-api-03.txt" 303.%O work in progress material 304.Re 305.Sh HISTORY 306The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack. 307.Sh BUGS 308The IPsec support is subject to change as the IPsec protocols develop. 309.Pp 310There is no single standard for the policy engine API, 311so the policy engine API described herein is just for KAME implementation. 312.Pp 313AH and tunnel mode encapsulation may not work as you might expect. 314If you configure inbound 315.Dq require 316policy with an AH tunnel or any IPsec encapsulating policy with AH 317(like 318.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) , 319tunnelled packets will be rejected. 320This is because the policy check is enforced on the inner packet on reception, 321and AH authenticates encapsulating 322(outer) 323packet, not the encapsulated 324(inner) 325packet 326(so for the receiving kernel there is no sign of authenticity). 327The issue will be solved when we revamp our policy engine to keep all the 328packet decapsulation history. 329.Pp 330When a large database of security associations or policies is present 331in the kernel the 332.Dv SADB_DUMP 333and 334.Dv SADB_SPDDUMP 335operations on 336.Dv PF_KEY 337sockets may fail due to lack of space. 338Increasing the socket buffer 339size may alleviate this problem. 340