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.In sys/types.h 40.In netinet/in.h 41.In netinet6/ipsec.h 42.Cd "options IPSEC" 43.Cd "options IPSEC_DEBUG" 44.Cd "options IPSEC_ESP" 45.Cd "options IPSEC_FILTERGIF" 46.Sh DESCRIPTION 47.Nm 48is a security protocol implemented within the Internet Protocol layer 49of the TCP/IP stack. 50.Nm 51is defined for both IPv4 and IPv6 52.Xr ( inet 4 53and 54.Xr inet6 4 ) . 55.Nm 56contains two protocols, 57ESP, the encapsulated security payload protocol and 58AH, the authentication header protocol. 59ESP prevents unauthorized parties from reading the payload of an IP packet 60by encrypting it using 61secret key cryptography algorithms. 62AH both authenticates guarantees the integrity of an IP packet 63by attaching a cryptographic checksum computed using one-way hash functions. 64.Nm 65has operates in one of two modes: transport mode or tunnel mode. 66Transport mode is used to protect peer-to-peer communication between end nodes. 67Tunnel mode encapsulates IP packets within other IP packets 68and is designed for security gateways such as VPN endpoints. 69.\" 70.Ss Kernel interface 71.Nm 72is controlled by a key management and policy engine, 73that reside in the operating system kernel. Key management 74is the process of associating keys with security associations, also 75know as SAs. Policy management dictates when new security 76associations created or destroyed. 77.Pp 78The key management engine can be accessed from userland by using 79.Dv PF_KEY 80sockets. 81The 82.Dv PF_KEY 83socket API is defined in RFC2367. 84.Pp 85The policy engine is controlled by an extension to the 86.Dv PF_KEY 87API, 88.Xr setsockopt 2 89operations, and 90.Xr sysctl 3 91interface. 92The kernel implements 93an extended version of the 94.Dv PF_KEY 95interface, and allows the programmer to define IPsec policies 96which are similar to the per-packet filters. The 97.Xr setsockopt 2 98interface is used to define per-socket behavior, and 99.Xr sysctl 3 100interface is used to define host-wide default behavior. 101.Pp 102The kernel code does not implement a dynamic encryption key exchange protocol 103such as IKE 104(Internet Key Exchange). 105Key exchange protocols are beyond what is necessary in the kernel and 106should be implemented as daemon processes which call the 107.Nm APIs. 108.\" 109.Ss Policy management 110IPsec policies can be managed in one of two ways, either by 111configuring per-socket policies using the 112.Xr setsockopt 2 113system calls, or by configuring kernel level packet filter-based 114policies using the 115.Dv PF_KEY 116interface, via the 117.Xr setkey 8 118command. 119In either case, IPsec policies must be specified using the syntax described in 120.Xr ipsec_set_policy 3 . 121Please refer to the 122.Xr setkey 8 123man page for instructions on its use. 124.Pp 125When setting policies using the 126.Xr setkey 8 127command the 128.Dq Li default 129option you can have the system use its default policy, explained 130below, for processing packets. 131The following sysctl variables are available for configuring the 132system's IPsec behavior. The variables can have one of two values. 133A 134.Li 1 135means 136.Dq Li use , 137which means that if there is a security association then use it but if 138there is not then the packets are not processed by IPsec. The value 139.Li 2 140is synonymous with 141.Dq Li require , 142which requires that a security association must exist for the packets 143to move, and not be dropped. These terms are defined in 144.Xr ipsec_set_policy 8 . 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 157If the kernel does not find a matching, system wide, policy then the 158default value is applied. The system wide default policy is specified 159by 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 the kernel's 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 the type-of-service field in the IPv4 header 194during AH authentication data computation. 195This variable is used to get current systems to inter-operate 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 a 20216bit fragment offset field 203(including flag bits) 204in the IPv4 header, after computing logical AND with the variable. 205The variable is used for inter-operating 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 211This variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. 212If set to 0, the DF bit on the outer IPv4 header will be cleared while 2131 means that the outer DF bit is set regardless from the inner DF bit and 2142 indicates that the DF bit is copied from the inner header to the 215outer one. 216The variable is supplied to conform to RFC2401 chapter 6.1. 217.It Li ipsec.ecn 218If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will 219be friendly to ECN 220(explicit congestion notification), 221as documented in 222.Li draft-ietf-ipsec-ecn-02.txt . 223.Xr gif 4 224talks more about the behavior. 225.It Li ipsec.debug 226If set to non-zero, debug messages will be generated via 227.Xr syslog 3 . 228.El 229.Pp 230Variables under the 231.Li net.inet6.ipsec6 232tree have similar meanings to those described above. 233.\" 234.Sh PROTOCOLS 235The 236.Nm 237protocol acts as a plug-in to the 238.Xr inet 4 239and 240.Xr inet6 4 241protocols and therefore supports most of the protocols defined upon 242those IP-layer protocols. The 243.Xr icmp 4 244and 245.Xr icmp6 4 246protocols may behave differently with 247.Nm 248because 249.Nm 250can prevent 251.Xr icmp 4 252or 253.Xr icmp6 4 254routines from looking into the IP payload. 255.\" 256.Sh SEE ALSO 257.Xr ioctl 2 , 258.Xr socket 2 , 259.Xr ipsec_set_policy 3 , 260.Xr fast_ipsec 4 , 261.Xr icmp6 4 , 262.Xr intro 4 , 263.Xr ip6 4 , 264.Xr setkey 8 , 265.Xr sysctl 8 266.\".Xr racoon 8 267.Rs 268.%A "S. Kent" 269.%A "R. Atkinson" 270.%T "IP Authentication Header" 271.%O "RFC 2404" 272.Re 273.Rs 274.%A "S. Kent" 275.%A "R. Atkinson" 276.%T "IP Encapsulating Security Payload (ESP)" 277.%O "RFC 2406" 278.Re 279.Sh STANDARDS 280.Rs 281.%A Daniel L. McDonald 282.%A Craig Metz 283.%A Bao G. Phan 284.%T "PF_KEY Key Management API, Version 2" 285.%R RFC 286.%N 2367 287.Re 288.Pp 289.Rs 290.%A "D. L. McDonald" 291.%T "A Simple IP Security API Extension to BSD Sockets" 292.%R internet draft 293.%N "draft-mcdonald-simple-ipsec-api-03.txt" 294.%O work in progress material 295.Re 296.Sh HISTORY 297The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack. 298.Sh BUGS 299The IPsec support is subject to change as the IPsec protocols develop. 300.Pp 301There is no single standard for the policy engine API, 302so the policy engine API described herein is just for KAME implementation. 303.Pp 304AH and tunnel mode encapsulation may not work as you might expect. 305If you configure inbound 306.Dq require 307policy with an AH tunnel or any IPsec encapsulating policy with AH 308(like 309.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) , 310tunnelled packets will be rejected. 311This is because the policy check is enforced on the inner packet on reception, 312and AH authenticates encapsulating 313(outer) 314packet, not the encapsulated 315(inner) 316packet 317(so for the receiving kernel there is no sign of authenticity). 318The issue will be solved when we revamp our policy engine to keep all the 319packet decapsulation history. 320.Pp 321When a large database of security associations or policies is present 322in the kernel the 323.Dv SADB_DUMP 324and 325.Dv SADB_SPDDUMP 326operations on 327.Dv PF_KEY 328sockets may fail due to lack of space. Increasing the socket buffer 329size may alleviate this problem. 330