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 February 14, 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.Sh DESCRIPTION 43.Nm 44is a security protocol implemented within the Internet Protocol layer 45of the TCP/IP stack. 46.Nm 47is defined for both IPv4 and IPv6 48.Xr ( inet 4 49and 50.Xr inet6 4 ) . 51.Nm 52contains two protocols, 53ESP, the encapsulated security payload protocol and 54AH, the authentication header protocol. 55ESP prevents unauthorized parties from reading the payload of an IP packet 56by encrypting it using 57secret key cryptography algorithms. 58AH both authenticates guarantees the integrity of an IP packet 59by attaching a cryptographic checksum computed using one-way hash functions. 60.Nm 61has operates in one of two modes: transport mode or tunnel mode. 62Transport mode is used to protect peer-to-peer communication between end nodes. 63Tunnel mode encapsulates IP packets within other IP packets 64and is designed for security gateways such as VPN endpoints. 65.\" 66.Ss Kernel interface 67.Nm 68is controlled by a key management and policy engine, 69that reside in the operating system kernel. Key management 70is the process of associating keys with security associations, also 71know as SAs. Policy management dictates when new security 72associations created or destroyed. 73.Pp 74The key management engine can be accessed from userland by using 75.Dv PF_KEY 76sockets. 77The 78.Dv PF_KEY 79socket API is defined in RFC2367. 80.Pp 81The policy engine is controlled by an extension to the 82.Dv PF_KEY 83API, 84.Xr setsockopt 2 85operations, and 86.Xr sysctl 3 87interface. 88The kernel implements 89an extended version of the 90.Dv PF_KEY 91interface, and allows the programmer to define IPsec policies 92which are similar to the per-packet filters. The 93.Xr setsockopt 2 94interface is used to define per-socket behavior, and 95.Xr sysctl 3 96interface is used to define host-wide default behavior. 97.Pp 98The kernel code does not implement a dynamic encryption key exchange protocol 99such as IKE 100(Internet Key Exchange). 101Key exchange protocols are beyond what is necessary in the kernel and 102should be implemented as daemon processes which call the 103.Nm APIs. 104.\" 105.Ss Policy management 106IPsec policies can be managed in one of two ways, either by 107configuring per-socket policies using the 108.Xr setsockopt 2 109system calls, or by configuring kernel level packet filter-based 110policies using the 111.Dv PF_KEY 112interface, via the 113.Xr setkey 8 114command. 115In either case, IPsec policies must be specified using the syntax described in 116.Xr ipsec_set_policy 3 . 117Please refer to the 118.Xr setkey 8 119man page for instructions on its use. 120.Pp 121When setting policies using the 122.Xr setkey 8 123command the 124.Dq Li default 125option you can have the system use its default policy, explained 126below, for processing packets. 127The following sysctl variables are available for configuring the 128system's IPsec behavior. The variables can have one of two values. 129A 130.Li 1 131means 132.Dq Li use , 133which means that if there is a security association then use it but if 134there is not then the packets are not processed by IPsec. The value 135.Li 2 136is synonymous with 137.Dq Li require , 138which requires that a security association must exist for the packets 139to move, and not be dropped. These terms are defined in 140.Xr ipsec_set_policy 8 . 141.Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx 142.It Sy "Name Type Changeable" 143.It "net.inet.ipsec.esp_trans_deflev integer yes" 144.It "net.inet.ipsec.esp_net_deflev integer yes" 145.It "net.inet.ipsec.ah_trans_deflev integer yes" 146.It "net.inet.ipsec.ah_net_deflev integer yes" 147.It "net.inet6.ipsec6.esp_trans_deflev integer yes" 148.It "net.inet6.ipsec6.esp_net_deflev integer yes" 149.It "net.inet6.ipsec6.ah_trans_deflev integer yes" 150.It "net.inet6.ipsec6.ah_net_deflev integer yes" 151.El 152.Pp 153If the kernel does not find a matching, system wide, policy then the 154default value is applied. The system wide default policy is specified 155by the following 156.Xr sysctl 8 157variables. 158.Li 0 159means 160.Dq Li discard 161which asks the kernel to drop the packet. 162.Li 1 163means 164.Dq Li none . 165.Bl -column net.inet6.ipsec6.def_policy integerxxx 166.It Sy "Name Type Changeable" 167.It "net.inet.ipsec.def_policy integer yes" 168.It "net.inet6.ipsec6.def_policy integer yes" 169.El 170.\" 171.Ss Miscellaneous sysctl variables 172The following variables are accessible via 173.Xr sysctl 8 , 174for tweaking the kernel's IPsec behavior: 175.Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx 176.It Sy "Name Type Changeable" 177.It "net.inet.ipsec.ah_cleartos integer yes" 178.It "net.inet.ipsec.ah_offsetmask integer yes" 179.It "net.inet.ipsec.dfbit integer yes" 180.It "net.inet.ipsec.ecn integer yes" 181.It "net.inet.ipsec.debug integer yes" 182.It "net.inet6.ipsec6.ecn integer yes" 183.It "net.inet6.ipsec6.debug integer yes" 184.El 185.Pp 186The variables are interpreted as follows: 187.Bl -tag -width 6n 188.It Li ipsec.ah_cleartos 189If set to non-zero, the kernel clears the type-of-service field in the IPv4 header 190during AH authentication data computation. 191This variable is used to get current systems to inter-operate with devices that 192implement RFC1826 AH. 193It should be set to non-zero 194(clear the type-of-service field) 195for RFC2402 conformance. 196.It Li ipsec.ah_offsetmask 197During AH authentication data computation, the kernel will include a 19816bit fragment offset field 199(including flag bits) 200in the IPv4 header, after computing logical AND with the variable. 201The variable is used for inter-operating with devices that 202implement RFC1826 AH. 203It should be set to zero 204(clear the fragment offset field during computation) 205for RFC2402 conformance. 206.It Li ipsec.dfbit 207This variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. 208If set to 0, the DF bit on the outer IPv4 header will be cleared while 2091 means that the outer DF bit is set regardless from the inner DF bit and 2102 indicates that the DF bit is copied from the inner header to the 211outer one. 212The variable is supplied to conform to RFC2401 chapter 6.1. 213.It Li ipsec.ecn 214If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will 215be friendly to ECN 216(explicit congestion notification), 217as documented in 218.Li draft-ietf-ipsec-ecn-02.txt . 219.Xr gif 4 220talks more about the behavior. 221.It Li ipsec.debug 222If set to non-zero, debug messages will be generated via 223.Xr syslog 3 . 224.El 225.Pp 226Variables under the 227.Li net.inet6.ipsec6 228tree have similar meanings to those described above. 229.\" 230.Sh PROTOCOLS 231The 232.Nm 233protocol acts as a plug-in to the 234.Xr inet 4 235and 236.Xr inet6 4 237protocols and therefore supports most of the protocols defined upon 238those IP-layer protocols. The 239.Xr icmp 4 240and 241.Xr icmp6 4 242protocols may behave differently with 243.Nm 244because 245.Nm 246can prevent 247.Xr icmp 4 248or 249.Xr icmp6 4 250routines from looking into the IP payload. 251.\" 252.Sh SEE ALSO 253.Xr ioctl 2 , 254.Xr socket 2 , 255.Xr ipsec_set_policy 3 , 256.Xr icmp6 4 , 257.Xr intro 4 , 258.Xr ip6 4 , 259.Xr setkey 8 , 260.Xr sysctl 8 261.\".Xr racoon 8 262.Rs 263.%A "S. Kent" 264.%A "R. Atkinson" 265.%T "IP Authentication Header" 266.%O "RFC 2404" 267.Re 268.Rs 269.%A "S. Kent" 270.%A "R. Atkinson" 271.%T "IP Encapsulating Security Payload (ESP)" 272.%O "RFC 2406" 273.Re 274.Sh STANDARDS 275.Rs 276.%A Daniel L. McDonald 277.%A Craig Metz 278.%A Bao G. Phan 279.%T "PF_KEY Key Management API, Version 2" 280.%R RFC 281.%N 2367 282.Re 283.Pp 284.Rs 285.%A "D. L. McDonald" 286.%T "A Simple IP Security API Extension to BSD Sockets" 287.%R internet draft 288.%N "draft-mcdonald-simple-ipsec-api-03.txt" 289.%O work in progress material 290.Re 291.Sh HISTORY 292The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack. 293.Sh BUGS 294The IPsec support is subject to change as the IPsec protocols develop. 295.Pp 296There is no single standard for the policy engine API, 297so the policy engine API described herein is just for KAME implementation. 298.Pp 299AH and tunnel mode encapsulation may not work as you might expect. 300If you configure inbound 301.Dq require 302policy with an AH tunnel or any IPsec encapsulating policy with AH 303(like 304.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) , 305tunnelled packets will be rejected. 306This is because the policy check is enforced on the inner packet on reception, 307and AH authenticates encapsulating 308(outer) 309packet, not the encapsulated 310(inner) 311packet 312(so for the receiving kernel there is no sign of authenticity). 313The issue will be solved when we revamp our policy engine to keep all the 314packet decapsulation history. 315.Pp 316When a large database of security associations or policies is present 317in the kernel the 318.Dv SADB_DUMP 319and 320.Dv SADB_SPDDUMP 321operations on 322.Dv PF_KEY 323sockets may fail due to lack of space. Increasing the socket buffer 324size may alleviate this problem. 325