.\" $FreeBSD: src/share/man/man4/ipsec.4,v 126.96.36.199 2001/12/17 11:30:12 ru Exp $ .\" $KAME: ipsec.4,v 1.17 2001/06/27 15:25:10 itojun Exp $ .\" .\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the project nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd January 29, 1999 .Dt IPSEC 4 .Os .Sh NAME .Nm ipsec .Nd IP security protocol .Sh SYNOPSIS .In sys/types.h .In netinet/in.h .In netinet6/ipsec.h .Sh DESCRIPTION .Nm is a security protocol in Internet Protocol layer. .Nm is defined for both IPv4 and IPv6 .Xr ( inet 4 and .Xr inet6 4 ) . .Nm consists of two sub-protocols, namely ESP (encapsulated security payload) and AH (authentication header). ESP protects IP payload from wire-tapping by encrypting it by secret key cryptography algorithms. AH guarantees integrity of IP packet and protects it from intermediate alteration or impersonation, by attaching cryptographic checksum computed by one-way hash functions. .Nm has two operation modes: transport mode and tunnel mode. Transport mode is for protecting peer-to-peer communication between end nodes. Tunnel mode includes IP-in-IP encapsulation operation and is designed for security gateways, like VPN configurations. .\" .Ss Kernel interface .Nm is controlled by key management engine and policy engine, in the operating system kernel. .Pp Key management engine can be accessed from the userland by using .Dv PF_KEY sockets. The .Dv PF_KEY socket API is defined in RFC2367. .Pp Policy engine can be controlled by extended part of .Dv PF_KEY API, .Xr setsockopt 2 operations, and .Xr sysctl 3 interface. The kernel implements extended version of .Dv PF_KEY interface, and allows you to define IPsec policy like per-packet filters. .Xr setsockopt 2 interface is used to define per-socket behavior, and .Xr sysctl 3 interface is used to define host-wide default behavior. .Pp The kernel code does not implement dynamic encryption key exchange protocol like IKE (Internet Key Exchange). That should be implemented as userland programs (usually as daemons), by using the above described APIs. .\" .Ss Policy management The kernel implements experimental policy management code. You can manage the IPsec policy in two ways. One is to configure per-socket policy using .Xr setsockopt 2 . The other is to configure kernel packet filter-based policy using .Dv PF_KEY interface, via .Xr setkey 8 . In both cases, IPsec policy must be specified with syntax described in .Xr ipsec_set_policy 3 . .Pp With .Xr setsockopt 2 , you can define IPsec policy in per-socket basis. You can enforce particular IPsec policy onto packets that go through particular socket. .Pp With .Xr setkey 8 you can define IPsec policy against packets, using sort of packet filtering rule. Refer to .Xr setkey 8 on how to use it. .Pp In the latter case, .Dq Li default policy is allowed for use with .Xr setkey 8 . By configuring policy to .Li default , you can refer system-wide .Xr sysctl 8 variable for default settings. The following variables are available. .Li 1 means .Dq Li use , and .Li 2 means .Dq Li require in the syntax. .Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx .It Sy "Name Type Changeable" .It "net.inet.ipsec.esp_trans_deflev integer yes" .It "net.inet.ipsec.esp_net_deflev integer yes" .It "net.inet.ipsec.ah_trans_deflev integer yes" .It "net.inet.ipsec.ah_net_deflev integer yes" .It "net.inet6.ipsec6.esp_trans_deflev integer yes" .It "net.inet6.ipsec6.esp_net_deflev integer yes" .It "net.inet6.ipsec6.ah_trans_deflev integer yes" .It "net.inet6.ipsec6.ah_net_deflev integer yes" .El .Pp If kernel finds no matching policy system wide default value is applied. System wide default is specified by the following .Xr sysctl 8 variables. .Li 0 means .Dq Li discard which asks the kernel to drop the packet. .Li 1 means .Dq Li none . .Bl -column net.inet6.ipsec6.def_policy integerxxx .It Sy "Name Type Changeable" .It "net.inet.ipsec.def_policy integer yes" .It "net.inet6.ipsec6.def_policy integer yes" .El .\" .Ss Miscellaneous sysctl variables The following variables are accessible via .Xr sysctl 8 , for tweaking kernel IPsec behavior: .Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx .It Sy "Name Type Changeable" .It "net.inet.ipsec.ah_cleartos integer yes" .It "net.inet.ipsec.ah_offsetmask integer yes" .It "net.inet.ipsec.dfbit integer yes" .It "net.inet.ipsec.ecn integer yes" .It "net.inet.ipsec.debug integer yes" .It "net.inet6.ipsec6.ecn integer yes" .It "net.inet6.ipsec6.debug integer yes" .El .Pp The variables are interpreted as follows: .Bl -tag -width 6n .It Li ipsec.ah_cleartos If set to non-zero, the kernel clears type-of-service field in the IPv4 header during AH authentication data computation. The variable is for tweaking AH behavior to interoperate with devices that implement RFC1826 AH. It should be set to non-zero (clear the type-of-service field) for RFC2402 conformance. .It Li ipsec.ah_offsetmask During AH authentication data computation, the kernel will include 16bit fragment offset field (including flag bits) in IPv4 header, after computing logical AND with the variable. The variable is for tweaking AH behavior to interoperate with devices that implement RFC1826 AH. It should be set to zero (clear the fragment offset field during computation) for RFC2402 conformance. .It Li ipsec.dfbit The variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. If set to 0, DF bit on the outer IPv4 header will be cleared. 1 means that the outer DF bit is set regardless from the inner DF bit. 2 means that the DF bit is copied from the inner header to the outer. The variable is supplied to conform to RFC2401 chapter 6.1. .It Li ipsec.ecn If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will be friendly to ECN (explicit congestion notification), as documented in .Li draft-ietf-ipsec-ecn-02.txt . .Xr gif 4 talks more about the behavior. .It Li ipsec.debug If set to non-zero, debug messages will be generated via .Xr syslog 3 . .El .Pp Variables under .Li net.inet6.ipsec6 tree has similar meaning as the .Li net.inet.ipsec counterpart. .\" .Sh PROTOCOLS The .Nm protocol works like plug-in to .Xr inet 4 and .Xr inet6 4 protocols. Therefore, .Nm supports most of the protocols defined upon those IP-layer protocols. Some of the protocols, like .Xr icmp 4 or .Xr icmp6 4 , may behave differently with .Nm . This is because .Nm can prevent .Xr icmp 4 or .Xr icmp6 4 routines from looking into IP payload. .\" .Sh SEE ALSO .Xr ioctl 2 , .Xr socket 2 , .Xr ipsec_set_policy 3 , .Xr icmp6 4 , .Xr intro 4 , .Xr ip6 4 , .Xr setkey 8 , .Xr sysctl 8 .\".Xr racoon 8 .Sh STANDARDS .Rs .%A Daniel L. McDonald .%A Craig Metz .%A Bao G. Phan .%T "PF_KEY Key Management API, Version 2" .%R RFC .%N 2367 .Re .Pp .Rs .%A "D. L. McDonald" .%T "A Simple IP Security API Extension to BSD Sockets" .%R internet draft .%N "draft-mcdonald-simple-ipsec-api-03.txt" .%O work in progress material .Re .Sh HISTORY The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack. .Sh BUGS The IPsec support is subject to change as the IPsec protocols develop. .Pp There is no single standard for policy engine API, so the policy engine API described herein is just for KAME implementation. .Pp AH and tunnel mode encapsulation may not work as you might expect. If you configure inbound .Dq require policy against AH tunnel or any IPsec encapsulating policy with AH (like .Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) , tunnelled packets will be rejected. This is because we enforce policy check on inner packet on reception, and AH authenticates encapsulating (outer) packet, not the encapsulated (inner) packet (so for the receiving kernel there's no sign of authenticity). The issue will be solved when we revamp our policy engine to keep all the packet decapsulation history. .Pp Under certain condition, truncated result may be raised from the kernel against .Dv SADB_DUMP and .Dv SADB_SPDDUMP operation on .Dv PF_KEY socket. This occurs if there are too many database entries in the kernel and socket buffer for the .Dv PF_KEY socket is insufficient. If you manipulate many IPsec key/policy database entries, increase the size of socket buffer.