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.
$FreeBSD: head/share/man/man4/ipsec.4 162404 2006-09-18 15:24:20Z ru $
.Dd August 24, 2006 .Dt IPSEC 4 .Os .Sh NAME .Nm ipsec .Nd IP security protocol .Sh SYNOPSIS .Cd "options IPSEC" .Cd "options IPSEC_DEBUG" .Cd "options IPSEC_ESP" .Cd "options IPSEC_FILTERGIF"
p
n sys/types.h n netinet/in.h n netinet6/ipsec.h .Sh DESCRIPTION
.Nm
is a security protocol implemented within the Internet Protocol layer
of the TCP/IP stack.
.Nm
is defined for both IPv4 and IPv6
.Xr ( inet 4
and
.Xr inet6 4 ) .
.Nm
contains two protocols,
ESP, the encapsulated security payload protocol and
AH, the authentication header protocol.
ESP prevents unauthorized parties from reading the payload of an IP packet
by encrypting it using
secret key cryptography algorithms.
AH both authenticates guarantees the integrity of an IP packet
by attaching a cryptographic checksum computed using one-way hash functions.
.Nm
has operates in one of two modes: transport mode or tunnel mode.
Transport mode is used to protect peer-to-peer communication between end nodes.
Tunnel mode encapsulates IP packets within other IP packets
and is designed for security gateways such as VPN endpoints.
.Ss Kernel interface
.Nm
is controlled by a key management and policy engine,
that reside in the operating system kernel.
Key management
is the process of associating keys with security associations, also
know as SAs.
Policy management dictates when new security
associations created or destroyed.
p The key management engine can be accessed from userland by using .Dv PF_KEY sockets. The .Dv PF_KEY socket API is defined in RFC2367.
p The policy engine is controlled by an extension to the .Dv PF_KEY API, .Xr setsockopt 2 operations, and .Xr sysctl 3 interface. The kernel implements an extended version of the .Dv PF_KEY interface, and allows the programmer to define IPsec policies which are similar to the per-packet filters. The .Xr setsockopt 2 interface is used to define per-socket behavior, and .Xr sysctl 3 interface is used to define host-wide default behavior.
p
The kernel code does not implement a dynamic encryption key exchange protocol
such as IKE
(Internet Key Exchange).
Key exchange protocols are beyond what is necessary in the kernel and
should be implemented as daemon processes which call the
.Nm APIs.
.Ss Policy management
IPsec policies can be managed in one of two ways, either by
configuring per-socket policies using the
.Xr setsockopt 2
system calls, or by configuring kernel level packet filter-based
policies using the
.Dv PF_KEY
interface, via the
.Xr setkey 8
command.
In either case, IPsec policies must be specified using the syntax described in
.Xr ipsec_set_policy 3 .
Please refer to the
.Xr setkey 8
man page for instructions on its use.
p When setting policies using the .Xr setkey 8 command the .Dq Li default option you can have the system use its default policy, explained below, for processing packets. The following sysctl variables are available for configuring the system's IPsec behavior. The variables can have one of two values. A .Li 1 means .Dq Li use , which means that if there is a security association then use it but if there is not then the packets are not processed by IPsec. The value .Li 2 is synonymous with .Dq Li require , which requires that a security association must exist for the packets to move, and not be dropped. These terms are defined in .Xr ipsec_set_policy 8 . l -column net.inet6.ipsec6.esp_trans_deflev integerxxx t Sy "Name Type Changeable" t "net.inet.ipsec.esp_trans_deflev integer yes" t "net.inet.ipsec.esp_net_deflev integer yes" t "net.inet.ipsec.ah_trans_deflev integer yes" t "net.inet.ipsec.ah_net_deflev integer yes" t "net.inet6.ipsec6.esp_trans_deflev integer yes" t "net.inet6.ipsec6.esp_net_deflev integer yes" t "net.inet6.ipsec6.ah_trans_deflev integer yes" t "net.inet6.ipsec6.ah_net_deflev integer yes" .El
p
If the kernel does not find a matching, system wide, policy then the
default value is applied.
The system wide default policy 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 .
l -column net.inet6.ipsec6.def_policy integerxxx t Sy "Name Type Changeable" t "net.inet.ipsec.def_policy integer yes" t "net.inet6.ipsec6.def_policy integer yes" .El
.Ss Miscellaneous sysctl variables
The following variables are accessible via
.Xr sysctl 8 ,
for tweaking the kernel's IPsec behavior:
l -column net.inet6.ipsec6.inbonud_call_ike integerxxx t Sy "Name Type Changeable" t "net.inet.ipsec.ah_cleartos integer yes" t "net.inet.ipsec.ah_offsetmask integer yes" t "net.inet.ipsec.dfbit integer yes" t "net.inet.ipsec.ecn integer yes" t "net.inet.ipsec.debug integer yes" t "net.inet6.ipsec6.ecn integer yes" t "net.inet6.ipsec6.debug integer yes" .El
p The variables are interpreted as follows: l -tag -width 6n t Li ipsec.ah_cleartos If set to non-zero, the kernel clears the type-of-service field in the IPv4 header during AH authentication data computation. This variable is used to get current systems to inter-operate with devices that implement RFC1826 AH. It should be set to non-zero (clear the type-of-service field) for RFC2402 conformance. t Li ipsec.ah_offsetmask During AH authentication data computation, the kernel will include a 16bit fragment offset field (including flag bits) in the IPv4 header, after computing logical AND with the variable. The variable is used for inter-operating with devices that implement RFC1826 AH. It should be set to zero (clear the fragment offset field during computation) for RFC2402 conformance. t Li ipsec.dfbit This variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation. If set to 0, the DF bit on the outer IPv4 header will be cleared while 1 means that the outer DF bit is set regardless from the inner DF bit and 2 indicates that the DF bit is copied from the inner header to the outer one. The variable is supplied to conform to RFC2401 chapter 6.1. t 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. t Li ipsec.debug If set to non-zero, debug messages will be generated via .Xr syslog 3 . .El
p
Variables under the
.Li net.inet6.ipsec6
tree have similar meanings to those described above.
.Sh PROTOCOLS
The
.Nm
protocol acts as a plug-in to the
.Xr inet 4
and
.Xr inet6 4
protocols and therefore supports most of the protocols defined upon
those IP-layer protocols.
The
.Xr icmp 4
and
.Xr icmp6 4
protocols may behave differently with
.Nm
because
.Nm
can prevent
.Xr icmp 4
or
.Xr icmp6 4
routines from looking into the IP payload.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr ipsec_set_policy 3 ,
.Xr fast_ipsec 4 ,
.Xr icmp6 4 ,
.Xr intro 4 ,
.Xr ip6 4 ,
.Xr setkey 8 ,
.Xr sysctl 8
.Xr racoon 8
.Rs
.%A "S. Kent"
.%A "R. Atkinson"
.%T "IP Authentication Header"
.%O "RFC 2404"
.Re
.Rs
.%A "S. Kent"
.%A "R. Atkinson"
.%T "IP Encapsulating Security Payload (ESP)"
.%O "RFC 2406"
.Re
.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
p .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.
p There is no single standard for the policy engine API, so the policy engine API described herein is just for KAME implementation.
p AH and tunnel mode encapsulation may not work as you might expect. If you configure inbound .Dq require policy with an 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 the policy check is enforced on the inner packet on reception, and AH authenticates encapsulating (outer) packet, not the encapsulated (inner) packet (so for the receiving kernel there is no sign of authenticity). The issue will be solved when we revamp our policy engine to keep all the packet decapsulation history.
p When a large database of security associations or policies is present in the kernel the .Dv SADB_DUMP and .Dv SADB_SPDDUMP operations on .Dv PF_KEY sockets may fail due to lack of space. Increasing the socket buffer size may alleviate this problem.