325 lines
10 KiB
Groff
325 lines
10 KiB
Groff
.\" $KAME: ipsec.4,v 1.17 2001/06/27 15:25:10 itojun Exp $
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.\"
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.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the project nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 14, 2006
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.Dt IPSEC 4
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.Os
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.Sh NAME
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.Nm ipsec
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.Nd IP security protocol
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.Sh SYNOPSIS
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.In sys/types.h
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.In netinet/in.h
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.In netinet6/ipsec.h
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.Sh DESCRIPTION
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.Nm
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is a security protocol implemented within the Internet Protocol layer
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of the TCP/IP stack.
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.Nm
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is defined for both IPv4 and IPv6
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.Xr ( inet 4
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and
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.Xr inet6 4 ) .
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.Nm
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contains two protocols,
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ESP, the encapsulated security payload protocol and
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AH, the authentication header protocol.
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ESP prevents unauthorized parties from reading the payload of an IP packet
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by encrypting it using
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secret key cryptography algorithms.
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AH both authenticates guarantees the integrity of an IP packet
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by attaching a cryptographic checksum computed using one-way hash functions.
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.Nm
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has operates in one of two modes: transport mode or tunnel mode.
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Transport mode is used to protect peer-to-peer communication between end nodes.
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Tunnel mode encapsulates IP packets within other IP packets
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and is designed for security gateways such as VPN endpoints.
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.\"
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.Ss Kernel interface
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.Nm
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is controlled by a key management and policy engine,
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that reside in the operating system kernel. Key management
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is the process of associating keys with security associations, also
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know as SAs. Policy management dictates when new security
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associations created or destroyed.
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.Pp
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The key management engine can be accessed from userland by using
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.Dv PF_KEY
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sockets.
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The
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.Dv PF_KEY
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socket API is defined in RFC2367.
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.Pp
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The policy engine is controlled by an extension to the
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.Dv PF_KEY
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API,
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.Xr setsockopt 2
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operations, and
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.Xr sysctl 3
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interface.
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The kernel implements
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an extended version of the
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.Dv PF_KEY
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interface, and allows the programmer to define IPsec policies
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which are similar to the per-packet filters. The
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.Xr setsockopt 2
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interface is used to define per-socket behavior, and
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.Xr sysctl 3
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interface is used to define host-wide default behavior.
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.Pp
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The kernel code does not implement a dynamic encryption key exchange protocol
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such as IKE
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(Internet Key Exchange).
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Key exchange protocols are beyond what is necessary in the kernel and
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should be implemented as daemon processes which call the
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.Nm APIs.
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.\"
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.Ss Policy management
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IPsec policies can be managed in one of two ways, either by
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configuring per-socket policies using the
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.Xr setsockopt 2
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system calls, or by configuring kernel level packet filter-based
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policies using the
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.Dv PF_KEY
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interface, via the
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.Xr setkey 8
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command.
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In either case, IPsec policies must be specified using the syntax described in
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.Xr ipsec_set_policy 3 .
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Please refer to the
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.Xr setkey 8
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man page for instructions on its use.
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.Pp
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When setting policies using the
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.Xr setkey 8
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command the
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.Dq Li default
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option you can have the system use its default policy, explained
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below, for processing packets.
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The following sysctl variables are available for configuring the
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system's IPsec behavior. The variables can have one of two values.
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A
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.Li 1
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means
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.Dq Li use ,
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which means that if there is a security association then use it but if
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there is not then the packets are not processed by IPsec. The value
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.Li 2
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is synonymous with
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.Dq Li require ,
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which requires that a security association must exist for the packets
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to move, and not be dropped. These terms are defined in
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.Xr ipsec_set_policy 8 .
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.Bl -column net.inet6.ipsec6.esp_trans_deflev integerxxx
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.It Sy "Name Type Changeable"
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.It "net.inet.ipsec.esp_trans_deflev integer yes"
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.It "net.inet.ipsec.esp_net_deflev integer yes"
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.It "net.inet.ipsec.ah_trans_deflev integer yes"
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.It "net.inet.ipsec.ah_net_deflev integer yes"
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.It "net.inet6.ipsec6.esp_trans_deflev integer yes"
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.It "net.inet6.ipsec6.esp_net_deflev integer yes"
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.It "net.inet6.ipsec6.ah_trans_deflev integer yes"
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.It "net.inet6.ipsec6.ah_net_deflev integer yes"
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.El
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.Pp
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If the kernel does not find a matching, system wide, policy then the
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default value is applied. The system wide default policy is specified
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by the following
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.Xr sysctl 8
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variables.
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.Li 0
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means
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.Dq Li discard
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which asks the kernel to drop the packet.
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.Li 1
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means
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.Dq Li none .
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.Bl -column net.inet6.ipsec6.def_policy integerxxx
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.It Sy "Name Type Changeable"
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.It "net.inet.ipsec.def_policy integer yes"
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.It "net.inet6.ipsec6.def_policy integer yes"
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.El
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.\"
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.Ss Miscellaneous sysctl variables
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The following variables are accessible via
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.Xr sysctl 8 ,
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for tweaking the kernel's IPsec behavior:
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.Bl -column net.inet6.ipsec6.inbonud_call_ike integerxxx
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.It Sy "Name Type Changeable"
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.It "net.inet.ipsec.ah_cleartos integer yes"
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.It "net.inet.ipsec.ah_offsetmask integer yes"
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.It "net.inet.ipsec.dfbit integer yes"
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.It "net.inet.ipsec.ecn integer yes"
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.It "net.inet.ipsec.debug integer yes"
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.It "net.inet6.ipsec6.ecn integer yes"
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.It "net.inet6.ipsec6.debug integer yes"
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.El
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.Pp
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The variables are interpreted as follows:
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.Bl -tag -width 6n
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.It Li ipsec.ah_cleartos
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If set to non-zero, the kernel clears the type-of-service field in the IPv4 header
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during AH authentication data computation.
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This variable is used to get current systems to inter-operate with devices that
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implement RFC1826 AH.
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It should be set to non-zero
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(clear the type-of-service field)
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for RFC2402 conformance.
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.It Li ipsec.ah_offsetmask
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During AH authentication data computation, the kernel will include a
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16bit fragment offset field
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(including flag bits)
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in the IPv4 header, after computing logical AND with the variable.
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The variable is used for inter-operating with devices that
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implement RFC1826 AH.
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It should be set to zero
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(clear the fragment offset field during computation)
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for RFC2402 conformance.
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.It Li ipsec.dfbit
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This variable configures the kernel behavior on IPv4 IPsec tunnel encapsulation.
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If set to 0, the DF bit on the outer IPv4 header will be cleared while
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1 means that the outer DF bit is set regardless from the inner DF bit and
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2 indicates that the DF bit is copied from the inner header to the
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outer one.
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The variable is supplied to conform to RFC2401 chapter 6.1.
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.It Li ipsec.ecn
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If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation behavior will
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be friendly to ECN
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(explicit congestion notification),
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as documented in
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.Li draft-ietf-ipsec-ecn-02.txt .
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.Xr gif 4
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talks more about the behavior.
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.It Li ipsec.debug
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If set to non-zero, debug messages will be generated via
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.Xr syslog 3 .
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.El
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.Pp
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Variables under the
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.Li net.inet6.ipsec6
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tree have similar meanings to those described above.
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.\"
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.Sh PROTOCOLS
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The
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.Nm
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protocol acts as a plug-in to the
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.Xr inet 4
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and
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.Xr inet6 4
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protocols and therefore supports most of the protocols defined upon
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those IP-layer protocols. The
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.Xr icmp 4
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and
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.Xr icmp6 4
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protocols may behave differently with
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.Nm
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because
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.Nm
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can prevent
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.Xr icmp 4
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or
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.Xr icmp6 4
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routines from looking into the IP payload.
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.\"
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr socket 2 ,
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.Xr ipsec_set_policy 3 ,
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.Xr icmp6 4 ,
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.Xr intro 4 ,
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.Xr ip6 4 ,
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.Xr setkey 8 ,
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.Xr sysctl 8
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.\".Xr racoon 8
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.Rs
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.%A "S. Kent"
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.%A "R. Atkinson"
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.%T "IP Authentication Header"
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.%O "RFC 2404"
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.Re
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.Rs
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.%A "S. Kent"
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.%A "R. Atkinson"
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.%T "IP Encapsulating Security Payload (ESP)"
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.%O "RFC 2406"
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.Re
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.Sh STANDARDS
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.Rs
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.%A Daniel L. McDonald
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.%A Craig Metz
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.%A Bao G. Phan
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.%T "PF_KEY Key Management API, Version 2"
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.%R RFC
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.%N 2367
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.Re
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.Pp
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.Rs
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.%A "D. L. McDonald"
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.%T "A Simple IP Security API Extension to BSD Sockets"
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.%R internet draft
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.%N "draft-mcdonald-simple-ipsec-api-03.txt"
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.%O work in progress material
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.Re
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.Sh HISTORY
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The implementation described herein appeared in WIDE/KAME IPv6/IPsec stack.
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.Sh BUGS
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The IPsec support is subject to change as the IPsec protocols develop.
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.Pp
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There is no single standard for the policy engine API,
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so the policy engine API described herein is just for KAME implementation.
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.Pp
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AH and tunnel mode encapsulation may not work as you might expect.
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If you configure inbound
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.Dq require
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policy with an AH tunnel or any IPsec encapsulating policy with AH
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(like
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.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require ) ,
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tunnelled packets will be rejected.
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This is because the policy check is enforced on the inner packet on reception,
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and AH authenticates encapsulating
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(outer)
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packet, not the encapsulated
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(inner)
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packet
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(so for the receiving kernel there is no sign of authenticity).
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The issue will be solved when we revamp our policy engine to keep all the
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packet decapsulation history.
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.Pp
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When a large database of security associations or policies is present
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in the kernel the
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.Dv SADB_DUMP
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and
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.Dv SADB_SPDDUMP
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operations on
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.Dv PF_KEY
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sockets may fail due to lack of space. Increasing the socket buffer
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size may alleviate this problem.
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