.\"	$NetBSD: ipsec.4,v 1.41.2.1 2018/02/11 21:17:34 snj Exp $
.\"	$KAME: ipsec.4,v 1.17 2001/06/27 15:25:10 itojun Exp $
.\"
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.Dd January 10, 2018
.Dt IPSEC 4
.Os
.Sh NAME
.Nm ipsec
.Nd IP security protocol
.Sh DESCRIPTION
This manual pages describes the IPsec protocol.
For the network device driver please see
.Xr ipsecif 4 .
.Pp
.Nm
is a security protocol in the Internet Protocol (IP) layer.
.Nm
is defined for both IPv4 and IPv6
.Po
.Xr inet 4
and
.Xr inet6 4
.Pc .
.Nm
consists of two sub-protocols:
.Bl -hang
.It Em Encapsulated Security Payload Pq ESP
protects IP payloads from wire-tapping (interception) by encrypting them with
secret key cryptography algorithms.
.It Em Authentication Header Pq AH
guarantees the integrity of IP packets
and protects them from intermediate alteration or impersonation,
by attaching cryptographic checksums computed by one-way hash functions.
.El
.Pp
.Nm
has two operation modes:
.Bl -hang
.It Em Transport mode
is for protecting peer-to-peer communication between end nodes.
.It Em Tunnel mode
includes IP-in-IP encapsulation operation
and is designed for security gateways, as in Virtual Private Network (VPN)
configurations.
.El
.Pp
Since version 6,
.Nx
uses the IPsec implementation formerly known as FAST_IPSEC.
Its specifics and kernel options are described in the
.Xr fast_ipsec 4
manual page.
.Ss Kernel interface
.Nm
is controlled by two engines in the kernel: one for key management
and one for policy.
.Pp
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.
.Pp
The policy engine can be controlled through the
.Dv PF_KEY
API,
.Xr setsockopt 2
operations, and
the
.Xr sysctl 3
interface.
The kernel implements an
extended version of the
.Dv PF_KEY
interface and allows you to define IPsec policy like per-packet filters.
.Xr setsockopt 2
is used to define per-socket behavior, and
.Xr sysctl 3
is used to define host-wide default behavior.
.Pp
The kernel does not implement dynamic encryption key exchange protocols
like IKE
.Pq Internet Key Exchange .
That should be done in userland
.Pq usually as a daemon ,
using the APIs described above.
.\"
.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 the
.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 on a per-socket basis.
You can enforce particular IPsec policy on packets that go through a
particular socket.
.Pp
With
.Xr setkey 8
you can define IPsec policy for packets using a form of packet
filtering rules.
See
.Xr setkey 8
for details.
.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 to system-wide
.Xr sysctl 8
variables 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 Ta Sy Type Ta Sy Changeable
.It net.inet.ipsec.esp_trans_deflev Ta integer Ta yes
.It net.inet.ipsec.esp_net_deflev Ta integer Ta yes
.It net.inet.ipsec.ah_trans_deflev Ta integer Ta yes
.It net.inet.ipsec.ah_net_deflev Ta integer Ta yes
.It net.inet6.ipsec6.esp_trans_deflev Ta integer Ta yes
.It net.inet6.ipsec6.esp_net_deflev Ta integer Ta yes
.It net.inet6.ipsec6.ah_trans_deflev Ta integer Ta yes
.It net.inet6.ipsec6.ah_net_deflev Ta integer Ta yes
.El
.Pp
If the kernel finds no matching policy, the system-wide default
value is applied.
System-wide defaults are 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.esp_trans_deflev integerxxx
.It Sy Name Ta Sy Type Ta Sy Changeable
.It net.inet.ipsec.def_policy Ta integer Ta yes
.It net.inet6.ipsec6.def_policy Ta integer Ta 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.esp_trans_deflev integerxxx
.It Sy Name Ta Sy Type Ta Sy Changeable
.It net.inet.ipsec.ah_cleartos Ta integer Ta yes
.It net.inet.ipsec.ah_offsetmask Ta integer Ta yes
.It net.inet.ipsec.crypto_support Ta integer Ta yes
.It net.inet.ipsec.dfbit Ta integer Ta yes
.It net.inet.ipsec.ecn Ta integer Ta yes
.It net.inet.ipsec.debug Ta integer Ta yes
.It net.inet6.ipsec6.ecn Ta integer Ta yes
.It net.inet6.ipsec6.debug Ta integer Ta yes
.El
.Pp
The variables are interpreted as follows:
.Bl -tag -width "123456"
.It 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.
The variable is for tweaking AH behavior to interoperate with devices that
implement RFC1826 AH.
It should be set to non-zero
.Pq clear the type-of-service field
for RFC2402 conformance.
.It Li ipsec.ah_offsetmask
During AH authentication data computation, the kernel will include a
16 bit fragment offset field
.Pq including flag bits
in the 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
.Pq clear the fragment offset field during computation
for RFC2402 conformance.
.It Li ipsec.crypto_support
This variable configures the kernel behavior for selecting encryption drivers.
If set to > 0, the kernel will select a hardware encryption driver first.
If set to < 0, the kernel will select a software encryption driver first.
If set to 0, the kernel will select either a hardware or software driver.
.It 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.
1 means that the outer DF bit is set 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
.Pq 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 the
.Li net.inet6.ipsec6
tree have similar meanings to their
.Li net.inet.ipsec
counterparts.
.\"
.Sh PROTOCOLS
The
.Nm
protocol works like a 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 ipsec .
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 fast_ipsec 4 ,
.Xr icmp6 4 ,
.Xr intro 4 ,
.Xr ip6 4 ,
.Xr ipsecif 4 ,
.Xr racoon 8 ,
.Xr setkey 8 ,
.Xr sysctl 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
.Sh BUGS
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 the version
introduced by KAME.
.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
.Po
like
.Dq Li esp/tunnel/A-B/use ah/transport/A-B/require
.Pc ,
tunneled packets will be rejected.
This is because we enforce policy check on inner packet on reception,
and AH authenticates encapsulating
.Pq outer
packet, not the encapsulated
.Pq inner
packet
.Po
so for the receiving kernel there's no sign of authenticity
.Pc .
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 or use
.Xr sysctl 8
interface.