man/man4/ipsec.4

.\"	$NetBSD: ipsec.4,v 1.37 2012/01/23 00:02:42 wiz Exp $
.\"	$KAME: ipsec.4,v 1.17 2001/06/27 15:25:10 itojun Exp $
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.Dd January 16, 2012
.Dt IPSEC 4
.Os
.Sh NAME
.Nm ipsec
.Nd IP security protocol
.Sh DESCRIPTION
.Nm
is a security protocol in 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:
.Pp
.Bl -hang
.It Em Encapsulated Security Payload Pq ESP
protects IP payload from wire-tapping (interception) by encrypting it with
secret key cryptography algorithms.
.It Em Authentication Header Pq AH
guarantees integrity of IP packet
and protects it from intermediate alteration or impersonation,
by attaching cryptographic checksum computed by one-way hash functions.
.El
.Pp
.Nm
has two operation modes:
.Pp
.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
.Pq Tn VPN
configurations.
.El
.Pp
Since version 6,
.Nx
uses the IPSEC implementation formerly known as FAST_IPSEC.
Its specifics and kernel options are describes in the
.Xr fast_ipsec 4
manual page.
The previous implementation is still supported for a transition
period.
See
.Xr kame_ipsec 4
for details.
.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
.Pq Internet Key Exchange .
That should be implemented as userland programs
.Pq 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 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 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.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.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 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
16bit fragment offset field
.Pq 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
.Pq 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
.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
.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 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 kame_ipsec 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
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 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.