freebsd-skq/share/man/man4/ipsec.4

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.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.