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

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.Dd August 24, 2006
.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
.Cd "options IPSEC"
.Cd "options IPSEC_DEBUG"
.Cd "options IPSEC_ESP"
.Cd "options IPSEC_FILTERGIF"
.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.
.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 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.
.Pp
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.
.Pp
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 .
.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 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 .
.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 the kernel's 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 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.
.It 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.
.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 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.
.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 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
.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 the 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 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.
.Pp
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.