$KAME: ipsec.4,v 1.11 2000/06/14 12:35:02 itojun Exp $
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.Dd January 29, 1999 .Dt IPSEC 4 .Os .Sh NAME .Nm ipsec .Nd IP security protocol .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <netinet/in.h> .Fd #include <netinet6/ipsec.h> .Sh DESCRIPTION .Nm is a security protocol in Internet Protocol layer. .Nm is defined for both IPv4 and IPv6
o .Xr inet 4 and .Xr inet6 4
c . .Nm consists of two sub-protocols, namely ESP
q encapsulated security payload and AH
q 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 commuication 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.
p 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.
p 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.
p The kernel code does not implement dynamic encryption key exchange protocol like IKE
q Internet Key Exchange . That should be implemented as userland programs
q 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 3 .
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 .
p With .Xr setsockopt 3 , you can define IPsec policy in per-socket basis. You can enforce particular IPsec policy onto packets that go through particular socket.
p 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.
p 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. l -column net.inet6.ipsec6.esp_trans_deflev integerxxx t Sy Name Type Changeable t net.inet.ipsec.esp_trans_deflev integer yes t net.inet.ipsec.esp_net_deflev integer yes t net.inet.ipsec.ah_trans_deflev integer yes t net.inet.ipsec.ah_net_deflev integer yes t net.inet6.ipsec6.esp_trans_deflev integer yes t net.inet6.ipsec6.esp_net_deflev integer yes t net.inet6.ipsec6.ah_trans_deflev integer yes t net.inet6.ipsec6.ah_net_deflev integer yes .El
p
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 .
l -column net.inet6.ipsec6.def_policy integerxxx t Sy Name Type Changeable t net.inet.ipsec.def_policy integer yes t net.inet6.ipsec6.def_policy integer yes .El
.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 icmp6 4 ,
.Xr intro 4 ,
.Xr ip6 4 ,
.Xr setkey 8 ,
.Xr sysctl 8 ,
.Xr racoon 8
p .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
p .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.
p There is no single standard for policy engine API, so the policy engine API described herein is just for KAME implementation.
p AH tunnel may not work as you might expect. If you configure .Dq require policy against AH tunnel for inbound, tunnelled packets will be rejected. This is because AH authenticates encapsulating
q outer packet, not the encapsulated
q inner packet.
p 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.
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