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$FreeBSD: head/share/man/man4/ipsec.4 155673 2006-02-14 13:02:00Z gnn $
.Dd January 11, 2005 .Dt IPSEC 4 .Os .Sh NAME .Nm ipsec .Nd IP security protocol .Sh SYNOPSIS n sys/types.h n netinet/in.h n netinet6/ipsec.h .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.
p 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.
p 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.
p
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 cases, 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 instructionson its use.
p When setting policies using the .Xr setkey 8 command the .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
.Ss Miscellaneous sysctl variables
The following variables are accessible via
.Xr sysctl 8 ,
for tweaking kernel IPsec behavior:
l -column net.inet6.ipsec6.inbonud_call_ike integerxxx t Sy "Name Type Changeable" t "net.inet.ipsec.ah_cleartos integer yes" t "net.inet.ipsec.ah_offsetmask integer yes" t "net.inet.ipsec.dfbit integer yes" t "net.inet.ipsec.ecn integer yes" t "net.inet.ipsec.debug integer yes" t "net.inet6.ipsec6.ecn integer yes" t "net.inet6.ipsec6.debug integer yes" .El
p The variables are interpreted as follows: l -tag -width 6n t 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. t 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. t 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. t 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. t Li ipsec.debug If set to non-zero, debug messages will be generated via .Xr syslog 3 . .El
p
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
.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
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 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 is no sign of authenticity). The issue will be solved when we revamp our policy engine to keep all the packet decapsulation history.
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.