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IPSEC(4)                     Device Drivers Manual                    IPSEC(4)

     ipsec - IP security protocol

     options IPSEC
     options IPSEC_DEBUG

     This manual pages describes the IPsec protocol.  For the network device
     driver please see ipsecif(4).

     ipsec is a security protocol in the Internet Protocol (IP) layer.  ipsec
     is defined for both IPv4 and IPv6 (inet(4) and inet6(4)).  ipsec consists
     of three sub-protocols:

     Encapsulated Security Payload (ESP) protects IP payloads from wire-
             tapping (interception) by encrypting them with secret key
             cryptography algorithms.

     Authentication Header (AH) guarantees the integrity of IP packets and
             protects them from intermediate alteration or impersonation, by
             attaching cryptographic checksums computed by one-way hash

     IP Payload Compression Protocol (IPComp) increases the communication
             performance by compressing the datagrams.

     ipsec has two operation modes:

     Transport mode is for protecting peer-to-peer communication between end

     Tunnel mode includes IP-in-IP encapsulation operation and is designed for
             security gateways, as in Virtual Private Network (VPN)

   Kernel interface
     ipsec is controlled by two engines in the kernel: one for key management
     and one for policy.

     The key management engine can be accessed from userland by using PF_KEY
     sockets.  The PF_KEY socket API is defined in RFC2367.

     The policy engine can be controlled through the PF_KEY API, setsockopt(2)
     operations, and the sysctl(3) interface.  The kernel implements an
     extended version of the PF_KEY interface and allows you to define IPsec
     policy like per-packet filters.  setsockopt(2) is used to define per-
     socket behavior, and sysctl(3) is used to define host-wide default

     The kernel does not implement dynamic encryption key exchange protocols
     like IKE (Internet Key Exchange).  That should be done in userland
     (usually as a daemon), using the APIs described above.

   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 setsockopt(2).  The other is to configure kernel packet
     filter-based policy using the PF_KEY interface, via setkey(8).  In both
     cases, IPsec policy must be specified with syntax described in

     With setsockopt(2), you can define IPsec policy on a per-socket basis.
     You can enforce particular IPsec policy on packets that go through a
     particular socket.

     With setkey(8) you can define IPsec policy for packets using a form of
     packet filtering rules.  See setkey(8) for details.

     In the latter case, "default" policy is allowed for use with setkey(8).
     By configuring policy to default, you can refer to system-wide sysctl(8)
     variables for default settings.  The following variables are available.
     1 means "use", and 2 means "require" in the syntax.

     Name                                 Type          Changeable
     net.inet.ipsec.esp_trans_deflev      integer       yes
     net.inet.ipsec.esp_net_deflev        integer       yes
     net.inet.ipsec.ah_trans_deflev       integer       yes
     net.inet.ipsec.ah_net_deflev         integer       yes
     net.inet6.ipsec6.esp_trans_deflev    integer       yes
     net.inet6.ipsec6.esp_net_deflev      integer       yes
     net.inet6.ipsec6.ah_trans_deflev     integer       yes
     net.inet6.ipsec6.ah_net_deflev       integer       yes

     If the kernel finds no matching policy, the system-wide default value is
     applied.  System-wide defaults are specified by the following sysctl(8)
     variables.  0 means "discard" which asks the kernel to drop the packet.
     1 means "none".

     Name                                 Type          Changeable
     net.inet.ipsec.def_policy            integer       yes
     net.inet6.ipsec6.def_policy          integer       yes

   Miscellaneous sysctl variables
     The following variables are accessible via sysctl(8), for tweaking kernel
     IPsec behavior:

     Name                                 Type          Changeable
     net.inet.ipsec.ah_cleartos           integer       yes
     net.inet.ipsec.ah_offsetmask         integer       yes
     net.inet.ipsec.crypto_support        integer       yes
     net.inet.ipsec.dfbit                 integer       yes
     net.inet.ipsec.ecn                   integer       yes
     net.inet.ipsec.debug                 integer       yes
     net.inet6.ipsec6.ecn                 integer       yes
     net.inet6.ipsec6.debug               integer       yes

     The variables are interpreted as follows:

             If set to non-zero, the kernel clears the 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.

             During AH authentication data computation, the kernel will
             include a 16 bit fragment offset field (including flag bits) in
             the 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

             This variable configures the kernel behavior for selecting
             encryption drivers.  If set to > 0, the kernel will select a
             hardware encryption driver first.  If set to < 0, the kernel will
             select a software encryption driver first.  If set to 0, the
             kernel will select either a hardware or software driver.

             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.  1 means that the outer DF bit is set 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.

             If set to non-zero, IPv4 IPsec tunnel encapsulation/decapsulation
             behavior will be friendly to ECN (explicit congestion
             notification), as documented in draft-ietf-ipsec-ecn-02.txt.
             gif(4) talks more about the behavior.

             If set to non-zero, debug messages will be generated via

     Variables under the net.inet6.ipsec6 tree have similar meanings to their
     net.inet.ipsec counterparts.

   Cryptographic operations
     The current IPsec implementation, formerly called Fast IPsec, uses the
     opencrypto(9) subsystem to carry out cryptographic operations.  This
     means, in particular, that cryptographic hardware devices are employed
     whenever possible to optimize the performance of sub-protocols.

     System configuration requires the opencrypto(9) subsystem.  When the Fast
     IPsec protocols are configured for use, all protocols are included in the
     system.  To selectively enable/disable protocols, use sysctl(8).

     The ipsec protocol works like a plug-in to inet(4) and inet6(4)
     protocols.  Therefore, ipsec supports most of the protocols defined upon
     those IP-layer protocols.  Some of the protocols, like icmp(4) or
     icmp6(4), may behave differently with ipsec.  This is because ipsec can
     prevent icmp(4) or icmp6(4) routines from looking into IP payload.

     ioctl(2), socket(2), ipsec_set_policy(3), icmp6(4), intro(4), ip6(4),
     ipsecif(4), racoon(8), setkey(8), sysctl(8)

     Daniel L. McDonald, Craig Metz, and Bao G. Phan, PF_KEY Key Management
     API, Version 2, RFC, 2367.

     The protocols draw heavily on the OpenBSD implementation of the IPsec
     protocols.  The policy management code is derived from the KAME
     implementation found in their IPsec protocols.  The Fast IPsec protocols
     are based on code which appeared in FreeBSD 4.7.  The NetBSD version is a
     close copy of the FreeBSD original, and first appeared in NetBSD 2.0.

     Support for IPv6 and IPcomp protocols has been added in NetBSD 4.0.

     Support for Network Address Translator Traversal as described in RFCs
     3947 and 3948 has been added in NetBSD 5.0.

     Since NetBSD 6.0, the IPsec implementation formerly known as Fast IPsec
     is used.

     IPsec support is subject to change as the IPsec protocols develop.

     There is no single standard for policy engine API, so the policy engine
     API described herein is just for the version introduced by KAME.

     AH and tunnel mode encapsulation may not work as you might expect.  If
     you configure inbound "require" policy against AH tunnel or any IPsec
     encapsulating policy with AH (like "esp/tunnel/A-B/use
     ah/transport/A-B/require"), tunneled 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.

     Under certain condition, truncated result may be raised from the kernel
     against SADB_DUMP and SADB_SPDDUMP operation on PF_KEY socket.  This
     occurs if there are too many database entries in the kernel and socket
     buffer for the PF_KEY socket is insufficient.  If you manipulate many
     IPsec key/policy database entries, increase the size of socket buffer or
     use sysctl(8) interface.

     Certain legacy authentication algorithms are not supported because of
     issues with the opencrypto(9) subsystem.

NetBSD 10.99                     June 13, 2018                    NetBSD 10.99