NAME

     ipsec_set_policy, ipsec_get_policylen, ipsec_dump_policy — manipulate IPsec policy
     specification structure from human-readable policy string

LIBRARY

     IPsec Policy Control Library (libipsec, -lipsec)

SYNOPSIS

     #include <netinet6/ipsec.h>

     char *
     ipsec_set_policy(char *policy, int len);

     int
     ipsec_get_policylen(char *buf);

     char *
     ipsec_dump_policy(char *buf, char *delim);

DESCRIPTION

     ipsec_set_policy() generates an IPsec policy specification structure, namely struct
     sadb_x_policy and/or struct sadb_x_ipsecrequest from a human-readable policy specification.
     The policy specification must be given as a C string policy and its length len.
     ipsec_set_policy() will return a buffer with the corresponding IPsec policy specification
     structure.  The buffer is dynamically allocated, and must be free(3)'d by the caller.

     You can get the length of the generated buffer with ipsec_get_policylen() (i.e. for calling
     setsockopt(2)).

     ipsec_dump_policy() converts an IPsec policy structure into human-readable form.  Therefore,
     ipsec_dump_policy() can be regarded as the inverse function to ipsec_set_policy().  buf
     points to an IPsec policy structure, struct sadb_x_policy.  delim is a delimiter string,
     which is usually a blank character.  If you set delim to NULL, a single whitespace is
     assumed.  ipsec_dump_policy() returns a pointer to a dynamically allocated string.  It is
     the caller's responsibility to free(3) it.

     policy is formatted as either of the following:

     direction [priority specification] discard
              direction must be in, out, or fwd.  direction specifies in which direction the
              policy needs to be applied.  The non-standard direction fwd is substituted with in
              on platforms which do not support forward policies.

              priority specification is used to control the placement of the policy within the
              SPD.  The policy position is determined by a signed integer where higher priorities
              indicate the policy is placed closer to the beginning of the list and lower
              priorities indicate the policy is placed closer to the end of the list.  Policies
              with equal priorities are added at the end of the group of such policies.

              Priority can only be specified when libipsec has been compiled against kernel
              headers that support policy priorities (Linux >= 2.6.6).  It takes one of the
              following formats:

              {priority,prio} offset
                       offset is an integer in the range -2147483647..214783648.

              {priority,prio} base {+,-} offset
                       base is either low (-1073741824), def (0), or high (1073741824).

                       offset is an unsigned integer.  It can be up to 1073741824 for positive
                       offsets, and up to 1073741823 for negative offsets.

              The interpretation of policy priority in these functions and the kernel DOES
              differ.  The relationship between the two can be described as p(kernel) =
              0x80000000 - p(func)

              With discard policy, packets will be dropped if they match the policy.

     direction [priority specification] entrust
              entrust means to consult the SPD defined by setkey(8).

     direction [priority specification] bypass
              bypass means to bypass the IPsec processing.  (the packet will be transmitted in
              clear).  This is for privileged sockets.

     direction [priority specification] ipsec request ...
              ipsec means that the matching packets are subject to IPsec processing.  ipsec can
              be followed by one or more request strings, which are formatted as below:

              protocol / mode / src - dst [/level]
                       protocol is either ah, esp, or ipcomp.

                       mode is either transport or tunnel.

                       src and dst specifies the IPsec endpoint.  src always means the “sending
                       node” and dst always means the “receiving node”.  Therefore, when
                       direction is in, dst is this node and src is the other node (peer).  If
                       mode is transport, Both src and dst can be omitted.

                       level must be set to one of the following: default, use, require, or
                       unique.  default means that the kernel should consult the system default
                       policy defined by sysctl(8), such as net.inet.ipsec.esp_trans_deflev.  See
                       ipsec(4) regarding the system default.  use means that a relevant SA can
                       be used when available, since the kernel may perform IPsec operation
                       against packets when possible.  In this case, packets can be transmitted
                       in clear (when SA is not available), or encrypted (when SA is available).
                       require means that a relevant SA is required, since the kernel must
                       perform IPsec operation against packets.  unique is the same as require,
                       but adds the restriction that the SA for outbound traffic is used only for
                       this policy.  You may need the identifier in order to relate the policy
                       and the SA when you define the SA by manual keying.  You can put the
                       decimal number as the identifier after unique like unique: number.  number
                       must be between 1 and 32767 .  If the request string is kept unambiguous,
                       level and slash prior to level can be omitted.  However, it is encouraged
                       to specify them explicitly to avoid unintended behavior.  If level is
                       omitted, it will be interpreted as default.

              Note that there are slight differences to the specification of setkey(8).  In the
              specification of setkey(8), both entrust and bypass are not used.  Refer to
              setkey(8) for details.

              Here are several examples (long lines are wrapped for readability):

                    in discard
                    out ipsec esp/transport//require
                    in ipsec ah/transport//require
                    out ipsec esp/tunnel/10.1.1.2-10.1.1.1/use
                    in ipsec ipcomp/transport//use
                            esp/transport//use

RETURN VALUES

     ipsec_set_policy() returns a pointer to the allocated buffer with the policy specification
     if successful; otherwise a NULL pointer is returned.  ipsec_get_policylen() returns a
     positive value (meaning the buffer size) on success, and a negative value on errors.
     ipsec_dump_policy() returns a pointer to a dynamically allocated region on success, and NULL
     on errors.

SEE ALSO

     ipsec_strerror(3), ipsec(4), setkey(8)

HISTORY

     The functions first appeared in the WIDE/KAME IPv6 protocol stack kit.