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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.