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IPSEC_SET_POLICY(3)      BSD Library Functions Manual      IPSEC_SET_POLICY(3)

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

     IPsec Policy Control Library (libipsec, -lipsec)

     #include <netinet6/ipsec.h>

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

     ipsec_get_policylen(caddr_t buf);

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

     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

     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 trans-mitted transmitted
                       mitted 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 unam-biguous, unambiguous,
                       biguous, 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 specifica-tion specification
              tion 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/
                    in ipsec ipcomp/transport//use

     ipsec_set_policy() returns a pointer to the allocated buffer with the policy specification if success-ful; successful;
     ful; 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.

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

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

BSD                               May 5, 1998                              BSD

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