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# Chapter 51. libipsec Reference

# ipsec_set_policy

    IPSEC_SET_POLICY(3)     System Library Functions Manual    IPSEC_SET_POLICY(3)

    NAME
         ipsec_set_policy, ipsec_get_policylen, ipsec_dump_policy - manipulate
         IPsec policy specification structure from readable 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 IPsec policy specification structure, namely
         struct sadb_x_policy and/or struct sadb_x_ipsecrequest from human-read-
         able policy specification.  policy specification must be given as C
         string policy and length len of policy.  ipsec_set_policy() will return
         the buffer of IPsec policy specification structure.  The buffer is dynam-
         ically allocated, and must be freed by the caller by calling free(3).

         You may want the length of the generated buffer such when calling
         setsockopt(2).  ipsec_get_policylen() will return the length.

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

         policy is formatted as either of the following:

         direction discard
                  direction must be in or out.  direction specifies which direc-
                  tion the policy needs to be applied.  With discard policy, pack-
                  ets will be dropped if they match the policy.

         direction entrust
                  entrust means to consult to SPD defined by setkey(8).

         direction bypass
                  bypass means to be bypassed the IPsec processing.  (packet will
                  be transmitted in clear).  This is for privileged socket.

         direction ipsec request ...
                  ipsec means that the matching packets are subject to IPsec pro-
                  cessing.  ipsec can be followed by one or more request string,
                  which is 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 IPsec endpoint.  src always means
                           ``sending node'' and dst always means ``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 omited.

                           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 transmit-
                           ted 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 out-
                           bound 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.  How-
                           ever, it is encouraged to specify them explicitly to
                           avoid unintended behaviors.  If level is omitted, it
                           will be interpreted as default.

         Note that there is a bit difference of specification from setkey(8).  In
         specification by setkey(8), both entrust and bypass are not used.  Refer
         to setkey(8) for detail.

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

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

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

    KAME                              May 5, 1998                             KAME

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