NAME

       ipsec_initsubnet,    ipsec_addrtosubnet,    ipsec_subnettypeof,    ipsec_masktocount,    ipsec_networkof,
       ipsec_maskof - initialize an ip_subnet,  initialize  a  singleton  ip_subnet,  get  address  type  of  an
       ip_subnet,  convert  subnet  mask  to  bit count, get base address of an ip_subnet, get subnet mask of an
       ip_subnet

SYNOPSIS

       #include <freeswan.h>

       const char *initsubnet(const ip_address *addr,
           int maskbits, int clash, ip_subnet *dst);
       const char *addrtosubnet(const ip_address *addr,
           ip_subnet *dst);

       int subnettypeof(const ip_subnet *src);
       int masktocount(const ip_address *src);
       void networkof(const ip_subnet *src, ip_address *dst);
       void maskof(const ip_subnet *src, ip_address *dst);

DESCRIPTION

       The <freeswan.h> library uses an internal type ip_subnet to contain a description of an IP  subnet  (base
       address plus mask).  These functions provide basic tools for creating and examining this type.

       Initsubnet  initializes  a  variable *dst of type ip_subnet from a base address and a count of mask bits.
       The clash parameter specifies what to do if the base address includes 1 bits outside the prefix specified
       by the mask (that is, in the ``host number'' part of the address):

              '0'  zero out host-number bits

              'x'  non-zero host-number bits are an error

       Initsubnet returns NULL for success and a pointer to a string-literal  error  message  for  failure;  see
       DIAGNOSTICS.

       Addrtosubnet  initializes  an  ip_subnet  variable  *dst  to a ``singleton subnet'' containing the single
       address *addr.  It returns NULL for success and a pointer to a string-literal error message for failure.

       Subnettypeof returns the address type of a subnet,  normally  AF_INET  or  AF_INET6.   (The  <freeswan.h>
       header file arranges to include the necessary headers for these names to be known.)

       Masktocount  converts  a  subnet  mask,  expressed  as  an  address, to a bit count suitable for use with
       initsubnet.  It returns -1 for error; see DIAGNOSTICS.

       Networkof fills in *dst with the base address of subnet src.

       Maskof fills in *dst with the subnet mask of subnet src, expressed as an address.

SEE ALSO

       inet(3), ipsec_ttosubnet(3), ipsec_rangetosubnet(3)

DIAGNOSTICS

       Fatal errors in initsubnet are: unknown address family; unknown clash value; impossible mask  bit  count;
       non-zero  host-number  bits  and clash is 'x'.  Fatal errors in addrtosubnet are: unknown address family.
       Fatal errors in masktocount are: unknown address family; mask bits not contiguous.

HISTORY

       Written for the FreeS/WAN project by Henry Spencer.

                                                  12 March 2002                              IPSEC_INITSUBNET(3)