ipsec_addrtosubnet(3) 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

Other Alias

ipsec_initsubnet, ipsec_subnettypeof, ipsec_masktocount, ipsec_networkof, ipsec_maskof


#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);


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):

zero out host-number bits
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.


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.


Written for the FreeS/WAN project by Henry Spencer.