initsubnet.3

This a good VPN source

.TH IPSEC_INITSUBNET 3 "12 March 2002"
.\" RCSID $Id: initsubnet.3,v 1.6 2004/04/09 18:00:39 mcr Exp $
.SH NAME
ipsec initsubnet \- initialize an ip_subnet
.br
ipsec addrtosubnet \- initialize a singleton ip_subnet
.br
ipsec subnettypeof \- get address type of an ip_subnet
.br
ipsec masktocount \- convert subnet mask to bit count
.br
ipsec networkof \- get base address of an ip_subnet
.br
ipsec maskof \- get subnet mask of an ip_subnet
.SH SYNOPSIS
.B "#include <freeswan.h>"
.sp
.B "const char *initsubnet(const ip_address *addr,"
.ti +1c
.B "int maskbits, int clash, ip_subnet *dst);"
.br
.B "const char *addrtosubnet(const ip_address *addr,"
.ti +1c
.B "ip_subnet *dst);"
.sp
.B "int subnettypeof(const ip_subnet *src);"
.br
.B "int masktocount(const ip_address *src);"
.br
.B "void networkof(const ip_subnet *src, ip_address *dst);"
.br
.B "void maskof(const ip_subnet *src, ip_address *dst);"
.SH DESCRIPTION
The
.B <freeswan.h>
library uses an internal type
.I 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.
.PP
.I Initsubnet
initializes a variable
.I *dst
of type
.I ip_subnet
from a base address and
a count of mask bits.
The
.I clash
parameter specifies what to do if the base address includes
.B 1
bits outside the prefix specified by the mask
(that is, in the ``host number'' part of the address):
.RS
.IP '0' 5
zero out host-number bits
.IP 'x'
non-zero host-number bits are an error
.RE
.PP
.I Initsubnet
returns
.B NULL
for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
.PP
.I Addrtosubnet
initializes an
.I ip_subnet
variable
.I *dst
to a ``singleton subnet'' containing the single address
.IR *addr .
It returns
.B NULL
for success and
a pointer to a string-literal error message for failure.
.PP
.I Subnettypeof
returns the address type of a subnet,
normally
.B AF_INET
or
.BR AF_INET6 .
(The
.B <freeswan.h>
header file arranges to include the necessary headers for these
names to be known.)
.PP
.I Masktocount
converts a subnet mask, expressed as an address, to a bit count
suitable for use with
.IR initsubnet .
It returns
.B \-1
for error; see DIAGNOSTICS.
.PP
.I Networkof
fills in
.I *dst
with the base address of subnet
.IR src .
.PP
.I Maskof
fills in
.I *dst
with the subnet mask of subnet
.IR src ,
expressed as an address.
.SH SEE ALSO
inet(3), ipsec_ttosubnet(3), ipsec_rangetosubnet(3)
.SH DIAGNOSTICS
Fatal errors in
.I initsubnet
are:
unknown address family;
unknown
.I clash
value;
impossible mask bit count;
non-zero host-number bits and
.I clash
is
.BR 'x' .
Fatal errors in
.I addrtosubnet
are:
unknown address family.
Fatal errors in
.I masktocount
are:
unknown address family;
mask bits not contiguous.
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.