goodmask.3

This a good VPN source

.TH IPSEC_GOODMASK 3 "11 June 2001"
.\" RCSID $Id: goodmask.3,v 1.7 2004/04/09 18:00:39 mcr Exp $
.SH NAME
ipsec goodmask \- is this Internet subnet mask a valid one?
.br
ipsec masktobits \- convert Internet subnet mask to bit count
.br
ipsec bitstomask \- convert bit count to Internet subnet mask
.SH SYNOPSIS
.B "#include <freeswan.h>
.sp
.B "int goodmask(struct in_addr mask);"
.br
.B "int masktobits(struct in_addr mask);"
.br
.B "struct in_addr bitstomask(int n);"
.SH DESCRIPTION
These functions are obsolete;
see
.IR ipsec_masktocount (3)
for a partial replacement.
.PP
.I Goodmask
reports whether the subnet
.I mask
is a valid one,
i.e. consists of a (possibly empty) sequence of
.BR 1 s
followed by a (possibly empty) sequence of
.BR 0 s.
.I Masktobits
takes a (valid) subnet mask and returns the number of
.B 1
bits in it.
.I Bitstomask
reverses this,
returning the subnet mask corresponding to bit count
.IR n .
.PP
All masks are in network byte order.
.SH SEE ALSO
inet(3), ipsec_atosubnet(3)
.SH DIAGNOSTICS
.I Masktobits
returns
.B \-1
for an invalid mask.
.I Bitstomask
returns an all-zeros mask for a negative or out-of-range
.IR n .
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
The error-reporting convention of
.I bitstomask
is less than ideal;
zero is sometimes a legitimate mask.