sub nets {
        # takes 2 args - IP address and network mask
        my $ip = $_[0];
        my $mask = $_[1];
        my $nets = inet_ntoa ((inet_aton($ip)) & (inet_aton($mask)));
        my $binmask = unpack ("B32", pack ("C4", split(/\./, $mask)));
        $binmask =~ /(10)/;
        my $bits = $-[1]+1;
        my $network = "$nets\/$bits";
        return $network;
}