sub mask_short_to_long3 {

        my $mask = shift;
        my @octets = (0,0,0,0);

        for (@octets) {
            $_    = $mask > 8 ? 255 : 256 - 2**(8-$mask);
            $mask = $mask > 8 ? $mask -8 : 0;
        }

        join '.', @octets;
    }