private function calculateIpRange(int $cidrIpLong, int $cidrMask): array
    {
        $netWork = $cidrIpLong & $this->netMask($cidrMask);
        $lower   = $netWork + 1; // ignore network ID (eg: 192.168.1.0)
        $upper   = ($netWork | $this->inverseNetMask($cidrMask)) - 1 ; //  ignore broadcast IP (eg: 192.168.1.255)
        return array($lower, $upper);
    }