private function ip2bin($ip)
    {
        if ($this->getIpVersion($ip) === 4) {
            return str_pad(base_convert(ip2long($ip), 10, 2), static::IPV4_ADDRESS_LENGTH, '0', STR_PAD_LEFT);
        } else {
            $unpack = unpack('A16', inet_pton($ip));
            $binStr = array_shift($unpack);
            $bytes = static::IPV6_ADDRESS_LENGTH / 8; // 128 bit / 8 = 16 bytes
            $result = '';
            while ($bytes-- > 0) {
                $result = sprintf('%08b', isset($binStr[$bytes]) ? ord($binStr[$bytes]) : '0') . $result;
            }
            return $result;
        }
    }