Sometime this is need to know that some port is active or not cause a port is used to recognize a specific service which is being executed in a computer. To recognize a port and to send packets, 16 bit numbers known as port numbers are used. A port number along with IP address serves as a destination for packets to be sent.

Suppose domain name https://techparkbd.com/ so get this ip address so ip is 184.107.37.81. There are many website to know ip. Then check port that open or not.

<?php
$host_connection = '184.107.37.81'; // techparkbd
$ports_number = array(21, 25, 80, 81, 110,143, 443, 3306); //checking port number

foreach ($ports_number as $port)
{
    $connection_check = @fsockopen($host_connection, $port);

    if (is_resource($connection_check))
    {
        echo '<h5>' . $host_connection . ':' . $port . ' ' . '(' . getservbyport($port, 'tcp') . ') is open now.</h5>' . "\n";

        fclose($connection_check);
    }

    else
    {
        echo '<h5 style="color: red">' . $host_connection . ':' . $port . ' is not open now.</h5>' . "\n";
    }
}

?>

when you run this code it will show result like this

184.107.37.81:21 (ftp) is open now.
184.107.37.81:25 (smtp) is open now.
184.107.37.81:80 (http) is open now.
184.107.37.81:81 is not open now.
184.107.37.81:110 (pop3) is open now.
184.107.37.81:143 (imap) is open now.
184.107.37.81:443 (https) is open now.
184.107.37.81:3306 () is open now.

This is very simple way to know port open or not. If you face any problem then please inform me.

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