dns_get_record问题

Question

I am setting up a dns lookup form using dns_get_record. I set it up to check the A Record and MX Records of the domain that is input. However, I would like it to also display the IP address of the displayed MX Records. Is this possible?

Answer 1

No, at least not in one step. You'll have to do another dns request for the "target" of the MX record, which is the "real" address of the mail server.

A simple script could look like this

$email = "[e-mail]";
list( $tmp, $email ) = explode( "@", $email );  // Gets the domain name

$dns = dns_get_record( $email, DNS_MX );
if( count($dns) <= 0 )
    die( "Error looking up dns information." ); // Return value is an empty array if there aren't any MX records but domain exists

// Looks up the first returned MX (note that there can be more than one)
// Each MX record has a 'pri' value where the lowest value is the record with the highest priority
$mx = dns_get_record( $dns[0]['target'], DNS_A );
if( count($mx) <= 0 )
    die( "Error looking up mail server." );
$mx = $mx[0]['ip'];

A full blown A and MX record displaying script

$domain = "google.com";

$dns = dns_get_record( $domain, DNS_ANY );
foreach( $dns as $d ) {
    // Only print A and MX records
    if( $d['type'] != "A" and $d['type'] != "MX" )
        continue;
    // First print all fields
    echo "--- " . $d['host'] . ": <br />
";
    foreach( $d as $key => $value ) {
        if( $key != "host" )    // Don't print host twice
            echo " {$key}: {$value} <br />
";
    }
    // Print type specific fields
    switch( $d['type'] ) {
        case 'A':
            // Display annoying message
            echo "A records always contain an IP address. <br />
";
            break;
        case 'MX':
            // Resolve IP address of the mail server
            $mx = dns_get_record( $d['target'], DNS_A );
            foreach( $mx as $server ) {
                echo "The MX record for " . $d['host'] . " points to the server " . $d['target'] . " whose IP address is " . $server['ip'] . ". <br />
";
            }
            break;
    }
}