checkdnsrr

(PHP 4, PHP 5, PHP 7, PHP 8)

checkdnsrr — Controlla i record DNS relativi ad un host Internet o indirizzo IP

Descrizione

checkdnsrr(string $host, string $type = ?): int

Cerca i record DNS del tipo type corrispondenti a host. Restituisce vero se dei records sono trovati; falso se nessun record viene trovato o in caso di errore.

type può essere uno dei seguenti: A, MX, NS, SOA, PTR, CNAME, oppure ANY. Il default è MX.

Host può essere sia l'indirizzo IP in notazione decimale o il nome dell'host.

Nota: Questa funzione non è implementata sulle piattaforme Windows.

Vedere anche getmxrr(), gethostbyaddr(), gethostbyname(), gethostbynamel() e la man page named(8).

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User Contributed Notes 6 notes

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Krisztin Ferenczi ¶

11 years ago


criffoh at gmail dot com is right. Before you check domain, you must convert to ascii with idn_to_ascii function:
http://us2.php.net/manual/en/function.idn-to-ascii.php .

var_dump(checkdnsrr('ñandu.cl', 'A')); // returns false
var_dump(checkdnsrr(idn_to_ascii('ñandu.cl'), 'A')); // return true

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Martin ¶

8 years ago


Important Warning:

You need to add a dot to the end of the host name to make a fully qualified domain name.

To see why, try executing the following pieces of code:

$d1="gmail.con";
$d2="gmail.con.";
$r1=checkdnsrr($d1, "MX"); 
$r2=checkdnsrr($d2, "MX"); 
var_dump($r1);
var_dump($r2);

You will see that without the dot it claims that the domain "gmail.con" is valid.

Note that if you time the "checkdnsrr()" calls you will also see it takes longer without the dot because it treats it as a relative domain and does several tries based on the host name it is running on.

NB: in case you're interested, being treated as a relative domain explains what is happening. If your host is "example.com" the relative domain will eventually resolve to "gmail.con.com." which can be looked up, hence it wrongly claims "gmail.con" exists

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Patrick ¶

19 years ago


This is a little code example that will validate an email address in two ways:
- first the general syntax of the string is checked with a regular expression
- then the domain substring (after the '@') is checked using the 'checkdnsrr' function

<?php

function validate_email($email){

   $exp = "^[a-z\'0-9]+([._-][a-z\'0-9]+)*@([a-z0-9]+([._-][a-z0-9]+))+$";

   if(eregi($exp,$email)){

      if(checkdnsrr(array_pop(explode("@",$email)),"MX")){
        return true;
      }else{
        return false;
      }

   }else{

      return false;

   }    
}

?>

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n at zay dot uk ¶

3 years ago


I always think you should state the blindingly obvious.
A function that contains checkdnsrr will return false without an internet connection.
So in a production environment you need an active internet connection to return a true result with a valid email address.

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-5

criffoh at gmail dot com ¶

11 years ago


Is not possible validate domains with 'ñ' for my country.

In my country is possible to register domain using 'ñ' character. For example:

ñandu.cl
http://nic.cl/cgi-bin/dom-CL?q=%F1andu

If I use this function to check DNS record, it return false, but the domain already exists:

var_dump(checkdnsrr('ñandu.cl', 'A')); // returns false

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-9

dobs ¶

6 years ago


$this->_buf - for bulk check cache

function ValidateEmail($email)
    {
        list($user, $domain) = explode('@', $email);

        if (!filter_var($email, FILTER_VALIDATE_EMAIL) !== FALSE)
            return 0;

        if (isset($this->_buf[$domain]))
            return $this->_buf[$domain];

        if (checkdnsrr($domain) === FALSE) {
            $this->_buf[$domain] = 0;
            return 0;
        }
        $this->_buf[$domain] = 1;

        return 1;
    }

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