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checkdnsrr

(PHP 4, PHP 5, PHP 7)

checkdnsrr — Check DNS records corresponding to a given Internet host name or IP address

설명

bool checkdnsrr ( string $host [, string $type = "MX" ] )

Searches DNS for records of type type corresponding to host.

인수

host: host may either be the IP address in dotted-quad notation or the host name.
type: type may be any one of: A, MX, NS, SOA, PTR, CNAME, AAAA, A6, SRV, NAPTR, TXT or ANY.

반환값

Returns TRUE if any records are found; returns FALSE if no records were found or if an error occurred.

변경점

버전	설명
5.3.0	This function is now available on Windows platforms.
5.2.4	TXT `type` was added.

주의

Note:
For compatibility with Windows before this was implemented, then try the » PEAR class » Net_DNS.

참고

dns_get_record() - Fetch DNS Resource Records associated with a hostname
getmxrr() - Get MX records corresponding to a given Internet host name
gethostbyaddr() - Get the Internet host name corresponding to a given IP address
gethostbyname() - Get the IPv4 address corresponding to a given Internet host name
gethostbynamel() - Get a list of IPv4 addresses corresponding to a given Internet host name
the named(8) manual page

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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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