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dns_get_mx

[edit] Last updated: Fri, 26 Apr 2013

dns_get_record

(PHP 5)

dns_get_record — Fetch DNS Resource Records associated with a hostname

Description

array dns_get_record ( string $hostname [, int $type = DNS_ANY [, array &$authns [, array &$addtl ]]] )

Fetch DNS Resource Records associated with the given hostname.

Parameters

hostname: hostname should be a valid DNS hostname such as "www.example.com". Reverse lookups can be generated using in-addr.arpa notation, but gethostbyaddr() is more suitable for the majority of reverse lookups.

Note:
Per DNS standards, email addresses are given in user.host format (for example: hostmaster.example.com as opposed to hostmaster@example.com), be sure to check this value and modify if necessary before using it with a functions such as mail().
type: By default, dns_get_record() will search for any resource records associated with hostname. To limit the query, specify the optional type parameter. May be any one of the following: DNS_A, DNS_CNAME, DNS_HINFO, DNS_MX, DNS_NS, DNS_PTR, DNS_SOA, DNS_TXT, DNS_AAAA, DNS_SRV, DNS_NAPTR, DNS_A6, DNS_ALL or DNS_ANY.

Note:
Because of eccentricities in the performance of libresolv between platforms, DNS_ANY will not always return every record, the slower DNS_ALL will collect all records more reliably.
authns: Passed by reference and, if given, will be populated with Resource Records for the Authoritative Name Servers.
addtl: Passed by reference and, if given, will be populated with any Additional Records.

Return Values

This function returns an array of associative arrays, or FALSE on failure. Each associative array contains at minimum the following keys:

**Basic DNS attributes**
Attribute	Meaning
host	The record in the DNS namespace to which the rest of the associated data refers.
class	dns_get_record() only returns Internet class records and as such this parameter will always return IN.
type	String containing the record type. Additional attributes will also be contained in the resulting array dependant on the value of type. See table below.
ttl	"Time To Live" remaining for this record. This will not equal the record's original ttl, but will rather equal the original ttl minus whatever length of time has passed since the authoritative name server was queried.

**Other keys in associative arrays dependant on 'type'**
Type	Extra Columns
A	ip: An IPv4 addresses in dotted decimal notation.
MX	pri: Priority of mail exchanger. Lower numbers indicate greater priority. target: FQDN of the mail exchanger. See also dns_get_mx().
CNAME	target: FQDN of location in DNS namespace to which the record is aliased.
NS	target: FQDN of the name server which is authoritative for this hostname.
PTR	target: Location within the DNS namespace to which this record points.
TXT	txt: Arbitrary string data associated with this record.
HINFO	cpu: IANA number designating the CPU of the machine referenced by this record. os: IANA number designating the Operating System on the machine referenced by this record. See IANA's » Operating System Names for the meaning of these values.
SOA	mname: FQDN of the machine from which the resource records originated. rname: Email address of the administrative contain for this domain. serial: Serial # of this revision of the requested domain. refresh: Refresh interval (seconds) secondary name servers should use when updating remote copies of this domain. retry: Length of time (seconds) to wait after a failed refresh before making a second attempt. expire: Maximum length of time (seconds) a secondary DNS server should retain remote copies of the zone data without a successful refresh before discarding. minimum-ttl: Minimum length of time (seconds) a client can continue to use a DNS resolution before it should request a new resolution from the server. Can be overridden by individual resource records.
AAAA	ipv6: IPv6 address
A6(PHP >= 5.1.0)	masklen: Length (in bits) to inherit from the target specified by `chain`. ipv6: Address for this specific record to merge with `chain`. chain: Parent record to merge with `ipv6` data.
SRV	pri: (Priority) lowest priorities should be used first. weight: Ranking to weight which of commonly prioritized `targets` should be chosen at random. target and port: hostname and port where the requested service can be found. For additional information see: » RFC 2782
NAPTR	order and pref: Equivalent to `pri` and `weight` above. flags, services, regex, and replacement: Parameters as defined by » RFC 2915.

Changelog

Version	Description
5.3.0	This function is now available on Windows platforms.
5.3.0	Prior to this release, if the `authns` parameter was given, the `addtl` parameter was also required.

Examples

Example #1 Using dns_get_record()


<?php
$result = dns_get_record("php.net");
print_r($result);
?>

The above example will output something similar to:

Array
(
    [0] => Array
        (
            [host] => php.net
            [type] => MX
            [pri] => 5
            [target] => pair2.php.net
            [class] => IN
            [ttl] => 6765
        )

    [1] => Array
        (
            [host] => php.net
            [type] => A
            [ip] => 64.246.30.37
            [class] => IN
            [ttl] => 8125
        )

)

Example #2 Using dns_get_record() and DNS_ANY

Since it's very common to want the IP address of a mail server once the MX record has been resolved, dns_get_record() also returns an array in addtl which contains associate records. authns is returned as well containing a list of authoritative name servers.


<?php
/* Request "ANY" record for php.net,
   and create $authns and $addtl arrays
   containing list of name servers and
   any additional records which go with
   them */
$result = dns_get_record("php.net", DNS_ANY, $authns, $addtl);
echo "Result = ";
print_r($result);
echo "Auth NS = ";
print_r($authns);
echo "Additional = ";
print_r($addtl);
?>

The above example will output something similar to:

Notes

Note:
For compatibility with versions before PHP 5.3.0 on some operating systems, try the » PEAR class » Net_DNS.


Get more than one type at once like this:

<?php

$dnsr = dns_get_record('php.net', DNS_A + DNS_NS);

print_r($dnsr);

?>



Using DNS_ALL fails on some domains where DNS_ANY works. I noticed the function getting stuck on the DNS_PTR record, which caused it to return FALSE with this error:

PHP Warning:  dns_get_record(): res_nsend() failed in ....



This gets all records except DNS_PTR:

<?php

$dnsr = dns_get_record('php.net', DNS_ALL - DNS_PTR);

print_r($dnsr);

?>

down

axelm-php at nona dot net ¶

9 years ago


I've done a backport of the function to PHP4. 

It is available as extension at: 



http://nona.net/software/dns_get_record/



comments & feedback appreciated. 



--

Alexander Mayrhofer

axelm-php@nona.net

down

karl at influ dot io ¶

6 days ago

down

-1

rahbari at gmail dot com ¶

1 year ago


If only NS records are set (when the domain is not configured on the host), DNS_NS must be used, otherwise an error occurs and it returns nothing!

down

-1

nick at carbidefinger dot net ¶

4 years ago


Its worth nothing that this function returns nothing if the server you are running it from is authoritative for the domain you are checking (common on shared hosting platforms) when looking up 'NS' records



In this instance $authns is an array containing no keys or values:

dns_get_record("alocaldomain.com","NS",$authns,$addtl);

down

-1

ed at noxserver dot com ¶

8 years ago


I recently needed to do some name server and IP discovery on the fly.

Server and domain monitoring system.  If you've got a system with dig 

the below seems to work fine for discovering name server and a 

addresses.  Shouldn't be hard for you to modify it for the other records if 

needed.



$_REQUEST[url] = "http://www.example.com/";



$url_parts = parse_url($_REQUEST[url]);



$dns = Dig($url_parts[host]);

print_r($dns[name_servers]);

print_r($dns[ips]);



function Dig ($domain) {

    $dig = `dig $domain`;

    preg_match_all("/in\s+ns\s+(.+?)\s+/is"

,$dig,$name_servers,PREG_PATTERN_ORDER);

    preg_match_all("/$domain.\s+[0-9]+\s+in\s+a\s+([0-9.]+)\s+/is"

,$dig,$ips,PREG_PATTERN_ORDER);

    $dns[name_servers] = $name_servers[1];

    $dns[ips] = $ips[1];

    return($dns);

}

down

-2

geo at vzemibg dot com ¶

4 years ago


Note that if you check a non-existing domain you will get:



Warning: dns_get_record() [function.dns-get-record]: res_nsend() failed in ...



and the function will return an empty srtring (not array). I do not see this described above.

down

-2

marcus at synchromedia dot co dot uk ¶

7 years ago


The docs say "nor does it (currently) work on *BSD systems". Unfortunately this includes MacOS X. It's just not there in my build of 5.1.2 running on 10.4.4.

add a note

dns_get_record

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also