dns_get_record

(PHP 5, PHP 7, PHP 8)

dns_get_record — Fetch DNS Resource Records associated with a hostname

Description

dns_get_record(
    string $hostname,
    int $type = DNS_ANY,
    array &$authoritative_name_servers = null,
    array &$additional_records = null,
    bool $raw = false
): array|false

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_CAA, 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.

Note:
Windows: DNS_CAA is not supported. Support for DNS_A6 is not implemented.
authoritative_name_servers: Passed by reference and, if given, will be populated with Resource Records for the Authoritative Name Servers.
additional_records: Passed by reference and, if given, will be populated with any Additional Records.
raw: The type will be interpreted as a raw DNS type ID (the DNS_* constants cannot be used). The return value will contain a data key, which needs to be manually parsed.

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.
`CAA`	`flags`: A one-byte bitfield; currently only bit 0 is defined, meaning 'critical'; other bits are reserved and should be ignored. `tag`: The CAA tag name (alphanumeric ASCII string). `value`: The CAA tag value (binary string, may use subformats). For additional information see: » RFC 6844
`SOA`	`mname`: FQDN of the machine from which the resource records originated. `rname`: Email address of the administrative contact 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`	`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
7.0.16, 7.1.2	Added support for CAA record type.

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 additional_records which contains associate records. authoritative_name_servers 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:

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User Contributed Notes 7 notes

down

tobias at herkula dot info ¶

9 years ago

This method has no error handling, it simply puts out "false" and it is impossible to check for NXDOMAIN, SERVFAIL, TIMEOUT or any other error...

down

dylan at pow7 dot com ¶

15 years ago

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

PHP Joe ¶

11 years ago

Although this works very well for general DNS queries if you want to do a direct DNS query to a specified DNS server (rather than using OS resolution) try PHPDNS: http://www.purplepixie.org/phpdns/

You can do direct (TCP or UDP) low-level queries to a nameserver and recurse at will. Very useful for testing specific servers and also for walking through a recursive resolution.

down

NaturalBornCamper ¶

7 years ago

You might have the same problem as me, where testing a non-existent domain will search for a subdomain relative to the domain you are executing from, for example:

// Test with working domain
var_dump( dns_get_record('google.com', DNS_A) );
/* works, returns
Array
(
    [host] => google.com
    [class] => IN
    [ttl] => 299
    [type] => A
    [ip] => 172.217.12.142
)
*/

// Test with invalid domain on our website (example.com)
var_dump( dns_get_record('invalidtestingname.com', DNS_A) );
/* Doesn't work, pretend it's a subdomain
Array
(
    [host] => invalidtestingname.com.example.com
    [class] => IN
    [ttl] => 299
    [type] => A
    [ip] => xxx.xxx.xxx.xxx
)
*/

If anyone has that problem, add a "dot" at the end of the domain name, for example, instead of
dns_get_record('invalidtestingname.com', DNS_A);
Do this:
dns_get_record('invalidtestingname.com.', DNS_A);

down

heinjan at eendrachtstraat dot nl ¶

7 years ago

Please note that Firewalls and anti malware software detects  (and depending on company policies even blocks) DNS_ANY requests. 
In that case the usage of this function fails.
This is because DNS_ANY requests can be  exploited for creating "amplification (D)DOS attackes": You send 1 DNS_ANY request and get a huge amount of information back, thus even small requests can result into hugh network load.

I advise to use a more explicit name-request instead of using DNS_ANY.

down

ohcc at 163 dot com ¶

6 years ago

When I use DNS_ALL as the second parameter to invoke dns_get_record() on the OS of Windows, PHP emits a warning with the message "Warning: dns_get_record(): Type '251721779' not supported in blah.php on line blah", and DNS_ANY is always OKAY.

down

bohwaz ¶

1 year ago

Sadly this method does not allow for using an arbitrary nameserver.

If you need to make a request  using a specific DNS server, you'll need to use either Pear/Net_DNS2, or libdns ( https://github.com/DaveRandom/LibDNS ).

If you want something shorter and lighter, you can also use this 150 lines function: https://gist.github.com/bohwaz/ddc61c4f7e031c3221a89981e70b830c

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dns_get_record

Description

Parameters

Return Values

Changelog

Examples

See Also

Improve This Page

User Contributed Notes 7 notes