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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 [, array &authns, array &addtl]] )

Note: This function is not implemented on Windows platforms, nor does it (currently) work on *BSD systems. Try the PEAR class Net_DNS.

This function returns an array of associative arrays. Each associative array contains at minimum the following keys:

Table 1. Basic DNS attributes

AttributeMeaning
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.

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.

By default, dns_get_record() will search for any resource records associated with hostname. To limit the query, specify the optional type parameter. type 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. The default is 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.

The optional third and fourth arguments to this function, authns and addtl are passed by reference and, if given, will be populated with Resource Records for the Authoritative Name Servers, and any Additional Records respectively. See the example below.

Table 2. Other keys in associative arrays dependant on 'type'

TypeExtra 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.

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().

Example 1. Using dns_get_record()

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

Produces output similar to the following: 

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
        )

)

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.

Example 2. Using dns_get_record() and DNS_ANY

<?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);
?>

Produces output similar to the following: 

Result = 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
        )

)
Auth NS = Array
(
    [0] => Array
        (
            [host] => php.net
            [type] => NS
            [target] => remote1.easydns.com
            [class] => IN
            [ttl] => 10722
        )

    [1] => Array
        (
            [host] => php.net
            [type] => NS
            [target] => remote2.easydns.com
            [class] => IN
            [ttl] => 10722
        )

    [2] => Array
        (
            [host] => php.net
            [type] => NS
            [target] => ns1.easydns.com
            [class] => IN
            [ttl] => 10722
        )

    [3] => Array
        (
            [host] => php.net
            [type] => NS
            [target] => ns2.easydns.com
            [class] => IN
            [ttl] => 10722
        )

)
Additional = Array
(
    [0] => Array
        (
            [host] => pair2.php.net
            [type] => A
            [ip] => 216.92.131.5
            [class] => IN
            [ttl] => 6766
        )

    [1] => Array
        (
            [host] => remote1.easydns.com
            [type] => A
            [ip] => 64.39.29.212
            [class] => IN
            [ttl] => 100384
        )

    [2] => Array
        (
            [host] => remote2.easydns.com
            [type] => A
            [ip] => 212.100.224.80
            [class] => IN
            [ttl] => 81241
        )

    [3] => Array
        (
            [host] => ns1.easydns.com
            [type] => A
            [ip] => 216.220.40.243
            [class] => IN
            [ttl] => 81241
        )

    [4] => Array
        (
            [host] => ns2.easydns.com
            [type] => A
            [ip] => 216.220.40.244
            [class] => IN
            [ttl] => 81241
        )

)

See also dns_get_mx(), and dns_check_record()

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