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dns_get_record
Fetch DNS Resource Records associated with a hostname
Description
arrayfalse dns_get_record( string $hostname , int $type = DNS_ANY , array &$authoritative_name_servers = null , array &$additional_records = null , bool $raw = false )
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.
|
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:
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
- dns_check_record
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