Background

The 'PTR' Resource Record (RR) is standarized in RFC 1035 and are used only for reverse-mapping zones and are the corollary of the address 'A' or 'AAAA' RRs. PTR RRs map an IPv4 or IPv6 address to a name. This process is sometimes also referred to as rDNS or Reverse DNS.


Details

RR Type: PTR
ID: 12 (0x000C)
Defining RFC: RFC 1035,  Section 3.3.12,  Page 18
Description: PTR Resource Record
Function: Pointer to a canonical name. Unlike a CNAME, DNS processing stops and just the name is returned. The most common use is for implementing reverse DNS lookups, but other uses include such things as DNS-SD.
Status: Active

'PTR' RR Syntax

name ttl class type rdata {ptrdname}

RR Field Example Description
name 99 In this example, this is the last octet of a class C [/24] network IP [104.16.45.99]. The reverse lookup zone would be '45.16.105.in-addr.arpa' (Notice the octets are listed in reverse order from the IP.)
ttl This is the records time to live value (in seconds). If there is no TTL specified, the zone's default $TTL Directive will be used.
class IN Specifies the class to be 'Internet'.
type PTR Specifies the RDATA field will contain data in the PTR RDATA format.
rdata ptrdname www.yourdomain.com. Specifies the name server that is authoritative for the domain.

Examples

Snippets from a fictitious forward lookup 'yourdomain.com' zone and reverse lookup '45.16.105.in-addr.arpa' zone files

Typical 'A' Record Entry (in your Forward Lookup zone)

;
;   Zone records
;
www IN A 104.16.45.99

Typical 'PTR' Record Entry (in your Reverse Lookup zone)

;
;   Zone records
;
99 IN PTR www.yourdomain.com.


See Also




This content was last updated on December 10, 2020
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