PTR Record

From XpertDNS

Pointer Record. Also called a reverse DNS record. A PTR record associates an IP address with a canonical name (domain.com). PTR records should point to a name that can be resolved back to the IP address. The name of the pointer record is not the IP address itself, but is the IP address’ four IP octets in reverse order followed by IN-ADDR.ARPA. for Example:

192.168.1.224 becomes 224.1.168.192.IN-ADDR.ARPA

If your ISP has given you delegation over a block of IPs you can add the PTR as a normal domain name and add your PTRs from there. Depending on the size of the block these are examples.

1.168.192.IN-ADDR.ARPA
168.192.IN-ADDR.ARPA

Then add the PTR like so:

65.1.168.192.IN-ADDR.ARPA   PTR   ptr.example.com

Most ISPs now delegate control over a block of IPs with the standard set in RFC 2317 Classless IN-ADDR.ARPA delegation. Which is a way of delegating control with blocks of smaller than 256 IP addresses.

If your ISP gives you a block such as this 64/27.1.168.192.IN-ADDR.ARPA then it means you have control of the following IPs 192.168.1.64/27.

Network:   192.168.1.64/27
Broadcast: 192.168.1.95   
HostMin:   192.168.1.65    
HostMax:   192.168.1.94    
Hosts/Net: 30    

Just add 64/27.1.168.192.IN-ADDR.ARPA as domain and PTRs as shown here.

65.64/27.1.168.192.IN-ADDR.ARPA   PTR   ptr.example.com