What is rDNS?
The rDNS, also known as reverse DNS, is the DNS lookup using an IP address and searching for its corresponding domain name. It is simply the opposite of the normal forward DNS lookup, where the goal is to find the associated IP address of a domain name.
It is common for Managed DNS providers to supply the rDNS service. When you decide to get it, you are going to have the opportunity to make a reverse Master zone. Next, by creating PTR records in this zone, you are able to verify the accurate equivalent linking IP addresses and their hostnames. PTR records act as a piece of evidence when you have to prove the IP address actually belongs to the domain name. That way, you are making sure to avoid fraud. In addition, rDNS is able to operate with IPv4 addresses and with the newer IPv6 addresses.
How does it work?
For the reverse process of resolving an IP address to a domain name, some participants are required. They are the Reverse Master zone, plus PTR records.
Reverse Master Zone. This is a Primary DNS zone on an authoritative DNS server utilized to resolve IP addresses to domains. It would help if you created such a zone because it is the only place where PTR records are able to exist and operate correctly.
The reverse lookup is performed among the DNS hierarchy, similar to the more common forward DNS lookup. Yet, for completing reverse lookups, there is a precise root domain in-addr.arpa. In this domain, subdomains are produced utilizing the IP address numbers’ order in reverse. The reason for that is because the data on it gets more precise from the left to the right direction. For illustration, this 18.104.22.168/32 becomes 22.214.171.124.in-addr.arpa (reverse lookup domain).
PTR record. The PTR, also known as pointer record, carries precisely the linking of the IP address to the domain name. In addition, for each PTR record that you create it is necessary to have an A or AAAA record. The reason for that is that the PTR record operates in the opposite direction of the A and AAAA records. They link domains to their IP addresses, and PTR works exactly in the opposite way.
With PTR records, servers are able to provide surety about the integrity of the senders. Receivers understand spammers haven’t modified that sender’s IP address. Reducing or eliminating spam is an everyday mission. So, without a PTR record, mail servers (receivers) are going to deny well-configured emails.
rDNS – reasons to use it
- It is filtering spam emails. A lot of email servers implement rDNS for the purpose of blocking spam mail and rejecting messages coming from IP addresses without Reverse DNS. Yet, rDNS is commonly utilized as an extra layer of security. Yet, it is very important to set up the A or AAAA records and PTR records.
- Security. A reverse IP lookup could be utilized to get the IP address’ A records, linking a domain name to the IP address of the machine hosting that domain. This result will help determine the virtual hosts served from a web server and recognize server vulnerabilities.