Reverse DNS – Definition
Reverse DNS, also commonly called simply rDNS, is a method that resolves an IP address into its corresponding domain name. It has exactly the opposite function compared to the traditional Forward DNS lookup where the domain name is resolved to its IP address.
Thanks to it, you are able to prove that the particular IP address actually matches the domain name. A common reason to use it is to provide trust in the email servers. They perform Reverse DNS lookups to ensure that the email is sent from an authoritative source and it is not some type of scam.
How does it work?
Reverse DNS operates successfully thanks to two main things – the Reverse Master zone and the PTR record.
Reverse Master Zone. It is a Primary DNS zone that lives on an authoritative DNS server that has the main purpose of resolving IP addresses to domain names. That is the place where PTR records are able to exist and operate properly. Similar to the Forward DNS lookup, Reverse DNS lookups are completed through the DNS hierarchy. However, there is a specific root domain in-addr.arpa that uses the IP addresses in reverse order. For example, the IP address 18.104.22.168 becomes 22.214.171.124.in-addr.arpa.
PTR record. It is also commonly known as a pointer record, and its main goal is to link the IP address to its corresponding domain name. To achieve that, it is important to note that you should have an A or AAAA record for each PTR record you add. The reason for that is pretty simple. An A record or AAAA record points a domain name to its IP address, and PTR goes exactly in the opposite direction.
Thanks to the PTR records, servers are capable of guaranteeing the integrity of the senders. As a result, the recipients are safe from any malicious attempts aiming to modify the sender’s IP address. Additionally, you probably know that stopping spam is an everyday problem. Therefore, it is not uncommon for emails to get denied based on the fact that they don’t have a PTR record.
Why should you use Reverse DNS?
- When you are implementing Reverse DNS and creating PTR records, you are able to establish proof that there is a complete match between the IP address and the domain name. As a result, the servers of other companies could verify it and be kept safe from criminals.
- Thanks to rDNS, the email servers of your recipients can check the IP address of each incoming message. When there is a match, the message is accepted as legit.
- rDNS provides trustability to your domain and supports the image of a legit service or product supplier.
- It is very beneficial for filtering spam. Cybercriminals commonly send messages using a trustable and legit domain name, for instance, of banks, to their potential victims. Thanks to rDNS, recipients could filter that type of risk.
- Oftentimes DNS validation is necessary, for instance, for cloud services, data storage, backup services, office applications, and more.
- It is helpful when you want to make sure that your message is going to get to your clients. Nobody wants their email MKT campaigns, promotions, special sales, etc., to land directly to the spam folder of their clients. Reverse DNS could be helpful to avoid that!