What is Reverse DNS Lookup and Forward DNS?

Today we are going to share what is Reverse DNS and how it is different from forward DNS.
In forwarding DNS your query for the IP address and that returns the detail of hostname. However, in the reverse DNS, lookup your query for the hostname returns the IP address.

reverse dns and forward dns lookup
Forward DNS and Reverse DNS Query

The use of DNS is to resolve your query of domain name to an IP address. This is known as the forward resolution and works every time you visit a website on internet. Reverse DNS or rDNS as the name specify, is a method to resolve an IP address to a domain name.

What is Reverse DNS in simple terms?

Every time you visit a website, eg. google.com, the browser checks for IP address of that domain name and displays the right pages from that location.
DNS (Domain Name System), is an address list of computers that are connected to the internet. When we enter the URL of any website in the browser, it basically asks DNS for their exact location. It is like having an address book in normal life which contains a list of all businesses and it’s a corresponding street address.
Remember the above approach is Forward DNS query but if you were given a random address and asked to find who lives there is the hard part. This is what we called reverse DNS query, where you are given the IP address of a server and you ask for its corresponding hostname details. Thus the name implies ‘Reverse’.

Reverse DNS works the other way around than forward DNS

Every internet connected devices hav an IP address. Even the device you are using right now to read this post has one and the computer that stores this page has one. While not every server have a reverse DNS record. You can check reverse DNS record using the tools below:

https://mxtoolbox.com/ReverseLookup.aspx
https://www.whatismyip.com/reverse-dns-lookup/
https://www.iplocation.net/reverse-dns

What are the uses of rDNS?

It is much easier to remember and identify a domain name than a string of numbers. The forward DNS records are required to display websites in your browser by making a query for a simple URL.
The website will load fine even in the absence of reverse DNS, so why do we use it?
Well, Email servers commonly use rDNS to block emails and mark them as SPAM. Most of the mail servers are set to automatically block/reject mails from an IP address that does not have rDNS in place. rDNS is used as an extra layer of protection from SPAM, though it is not a reliable means. In addition, rDNS also helps in logging human-readable data instead of logs that contain only IP addresses.

What are PTR records in rDNS?

DNS is also called a zone. Each domain is often one zone.
The owner of the zone points the different domain to different addresses. Example, the IP address 23.9.12.8 points to hostname www in zone example.com. This is done via DNS records.
What this means is, when we query for www.example.com, it would direct our browser to address 23.9.12.8. This is done by having an A record (Alias) and it is usual forward DNS.


So how does reverse DNS works? Well, in reverse DNS case we use PTR record. It is the record for reverse DNS. The entry of IP address to the zone by zone owner is not enough. Reverse DNS works the other way around.
PTR records are stored in a special zone file called .in-addr.arpa. This zone is always administrated by the whoever owns the block/pool of IP addresses. In our case, the zone for PTR record would be 8.12.9.23.in-addr.arpa.

Setup of rDNS record at Microcen Hosting


The owner of the IP address is usually the ISP. If you want to add a PTR record for your dedicated server IP address, you can do so directly by logging to your client area. You can also submit a ticket and our technical engineers will setup rDNS record for you.

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