As marketing becomes increasingly digitized, marketers need to keep up with tech terminology. One buzzword currently making the rounds is DNS — short for Domain Name System. DNS is what makes the internet work, connecting web browsers and websites with one another.
Generally, a DNS lookup is how the DNS translates domain names to the IP addresses connected to them. There is also a reverse DNS lookup.
So what is a reverse DNS lookup, why should you care, and how can you perform a reverse DNS lookup?
This article aims to answer all these burning questions. We’ll look at what a reverse DNS lookup is, what the benefits are of performing it, and finally, we’ll walk you through a step-by-step guide to manually performing a reverse DNS lookup.
What is a reverse DNS lookup?
Before we dive into what is a reverse lookup, let’s back up a little and understand the link between an IP address and a domain name.
Every single device that is connected to the Internet has an IP (Internet Protocol) address which is used to identify it. It is with the help of these IP addresses that you can navigate to your favorite sites on the Internet.
But you don’t type an IP address every time you visit YoutTube, right?
Whenever you navigate to a certain webpage, your browser checks for the IP address in the DNS of that domain name and uses that address to find the correct page. But how does the browser use the domain to find the correct IP address?
This is where a forward DNS (Domain Name System) lookup comes into play.
A forward DNS lookup is a process by which domain names are mapped to the IP address of a particular hostname. If it wasn’t for this system, you’d need to remember the IP address for every single website that you wanted to visit — and nobody’s got time for that!
Thankfully, this isn’t necessary.
However, it sets the scene for us to explore the opposite process to the forward DNS lookup — the reverse DNS (rDNS) lookup.
An rDNS lookup is a process through which an IP address is mapped to its respective domain name.
How does a reverse DNS lookup work?
A DNS lookup involves using a domain name to look up an IP address.
A reverse DNS lookup, on the other hand, involves using an IP address to look up a domain name.
This involves mapping through DNS zones that are part of the domain namespace and store the DNS records.
We won’t need to worry too much about DNS zones in order to actually perform the reverse DNS lookup, but it can be helpful to understand the context of what we’re searching.
Pointer Records and PTR Lookup
A pointer (PTR) record is the record for a reverse DNS that is stored in a special zone.
When a reverse DNS lookup is performed, DNS servers are queried for a pointer (PTR) record. A PTR record maps an IPv4 or IPv6 address to the canonical name for the host. If there is no PTR record on the server, the lookup fails.
What’s the benefit of performing a reverse DNS check?
Reverse DNS check helps in spam filtering
Email servers utilize reverse DNS in conjunction with the forward DNS to verify the identity of the sending server to determine whether it’s from who it says it is.
Let’s say you receive an email from the address [email protected]. Your email server would check if the IP address of the sender’s server has a reverse DNS that is tied to domain.com.
If there is a mismatch, this adds to the data signaling that this may be spam; if there is enough data to suggest this, the email will be labeled as spam and be automatically rejected by your email server.
How to manually perform reverse DNS lookups
Performing a reverse DNS lookup on Windows
Windows users can take advantage of a reverse DNS lookup command "nslookup" to easily perform a DNS check. All you have to do is open the command prompt and enter the following command:
nslookup < IP Address >
Replace < IP Address > with the IP address that you want to map.
The image below shows the results obtained once a reverse DNS lookup is performed for an IP address of 8.8.8.8.
Performing a reverse DNS lookup on Linux
Open the console terminal and type in the following command:
dig -x IP_ADDRESS
As before, replace IP_ADDRESS with the IP address that you want to map, and you’ll then be able to see the results of the DNS reverse lookupwith the dig command.
Performing a reverse DNS lookup on Mac
If you’re using macOS, open the terminal window and type the following command. Just as before, replace IP_ADDRESS with the IP address that you want to map.
dig -x IP_ADDRESS
This will perform a reverse check for domain name servers and show you the results.
Web analytics tools for reverse DNS checks
There are a range of web analytic tools available on the internet that can help you perform a reverse DNS check. It’s as simple as entering the target IP address in the tool of your choice and getting the results.
For instance, if we take XNND as an example, all you have to do is enter the IP address of the target website and it’ll look it up automatically.
Having to manually type in reverse DNS lookup commands on a terminal or using an online web analytics tool can be inconvenient and time-consuming.
Furthermore, these tools don’t give the ability to verify the identity of emails, which helps to determine if they’re malicious spammers.
We’re here to help when it comes to email-related DNS records. With Kickbox DMARC Monitoring, you can easily investigate if malicious senders are using your domains—all in one place.
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