Reverse DNS (rDNS) lookup is the reverse of the usual “forward DNS lookup” where the DNS is queried for the IP Address of a certain hostname. In reverse DNS, the DNS is queried for the hostname of a certain IP address. A reverse DNS lookup returns the hostname of an IP address.

Whenever we navigate to a certain webpage, say google.com, our browser checks for the IP address of that domain name and uses that address to find the correct page.

DNS, Domain Name System, is an address list of computers connected to the internet. If you want to go to Amazon, you’ll ask DNS where they are located. Just like you would use an Address Book in normal life (wait a minute, no one actually uses an address book these days, do they?).

An address book only works in a one dimensional way. It’s easy to find the address of John Smith from your address book but if you are given an address, it’s pretty hard to find out in your address book who lives there - even if you have their address stored somewhere in your address book.

Reverse DNS lookup is the act of looking up internet hosts by their address. Hence the “reverse” part in the name. It’s the opposite or reverse way of using the internet’s address book, something your old address book can’t even do.

While the internet overall can seem pretty anarchistic at times, this DNS address book is a stable system that everyone on the internet must agree upon. You can pretty much trust that if DNS says someone is google.com they pretty sure are them (and while this blind trust has led to some significant problems, it’s the best system we’ve got).

Reverse DNS works the other way around from the usual forward DNS

Now, all internet connected devices have an IP address. The device you are reading this post has one and the computer that hosts this page has one. If they didn’t you couldn’t access this page.

While not all, a clear majority of all IP addresses have a reverse DNS record(reverse DNS lookup, as they are called). So most computers have an entry of our address book. If we know an IP address, we can know who it is.

When your browser loaded this page, our server was aware of your IP address and your browser was aware of our IP address. This is how the internet works.

But why is this important?

What this means is that if you have a website, you know all the IP addresses that visit that website. And with reverse DNS address book we can translate these IP addresses into hostnames.

While most IP addresses can be translated into hostnames, sometimes that hostname is not very useful. Because there’s a finite amount of IP addresses and seemingly unfinite amount of new mobile phones, laptops and refridgerators connecting to the internet most of the time normal people don’t own their addresses. They are merely using an IP address their Internet Service Provider has allocated them for a while.

That’s the case usually with mobile phones and home broadband connections. In those cases your hostname will be something like 62-78-145-65.bb.dnainternet.fi (that was mine when writing this). But there’s a lot you can already do with this address.

For example, that address tells you I’m from Helsinki, Finland and my ISP is DNA. You can even pinpoint a more accurate location inside Helsinki where the connection was made from. Nice, but there’s no way you can identify me with this information.

A simple whois search can reveal more information about an IP address or a hostname

For B2C marketers, this is all you can do with reverse DNS. Sometimes even that is useful. An IP address can give quite detailed location data and this can help you find good locations to expand your business, for example. But it’s all different with B2B marketing.

Most companies have their own IP addresses. This means you can use reverse DNS to see which companies visit your website. In case of a larger company, you can even see from which of their offices the connection was made from - just like with my IP address above.

Using reverse DNS lookup for identifying the visitor is a great B2B marketing tactic. While it can’t tell you the name of the person who visited, most of the time just the name of the company can help a great deal (you probably wouldn’t want to show your name to every webpage you visit, would you).

Web analytics software and reverse DNS

Most web analytics software have reverse DNS built-in. Google Analytics, for example, shows this data under Audience - Technology - Network. If you are using some other analytics software, that probably has similar features somewhere too.

The problem of course is that your report is going to be filled with these home broadband and mobile phone visitors which are skewing your data and making it harder to find what’s useful from a sales and lead generation perspective.

It’s possible to create filters for filters for Google Analytics but if you are really serious in seeing a clean list of filtered companies visiting your website, try out a 30-day trial of Leadfeeder so you don’t have the hassle of lots of manual and time-consuming work in Google Analytics.

Leadfeeder uses machine learning to filter ISPs and non-relevant hostnames out of your data. It also integrates to other marketing and sales tools for better data sharing.

If you are currently only using web analytics to see statistical changes on your website try reverse DNS and see who really visits your website. It can help you focus on individuals and companies rather than masses.