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The Concept of Reverse DNS and Why It Is Vital for You in Business?

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Charlie Brown
April 10, 2017


Charlie Brown
Charlie Brown has written 6 articles for CGIDir.
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There are many administrators still confused about the concept of reverse DNS. In real, reverse DNS (also abbreviated as rDNS) is the actual reversal of the common forward DNS lookup that is usually performed. In this, the DNS is sent queries to get the IP address of a particular hostname or domain. In rDNS process, a DNS query is raised for getting the hostname of a particular IP address. One can get the actual hostname of an IP address by doing a reverse DNS lookup.

Usually, when we try to navigate to a particular webpage, the browser actually checks for the real IP address of the domain name we enter and uses that address to locate the correct page and display it.

What is DNS?

DNS is basically the Domain Name System, which is a huge address list of all the computers connected to the World Wide Web. If you want to access Amazon or Yahoo, you are actually asking the DNS to spot where those site/pages are located. In simpler terms, this process is like looking up an address book to find a particular destination.

However, when we take the example of an address book, it only works in a single dimension. You can easily spot the address of John Smith from an address book, but when provided with the address, it is a real difficult affair for you to identify who lives at that particular address. This is actually the reverse searching process, and this is where reverse DNS mapping of IP address back to domain name comes into play as an easy solution.

¨  Reverse DNS is actually separate from (in fact opposite to) forward DNS.

¨  If you perform the DNS for "sample.com", which points towards IP address "1.2.3.4"r, this doesn’t mean that the rDNS for IP "1.2.3.4" may always point to "sample.com".

This is what you need to identify as the distinct forward DNS and reverse DNS come from two separate sets of data.

Use of reverse DNS

There are plenty of uses for reverse DNS in real world administration. rDNS is primarily used by the human administrators to track where a particular visitor to a website comes from or to identify the origin of an e-mail message. It is not typically as critical as forward DNS as the common visitors will easily reach your website without the knowledge of any reverse DNS for your web server IP.

Unlike forward DNS, it is a special type of PTR-record that is usually used for storing rDNS entries. The IP address is basically the name of such PTR-record, with the instance of having the various segments reversed as ".in-addr.arpa". For instance, the actual reverse DNS PTR record for IP address of 1.2.3.4 may get stored as "4.3.2.1.in-addr.arpa".

¨  With forward DNS, one points the domain name or zone to the DNS server by indexing the host name with the registry.

¨  In reverse DNS, the ISP (Internet Service Provider) points the zone to your DNS server.

In real, without the sub-delegation performed by the internet service provider, the process will not be working.

Importance of reverse DNS

In typical internet business environment, reverse DNS is mostly important due to the reason that:

¨   Many e-mail servers may have been configured to block or reject the incoming mails from particular IP addresses, which don’t have reverse DNS.

¨  When you run an e-mail server to do mailing, there should be a valid reverse DNS existing for the IP address of the outgoing e-mail server to ensure that the recipient gets it successfully.

¨  It doesn’t actually matter to where the DNS record of your real IP address points to. If there are multiple domains on a single mail server, you can point the reverse DNS to any domain name as you wish.

Using the rDNS lookup to identify the visitor to a particular web page is now one of the most reliable B2B marketing strategies. Even if it cannot tell you the actual name of the person, getting the name of the organization itself can help you a big deal to get a valuable lead.

Reverse DNS and web analytics

Nowadays, all the leading web analytics software features reverse DNS as a built-in tool. You can see the same data under the Audience > Technology > Network tab of Google Analytics tool.

If you rely on it, one major problem you may be facing is that your reports may get filled with all the home broadband and mobile phone users from across the globe skewing your data. However, it is possible to implement some filters on Google Analytics and other analytics tools. But these may still have some limitations.

If you want to get a clear filtered lead list, you can try the premium options like Leadfeeder tools, which also offer a 30-day free trial. Software like Leadfeeder uses advanced machine learning capabilities to filter out the ISPs of irrelevant hostnames to get customized data. It also has capabilities to get integrated to other major marketing, data analytics, and sales tools for better data management.

If you are only using basic web analytics to see the statistical info generated through your website, then rDNS can give it more relevance and precision by seeing who actually visits your website and from where. Rather than focusing on masses, the filtered rDNS lookup can help you focus more on the most prospective companies and individual clients.

Even though the internet may overall seem to be pretty anarchistic most of the time, the DNS address book may always act as a much more stable and reliable system as everyone on the World Wide Web may agree upon. This means you can pretty much rely on what the DNS says. You do some further reading to understand a few more in-depth aspects of rDNS.

The rDNS lookups for the IPv4 addresses use the special domain mentioned above as ‘in-addr.arpa’, whereas the latest IPv6 addresses use ‘ip6.arpa’ domain. There are subdomains with that parent domain for each network based on the particular network number. For natural grouping and ensuring consistency, four octets of the numbers get reversed. Say for example, in-addr.arpa domain name reverse for the IP address 192.168.0.1 may be ‘1.0.168.192.in-addr.arpa.’

In order to set up a reverse domain name to ensure its business advantages, you can contact your ISP or the organization which supplied your IP addresses.


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