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Although Google and search engines in general tend to give guidelines to developers, technicians, systems engineers and SEOs, the algorithm still remains hidden and secret to all intents and purposes. After the data theft from YANDEX, the Russian search engine at the end of January 2023, it emerged publicly for the first time, as YANDEX, for example, makes use of 1992 ranking factors. And therefore, one can peacefully and probably think that Google also makes such massive and probably even much greater use of it.
This awareness suggests that it is not enough to know what Google deliberately makes public as official guidelines or best practices, but that undocumented virtuosities and technicalities can often be deduced with a little common sense and development expertise, SEO and networking.
In this post we want to focus on the introduction of what a Reverse DNS is and how it can be associated with the more common and famous idea that a static IP can be profitable at an SEO level. Adopting the correct reverse DNS in the presence of a static IP is certainly the best option to take advantage of the advantages of having a static IP.
What is Reverse DNS?
Reverse DNS, also known as rDNS, is a service of the Domain Name System (DNS) which, as the name suggests, operates in reverse compared to standard DNS. While standard DNS translates domain names into IP addresses (for example, it transforms “www.google.com” into “188.8.131.52”), Reverse DNS does exactly the opposite: it converts IP addresses into their respective domain names.
This reverse translation process is central to many features in the Internet. Of these, the most important is probably email security. In fact, email servers often use Reverse DNS to check the reputation of the IP address of a server that sends email, thus reducing the chances of receiving spam messages.
Technically, Reverse DNS works through a special DNS zone called “in-addr.arpa”, which is responsible for reverse mapping IP addresses to domain names.
Practical Example: Using the Linux Dig Utility with Google.com
Let's say you want to check the Reverse DNS for the “managedserver.it” IP address. First, you need to determine the IP address of “managedserver.it” using the dig command. In a Linux console, the command would be:
dig managedserver.it +short
This command will return the IP address for “managedserver.it”. For example, it might return "184.108.40.206".
At this point, you can use the dig command with the “-x” option to perform a Reverse DNS query on this IP address. The command would then be:
dig -x 220.127.116.11 +short
This command will return the domain name associated with the IP address. In this case, it should return “managedserver.it” as reverse DNS.
root@MANAGEDSERVER:~# dig -x 18.104.22.168 +short managedserver.it.
What are “ptr-record” and “in-addr.arpa”?
DNS is defined by zones. A zone is a separate portion of the domain name space. Historically, it was administered as a single zone file.
Often, a domain corresponds to a zone.
The zone owner associates different addresses with different domain names in their zone.
For example, associate the IP address 22.214.171.124 with the hostname "www" in the "example.com" zone. This is done with DNS records.
This would mean that by typing www.example.com, your browser would be directed to the address 126.96.36.199. This is usually done with an A record (or ALIAS record) and is usually direct DNS.
And what about reverse DNS zone?
A PTR record is the record for reverse DNS.
So, the zone owner just adds that IP address to their zone and everything is good? No. Reverse DNS works the other way around.
The PTR record is stored in a special area called .in-addr.arpa.
This zone is administered by whoever owns the block of IP addresses. In the example case, the zone for the PTR record would be 188.8.131.52.in-addr.arpa. The owner of the IP address is usually the Internet Service Provider (ISP) and if you want to add a PTR record to your IP address, you need to contact your ISP.
The need for a dedicated IP to set up reverse DNS
To properly set up a reverse DNS, you need to have a dedicated IP address. This is because, in the reverse DNS resolution process, a single IP address maps to a single domain name. If several websites share the same IP address (as is often the case with shared hosting services), it will not be possible to set up a custom reverse DNS for each of them.
The motivation behind this need lies in the way DNS works. In a normal DNS system, one domain name can resolve to multiple IP addresses, allowing traffic to be distributed among different servers. However, in the case of reverse DNS, the resolution occurs in reverse, from IP to domain name. This process is designed to be unique: a single IP address resolves to a single domain name.
Therefore, if several sites share the same IP, setting up a custom reverse DNS for each of them would be technically impossible. This limitation underscores the importance of having a dedicated IP for each website if you plan to use reverse DNS as part of your SEO strategy. A dedicated IP not only allows you to set up a custom reverse DNS, but it can also improve site stability and performance, as well as offer a higher level of security.
Despite the scarcity of IPv4 addresses globally, acquiring a dedicated IP address for your website or server remains a relatively inexpensive investment. Most Internet service providers or hosting offer dedicated IPv4 addresses for a very affordable monthly cost, usually 1 or 2 euros per month. Furthermore, an initial activation cost may be required, which is normally between 20 and 30 euros, paid once. Considering the potential benefits in terms of SEO, security and stability, a dedicated IP address can be a sensible investment for any website or server owner.
How to set up custom Reverse DNS?
Setting up custom Reverse DNS is a technical task that requires some control over your website infrastructure. To do this properly, you'll need to have authority over both the IP address you want to use, and the domain name you want to associate with that IP address. The implementation of this process may differ slightly depending on your Internet Service Provider or your web hosting service.
In general terms, here are the basic steps for setting up a Reverse DNS:
- Log in to your provider control panel: The first step is to access the control panel of your Internet service provider or web hosting service. This is usually where you manage the settings for your website or server.
- Find the DNS or Reverse DNS settings: Once you enter the control panel, you will need to find the settings section where you can manage your DNS settings. This section could be called “DNS settings”, “Network settings”, “Reverse DNS” or something similar, depending on the provider.
- Set up Reverse DNS: In this section, you will have to enter the IP address you wish to associate and the corresponding domain name. This is usually done through a simple interface that allows you to enter the IP address and domain name, and then save the changes.
- Contact technical support if necessary: Some providers do not offer an option to set up Reverse DNS directly through the control panel, and may require you to contact their technical support to implement this change. In this case, you will have to follow the instructions provided by technical support.
- Check your Reverse DNS settings: After setting up Reverse DNS, it is important to verify that everything is working as expected. You can do this by using the “dig -x” command in a Linux terminal, as described in the previous example. If the command returns the domain name you associated with the IP address, then Reverse DNS has been set up correctly.
Please note that it may take a few hours for Reverse DNS changes to take effect, due to the nature of the DNS system and the timing of propagation of DNS information.
If you are not an expert in systems engineering and networking, the best advice is to contact your hosting provider or request a consultation from Linux systems engineers like our company.
What advantages to expect at SEO level?
Certainly not miracles. Using Reverse DNS as an SEO strategy is not common, nor documented, but it is best practice and could have potential benefits.
One of them could be increased trustworthiness in the eyes of search engines. A site with a static IP and properly set Reverse DNS may appear more trustworthy because it suggests that the entity behind the site has some level of technical expertise and is making an investment to maintain a stable online presence.
Also, Reverse DNS can help prevent spam email problems. Many email servers use Reverse DNS to verify the identity of incoming servers. If your email server's Reverse DNS does not match the domain the email is from, it may be marked as spam.
Although SEO is an aspect that exclusively concerns websites, it is not equally true that the factors that influence trust, as well as positioning, can also be derived from other services.
In summary, the Reverse DNS represents a minor technical element which could however have significant repercussions on the SEO and overall reputation of a website. Although it is not listed among the ranking factors officially recognized by Google, correct use of Reverse DNS can certainly improve the perception of reliability and authority of a site, fundamental elements in the panorama of modern SEO.
But Reverse DNS is not only important for SEO. Its correct use can, in fact, prove crucial to prevent problems related to the sending of emails, reducing the risk that these are labeled as spam. A smaller number of emails classified as spam translates into a more solid online reputation, with obvious benefits for the visibility and communicative effectiveness of a website or online service.
Furthermore, Reverse DNS can be used to improve the security of a website, allowing you to authenticate hosts and detect potential threats.
Finally, for those who use a static IP, setting up an adequate Reverse DNS is a practically obligatory step, a further element to be included in a well-planned and carefully implemented SEO strategy. In an increasingly competitive digital world, every detail can make a difference, and Reverse DNS is no exception to this rule. Implementing it correctly may not guarantee immediate success, but it will certainly help create an online ecosystem that is safer, more reliable and, therefore, more likely to succeed in the long term.