Ever wondered why some emails land in spam while others get delivered? The guy behind this is reverse DNS.

Reverse DNS is the Internet ID checker for servers. It does the opposite of regular DNS. Instead of turning names into numbers, it verifies the numbers (IP addresses) that lead to websites.

If you are a website owner, understanding reverse DNS and setting it up can save you internet headaches.

This guide’ll explain everything you should know about reverse DNS. Spoilers: You cannot set it up by yourself.

What Is Reverse DNS?

When you type a domain name in a browser, the Domain Name System (DNS) looks up the correct IP address for that domain. For example, if you look up google.com, the DNS will match it to an IP address such as 172.217.0.46. This is how a forward DNS lookup works.

Now, reverse DNS works in the exact opposite manner. Instead of browsing the domain name for the DNS to match to an IP address, it takes an IP address to find a domain name. 

For example, if you have an IP address like 192.0.2.1, a reverse DNS can match it to a domain like mail.example.com. 

How Reverse DNS Works

Reverse DNS (rDNS) relies on PTR records to find domain names from IP addresses. PTR records are stored in reverse DNS zones. 

For instance, if you look up an IP address like 192.0.2.1, the PTR record is business.example.com.

Unlike regular DNS, which relies on A, CNAME, and MX records, reverse DNS cannot function without PTR records.

Who Manages Reverse DNS?

The organization that owns the IP address is in charge of managing reverse DNS. Unlike the regular DNS, where you can control your domains’ records, reverse DNS falls under organizations such as:

• If you are using a residential connection, your internet service provider controls the reverse DNS
• If you are renting a server, your hosting provider manages the reverse DNS
• If you manage your IP block, the company’s IT manages reverse DNS

Who Manages PTR Records?

PTR records are the backbone of reverse DNS. As a domain name owner, you do not control the records. 

If you have a business or home internet service provider, they set up the PTR records for you. You can request the records by contacting your customer support. 

Domain name owners can set up the PTR records with a hosting provider. However, your host manages the records. 

Large organizations with IP blocks manage their PTR records and submit them to their upstream internet service provider. 

How To Set Up Reverse DNS

Get the Needed Information

You need the correct information about the IP address you want to assign to a domain name and a domain name that resolves to that IP address. 

For example:

IP: 192.0.2.1

Domain: mail.example.com (must have an A record pointing to 192.0.2.1)

Contact Your IP Provider

As mentioned earlier, you cannot pick your IP. You need to contact your IP provider to set up the reverse DNS. You can request a PTR record from: 

• Your IPS for business connections
• Your hosting provider for a VPS or cloud server

Some hosting providers allow you to set up reverse DNS through cPanel. For example, if you have DigitalOcean hosting, this is how you can set up a reverse DNS:

1. Go to Networking and find DNS.
2. Find your Droplet (server) and click Edit.
3. Under Reverse DNS, fill in your domain, for example: your.example.com.
4. Save changes.

Reverse DNS Verification

After setting up the reverse DNS, don’t just leave it at that. You need to test it. To verify if the reverse DNS is working, type this command on Windows: nslookup 192.0.2.1 (use the real IP address)

If you have a Mac, you can use this command: dig -x 192.0.2.1 with the real IP address.

If you set up the reverse DNS correctly, it should lead back to the correct domain name.  

How To Set Up Reverse DNS With True Host

If you have a VPS or dedicated server with an assigned IP address, you can set up an rDNS with Truehost KE. However, this setup requires support intervention, and you cannot do it alone.

Here’s how you can achieve  rDNS setup with Truehost KE:

1. You must have an active VPS or dedicated server service with Truehost.
2. Identify the IP address for which you want to set the reverse DNS.
3. Contact Truehost support (or request via client area) with the IP address and desired PTR record (hostname).
4. Truehost support configures the rDNS PTR record on the IP to point to your hostname.
5. Then wait a few hours for the change to propagate. 

Why Does True Host Intervene in Reverse DNS Setup 

Truehost restricts rDNS setup and supports intervention because:

rDNS Setup Needs Backend Access

While you can control domain records via DNS hosting, rDNS is linked to the IP address. 

In this case, Truehost owns the IP block and manages reverse DNS zones that store PTR records. Hence, to modify the PTR records, you need to access an authoritative DNS server, where the support team assists. 

To Prevent Email and Network Issues

If Truehost allows self-registered rDNS setup, it can lead to email delivery failures. For instance, if a customer sets an incorrect PTR, their emails could: 

• Get blocked
• Labeled as spam
• Fail DMARC/DKIM authentication

PTR misconfigurations can also cause network and security problems, such as breaking log monitoring, making troubleshooting difficult. They can also break the firewall and access control rules. 

Hence, any hosting organization must verify the correct PTR records before making changes during reverse DNS setup. 

Enhancing Consistency

Truehost manages many IPs in its dedicated and shared servers. Therefore, unrestricted reverse DNS changes can lead to: 

• Multiple clients are claiming duplicate PTR records
• PTR record failing to match the A record
• Security risks that can result in fake reverse DNS for spoofing

When the Truehost team takes charge of setting up rDNS, they ensure: 

• The requested domain matches the server’s A record.
• The PTR record follows the required standards (no typos, invalid formats).
• The change doesn’t disrupt other customers using the same server.

To Enhance Reliability

Reverse DNS setup can take a while, especially if you are trying to figure it out without technical skills. Truehost ensures the correct configurations upon request to avoid mistakes. 

Why Is Reverse DNS Important

Some of the key reasons why reverse DNS is Important include:

Network Troubleshooting

Reverse DNS can help track and troubleshoot network issues. It helps identify domain names from IP addresses, making identifying misconfigured devices and unauthorized access attempts easier. It can also trace the sources of traffic in a network.

Also, if you encounter an unreachable server, you can use rDNS to determine whether the IP belongs to the real host. 

If multiple services use the same IP range, rDNS can resolve the conflict by distinguishing them. 

Email Performance

Reverse DNS plays a crucial role in email authentication. Email providers perform reverse DNS to verify email legitimacy. 

When you send an email, the recipient’s server checks your PTR record and verifies whether the IP address resolves to a valid domain. Your email may land in spam or bounce back if there is a mismatch. 

Reverse DNS prevents communication from breaking down through spam prevention and ensures that organizations comply with email standards. 

Enhancing Security

You can use reverse DNS to verify remote systems and enhance security. For example, when rDNS performs email server verification, it prevents phishing by ensuring the sender’s IP matches the claimed domain. 

In addition, reverse DNS performs firewall and access control and helps prevent online attacks by displaying domain names instead of raw IP addresses. 

For example, if an attacker sends messages with an IP address pretending to be a specific domain, a proper rDNS search can reveal the mismatch and block the emails. 

Simplifying System Administration

Raw IP addresses can be challenging to interpret, especially if you are new to such technological concepts. Reverse DNS streamlines system administration by converting IP addresses into domain names. 

Therefore, rDNS creates a system that allows easier debugging, simpler website tracking for traffic analysis, and easier security and audit compliance reporting. 

Differences Between DNS and rDNS

While both DNS and rDNS are critical to the internet’s functioning, they vary in purpose and functionality. 

Function

Concept	DNS	rDNS
Purpose	Translates human-readable domain names like example.com into machine-readable IP addresses like 192.0.2.1	It maps an IP address back to a domain name. It works the opposite of the DNS
How it works	When you search a domain like  google.com in a browser, DNS queries its A record (for IPv4) or AAAA record (for IPv6) to find the correct IP.	It uses PTR (Pointer) records stored in special reverse lookup zones
Example	Searching example.com on a browser  results in an IP: 192.0.2.1	Searching for an IP address like 192.0.2.1 results in a domain like  mail.example.com

The key difference in functionality is that DNS finds IP addresses for domain names and is commonly used by internet users to access websites, while rDNS matches IP addresses to domain names and is used for server verification. 

Records

DNS uses various records to match a domain to an IP address. Such records include:

• A records: match a domain to an IPv4 address
• AAAA records: they map a domain to an IPv6 address
• MX records: they specify email servers

On the other hand, reverse DNS uses PTR records that map an IP address to a domain. 

Management

The domain owner manages regular DNS. If you own a domain, you can control and manage it through your hosting provider’s or domain registrar’s dashboard. 

Reverse DNS, on the other hand, requires management by the owner of an IP address, who could be: 

• Your internet provider
• The data center
• Your cloud provider

Note: You can control your DNS, but not reset your rDNS.

The Look Up Process

DNS Look Up	rDNS Look Up
User types a domain name (business.com)	The system queries 192.0.2.1.
Resolver checks:The order of operations is local cache, followed by the ISP’s DNS, Root servers, and TLD (.com), the Authoritative DNS.	Resolver checks:The reverse DNS zone Follows the PTR record chain.
Returns the IP example: 192.0.2.1	Returns with a domain like business.com

Common Uses

Forward DNS serves purposes like email routing and helping people access the correct web resources. Meanwhile, reverse DNS is useful for email authentication, security checks, and troubleshooting.

Also, forward DNS makes the internet friendly, while reverse DNS keeps email systems reliable and networks safe.  

Common DNS Issues

Some of the DNS problems you might encounter include:

DNS Misconfiguration

Having a DNS misconfiguration can lead to email and website outages. Some DNS record mistakes are: 

• A/AAAA records are missing, leaving domains unresolved
• Incorrect MX records are causing email issues
• Typos in hostname
• Misplacing CNAME records

DNS misconfigurations can cause problems such as:

• Website inaccessibility
• SSL certificate violation
• Spammed emails

When performing DNS configurations, ensure the entries are correct before saving the changes. 

Propagation Delays

DNS changes do not take effect immediately. For example, changing your IP address can take up to two days to reflect globally. 

During propagation, website visitors can experience: 

• Email delivery failures
• Broken links
• Seeing older versions of the website

Try lowering the TTL (Time-to-live) in advance when making DNS changes. You can also use DNS propagation checkers to monitor global updates.  

Cache Poisoning

Hackers can inject malicious DNS records into the resolver caches to redirect users to fake websites. For example, a poisoned cache can redirect clients trying to access a bank’s website to a phishing page.

To avoid cache poisoning, it is vital to use a reliable DNS resolver. You can also use DNS security extensions to check the authenticity of records. 

Final Take

Reverse DNS keeps emails out of spam, secures your network, and makes troubleshooting easy. It works behind the scenes to keep communication smooth and verify servers. 

Unlike forward DNS, you cannot set up reverse DNS. Your hosting or internet service provider (ISP) will do that using PTR records. You achieve a reverse DNS setup by requesting PTR records from your web hosting provider or ISP. 

Need reverse DNS? Ask your web host to set it up.