PTR, also understood as reverse DNS, is a fundamental solution for configuring almost any server. PTR records are used to perform DNS reverse lookup, and by using the IP address, it will be possible to access the associated domain/hostname.
Configuring this record model is notably important sending and receiving e-mails. This is due to the fact that it will be feasible to give certain authenticity to the IP that sends or receives the e-mail.
With that in mind, ValueHost has prepared this exclusive content for you to know what it is and what is the importance of PTR configuration. Keep reading and check it out!
What is PTR (rDNS)?
Before knowing exactly what PTR is, you need to understand what it is DNS (Domain Name System). It represents the system that resolves names into IPs on the internet. In the world wide web, each and every device connected to it has an IP. This feature is nothing more than the number that identifies a particular device.
For example, if you enter the IP 142.250.73.227 in any browser, you will automatically be directed to the Google homepage.
We know it’s not practical to memorize a bunch of numbers, right? Because of this, DNS exists, as it is convenient for users to access and locate websites in a more intuitive way.
In other words, just type a name instead of a number. After all, it is much more practical to remember Google than your IP address.
Regarding the PTR (an acronym from the term pointer), it is a type of pointing similar to DNS of the type A – mentioned earlier.
In type A annotation:
- the domain responds to an IP, as in the example used for Google;
- You can configure several domains to respond to the same IP. That is, here, there is no limit of domains that respond to IP. If you have a server, you can host more than one domain even if this server has only one IP.
No note of type PTR:
- the IP responds to a certain domain. That is, if you query the IP, you will need to identify the server that owns that IP;
- You can configure your server’s IP to only a single domain . In this case, there is no possibility of querying an IP, since it will not have two different domains as a response.
How important is this configuration?
One of the main arguments related to configuring reverse DNS on your server is to create greater reliability in your e-mail shots. Many users with problems with this type of sending do not understand the reason to see several providers refusing their emails.
In certain situations, the reason is the lack of a PTR record on the server used to send emails. Based on this, when receiving one, the server performs a query for information in the email header.
Header is the part with various technical data of the email, containing the sender’s IP, name , if the content was enveloped or not, and various other information.
Thus, when an electronic mail server receives an e-mail sent from a server that does not have a PTR record, it can create , thus, loss of reliability. This is because it has a hidden origin, causing the sender to have a low reputation, which often results in the email being discarded.
What are the most important uses of PTR records?
One of the main applications of PTR records is based on reverse DNS lookups. Thus, the most common uses of this tool are:
- anti-spam: certain anti-spam email filters make use of reverse DNS in order to verify the domain names of email addresses and see if the associated IP addresses are likely to be used by legitimate email servers;
- solve email delivery issues: anti-spam filters work on these analyses,. As a result, email delivery failures can cause a PTR record with the wrong configuration. If a domain does not have this record, or it contains the wrong domain, emails may be blocked on this domain;
- record: the records of the system normally only store IP addresses. That way, a reverse DNS lookup can turn them into domain names for records that are better understood by humans.
How to check PTR record?
To create a PTR record, you must first configure a reverse DNS zone. It depends on the size of your IP network. In our example we will use an IPv4/24 network.
So on the /24 network you have 255 unique IP addresses. For example, if our network is “192.168.0.0/24”, the available IPs in this network are from “192.168.0.1 to 192.168.0.255” and our reverse zone has the following format: “0.168.192.in-addr.arpa ”.
To create a reverse DNS zone go to the Control Panel, click the Add new zone button and choose Reverse DNS zone, master and fill in the name of the reverse zone of your IP network. In our case this is “0.168.192.in-addr.arpa”.
Now in our reverse zone “0.168.192.in-addr.arpa”, we can add PTR records for each network IP. From the button “Add new record” it is possible to add a new PTR record and here are some examples for the first two IP addresses:
For 192.168.0.1:
- Type: PTR
- Host: 1
- Points for: hostname1.example.com
For 192.168.0.2:
- Type: PTR
- Host: 2
- points to: hostname2.example.com
After creating the record PTR, make sure the hosts have matching A records. In our example, hostname1.example.com should have a record pointed to “192.168.0.1” and hostname2.example.com should have a record pointing to “192.168.0.2”.
To complete the reverse DNS configuration , you need to change the nameservers of your reverse zone at your IP provider or ask them to help you with the modification. In our case, there should be NS records configured in the IP provider pointed to the nameservers listed in your control panel.
Anyway, the term PTR record can be a bit difficult to understand if this is your initial contact with him. But learning is valid for those who work with server management.
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