Reverse IP Lookup

The DNS PTR record, also known as Pointer record or Reverse DNS record, is the type of Domain Name System record used to store the domain or hostname associated with the IP address. It bridges the host or domain name with the IP address.

That record is used in Reverse DNS Lookup, also referred to as Reverse IP Lookup. The record lookup provides you the name of the domain or host related to the IP address.

The reverse DNS provides the answer to a question:

I have an IP address; what is the FQDN related to it?

When the user enters the domain name in its browser search bar, a DNS lookup process is performed that linked the domain name with its host IP address.

The reverse DNS or IP Lookup is the opposite of DNS lookup. It starts with a known IP address and ends with finding the domain or hostname associated with it.

DNS PTR record is the reverse of both A record for IPv4 address and an AAAA record for IPv6 address, referred to as "forward DNS" records.

Its structure is the same as other types of DNS records. However, one thing is essential; it's reverse mapping. Therefore, the IP address is specified in the reverse sequence.

In IPv4

For example, the PTR record for the domain DNS.google with IPv4 address 8.8.4.4 will be stored in the following way.

Here, a PTR record stored as the IP address is broken down into segments and then reversed, followed by .in-addr.arpa.

In IPv6

For example, the PTR record for the domain DNS.google with IPv6 address 2001:4860:4860::8844 will be stored in the following way.

Here, a PTR record stored as the IP address is reversed and then broken down into four-bit sections, followed by .ip6.arpa.

RFC 1912 section 2.1 states that every Internet-reachable host should have a name and make sure your PTR and A records match.

There are two methods to check PTR Record and Reverse DNS Lookup.

Using command

• InWindows, run nslookup IP_address in command prompt.
• In Linux or MAC OS, run dig -x IP_address on Linux's console terminal or MacOs's terminal.

Note: replace the IP_address with the domain's IP address.

Using Online Tool

• For that, open the online tool: Reverse IP Lookup.
• Enter the IP address, and click on the "Reverse IP lookup" button.
• The tool will process your query and provides you the domain associated with the corresponding IP.
• For example, one of the IPs of Google.com is 8.8.8.8. When you type that IP address into the Reverse IP lookup tool, it will return the hostname dns.google as listed in the database of the Address and Routing Parameter Area (ARPA) top-level domain of the Internet.

• You will find the domain or the host associated with the IP address.
• By getting the hostname, you can also get its location on Google maps.
• The DNS PTR records are a must for an outgoing mail server. The mail servers like Google and Yahoo use the antispam filters to check whether the mail server trying to deliver the email has matching forward and reverse DNS lookup.

A PTR record is a security tool, and it's in Google's best practices.

Email is an integral part of any business. No one wants its email to be part of someone's spam folder. Its harm your trustworthiness and raise question on your business credibility.

Whenever you receive an email, your mail server employs the PTR record that comes in with the email message to check whether the mail server sending the email matches the IP address it claims to use.

That sounds a bit complicated, but a PTR record acts like an ID card for your mail server. It tells everyone receiving emails from your end that you are who you claim to be. That's the way; email receivers know that spammers haven't taken over your IP address. You need a PTR record because many mail servers will reject emails from a mail server without one. After all, the objective is to keep the spam out of your inbox.

The PTR records point an IP address to a fully qualified domain name (FQDN), and it works as the opposite of what A record for IPv4 address and an AAAA record for IPv6 address does. The PTR records are also called reverse DNS records.

ASN Lookup service queries one of the five regional internet registries (RIRs) for an IP address and displays who owns the IP address and other information such as AS-name, organization name, registration date, and much more.