WhoisXML API Blog

FQDN to IP, IP to FQDN: The Queries that Power Domain Infrastructure Discovery

Identifying malicious infrastructure, implementing blocklists, analyzing IP or domain reputation — all of these (and many other) tasks rely on mapping fully qualified domain names (FQDNs, or so called "complete domains") to IPs and IPs to FQDNs. These mappings are crucial not only for network security analysis but also for troubleshooting and even basic website administration. 

There are lookup tools that can let you obtain the IP address that resolves to the FQDN (i.e., FQDN to IP or forward lookup tools) or retrieve a list of domains resolving to an IP address (i.e., IP to FQDN also known as reverse lookup tools). If you want to dig deeper—go back in time, if you will—there are also tools that let you perform historical FQDN to IP and IP to FQDN lookups based on passive DNS data. From there, you can create a timeline of the resource's resolutions. 

In this post, we'll show you how to do all of these. If you want to follow along and do the queries yourself, make sure to sign up for a free account to start using the tools we will be demonstrating.

February 2025: Domain Activity Highlights

The WhoisXML API research team analyzed 7.5+ million domains registered between 1 and 28 February 2025 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by 62.1+ billion domains from our DNS database’s A record full file dated 6 February 2025.

Next, we studied the top TLDs of 1.0+ million domains detected as indicators of compromise (IoCs) this February.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

January 2025: Domain Activity Highlights

The WhoisXML API research team analyzed 7.6+ million domains registered between 1 and 31 January 2025 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by 61.2+ billion domains from our DNS database’s A record full file released in the same month.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

December 2024: Domain Activity Highlights

The WhoisXML API research team analyzed 7.9+ million domains registered between 1 and 31 December 2024 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by 60.1+ billion domains from our DNS database’s A record full file released in the same month.

Next, we studied the top TLDs of 1.3+ million domains detected as indicators of compromise (IoCs) in December.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

November 2024: Domain Activity Highlights

The WhoisXML API research team analyzed 8.2 million domains registered between 1 and 30 November 2024 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by 59.6 billion domains from our DNS database’s A record full file released in the same month.

Next, we studied the top TLDs of 1.1 million domains detected as indicators of compromise (IoCs) in November.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

October 2024: Domain Activity Highlights

The WhoisXML API research team analyzed more than 8.2 million domains registered between 1 and 31 October 2024 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by the more than 57.4 billion domains from our DNS database’s A record full file released in the same month.

Next, we studied the top TLDs of more than 1.0 million domains detected as indicators of compromise (IoCs) in October.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

September 2024: Domain Activity Highlights

The WhoisXML API research team analyzed more than 7.1 million domains registered between 1 and 30 September 2024 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by the more than 60.1 billion domains from our DNS database’s A record full file released in the same month.

Next, we studied the top TLDs and associated threat types of more than 1.0 million domains detected as indicators of compromise (IoCs) in September.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.

August 2024: Domain Activity Highlights

The WhoisXML API research team analyzed more than 7.4 million domains registered between 1 and 31 August 2024 to identify the most popular registrars, top-level domain (TLD) extensions, and other global domain registration trends.

We also determined the top TLD extensions used by the more than 59.2 billion domains from our DNS database’s A record full file released in the same month.

Next, we studied the top TLDs and associated threat types of more than 1.0 million domains detected as indicators of compromise (IoCs) in August.

Finally, we summed up our findings and provided links to the threat reports produced using DNS, IP, and domain intelligence sources during the period.