How do services like 2ip.ru, ipinf.ru, www.similarweb.com and others collect analytics?

Question

Domain Name System

Good afternoon!

An interesting question is how, for example, ipinf.ru collects information about domains located on the same IP?
There is an idea, for the implementation of which it is necessary to receive this information in automatic mode. But few services provide information via API, some have API but unclear or expensive pricing. I'm trying to understand how best to organize this process, and in general to understand the primary sources of this information.

Thank you!

Sincerely, BruFor

Answer 1

I assume that the lists of domains are downloaded from registrars (they are in the public domain)
Only delegated domains are taken
Next, the domains go through the list and ip addresses are resolved
Everything is added to the database and we get the necessary bindings

Answer 2

Cheaper to pay
Google
There are a lot of things in open sources

Answer 3

You can parse something in the services themselves, something in the PS:
https://www.bing.com/search?q=ip%3A178.248.232.5
On the Internet, with proper Google, you can find gigabyte archives (and this is in the archive) with domains.
You write a dns resolver in your favorite programming language, run it in 100 threads, and in a few weeks or months ;) you will have such a base. Which would be nice to update...