Where do domain name registrars get data from?

Question

Domain Name System

Almost every domain name registrar site can check whether such a domain exists or not. Hence the question: Where do they get such data and is it in the public domain? For example, is it possible to parse a database of already registered domain names from somewhere?

Answer 1

Whois is a database of domain names. A registrar with a domain makes a request to it, receives an answer: free or not.
Whois is available for both domain registrars and the registry. For example, whois.internic.net
For access, they use a special protocol via tcp on port 43.
Some also have a web interface on http/https.
But it is almost impossible to get a complete database dump - not all domain zones publish them. For example, .RU has a full dump updated every day by the registry itself. .COM does not do such a dump.