Hello! I recently tried NextDNS and noticed that is detects my current DNS resolved on the go. I just opened its website and it immediately showed my current resolver:
When I tried changing private DNS to Cloudflatein settings it instantly showed my new resolver.
But how exactly it works? Does the browser send used DNS server to website? Or it is done somehow via JavaScript?
And also: So every website can know what I am using now? Can it be used for fingerprinting?
Put a record in DNS whose content differs from other servers’. When they look it up regularly, they get one answer. When they look it up with you, they get a special answer. Then the servers behind those records return the relevant answer.