22Tem
How does "on.quad9.net" know whether a user is using quad9?
To be able to know if a user is using quad9 by browsing https://on.quad9.net/, I was expecting the same technique as DNS leak test to be used (see How does dnsleaktest.com find my DNS provider).
However, it does not seem like https://on.quad9.net/ is using a random subdomain to do that.
So, how is https://on.quad9.net/ able to tell if a user is using quad9 or not?
