I noticed that Quad 9 is not able to respond to the spy.pet query:
$ dig spy.pet @9.9.9.9 +short
;; communications error to 9.9.9.9#53: timed out
But Cloudflare DNS is able to do it:
$ dig spy.pet @1.1.1.1 +short
104.26.0.165
104.26.1.165
172.67.74.73
And to be sure, I checked another domain with the same TLD to rule out the option that Quad9 is unable to handle the .pet TLD, but I received a correct answer…
$ dig hello.pet @9.9.9.9 +short
3.64.163.50
Does Quad9 censor DNS queries?
It would literally be easier to add that capability to your own custom DNS server software. After all it is literally an “if query.name in blocklist then drop connection”. Even replacing results would be simple as long as DNSSEC is not involved. You wouldn’t have to add it though since all major DNS servers already include it because it is so simple and has legitimate uses, such as blocking malware control server names or ad blocking.
Yes, it is likely that most providers running custom generic or custom stacks already have the functionally built in and also yes, adding an “if” is easy but then once you’ve thousands of servers running the same piece of software across the globe deploying updates and features becomes way slower and way harder. You’ve to consider tests, regressions, a way to properly store and sincronize the blocklists across nodes etc…