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?
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…
How much simpler can I make this…
You have a primary ‘master’ server in the pool.
Replica/cache servers periodically ask the master for any updates.
Master gives a new update, which is a sinkhole for a marked malicious domain.
Replica/cache server now resolves malicious domain to the sinkhole address.
This is not a ‘feature’ you have to implement, it’s a basic function of running a redundant DNS system.