Why won't 1.1.1.1 answer to NS record requests?

[guohouzuo]

Is 1.1.1.1 intentionally blocking NS requests that queries a subdomain’s NS records? Check this out:

dig -t ns a.hz.gl @1.1.1.1

; <<>> DiG 9.16.1-Ubuntu <<>> -t ns a.hz.gl @1.1.1.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 25147
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; OPT=15: 00 16 ("..")
;; QUESTION SECTION:
;a.hz.gl.                       IN      NS

;; Query time: 1956 msec
;; SERVER: 1.1.1.1#53(1.1.1.1)
;; WHEN: Wed Aug 25 08:02:57 IST 2021
;; MSG SIZE  rcvd: 42

dig -t ns a.hz.gl @8.8.8.8

; <<>> DiG 9.16.1-Ubuntu <<>> -t ns a.hz.gl @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51863
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;a.hz.gl.                       IN      NS

;; ANSWER SECTION:
a.hz.gl.                300     IN      NS      ans.hz.gl.

;; Query time: 80 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Aug 25 08:03:03 IST 2021
;; MSG SIZE  rcvd: 54

[sdayman]

@guohouzuo

Is 1.1.1.1 intentionally blocking NS requests that queries a subdomain’s NS records?

I don’t think so:

% dig -t ns mail.google.com @1.1.1.1

; <<>> DiG 9.10.6 <<>> -t ns mail.google.com @1.1.1.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 65401
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;mail.google.com.		IN	NS

;; ANSWER SECTION:
mail.google.com.	604800	IN	CNAME	googlemail.l.google.com.

;; AUTHORITY SECTION:
l.google.com.		60	IN	SOA	ns1.google.com. dns-admin.google.com. 392643555 900 900 1800 60

;; Query time: 75 msec
;; SERVER: 1.1.1.1#53(1.1.1.1)
;; WHEN: Wed Aug 25 06:27:10 PDT 2021
;; MSG SIZE  rcvd: 121