DNS/glue/unbound 1.9.1/netについて、ここに記述してください。

$ unbound-control flush_zone net
ok removed 95 rrsets, 82 messages and 0 key entries
tmaeno@u16:~$ unbound-control flush_zone com
ok removed 54 rrsets, 47 messages and 0 key entries
tmaeno@u16:~$ unbound-control flush_zone .
ok removed 361 rrsets, 284 messages and 0 key entries

tmaeno@u16:~$ dig -t ns net

; <<>> DiG 9.14.0 <<>> -t ns net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13754
;; flags: qr rd ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1220
;; QUESTION SECTION:
;net.                           IN      NS

;; ANSWER SECTION:
net.                    172800  IN      NS      f.gtld-servers.net.
net.                    172800  IN      NS      a.gtld-servers.net.
net.                    172800  IN      NS      l.gtld-servers.net.
net.                    172800  IN      NS      b.gtld-servers.net.
net.                    172800  IN      NS      k.gtld-servers.net.
net.                    172800  IN      NS      j.gtld-servers.net.
net.                    172800  IN      NS      i.gtld-servers.net.
net.                    172800  IN      NS      d.gtld-servers.net.
net.                    172800  IN      NS      e.gtld-servers.net.
net.                    172800  IN      NS      c.gtld-servers.net.
net.                    172800  IN      NS      g.gtld-servers.net.
net.                    172800  IN      NS      m.gtld-servers.net.
net.                    172800  IN      NS      h.gtld-servers.net.

;; Query time: 286 msec
;; SERVER: 127.0.0.3#53(127.0.0.3)
;; WHEN: 月  4月 01 22:38:07 JST 2019
;; MSG SIZE  rcvd: 253

tmaeno@u16:~$ dig +norec -t ns nstld.com

; <<>> DiG 9.14.0 <<>> +norec -t ns nstld.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51317
;; flags: qr ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1220
;; QUESTION SECTION:
;nstld.com.                     IN      NS

;; ANSWER SECTION:
nstld.com.              86390   IN      NS      av4.nstld.com.
nstld.com.              86390   IN      NS      av2.nstld.com.
nstld.com.              86390   IN      NS      av3.nstld.com.
nstld.com.              86390   IN      NS      av1.nstld.com.

;; Query time: 0 msec
;; SERVER: 127.0.0.3#53(127.0.0.3)
;; WHEN: 月  4月 01 22:38:17 JST 2019
;; MSG SIZE  rcvd: 110