Por que o DNS não vinculado falhou ao escavar um domínio?

Esta é uma pergunta de acompanhamento para minha pergunta anterior . Abaixo está o /etc/unbound/unbound.confarquivo:

# unbound.conf(5) config file for unbound(8).
server:
    directory: "/etc/unbound"
    username: "unbound"
    chroot: ""
    logfile: "/etc/unbound/unbound.log"
    pidfile: "/etc/unbound/unbound.pid"
    verbosity: 1
    # listen on all interfaces and answer queries from the local port 3000.
    interface: 0.0.0.0 
    interface: ::0
    port: 3000
    access-control: 10.0.0.0/8 allow
    #access-control: 2001:DB8::/64 allow

Com unbound.serviceiniciado, tentei digum domínio através do servidor local não vinculado:

root@DNS:/etc/unbound# dig example.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> example.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 8367
;; flags: qr rd ad; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; Query time: 0 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Tue Oct 29 16:18:19 UTC 2024
;; MSG SIZE  rcvd: 12

Não entendo por que WARNING: recursion requested but not availableunbound é configurado para ser um resolvedor recursivo por padrão. Também. SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)mostra que unbound foi usado, no entanto, ele falhou em obter o domínio. O que está errado e como eu conserto esse problema?

Abaixo mostramos a resposta via systemd-resolved.serviceservidor stub:

root@DNS:/etc/unbound# dig example.com

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36356
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;example.com.           IN  A

;; ANSWER SECTION:
example.com.        3304    IN  A   93.184.215.14

;; Query time: 12 msec
;; SERVER: 127.0.0.53#53(127.0.0.53) (UDP)
;; WHEN: Tue Oct 29 16:43:59 UTC 2024
;; MSG SIZE  rcvd: 56

Atualizar:

Após corrigir a sub-rede, como mencionado pela resposta de @mpboden, o digcomando só funcionou uma vez. Por que esse é o caso?

root@DNS:/etc/unbound/unbound.conf.d# systemctl start unbound.service
root@DNS:/etc/unbound/unbound.conf.d# [1730230920] unbound[5780:0] notice: init module 0: subnetcache
[1730230920] unbound[5780:0] notice: init module 1: validator
[1730230920] unbound[5780:0] notice: init module 2: iterator
[1730230921] unbound[5780:0] info: start of service (unbound 1.19.2).

root@DNS:/etc/unbound/unbound.conf.d# dig example.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> example.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40273
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;example.com.           IN  A

;; ANSWER SECTION:
example.com.        3600    IN  A   93.184.215.14

;; Query time: 712 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Tue Oct 29 19:42:34 UTC 2024
;; MSG SIZE  rcvd: 56

root@DNS:/etc/unbound/unbound.conf.d# dig google.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> google.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 49774
;; flags: qr rd ad; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; Query time: 0 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Tue Oct 29 19:42:56 UTC 2024
;; MSG SIZE  rcvd: 12


root@DNS:/etc/unbound/unbound.conf.d# dig example.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> example.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 46236
;; flags: qr rd ad; QUERY: 0, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; Query time: 0 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Tue Oct 29 19:43:36 UTC 2024
;; MSG SIZE  rcvd: 12