Por que consultar o DNS do test.com sempre retorna alguma coisa?

Question

Enquanto brincava com o DNS do test.com, descobri que, se eu consultar algo, recebo uma resposta válida.

Por exemplo:

dig superuser-is-awesome.test.com -t TXT

; <<>> DiG 9.10.5-P2-RedHat-9.10.5-2.P2.fc25 <<>> superuser-is-awesome.test.com -t TXT
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52365
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4000
;; QUESTION SECTION:
;superuser-is-awesome.test.com. IN  TXT

;; ANSWER SECTION:
superuser-is-awesome.test.com. 7200 IN TXT  "v=spf1 ~all"

;; Query time: 133 msec
;; SERVER: 89.2.0.1#53(89.2.0.1)
;; WHEN: ven. sept. 01 14:28:12 CEST 2017
;; MSG SIZE  rcvd: 86

Funciona da mesma forma com o tipo A ou mesmo sem nenhum tipo:

dig superuser-is-awesome.test.com

; <<>> DiG 9.10.5-P2-RedHat-9.10.5-2.P2.fc25 <<>> superuser-is-awesome.test.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9026
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4000
;; QUESTION SECTION:
;superuser-is-awesome.test.com. IN  A

;; ANSWER SECTION:
superuser-is-awesome.test.com. 3600 IN  A   69.172.200.109

;; Query time: 130 msec
;; SERVER: 89.2.0.1#53(89.2.0.1)
;; WHEN: ven. sept. 01 14:29:20 CEST 2017
;; MSG SIZE  rcvd: 74

Como isso é possível? Existe uma maneira de obter o valor real (não deve ser nada, exceto se realmente existir)?

    

Answer 1

ISENÇÃO DE RESPONSABILIDADE : não estou convencido de que esta é uma resposta correta, mas estou postando de qualquer forma a pedido do OP.

test.com é um domínio real, registrado por uma empresa chamado "Perfect Privacy, LLC" na Flórida.

Um domínio pode ter uma entrada de DNS curinga criada para ele.

This wildcard DNS record will cause DNS lookups on domain names ending in example.com that do not exist to have MX records synthesized for them. So, a lookup for the MX record for somerandomname.example.com would return an MX record pointing to host1.example.com.

No entanto, os registros DNS do test.com não indicam que eles têm uma entrada curinga que Eu posso ver:

DNS Records for test.com
==============

Name        TTL     Class  Type     Priority    Data
test.com.   7200    IN     SOA                  NS65.WORLDNIC.com. namehost.WORLDNIC.com. 117070512 10800 3600 604800 3600
test.com.   7200    IN     NS                   ns65.worldnic.com.
test.com.   7200    IN     NS                   ns66.worldnic.com.
test.com.   3600    IN     A                    69.172.200.235
test.com.   7200    IN     TXT                  "google-site-verification=kW9t2V_S7WjOX57zq0tP8Ae_WJhRwUcZoqpdEkvuXJk"
test.com.   7200    IN     MX       30          lastmx.spamexperts.net.
test.com.   7200    IN     MX       20          fallbackmx.spamexperts.eu.
test.com.   7200    IN     MX       10          mx.spamexperts.com.

    

Answer 2

Estas são entradas DNS de caractere curinga. Testado em meu próprio servidor DNS, é assim que fica:

dighans.xxx.xxx.netTXT;<<>>DiG9.9.5-3ubuntu0.15-Ubuntu<<>>hans.xxx.xxx.netTXT;;globaloptions:+cmd;;Gotanswer:;;->>HEADER<<-opcode:QUERY,status:NOERROR,id:64899;;flags:qraardra;QUERY:1,ANSWER:1,AUTHORITY:0,ADDITIONAL:1;;OPTPSEUDOSECTION:;EDNS:version:0,flags:;udp:4000;;QUESTIONSECTION:;hans.xxx.xxx.net.INTXT;;ANSWERSECTION:hans.xxx.xxx.net.3600INTXT"Test"

;; Query time: 22 msec
;; SERVER: 10.0.2.166#53(10.0.2.166)
;; WHEN: Fri Sep 01 15:13:36 DST 2017
;; MSG SIZE  rcvd: 65

dig hans.xxx.xxx.net

; <<>> DiG 9.9.5-3ubuntu0.15-Ubuntu <<>> hans.xxx.xxx.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42482
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4000
;; QUESTION SECTION:
;hans.xxx.xxx.net.           IN      A

;; ANSWER SECTION:
hans.xxx.xxx.net.    3600    IN      A       10.0.2.81

;; Query time: 13 msec
;; SERVER: 10.0.2.166#53(10.0.2.166)
;; WHEN: Fri Sep 01 15:19:46 DST 2017
;; MSG SIZE  rcvd: 64