Como descobrir o servidor de nomes que resolve um nome de host específico

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3

Estou executando o Ubuntu 14.04 e recentemente alterei algumas configurações de resolução do hostname. Então, agora estou tentando otimizá-los e, para isso, preciso descobrir quais servidores de nomes resolvem determinados nomes de host em minhas solicitações.

Eu posso tentar pingar um nome de host my.hostname.example.net para descobrir se ele é resolvido ou não, mas como posso descobrir qual servidor de nomes resolveu esse nome de host em particular?

    
por SergeyOvchinnik 05.12.2016 / 16:09

2 respostas

5

Existem vários comandos que são úteis para depurar a resolução de DNS e para mostrar o caminho percorrido para resolver pesquisas de DNS:

  • dnstracer

Instale-o com: 

sudo apt-get install dnstracer

exemplo de uso: 

$ dnstracer www.cnn.com
Tracing to www.cnn.com[a] via 193.136.188.1, maximum of 3 retries
193.136.188.1 (193.136.188.1) Got answer [received type is cname] 
 |\___ ns1.fastly.net [fastly.net] (23.235.32.32) 
 |\___ ns4.fastly.net [fastly.net] (104.156.84.32) 
 |\___ ns3.fastly.net [fastly.net] (23.235.36.32) 
  \___ ns2.fastly.net [fastly.net] (104.156.80.32) 

NAME
       dnstracer - trace a chain of DNS servers to the source


DESCRIPTION
       dnstracer determines where a given Domain Name Server (DNS) gets its
       information from, and follows the chain of DNS servers back to the
       servers which know the data.
  • modo de depuração do nslookup

Exemplo: 

$ nslookup
> set debug
> www.cnn.com
Server:     193.136.188.1
Address:    193.136.188.1#53

------------
    QUESTIONS:
    www.cnn.com, type = A, class = IN
    ANSWERS:
    ->  www.cnn.com
    canonical name = turner.map.fastly.net.
    ttl = 191
    ->  turner.map.fastly.net
    internet address = 151.101.36.73
    ttl = 30
    AUTHORITY RECORDS:
    ->  fastly.net
    nameserver = ns2.fastly.net.
    ttl = 13130
    ->  fastly.net
    nameserver = ns3.fastly.net.
    ttl = 13130
    ->  fastly.net
    nameserver = ns4.fastly.net.
    ttl = 13130
    ->  fastly.net
    nameserver = ns1.fastly.net.
    ttl = 13130
    ADDITIONAL RECORDS:
    ->  ns1.fastly.net
    internet address = 23.235.32.32
    ttl = 13130
    ->  ns2.fastly.net
    internet address = 104.156.80.32
    ttl = 13130
    ->  ns3.fastly.net
    internet address = 23.235.36.32
    ttl = 13130
    ->  ns4.fastly.net
    internet address = 104.156.84.32
    ttl = 13130
------------
Non-authoritative answer:
www.cnn.com canonical name = turner.map.fastly.net.
Name:   turner.map.fastly.net
Address: 151.101.36.73
  • dig - trace

Exemplo: 

$ dig +trace +recurse +all www.cnn.com. a

; <<>> DiG 9.8.3-P1 <<>> +trace +recurse +all www.cnn.com. a
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37660
;; flags: qr ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 13

;; QUESTION SECTION:
;.              IN  NS

;; ANSWER SECTION:
.           456885  IN  NS  j.root-servers.net.
.           456885  IN  NS  k.root-servers.net.
.           456885  IN  NS  l.root-servers.net.
.           456885  IN  NS  m.root-servers.net.
.           456885  IN  NS  a.root-servers.net.
.           456885  IN  NS  b.root-servers.net.
.           456885  IN  NS  c.root-servers.net.
.           456885  IN  NS  d.root-servers.net.
.           456885  IN  NS  e.root-servers.net.
.           456885  IN  NS  f.root-servers.net.
.           456885  IN  NS  g.root-servers.net.
.           456885  IN  NS  h.root-servers.net.
.           456885  IN  NS  i.root-servers.net.

;; ADDITIONAL SECTION:
a.root-servers.net. 543296  IN  A   198.41.0.4
a.root-servers.net. 111296  IN  AAAA    2001:503:ba3e::2:30
b.root-servers.net. 604618  IN  A   192.228.79.201
b.root-servers.net. 111296  IN  AAAA    2001:500:84::b
c.root-servers.net. 604618  IN  A   192.33.4.12
c.root-servers.net. 111296  IN  AAAA    2001:500:2::c
d.root-servers.net. 604618  IN  A   199.7.91.13
d.root-servers.net. 111296  IN  AAAA    2001:500:2d::d
e.root-servers.net. 604618  IN  A   192.203.230.10
f.root-servers.net. 604618  IN  A   192.5.5.241
f.root-servers.net. 111296  IN  AAAA    2001:500:2f::f
g.root-servers.net. 604618  IN  A   192.112.36.4
h.root-servers.net. 604618  IN  A   198.97.190.53

;; Query time: 22 msec
;; SERVER: 10.19.90.11#53(10.19.90.11)
;; WHEN: Mon Dec  5 18:06:06 2016
;; MSG SIZE  rcvd: 496

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16113
;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 14

;; QUESTION SECTION:
;www.cnn.com.           IN  A

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

;; ADDITIONAL SECTION:
a.gtld-servers.net. 172800  IN  A   192.5.6.30
b.gtld-servers.net. 172800  IN  A   192.33.14.30
c.gtld-servers.net. 172800  IN  A   192.26.92.30
d.gtld-servers.net. 172800  IN  A   192.31.80.30
e.gtld-servers.net. 172800  IN  A   192.12.94.30
f.gtld-servers.net. 172800  IN  A   192.35.51.30
g.gtld-servers.net. 172800  IN  A   192.42.93.30
h.gtld-servers.net. 172800  IN  A   192.54.112.30
i.gtld-servers.net. 172800  IN  A   192.43.172.30
j.gtld-servers.net. 172800  IN  A   192.48.79.30
k.gtld-servers.net. 172800  IN  A   192.52.178.30
l.gtld-servers.net. 172800  IN  A   192.41.162.30
m.gtld-servers.net. 172800  IN  A   192.55.83.30
a.gtld-servers.net. 172800  IN  AAAA    2001:503:a83e::2:30

;; Query time: 196 msec
;; SERVER: 192.112.36.4#53(192.112.36.4)
;; WHEN: Mon Dec  5 18:06:07 2016
;; MSG SIZE  rcvd: 489

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44429
;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 10, ADDITIONAL: 6

;; QUESTION SECTION:
;www.cnn.com.           IN  A

;; AUTHORITY SECTION:
cnn.com.        172800  IN  NS  pdns3.ultradns.org.
cnn.com.        172800  IN  NS  pdns4.ultradns.org.
cnn.com.        172800  IN  NS  pdns1.ultradns.net.
cnn.com.        172800  IN  NS  pdns2.ultradns.net.
cnn.com.        172800  IN  NS  pdns5.ultradns.info.
cnn.com.        172800  IN  NS  pdns6.ultradns.co.uk.
cnn.com.        172800  IN  NS  ns-47.awsdns-05.com.
cnn.com.        172800  IN  NS  ns-576.awsdns-08.net.
cnn.com.        172800  IN  NS  ns-1630.awsdns-11.co.uk.
cnn.com.        172800  IN  NS  ns-1086.awsdns-07.org.

;; ADDITIONAL SECTION:
pdns1.ultradns.net. 172800  IN  AAAA    2001:502:f3ff::1
pdns1.ultradns.net. 172800  IN  A   204.74.108.1
pdns2.ultradns.net. 172800  IN  A   204.74.109.1
pdns2.ultradns.net. 172800  IN  AAAA    2610:a1:1014::1
ns-47.awsdns-05.com.    172800  IN  A   205.251.192.47
ns-576.awsdns-08.net.   172800  IN  A   205.251.194.64

;; Query time: 58 msec
;; SERVER: 192.31.80.30#53(192.31.80.30)
;; WHEN: Mon Dec  5 18:06:07 2016
;; MSG SIZE  rcvd: 445

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47226
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.cnn.com.           IN  A

;; ANSWER SECTION:
www.cnn.com.        300 IN  CNAME   turner.map.fastly.net.

;; Query time: 64 msec
;; SERVER: 204.74.114.1#53(204.74.114.1)
;; WHEN: Mon Dec  5 18:06:07 2016
;; MSG SIZE  rcvd: 64
    
por 05.12.2016 / 19:07
3

O que você precisa saber é quais servidores de nomes resolvem os nomes de host de um determinado domínio.

Como afirmado, dig é o comando que você está procurando. Se você quiser saber quem resolve nomes para hosts google.com.br, por exemplo, você deve emitir o comando: 

dig google.com ns

que retorna o seguinte resultado: 

; <<>> DiG 9.10.3-P4-Ubuntu <<>> google.com ns
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62331
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;google.com.                    IN      NS

;; ANSWER SECTION:
google.com.             152786  IN      NS      ns4.google.com.
google.com.             152786  IN      NS      ns1.google.com.
google.com.             152786  IN      NS      ns3.google.com.
google.com.             152786  IN      NS      ns2.google.com.

;; Query time: 26 msec
;; SERVER: 127.0.1.1#53(127.0.1.1)
;; WHEN: Mon Dec 05 17:35:07 CET 2016
;; MSG SIZE  rcvd: 111
    
por 05.12.2016 / 17:38

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