有几个命令可用于调试 DNS 解析并显示解析 DNS 查找所经过的路径：
安装它：
sudo apt-get install dnstracer
使用示例：
$ 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)
Run Code Online (Sandbox Code Playgroud)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.
例子：
$ 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
例子：
$ 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
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