Dig命令模仿迭代

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导读	顶级域名服务器告诉我们，fasionchan.com 这个域应该去找 f1g1ns1.dnspod.net. 或 f1g1ns2.dnspod.net. 来解析。这二者就是 fasionchan.com 的权威域名服务器。

DNS 服务器的工作原理，它们可以分为很多个角色：

 根域名服务器
顶级域名服务器
权威域名服务器
递归解析器 (DNS 缓存服务器)

于此同时，我们还了解了域名迭代解析的过程。本节我们趁热打铁，安排一次实验——按步骤迭代解析域名 test.fasionchan.com，以此加深理解。

Dig 命令模仿迭代

迭代解析从根域名服务器开始，根服务器列表可以从 root-servers.org 上获取，也可以通过 dig 命令查询：

root@netbox [~]  ➜ dig . NS 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @10.2.66.66 . NS 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42791 
;; flags: qr rd ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 8 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 4000 
;; QUESTION SECTION: 
;.              IN  NS 
 
;; ANSWER SECTION: 
.           1700    IN  NS  k.root-servers.net. 
.           1700    IN  NS  m.root-servers.net. 
.           1700    IN  NS  l.root-servers.net. 
.           1700    IN  NS  b.root-servers.net. 
.           1700    IN  NS  g.root-servers.net. 
.           1700    IN  NS  f.root-servers.net. 
.           1700    IN  NS  d.root-servers.net. 
.           1700    IN  NS  e.root-servers.net. 
.           1700    IN  NS  i.root-servers.net. 
.           1700    IN  NS  a.root-servers.net. 
.           1700    IN  NS  h.root-servers.net. 
.           1700    IN  NS  j.root-servers.net. 
.           1700    IN  NS  c.root-servers.net. 
 
;; ADDITIONAL SECTION: 
k.root-servers.net. 3282    IN  A   193.0.14.129 
g.root-servers.net. 2845    IN  A   192.112.36.4 
d.root-servers.net. 118 IN  A   199.7.91.13 
e.root-servers.net. 494 IN  A   192.203.230.10 
a.root-servers.net. 1771    IN  A   198.41.0.4 
j.root-servers.net. 3197    IN  A   192.58.128.30 
c.root-servers.net. 1830    IN  A   192.33.4.12 
 
;; Query time: 14 msec 
;; SERVER: 10.2.66.66#53(10.2.66.66) 
;; WHEN: Thu Apr 08 09:01:17 CST 2021 
;; MSG SIZE  rcvd: 364

根域名服务器总共有 13 台，编号从 A 到 M。我们可以从中选择一台，比如 A，它的 IP 地址是 198.41.0.4。

接下来，我们执行 dig 命令，向根域名服务器 A 发起域名解析请求：

root@netbox [~]  ➜ dig @198.41.0.4 test.fasionchan.com 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @198.41.0.4 test.fasionchan.com 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44843 
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 27 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 1472 
;; QUESTION SECTION: 
;test.fasionchan.com.       IN  A 
 
;; AUTHORITY SECTION: 
com.            172800  IN  NS  a.gtld-servers.net. 
com.            172800  IN  NS  b.gtld-servers.net. 
com.            172800  IN  NS  c.gtld-servers.net. 
com.            172800  IN  NS  d.gtld-servers.net. 
com.            172800  IN  NS  e.gtld-servers.net. 
com.            172800  IN  NS  f.gtld-servers.net. 
com.            172800  IN  NS  g.gtld-servers.net. 
com.            172800  IN  NS  h.gtld-servers.net. 
com.            172800  IN  NS  i.gtld-servers.net. 
com.            172800  IN  NS  j.gtld-servers.net. 
com.            172800  IN  NS  k.gtld-servers.net. 
com.            172800  IN  NS  l.gtld-servers.net. 
com.            172800  IN  NS  m.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 
b.gtld-servers.net. 172800  IN  AAAA    2001:503:231d::2:30 
c.gtld-servers.net. 172800  IN  AAAA    2001:503:83eb::30 
d.gtld-servers.net. 172800  IN  AAAA    2001:500:856e::30 
e.gtld-servers.net. 172800  IN  AAAA    2001:502:1ca1::30 
f.gtld-servers.net. 172800  IN  AAAA    2001:503:d414::30 
g.gtld-servers.net. 172800  IN  AAAA    2001:503:eea3::30 
h.gtld-servers.net. 172800  IN  AAAA    2001:502:8cc::30 
i.gtld-servers.net. 172800  IN  AAAA    2001:503:39c1::30 
j.gtld-servers.net. 172800  IN  AAAA    2001:502:7094::30 
k.gtld-servers.net. 172800  IN  AAAA    2001:503:d2d::30 
l.gtld-servers.net. 172800  IN  AAAA    2001:500:d937::30 
m.gtld-servers.net. 172800  IN  AAAA    2001:501:b1f9::30 
 
;; Query time: 169 msec 
;; SERVER: 198.41.0.4#53(198.41.0.4) 
;; WHEN: Fri Apr 09 08:38:10 CST 2021 
;; MSG SIZE  rcvd: 843

其中，@ 指定目标 DNS 服务器的地址。

从 dig 命令的输出可以看到，根域名服务器告诉我们 .com 域名应该去找 a.gtld-servers.net. 等服务器。这些服务器都是 .com 的顶级域名服务器，根域名服务器把它们的地址一并告诉我们了。

我们可以从这些顶级域名服务器中选择一台，比如 a.gtld-servers.net.，它的 IP 地址是 192.5.6.30。然后，再次指定 dig 命令，向它发起域名解析请求：

root@netbox [~]  ➜ dig @192.5.6.30 test.fasionchan.com 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @192.5.6.30 test.fasionchan.com 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7836 
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 1 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 4096 
;; QUESTION SECTION: 
;test.fasionchan.com.       IN  A 
 
;; AUTHORITY SECTION: 
fasionchan.com.     172800  IN  NS  f1g1ns1.dnspod.net. 
fasionchan.com.     172800  IN  NS  f1g1ns2.dnspod.net. 
 
;; Query time: 212 msec 
;; SERVER: 192.5.6.30#53(192.5.6.30) 
;; WHEN: Fri Apr 09 08:38:58 CST 2021 
;; MSG SIZE  rcvd: 101

顶级域名服务器告诉我们，fasionchan.com 这个域应该去找 f1g1ns1.dnspod.net. 或 f1g1ns2.dnspod.net. 来解析。这二者就是 fasionchan.com 的权威域名服务器。

但这次 .com 域名没有告诉我们 f1g1ns1.dnspod.net. 或 f1g1ns2.dnspod.net. 的 IP 地址。因此，我们必须先自己动手，将它们的域名解析成 IP 地址。

我们可以直接执行 dig 命令，一键完成解析：

root@netbox [~]  ➜ dig f1g1ns1.dnspod.net. 
 
; <<>> DiG 9.16.1-Ubuntu <<>> f1g1ns1.dnspod.net. 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6244 
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0 
 
;; QUESTION SECTION: 
;f1g1ns1.dnspod.net.        IN  A 
 
;; ANSWER SECTION: 
f1g1ns1.dnspod.net. 15  IN  A   58.247.212.36 
f1g1ns1.dnspod.net. 15  IN  A   61.151.180.44 
f1g1ns1.dnspod.net. 15  IN  A   129.211.176.187 
f1g1ns1.dnspod.net. 15  IN  A   162.14.25.230 
f1g1ns1.dnspod.net. 15  IN  A   183.192.164.118 
 
;; Query time: 13 msec 
;; SERVER: 192.168.65.1#53(192.168.65.1) 
;; WHEN: Fri Apr 09 08:39:38 CST 2021 
;; MSG SIZE  rcvd: 116

如果 dig 命令未指定 DNS 服务器，它默认会到本地的递归解析器，也就是 DNS 缓存服务器上去查询。DNS 缓存服务器会帮我们做迭代解析，再把结果告诉我们。

如果亲不厌其烦，可以自己进行迭代解析。具体步骤也是类似的，附在本文后半部分。

得到权威域名服务器的 IP 地址后，我们就可以向它发起解析请求：

root@netbox [~]  ➜ dig @58.247.212.36 test.fasionchan.com 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @58.247.212.36 test.fasionchan.com 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42646 
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 4096 
;; QUESTION SECTION: 
;test.fasionchan.com.       IN  A 
 
;; ANSWER SECTION: 
test.fasionchan.com.    600 IN  A   10.0.0.1 
 
;; AUTHORITY SECTION: 
fasionchan.com.     600 IN  NS  f1g1ns2.dnspod.net. 
fasionchan.com.     600 IN  NS  f1g1ns1.dnspod.net. 
 
;; Query time: 57 msec 
;; SERVER: 58.247.212.36#53(58.247.212.36) 
;; WHEN: Fri Apr 09 08:55:47 CST 2021 
;; MSG SIZE  rcvd: 128

瞧，我们成功解析域名 test.fasionchan.com，得到它对应的 IP 地址 10.0.0.1 !

迭代解析 f1g1ns1.dnspod.net.
如果不想通过递归解析器，可以自行执行迭代解析，查询 f1g1ns1.dnspod.net. 的 IP 地址。

首先，向根域名服务器发起解析请求：

root@netbox [~]  ➜ dig @198.41.0.4 f1g1ns1.dnspod.net. 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @198.41.0.4 f1g1ns1.dnspod.net. 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49636 
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 27 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 1472 
;; QUESTION SECTION: 
;f1g1ns1.dnspod.net.        IN  A 
 
;; AUTHORITY SECTION: 
net.            172800  IN  NS  a.gtld-servers.net. 
net.            172800  IN  NS  b.gtld-servers.net. 
net.            172800  IN  NS  c.gtld-servers.net. 
net.            172800  IN  NS  d.gtld-servers.net. 
net.            172800  IN  NS  e.gtld-servers.net. 
net.            172800  IN  NS  f.gtld-servers.net. 
net.            172800  IN  NS  g.gtld-servers.net. 
net.            172800  IN  NS  h.gtld-servers.net. 
net.            172800  IN  NS  i.gtld-servers.net. 
net.            172800  IN  NS  j.gtld-servers.net. 
net.            172800  IN  NS  k.gtld-servers.net. 
net.            172800  IN  NS  l.gtld-servers.net. 
net.            172800  IN  NS  m.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 
b.gtld-servers.net. 172800  IN  AAAA    2001:503:231d::2:30 
c.gtld-servers.net. 172800  IN  AAAA    2001:503:83eb::30 
d.gtld-servers.net. 172800  IN  AAAA    2001:500:856e::30 
e.gtld-servers.net. 172800  IN  AAAA    2001:502:1ca1::30 
f.gtld-servers.net. 172800  IN  AAAA    2001:503:d414::30 
g.gtld-servers.net. 172800  IN  AAAA    2001:503:eea3::30 
h.gtld-servers.net. 172800  IN  AAAA    2001:502:8cc::30 
i.gtld-servers.net. 172800  IN  AAAA    2001:503:39c1::30 
j.gtld-servers.net. 172800  IN  AAAA    2001:502:7094::30 
k.gtld-servers.net. 172800  IN  AAAA    2001:503:d2d::30 
l.gtld-servers.net. 172800  IN  AAAA    2001:500:d937::30 
m.gtld-servers.net. 172800  IN  AAAA    2001:501:b1f9::30 
 
;; Query time: 172 msec 
;; SERVER: 198.41.0.4#53(198.41.0.4) 
;; WHEN: Fri Apr 09 08:40:49 CST 2021 
;; MSG SIZE  rcvd: 840

根域名服务器告诉我们，.net 应该去找 a.gtld-servers.net. 等服务器，服务器地址附在后面的附加节。

我们选择 a.gtld-servers.net. 这台顶级域名服务器，它的地址是 192.5.6.30。然后向它发起解析请求：

root@netbox [~]  ➜ dig @192.5.6.30 f1g1ns1.dnspod.net. 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @192.5.6.30 f1g1ns1.dnspod.net. 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53457 
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 7 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 4096 
;; QUESTION SECTION: 
;f1g1ns1.dnspod.net.        IN  A 
 
;; AUTHORITY SECTION: 
dnspod.net.     172800  IN  NS  v6ns3.dnsv2.net. 
dnspod.net.     172800  IN  NS  v6ns4.dnsv2.com. 
 
;; ADDITIONAL SECTION: 
v6ns3.dnsv2.net.    172800  IN  A   129.211.176.248 
v6ns3.dnsv2.net.    172800  IN  A   162.14.24.245 
v6ns3.dnsv2.net.    172800  IN  A   183.192.164.118 
v6ns3.dnsv2.net.    172800  IN  A   223.166.151.17 
v6ns3.dnsv2.net.    172800  IN  AAAA    2402:4e00:1430:1102:0:9136:2b2f:bf6b 
v6ns3.dnsv2.net.    172800  IN  A   61.129.8.141 
 
;; Query time: 213 msec 
;; SERVER: 192.5.6.30#53(192.5.6.30) 
;; WHEN: Fri Apr 09 08:41:27 CST 2021 
;; MSG SIZE  rcvd: 210

顶级域名服务器告诉我们，dnspod.net. 这个域应该去找 v6ns3.dnsv2.net. 或者 v6ns4.dnsv2.com.。这两者就是所谓的权威域名服务器。这次，顶级域名服务器已经在附加节中，附上了它们的 IP 地址。

我们从中挑选一个，比如 129.211.176.248，继续发起解析请求：

root@netbox [~]  ➜ dig @129.211.176.248 f1g1ns1.dnspod.net. 
 
; <<>> DiG 9.16.1-Ubuntu <<>> @129.211.176.248 f1g1ns1.dnspod.net. 
; (1 server found) 
;; global options: +cmd 
;; Got answer: 
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 23542 
;; flags: qr aa rd; QUERY: 1, ANSWER: 5, AUTHORITY: 2, ADDITIONAL: 1 
;; WARNING: recursion requested but not available 
 
;; OPT PSEUDOSECTION: 
; EDNS: version: 0, flags:; udp: 4096 
;; QUESTION SECTION: 
;f1g1ns1.dnspod.net.        IN  A 
 
;; ANSWER SECTION: 
f1g1ns1.dnspod.net. 172800  IN  A   183.192.164.118 
f1g1ns1.dnspod.net. 172800  IN  A   162.14.25.230 
f1g1ns1.dnspod.net. 172800  IN  A   58.247.212.36 
f1g1ns1.dnspod.net. 172800  IN  A   61.151.180.44 
f1g1ns1.dnspod.net. 172800  IN  A   129.211.176.187 
 
;; AUTHORITY SECTION: 
dnspod.net.     86400   IN  NS  v6ns3.dnsv2.net. 
dnspod.net.     86400   IN  NS  v6ns4.dnsv2.com. 
 
;; Query time: 34 msec 
;; SERVER: 129.211.176.248#53(129.211.176.248) 
;; WHEN: Fri Apr 09 08:42:07 CST 2021 
;; MSG SIZE  rcvd: 185

最终，我们成功解析到 f1g1ns1.dnspod.net. 对应的 IP 地址，总共有 5 个。