网络实验：用Dig命令模仿迭代解析-渔池IDC

摘要：本文转载自微信公众号「小菜学编程」，作者小菜学编程。转载本文请联系小菜学编程公众号。上一小节，我们学习了 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)...

本文转载自微信公众号「小菜学编程」，作者小菜学编程。转载本文请联系小菜学编程公众号。

上一小节，我们学习了 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。

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。

扩展阅读

dig (https://linux.die.net/man/1/dig)

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