今天发现办公室访问公司网站，DNS解析多次发生问题。由于最近工信部推出国内网站需在国内注册商登记的调查问卷，怀疑网络封锁与此有关。我们看到com域有如下NS服务器：
com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net.
运行如下查询，可看到这13台NS服务器有10台从办公室网络（电信光纤）无法抵达。
$ for i in i m f c g e b j l a k h d;do dig duowan.com @$i.gtld-servers.net;echo;done ; <<>> DiG 9.8.1-P1 <<>> duowan.com @i.gtld-servers.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39534 ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 3, ADDITIONAL: 12 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;duowan.com. IN A ;; AUTHORITY SECTION: duowan.com. 172800 IN NS ns1.duowanns.com. duowan.com. 172800 IN NS ns2.duowanns.com. duowan.com. 172800 IN NS ns3.duowanns.com. ;; ADDITIONAL SECTION: ns1.duowanns.com. 172800 IN A 119.188.71.249 ns1.duowanns.com. 172800 IN A 124.95.153.169 ns1.duowanns.com. 172800 IN A 183.61.2.249 ns1.duowanns.com. 172800 IN A 222.73.62.136 ns2.duowanns.com. 172800 IN A 119.188.71.250 ns2.duowanns.com. 172800 IN A 124.95.153.170 ns2.duowanns.com. 172800 IN A 183.61.2.250 ns2.duowanns.com. 172800 IN A 222.73.62.137 ns3.duowanns.com. 172800 IN A 119.188.71.251 ns3.duowanns.com. 172800 IN A 124.95.153.171 ns3.duowanns.com. 172800 IN A 183.61.2.251 ns3.duowanns.com. 172800 IN A 222.73.62.138 ;; Query time: 68 msec ;; SERVER: 192.43.172.30#53(192.43.172.30) ;; WHEN: Fri Apr 1 11:20:23 2016 ;; MSG SIZE rcvd: 283 ; <<>> DiG 9.8.1-P1 <<>> duowan.com @m.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @f.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @c.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @g.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @e.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @b.gtld-servers.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3644 ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 3, ADDITIONAL: 12 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;duowan.com. IN A ;; AUTHORITY SECTION: duowan.com. 172800 IN NS ns1.duowanns.com. duowan.com. 172800 IN NS ns2.duowanns.com. duowan.com. 172800 IN NS ns3.duowanns.com. ;; ADDITIONAL SECTION: ns1.duowanns.com. 172800 IN A 119.188.71.249 ns1.duowanns.com. 172800 IN A 124.95.153.169 ns1.duowanns.com. 172800 IN A 183.61.2.249 ns1.duowanns.com. 172800 IN A 222.73.62.136 ns2.duowanns.com. 172800 IN A 119.188.71.250 ns2.duowanns.com. 172800 IN A 124.95.153.170 ns2.duowanns.com. 172800 IN A 183.61.2.250 ns2.duowanns.com. 172800 IN A 222.73.62.137 ns3.duowanns.com. 172800 IN A 119.188.71.251 ns3.duowanns.com. 172800 IN A 124.95.153.171 ns3.duowanns.com. 172800 IN A 183.61.2.251 ns3.duowanns.com. 172800 IN A 222.73.62.138 ;; Query time: 75 msec ;; SERVER: 192.33.14.30#53(192.33.14.30) ;; WHEN: Fri Apr 1 11:21:43 2016 ;; MSG SIZE rcvd: 283 ; <<>> DiG 9.8.1-P1 <<>> duowan.com @j.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @l.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @a.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @k.gtld-servers.net ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62769 ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 3, ADDITIONAL: 12 ;; WARNING: recursion requested but not available ;; QUESTION SECTION: ;duowan.com. IN A ;; AUTHORITY SECTION: duowan.com. 172800 IN NS ns1.duowanns.com. duowan.com. 172800 IN NS ns2.duowanns.com. duowan.com. 172800 IN NS ns3.duowanns.com. ;; ADDITIONAL SECTION: ns1.duowanns.com. 172800 IN A 119.188.71.249 ns1.duowanns.com. 172800 IN A 124.95.153.169 ns1.duowanns.com. 172800 IN A 183.61.2.249 ns1.duowanns.com. 172800 IN A 222.73.62.136 ns2.duowanns.com. 172800 IN A 119.188.71.250 ns2.duowanns.com. 172800 IN A 124.95.153.170 ns2.duowanns.com. 172800 IN A 183.61.2.250 ns2.duowanns.com. 172800 IN A 222.73.62.137 ns3.duowanns.com. 172800 IN A 119.188.71.251 ns3.duowanns.com. 172800 IN A 124.95.153.171 ns3.duowanns.com. 172800 IN A 183.61.2.251 ns3.duowanns.com. 172800 IN A 222.73.62.138 ;; Query time: 208 msec ;; SERVER: 192.52.178.30#53(192.52.178.30) ;; WHEN: Fri Apr 1 11:22:28 2016 ;; MSG SIZE rcvd: 283 ; <<>> DiG 9.8.1-P1 <<>> duowan.com @h.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached ; <<>> DiG 9.8.1-P1 <<>> duowan.com @d.gtld-servers.net ;; global options: +cmd ;; connection timed out; no servers could be reached
作为对比，运行如下命令查了13台root NS服务器，基本都正常。
for i in i d f l e h k g b c m j a;do dig duowan.com @$i.root-servers.net;echo;done
由于com域的权威NS被墙的严重，导致办公室网络DNS解析各种超时，从而引发问题。
目前的解决方案是使用阿里、腾讯、114等第三方公共DNS，不过这样一些内部OA子系统无法使用。