DNS解析追踪
dig跟踪dns解析过程
dig可以跟踪dns的解析过程，+trace 表示开启跟踪查询，+nodnssec 表示禁止 DNS 安全扩展：
$ dig +trace +nodnssec time.geekbang.org
; <<>> DiG 9.11.3-1ubuntu1.3-Ubuntu <<>> +trace +nodnssec time.geekbang.org
;; global options: +cmd
. 322086 IN NS m.root-servers.net.
. 322086 IN NS a.root-servers.net.
. 322086 IN NS i.root-servers.net.
. 322086 IN NS d.root-servers.net.
. 322086 IN NS g.root-servers.net.
. 322086 IN NS l.root-servers.net.
. 322086 IN NS c.root-servers.net.
. 322086 IN NS b.root-servers.net.
. 322086 IN NS h.root-servers.net.
. 322086 IN NS e.root-servers.net.
. 322086 IN NS k.root-servers.net.
. 322086 IN NS j.root-servers.net.
. 322086 IN NS f.root-servers.net.
;; Received 239 bytes from 114.114.114.114#53(114.114.114.114) in 1340 ms
org. 172800 IN NS a0.org.afilias-nst.info.
org. 172800 IN NS a2.org.afilias-nst.info.
org. 172800 IN NS b0.org.afilias-nst.org.
org. 172800 IN NS b2.org.afilias-nst.org.
org. 172800 IN NS c0.org.afilias-nst.info.
org. 172800 IN NS d0.org.afilias-nst.org.
;; Received 448 bytes from 198.97.190.53#53(h.root-servers.net) in 708 ms
geekbang.org. 86400 IN NS dns9.hichina.com.
geekbang.org. 86400 IN NS dns10.hichina.com.
;; Received 96 bytes from 199.19.54.1#53(b0.org.afilias-nst.org) in 1833 ms
time.geekbang.org. 600 IN A 39.106.233.176
;; Received 62 bytes from 140.205.41.16#53(dns10.hichina.com) in 4 ms
