linux命令行学习-dig(DNS查询器)


在web开发中，总要熟悉的就是http协议，而发起一个http开始前最先要经历的一个过程就是DNS解析。简单说就是域名如何最终解析到实际服务器ip的过程。

而在研究DNS解析和排除DNS解析类故障问题的时候一个强大的工具就是dig。和他对应的有个比较传统的命令nslookup,不过dig作为更新的命令，其强大而简洁可定制的输出也使得运维其开发人员使用。

实例1（访问服务器本地DNSserver查询根域名服务器）: ~#: dig

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <<>>
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39027
;; flags: qr rd ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 13


;; QUESTION SECTION:
;. IN NS

;; ANSWER SECTION:
. 85715 IN NS a.root-servers.net.
. 85715 IN NS l.root-servers.net.
. 85715 IN NS f.root-servers.net.
. 85715 IN NS d.root-servers.net.
. 85715 IN NS e.root-servers.net.
. 85715 IN NS b.root-servers.net.
. 85715 IN NS c.root-servers.net.
. 85715 IN NS m.root-servers.net.
. 85715 IN NS k.root-servers.net.
. 85715 IN NS i.root-servers.net.
. 85715 IN NS j.root-servers.net.
. 85715 IN NS h.root-servers.net.
. 85715 IN NS g.root-servers.net.

实例2(百度首页DNS解析): dig www.baidu.com

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <<>> www.baidu.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15372
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.baidu.com. IN A

;; ANSWER SECTION:
www.baidu.com. 641 IN CNAME www.a.shifen.com.
www.a.shifen.com. 110 IN A 180.97.33.107
www.a.shifen.com. 110 IN A 180.97.33.108

;; Query time: 1 msec
;; SERVER: 192.168.100.52#53(192.168.100.52)
;; WHEN: Wed Aug 13 22:33:59 2014
;; MSG SIZE rcvd: 90

实例3(制定使用google域名服务器解析百度首页); dig @8.8.8.8 www.baidu.com

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <<>> @8.8.8.8 www.baidu.com
; (1 server found)
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44033
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.baidu.com. IN A


;; ANSWER SECTION:
www.baidu.com. 557 IN CNAME www.a.shifen.com.
www.a.shifen.com. 299 IN A 180.76.3.151


;; Query time: 615 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Aug 13 22:36:36 2014
;; MSG SIZE rcvd: 74

实例4(使用+trace选项查看从根域名服务器到最终解析到ip的过程): dig www.baidu.com +trace

. 84899 IN NS f.root-servers.net.
. 84899 IN NS d.root-servers.net.
. 84899 IN NS e.root-servers.net.
. 84899 IN NS b.root-servers.net.
. 84899 IN NS c.root-servers.net.
. 84899 IN NS m.root-servers.net.
. 84899 IN NS k.root-servers.net.
. 84899 IN NS i.root-servers.net.
. 84899 IN NS j.root-servers.net.
. 84899 IN NS h.root-servers.net.
. 84899 IN NS g.root-servers.net.
. 84899 IN NS a.root-servers.net.
. 84899 IN NS l.root-servers.net.
;; Received 509 bytes from 192.168.100.52#53(192.168.100.52) in 1 ms

说明：从本地DNS服务器得到若干各根域名服务器


com. 172800 IN NS a.gtld-servers.net.
com. 172800 IN NS e.gtld-servers.net.
com. 172800 IN NS h.gtld-servers.net.
com. 172800 IN NS j.gtld-servers.net.
com. 172800 IN NS i.gtld-servers.net.
com. 172800 IN NS k.gtld-servers.net.
com. 172800 IN NS b.gtld-servers.net.
com. 172800 IN NS m.gtld-servers.net.
com. 172800 IN NS f.gtld-servers.net.
com. 172800 IN NS g.gtld-servers.net.
com. 172800 IN NS c.gtld-servers.net.
com. 172800 IN NS d.gtld-servers.net.
com. 172800 IN NS l.gtld-servers.net.
;; Received 503 bytes from 192.5.5.241#53(f.root-servers.net) in 39 ms
说明：选取f.root-servers.net根域名服务器查询com域名服务器

baidu.com. 172800 IN NS dns.baidu.com.
baidu.com. 172800 IN NS ns2.baidu.com.
baidu.com. 172800 IN NS ns3.baidu.com.
baidu.com. 172800 IN NS ns4.baidu.com.
baidu.com. 172800 IN NS ns7.baidu.com.
;; Received 201 bytes from 192.5.6.30#53(a.gtld-servers.net) in 360 ms
说明:选取a.gtld-servers.net的com域名服务器解析baidu.com的域名服务器

www.baidu.com. 1200 IN CNAME www.a.shifen.com.
a.shifen.com. 1200 IN NS ns3.a.shifen.com.
a.shifen.com. 1200 IN NS ns5.a.shifen.com.
a.shifen.com. 1200 IN NS ns1.a.shifen.com.
a.shifen.com. 1200 IN NS ns4.a.shifen.com.
a.shifen.com. 1200 IN NS ns2.a.shifen.com.
;; Received 228 bytes from 202.108.22.220#53(dns.baidu.com) in 206 ms

说明:通过选择访问dns.baidu.com域名服务器解析到www.baidu.com作为www.a.shifen.com的别名;

于是我们再dig下www.a.shifen.com.

[root@local200-65 JakQuan]# dig www.a.shifen.com +short
180.97.33.108
180.97.33.107

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