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開始前最先要经历的一个过程就是DNS解析。简单说就是域名怎样终于解析到实际serverip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。

和他相应的有个比較传统的命令nslookup,只是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者使用。

 实例1（訪问server本地DNSserver查询根域名server）:  ~#: 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:
;.INNS

;; ANSWER SECTION:
.85715 INNSa.root-servers.net.
.85715 INNSl.root-servers.net.
.85715 INNSf.root-servers.net.
.85715 INNSd.root-servers.net.
.85715 INNSe.root-servers.net.
.85715 INNSb.root-servers.net.
.85715 INNSc.root-servers.net.
.85715 INNSm.root-servers.net.
.85715 INNSk.root-servers.net.
.85715 INNSi.root-servers.net.
.85715 INNSj.root-servers.net.
.85715 INNSh.root-servers.net.
.85715 INNSg.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.INA

;; ANSWER SECTION:
www.baidu.com.641INCNAMEwww.a.shifen.com.
www.a.shifen.com.110INA 180.97.33.107
www.a.shifen.com.110INA 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server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.INA


;; ANSWER SECTION:
www.baidu.com.557INCNAMEwww.a.shifen.com.
www.a.shifen.com.299INA 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server到终于解析到ip的过程): dig www.baidu.com +trace

.84899 INNSf.root-servers.net.
.84899 INNSd.root-servers.net.
.84899 INNSe.root-servers.net.
.84899 INNSb.root-servers.net.
.84899 INNSc.root-servers.net.
.84899 INNSm.root-servers.net.
.84899 INNSk.root-servers.net.
.84899 INNSi.root-servers.net.
.84899 INNSj.root-servers.net.
.84899 INNSh.root-servers.net.
.84899 INNSg.root-servers.net.
.84899 INNSa.root-servers.net.
.84899 INNSl.root-servers.net.
;; Received 509 bytes from 192.168.100.52#53(192.168.100.52) in 1 ms

说明：从本地DNSserver得到若干各根域名server


com.172800 INNSa.gtld-servers.net.
com.172800 INNSe.gtld-servers.net.
com.172800 INNSh.gtld-servers.net.
com.172800 INNSj.gtld-servers.net.
com.172800 INNSi.gtld-servers.net.
com.172800 INNSk.gtld-servers.net.
com.172800 INNSb.gtld-servers.net.
com.172800 INNSm.gtld-servers.net.
com.172800 INNSf.gtld-servers.net.
com.172800 INNSg.gtld-servers.net.
com.172800 INNSc.gtld-servers.net.
com.172800 INNSd.gtld-servers.net.
com.172800 INNSl.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server查询com域名server

baidu.com.172800INNS dns.baidu.com.
baidu.com.172800INNS ns2.baidu.com.
baidu.com.172800INNS ns3.baidu.com.
baidu.com.172800INNS ns4.baidu.com.
baidu.com.172800INNS 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server解析baidu.com的域名server

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

说明:通过选择訪问dns.baidu.com域名server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