Linux Command Line learning-dig (DNS finder)

In web development, the most familiar is the HTTP protocol, and the first thing to go through before initiating an HTTP start is DNS resolution. Simply said is how the domain name finally resolves to the actual server IP process.

A powerful tool in the study of DNS parsing and troubleshooting DNS resolution classes is dig. And he has a relatively traditional command nslookup, but dig as the updated command, its powerful and concise customizable output also makes operations and its developers use.

Instance 1 (Access server local dnsserver query root name 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:
;. Inch Ns

;; ANSWER section:
. 85715 Inch Ns A.root-servers.net.
. 85715 Inch Ns L.root-servers.net.
. 85715 Inch Ns F.root-servers.net.
. 85715 Inch Ns D.root-servers.net.
. 85715 Inch Ns E.root-servers.net.
. 85715 Inch Ns B.root-servers.net.
. 85715 Inch Ns C.root-servers.net.
. 85715 Inch Ns M.root-servers.net.
. 85715 Inch Ns K.root-servers.net.
. 85715 Inch Ns I.root-servers.net.
. 85715 Inch Ns J.root-servers.net.
. 85715 Inch Ns H.root-servers.net.
. 85715 Inch Ns G.root-servers.net.

Example 2 (Baidu Home DNS resolution): 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. InchA

;; ANSWER section:
Www.baidu.com. 641Inch CNAMEWww.a.shifen.com.
Www.a.shifen.com. 110Inch A 180.97.33.107
Www.a.shifen.com. 110Inch A 180.97.33.108

;; Query Time:1 msec
;; server:192.168.100.52#53 (192.168.100.52)
;; when:wed 13 22:33:59 2014
;; MSG SIZE rcvd:90

Example 3 (make use of Google domain name server resolution Baidu homepage); 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. InchA


;; ANSWER section:
Www.baidu.com. 557Inch CNAMEWww.a.shifen.com.
Www.a.shifen.com. 299Inch A 180.76.3.151


;; Query time:615 msec
;; server:8.8.8.8#53 (8.8.8.8)
;; when:wed 13 22:36:36 2014
;; MSG SIZE rcvd:74

Example 4 (using the +trace option to view the process from the root name server to the final resolution to IP): Dig www.baidu.com +trace

. 84899 Inch Ns F.root-servers.net.
. 84899 Inch Ns D.root-servers.net.
. 84899 Inch Ns E.root-servers.net.
. 84899 Inch Ns B.root-servers.net.
. 84899 Inch Ns C.root-servers.net.
. 84899 Inch Ns M.root-servers.net.
. 84899 Inch Ns K.root-servers.net.
. 84899 Inch Ns I.root-servers.net.
. 84899 Inch Ns J.root-servers.net.
. 84899 Inch Ns H.root-servers.net.
. 84899 Inch Ns G.root-servers.net.
. 84899 Inch Ns A.root-servers.net.
. 84899 Inch Ns L.root-servers.net.
;; Received 509 bytes from 192.168.100.52#53 (192.168.100.52) in 1 ms

Description: Obtain several root name servers from the local DNS server


Com. 172800 Inch Ns A.gtld-servers.net.
Com. 172800 Inch Ns E.gtld-servers.net.
Com. 172800 Inch Ns H.gtld-servers.net.
Com. 172800 Inch Ns J.gtld-servers.net.
Com. 172800 Inch Ns I.gtld-servers.net.
Com. 172800 Inch Ns K.gtld-servers.net.
Com. 172800 Inch Ns B.gtld-servers.net.
Com. 172800 Inch Ns M.gtld-servers.net.
Com. 172800 Inch Ns F.gtld-servers.net.
Com. 172800 Inch Ns G.gtld-servers.net.
Com. 172800 Inch Ns C.gtld-servers.net.
Com. 172800 Inch Ns D.gtld-servers.net.
Com. 172800 Inch Ns L.gtld-servers.net.
;; Received 503 bytes from 192.5.5.241#53 (f.root-servers.net) in
Description: Select the f.root-servers.net root name server to query the COM domain name server

Baidu.com. 172800Inch Ns Dns.baidu.com.
Baidu.com. 172800Inch Ns Ns2.baidu.com.
Baidu.com. 172800Inch Ns Ns3.baidu.com.
Baidu.com. 172800Inch Ns Ns4.baidu.com.
Baidu.com. 172800Inch Ns Ns7.baidu.com.
;; Received 201 bytes from 192.5.6.30#53 (a.gtld-servers.net) in MS
Description: Select the a.gtld-servers.net COM domain name server to resolve the baidu.com domain name server

Www.baidu.com. 1200Inch CNAMEWww.a.shifen.com.
A.shifen.com. 1200Inch Ns Ns3.a.shifen.com.
A.shifen.com. 1200Inch Ns Ns5.a.shifen.com.
A.shifen.com. 1200Inch Ns Ns1.a.shifen.com.
A.shifen.com. 1200Inch Ns Ns4.a.shifen.com.
A.shifen.com. 1200Inch Ns Ns2.a.shifen.com.
;; Received 228 bytes from 202.108.22.220#53 (dns.baidu.com) in 206 ms

Description: Resolve to www.baidu.com as www.a.shifen.com alias by selecting Access dns.baidu.com domain name server;

So we dig down www.a.shifen.com.

[Email protected] jakquan]# dig www.a.shifen.com +short
180.97.33.108
180.97.33.107