10 Linux DIG Command Examples for DNS Lookup--reference

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Dig stands for domain information groper.

Using dig command you can query DNS name servers for your DNS lookup related tasks. This article explains 10 examples on how to use dig command.

1. Simple dig Command Usage (Understand dig Output)

When you pass a domain name to the dig command,by default it displays the A record (the ip-address of the site that is queried) as shown below.In this example,it displays the A record of redhat.com in the “ANSWER SECTION” of the dig command output.

$ dig redhat.com
; <<>> DiG 9.7.3-RedHat-9.7.3-2.el6 <<>> redhat.com

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY,status: NOERROR,id: 62863

;; flags: qr rd ra; QUERY: 1,ANSWER: 1,AUTHORITY: 4,ADDITIONAL: 3
;; QUESTION SECTION:

;redhat.com.                    IN      A
;; ANSWER SECTION:

redhat.com.             37      IN      A       209.132.183.81
;; AUTHORITY SECTION:

redhat.com.             73      IN      NS      ns4.redhat.com.

redhat.com.             73      IN      NS      ns3.redhat.com.

redhat.com.             73      IN      NS      ns2.redhat.com.

redhat.com.             73      IN      NS      ns1.redhat.com.
;; ADDITIONAL SECTION:

ns1.redhat.com.         73      IN      A       209.132.186.218

ns2.redhat.com.         73      IN      A       209.132.183.2

ns3.redhat.com.         73      IN      A       209.132.176.100
;; Query time: 13 msec

;; SERVER: 209.144.50.138#53(209.144.50.138)

;; WHEN: Thu Jan 12 10:09:49 2012

;; MSG SIZE  rcvd: 164

The dig command output has the following sections:

• Header: This displays the dig command version number,the global options used by the dig command,and few additional header information.
• QUESTION SECTION: This displays the question it asked the DNS. i.e This is your input. Since we said ‘dig redhat.com’,and the default type dig command uses is A record,it indicates in this section that we asked for the A record of the redhat.com website
• ANSWER SECTION: This displays the answer it receives from the DNS. i.e This is your output. This displays the A record of redhat.com
• AUTHORITY SECTION: This displays the DNS name server that has the authority to respond to this query. Basically this displays available name servers of redhat.com
• ADDITIONAL SECTION: This displays the ip address of the name servers listed in the AUTHORITY SECTION.
• Stats section at the bottom displays few dig command statistics including how much time it took to execute this query

2. Display Only the ANSWER SECTION of the Dig command Output

For most part,all you need to look at is the “ANSWER SECTION” of the dig command. So,we can turn off all other sections as shown below.

• +nocomments – Turn off the comment lines
• +noauthority – Turn off the authority section
• +noadditional – Turn off the additional section
• +nostats – Turn off the stats section
• +noanswer – Turn off the answer section (Of course,you wouldn’t want to turn off the answer section)

The following dig command displays only the ANSWER SECTION.

$ dig redhat.com +nocomments +noquestion +noauthority +noadditional +nostats
; <<>> DiG 9.7.3-RedHat-9.7.3-2.el6 <<>> redhat.com +nocomments +noquestion +noauthority +noadditional +nostats

;; global options: +cmd

redhat.com.             9       IN      A       209.132.183.81

Instead of disabling all the sections that we don’t want one by one,we can disable all sections using +noall (this turns off answer section also),and add the +answer which will show only the answer section.

The above command can also be written in a short form as shown below,which displays only the ANSWER SECTION.

$ dig redhat.com +noall +answer
; <<>> DiG 9.7.3-RedHat-9.7.3-2.el6 <<>> redhat.com +noall +answer

;; global options: +cmd

redhat.com.             60      IN      A       209.132.183.81

3. Query MX Records Using dig -t MX

To query MX records,pass MX as an argument to the dig command as shown below.

$ dig redhat.com  MX +noall +answer
; <<>> DiG 9.7.3-RedHat-9.7.3-2.el6 <<>> redhat.com MX +noall +answer

;; global options: +cmd

redhat.com.             513     IN      MX      5 mx1.redhat.com.

redhat.com.             513     IN      MX      10 mx2.redhat.com.

You can also use option -t to pass the query type (for example: MX) as shown below.

$ dig -t MX redhat.com +noall +answer
; <<>> DiG 9.7.3-RedHat-9.7.3-2.el6 <<>> -t MX redhat.com +noall +answer

;; global options: +cmd

redhat.com.             489     IN      MX      10 mx2.redhat.com.

redhat.com.             489     IN      MX      5 mx1.redhat.com.

4. Query NS Records Using dig -t NS

To query the NS record use the type NS as shown below.

$ dig redhat.com NS +noall +answer

                                                
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