4. dig

dig


  • 0_1498988444620_dig.png

    Used for: Finding information on domain names.
    dig man page: http://bit.ly/2suSFzu

    Notes:

    Perform a dig query.

    $ dig www.hp.com

; <<>> DiG 9.9.4-RedHat-9.9.4-37.el7 <<>> www.hp.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14555
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 9

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.hp.com.			IN	A

;; ANSWER SECTION:
www.hp.com.		1753	IN	CNAME	www.hpgtm.nsatc.net.
www.hpgtm.nsatc.net.	120	IN	A	15.240.238.60
www.hpgtm.nsatc.net.	120	IN	A	15.201.49.153

;; AUTHORITY SECTION:
nsatc.NET.		40692	IN	NS	l.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	d.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	g.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	e.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	c.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	a.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	b.ns.nsatc.net.

;; ADDITIONAL SECTION:
a.ns.nsatc.NET.		40692	IN	A	8.26.215.27
b.ns.nsatc.NET.		40692	IN	A	8.254.92.155
b.ns.nsatc.NET.		40692	IN	A	198.78.208.155
c.ns.nsatc.NET.		40692	IN	A	8.26.204.25
d.ns.nsatc.NET.		40692	IN	A	4.27.16.155
e.ns.nsatc.NET.		40692	IN	A	4.26.227.27
g.ns.nsatc.NET.		40692	IN	A	205.128.88.25
l.ns.nsatc.NET.		40692	IN	A	8.26.197.27

;; Query time: 164 msec
;; SERVER: 10.211.55.1#53(10.211.55.1)
;; WHEN: Sun Jul 02 10:58:15 BST 2017
;; MSG SIZE  rcvd: 373

    Breaking it down, what does that output tell you?

    This part tells you what options you passed to dig, what version, a summary & what global options are set

    ; <<>> DiG 9.9.4-RedHat-9.9.4-37.el7 <<>> www.hp.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14555
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 9

    This part tells you any additional options and the questions section is what you asked dig to do.

    ;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.hp.com.			IN	A

    This part gives you the results of what you asked dig to do.

    ;; ANSWER SECTION:
www.hp.com.		1753	IN	CNAME	www.hpgtm.nsatc.net.
www.hpgtm.nsatc.net.	120	IN	A	15.240.238.60
www.hpgtm.nsatc.net.	120	IN	A	15.201.49.153

    The authorities section, tells you that these servers will give an the authoritative answer for your query.

    ;; AUTHORITY SECTION:
nsatc.NET.		40692	IN	NS	l.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	d.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	g.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	e.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	c.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	a.ns.nsatc.net.
nsatc.NET.		40692	IN	NS	b.ns.nsatc.net.

    The additional section tells you the IP addresses of the previous authority section.

    Do a short lookup rather than the lengthy output.

    $ dig www.hp.com +short
www.hpgtm.nsatc.net.
15.240.238.62
15.217.49.156

    Get the A records (the address record) from your query, with the option +noall, do not display everything, just the +answers section.

    $ dig www.hp.com A +noall +answer 

; <<>> DiG 9.9.4-RedHat-9.9.4-37.el7 <<>> www.hp.com A +noall +answer
;; global options: +cmd
www.hp.com.		3549	IN	CNAME	www.hpgtm.nsatc.net.
www.hpgtm.nsatc.NET.	69	IN	A	15.201.49.155
www.hpgtm.nsatc.NET.	69	IN	A	15.201.49.156

    Get the mail exchange record (MX). Does not have to be uppercase in the command.

    $ dig hp.com mx +noall  +answer 

; <<>> DiG 9.9.4-RedHat-9.9.4-37.el7 <<>> hp.com mx +noall +answer
;; global options: +cmd
hp.com.			3592	IN	MX	10 smtp.hp.com.

    You can run the previous command for NS (Nameserver Record), ANY record, and A.

    Run a trace on a query.

    $ dig hp.com mx  +trace

    SOA - Start of authority record:

    $ dig hp.com soa +noall  +answer 

; <<>> DiG 9.9.4-RedHat-9.9.4-37.el7 <<>> hp.com soa +noall +answer
;; global options: +cmd
hp.com.			3600	IN	SOA	txe01hpiibpe.ams.hp.net. hostmaster.hp.com. 443243001 3600 3600 2419200 900

    eg:

    nsatc.net.		883	IN	SOA	admin.nsatc.net. dns.level3.net. 1497384039 10800 2700 3600000 900

    Contains the following information:

    • The primary name server for the domain. admin.nsatc.net.
    • The responsible party for the domain. dns.level3.net.
    • A timestamp that changes whenever you update your domain. 1497384039
    • The number of seconds before the zone should be refreshed. 10800
    • The number of seconds before a failed refresh should be retried. 2700
    • The upper limit in seconds before a zone is considered no longer authoritative. 3600000
    • The negative result TTL (for example, how long a resolver should consider a negative result for a subdomain to be valid before retrying). 900
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