WHAT IS DIG?

DIG is a comand line diagnostic tool for troubleshooting DNS. Dig allows the user to get DNS information directly from a DNS server and perform all functions performed by a normal DNS server as per the RFC's and the Draft Standard for DNS. By default it sends an non-recursive or iterative query, assuring you that you are checking only the DNS server you are querying and not checking the servers it refers you to. To the DNS server, the query looks like any other query sent by any other server.

To do a DIG, you need the DIG software, which comes with the BIND DNS distribution. Linux and Unix come with DIG. Windows and MacOS 9 or earlier do not.

When performing a DIG you need to know one of the following:

  1. Host name you are trying to look up
  2. The Domain a host belongs to (forward or reverse)
  3. Name or IP address of the authoritative server
  4. Type of Resource Record you need (A, MX, NS etc.)

If you need help tracking down the authoritative DNS server, use the WHOIS tool to check the WHOIS registry, or use a DIG for the host or domain in question and send a query for NS resource record information to one of the root servers.

OBTAINING DIG

You can get a copy of DIG from the Internet Systems Consortium (ISC).

Internet Systems Consortium, Inc. (ISC) is a nonprofit public benefit corporation dedicated to supporting the infrastructure of the universal connected self-organizing Internet—and the autonomy of its participants—by developing and maintaining core production quality software, protocols, and operations. -- http://www.isc.org/

DIG is part of the BIND software distribution produced by the ISC. ALL the root name servers run ISC's BIND. You can download the source from the ISC website.

USING DIG

You use dig from the command line. Below is the structure for the command, the flags and options it supports.

dig [@server] [-b address] [-c class] [-f filename] [-k filename]
    [-p port#]
[-t type] [-x addr] [-y name:key] [-4] [-6] [name]
    [type] [class] [queryopt...]

Example: Lookup the name servers at the root NIC

dig @g.root-servers.net domain.com ns

READING DIG RESULTS

Example #1: Finding an authoritative name server for a domain

;; First, check the root servers
[[email protected]]/home/user> dig @f.root-servers.net. yahoo.com. ns

; <<>> DiG 8.3 <<>> @f.root-servers.net. yahoo.com. ns
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4034
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 13, ADDITIONAL: 13
;; QUERY SECTION:
;; yahoo.com, type = NS, class = IN

;; AUTHORITY SECTION:
com. 2D IN NS M.GTLD-SERVERS.NET.
com. 2D IN NS A.GTLD-SERVERS.NET.
com. 2D IN NS B.GTLD-SERVERS.NET.
com. 2D IN NS C.GTLD-SERVERS.NET.
com. 2D IN NS D.GTLD-SERVERS.NET.
com. 2D IN NS E.GTLD-SERVERS.NET.
com. 2D IN NS F.GTLD-SERVERS.NET.
com. 2D IN NS G.GTLD-SERVERS.NET.
com. 2D IN NS H.GTLD-SERVERS.NET.
com. 2D IN NS I.GTLD-SERVERS.NET.
com. 2D IN NS J.GTLD-SERVERS.NET.
com. 2D IN NS K.GTLD-SERVERS.NET.
com. 2D IN NS L.GTLD-SERVERS.NET.

;; ADDITIONAL SECTION:
A.GTLD-SERVERS.NET. 2D IN A 192.5.6.30
B.GTLD-SERVERS.NET. 2D IN A 192.33.14.30
C.GTLD-SERVERS.NET. 2D IN A 192.26.92.30
D.GTLD-SERVERS.NET. 2D IN A 192.31.80.30
E.GTLD-SERVERS.NET. 2D IN A 192.12.94.30
F.GTLD-SERVERS.NET. 2D IN A 192.35.51.30
G.GTLD-SERVERS.NET. 2D IN A 192.42.93.30
H.GTLD-SERVERS.NET. 2D IN A 192.54.112.30
I.GTLD-SERVERS.NET. 2D IN A 192.43.172.30
J.GTLD-SERVERS.NET. 2D IN A 192.48.79.30
K.GTLD-SERVERS.NET. 2D IN A 192.52.178.30
L.GTLD-SERVERS.NET. 2D IN A 192.41.162.30
M.GTLD-SERVERS.NET. 2D IN A 192.55.83.30

;; Total query time: 105 msec
;; FROM: localhost.saaridin.inetdaemon.com to SERVER: 192.5.5.241
;; WHEN: Mon Jun 14 02:11:19 2004
;; MSG SIZE sent: 27 rcvd: 459

;; Next, check the greater top level servers
[[email protected]]/home/user> dig @a.gtld-servers.net yahoo.com ns

; <<>> DiG 8.3 <<>> @a.gtld-servers.net yahoo.com ns
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8822
;; flags: qr rd; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 5
;; QUERY SECTION:
;; yahoo.com, type = NS, class = IN

;; ANSWER SECTION:
yahoo.com. 2D IN NS ns1.yahoo.com.
yahoo.com. 2D IN NS ns2.yahoo.com.
yahoo.com. 2D IN NS ns3.yahoo.com.
yahoo.com. 2D IN NS ns4.yahoo.com.
yahoo.com. 2D IN NS ns5.yahoo.com.

;; ADDITIONAL SECTION:
ns1.yahoo.com. 2D IN A 66.218.71.63
ns2.yahoo.com. 2D IN A 66.163.169.170
ns3.yahoo.com. 2D IN A 217.12.4.104
ns4.yahoo.com. 2D IN A 63.250.206.138
ns5.yahoo.com. 2D IN A 216.109.116.17

;; Total query time: 32 msec
;; FROM: localhost.saaridin.inetdaemon.com to SERVER: 192.5.6.30
;; WHEN: Mon Jun 14 02:13:13 2004
;; MSG SIZE sent: 27 rcvd: 197

EXAMPLE #2: Determining authority for the zone
[[email protected]]/home/user> dig @a.gtld-servers.net www.yahoo.com a

; <<>> DiG 8.3 <<>> @a.gtld-servers.net www.yahoo.com a
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1800
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 5, ADDITIONAL: 5
;; QUERY SECTION:
;; www.yahoo.com, type = A, class = IN

;; AUTHORITY SECTION:
yahoo.com. 2D IN NS ns1.yahoo.com.
yahoo.com. 2D IN NS ns2.yahoo.com.
yahoo.com. 2D IN NS ns3.yahoo.com.
yahoo.com. 2D IN NS ns4.yahoo.com.
yahoo.com. 2D IN NS ns5.yahoo.com.

;; ADDITIONAL SECTION:
ns1.yahoo.com. 2D IN A 66.218.71.63
ns2.yahoo.com. 2D IN A 66.163.169.170
ns3.yahoo.com. 2D IN A 217.12.4.104
ns4.yahoo.com. 2D IN A 63.250.206.138
ns5.yahoo.com. 2D IN A 216.109.116.17

;; Total query time: 28 msec
;; FROM: localhost.saaridin.inetdaemon.com to SERVER: 192.5.6.30
;; WHEN: Mon Jun 14 02:21:16 2004
;; MSG SIZE sent: 31 rcvd: 201

EXAMPLE #3: Finding the valid Mail Exchangers for a zone.

[[email protected]]/home/johnp> dig @ns1.yahoo.com yahoo.com mx

; <<>> DiG 8.3 <<>> @ns1.yahoo.com yahoo.com mx
; (1 server found)
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2771
;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 5, ADDITIONAL: 19
;; QUERY SECTION:
;; yahoo.com, type = MX, class = IN

;; ANSWER SECTION:
yahoo.com. 2H IN MX 5 mx4.mail.yahoo.com.
yahoo.com. 2H IN MX 1 mx1.mail.yahoo.com.
yahoo.com. 2H IN MX 1 mx2.mail.yahoo.com.
yahoo.com. 2H IN MX 1 mx3.mail.yahoo.com.

;; Note that mx1, mx2 and mx3 have the lowest weights and are
;; thus preferred. Their weight is equal and will be used
;; in a round-robin fashion.
mx4 will only be used if mx1-mx3
;;
are unavailable.

;; AUTHORITY SECTION:
yahoo.com. 2D IN NS ns1.yahoo.com.
yahoo.com. 2D IN NS ns2.yahoo.com.
yahoo.com. 2D IN NS ns3.yahoo.com.
yahoo.com. 2D IN NS ns4.yahoo.com.
yahoo.com. 2D IN NS ns5.yahoo.com.

;; ADDITIONAL SECTION:
mx4.mail.yahoo.com. 30M IN A 216.136.129.5
mx4.mail.yahoo.com. 30M IN A 66.218.86.197
mx4.mail.yahoo.com. 30M IN A 66.218.86.199
mx4.mail.yahoo.com. 30M IN A 66.94.234.252
mx4.mail.yahoo.com. 30M IN A 206.190.36.244
mx1.mail.yahoo.com. 30M IN A 64.157.4.78
mx1.mail.yahoo.com. 30M IN A 64.156.215.19
mx1.mail.yahoo.com. 30M IN A 64.156.215.20
mx2.mail.yahoo.com. 30M IN A 64.156.215.8
mx2.mail.yahoo.com. 30M IN A 64.156.215.18
mx2.mail.yahoo.com. 30M IN A 67.28.113.10
mx2.mail.yahoo.com. 30M IN A 67.28.113.11
mx3.mail.yahoo.com. 30M IN A 64.156.215.5
mx3.mail.yahoo.com. 30M IN A 64.156.215.6
mx3.mail.yahoo.com. 30M IN A 64.156.215.7
mx3.mail.yahoo.com. 30M IN A 67.28.114.35
mx3.mail.yahoo.com. 30M IN A 67.28.114.36
ns1.yahoo.com. 2D IN A 66.218.71.63
ns2.yahoo.com. 2D IN A 66.163.169.170

;; Note that there are multiple IP addresses for each
;; mail exchanger, thus helping to distribute the load

;; Total query time: 112 msec
;; FROM: mudserv.saaridin.inetdaemon.com to SERVER: 66.218.71.63
;; WHEN: Mon Jun 14 03:12:52 2004
;; MSG SIZE sent: 27 rcvd: 506

Web Based Dig Sites

 


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