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2005/04/25 host, dig

© April 2005 Tony Lawrence

I tend to use "dig" for DNS lookups, but it's more habit than anything else. The man page for host says "host is a simple utility for performing DNS lookup" while dig's brags "Most DNS administrators use dig to troubleshoot DNS problems because of its flexibility, ease of use and clarity of output. Other lookup tools tend to have less functionality than dig."

Well, yes, dig does perhaps have more power than host, but the need for that power doesn't come up all that often and host is both easier to use and more direct with its output. For getting an ip address from a hostname, the usage is the same, either "dig hostname" or "host hostname", but "host" returns only the ip address. Almost always, that's all I care about:

$ host aplawrence.com
aplawrence.com has address
$ dig aplawrence.com

; <<>> DiG 9.2.2 <<>> aplawrence.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 187
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

;aplawrence.com.                        IN      A

aplawrence.com.         5065    IN      A

aplawrence.com.         149065  IN      NS      ns24.worldnic.com.
aplawrence.com.         149065  IN      NS      ns23.worldnic.com.

ns24.worldnic.com.      172325  IN      A
ns23.worldnic.com.      172325  IN      A

;; Query time: 59 msec
;; WHEN: Sun Apr 17 10:46:37 2005
;; MSG SIZE  rcvd: 130

For reverse lookups, dig needs a "-x" while host does not:

$ host domain name pointer mta-v4.level3.mail.yahoo.com.
$ dig -x

; <<><>> DiG 9.2.2 <<>>>> -x
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16610
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 5

;     IN      PTR

;; ANSWER SECTION: 1200 IN      PTR     mta-v4.level3.mail.yahoo.com.

113.28.67.in-addr.arpa. 172800  IN      NS      ns1.yahoo.com.
113.28.67.in-addr.arpa. 172800  IN      NS      ns2.yahoo.com.
113.28.67.in-addr.arpa. 172800  IN      NS      ns3.yahoo.com.
113.28.67.in-addr.arpa. 172800  IN      NS      ns4.yahoo.com.
113.28.67.in-addr.arpa. 172800  IN      NS      ns5.yahoo.com.

ns1.yahoo.com.          172800  IN      A
ns2.yahoo.com.          172800  IN      A
ns3.yahoo.com.          172800  IN      A
ns4.yahoo.com.          172800  IN      A
ns5.yahoo.com.          172800  IN      A

;; Query time: 210 msec
;; WHEN: Sun Apr 17 10:53:29 2005
;; MSG SIZE  rcvd: 255

Keep in mind that both of these are actually looking for a PTR record.

Looking up MX records is easy with either tool:

$ dig pcunix.com mx

; <<>> DiG 9.2.2 <<>> pcunix.com mx
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33484
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;pcunix.com.                    IN      MX

pcunix.com.             7200    IN      MX      10

pcunix.com.             7200    IN      NS      NS39.WORLDNIC.com.
pcunix.com.             7200    IN      NS      NS40.WORLDNIC.com.

;; Query time: 106 msec
;; WHEN: Sun Apr 17 14:46:11 2005
;; MSG SIZE  rcvd: 103

But again "host" just gives us the bare facts:

$ host  -t MX pcunix.com     
pcunix.com mail is handled by 10

Another common use is to look up using some other DNS server. I'll do this to check for propagation progress and sometimes for errors:

$ dig @NS40.WORLDNIC.com yahoo.com
..(typical dig output)
$ host www.yahoo.com NS40.WORLDNIC.com                 
Using domain server:
Name: NS40.WORLDNIC.com

Again, host tells us less, but more directly gives what we usually want to see.

There are more options for both commands; this only covered the basic usage.

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Inexpensive and informative Apple related e-books:

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Photos: A Take Control Crash Course

Take Control of the Mac Command Line with Terminal, Second Edition

Take Control of Automating Your Mac

iOS 8: A Take Control Crash Course

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