A.P. Lawrence

2005/04/25 host, dig

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 64.226.42.29
$ 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

;; QUESTION SECTION:
;aplawrence.com.                        IN      A

;; ANSWER SECTION:
aplawrence.com.         5065    IN      A       64.226.42.29

;; AUTHORITY SECTION:
aplawrence.com.         149065  IN      NS      ns24.worldnic.com.
aplawrence.com.         149065  IN      NS      ns23.worldnic.com.

;; ADDITIONAL SECTION:
ns24.worldnic.com.      172325  IN      A       216.168.225.154
ns23.worldnic.com.      172325  IN      A       216.168.228.14

;; Query time: 59 msec
;; SERVER: 10.1.36.249#53(10.1.36.249)
;; WHEN: Sun Apr 17 10:46:37 2005
;; MSG SIZE  rcvd: 130

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

$ host  67.28.113.10
10.113.28.67.in-addr.arpa domain name pointer mta-v4.level3.mail.yahoo.com.
$ dig -x  67.28.113.10

; <<><>> DiG 9.2.2 <<>>>> -x 67.28.113.10
;; 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

;; QUESTION SECTION:
;10.113.28.67.in-addr.arpa.     IN      PTR

;; ANSWER SECTION:
10.113.28.67.in-addr.arpa. 1200 IN      PTR     mta-v4.level3.mail.yahoo.com.

;; AUTHORITY SECTION:
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.

;; ADDITIONAL SECTION:
ns1.yahoo.com.          172800  IN      A       66.218.71.63
ns2.yahoo.com.          172800  IN      A       66.163.169.170
ns3.yahoo.com.          172800  IN      A       217.12.4.104
ns4.yahoo.com.          172800  IN      A       63.250.206.138
ns5.yahoo.com.          172800  IN      A       216.109.116.17

;; Query time: 210 msec
;; SERVER: 10.1.36.249#53(10.1.36.249)
;; 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

;; QUESTION SECTION:
;pcunix.com.                    IN      MX

;; ANSWER SECTION:
pcunix.com.             7200    IN      MX      10 64.226.42.29.

;; AUTHORITY SECTION:
pcunix.com.             7200    IN      NS      NS39.WORLDNIC.com.
pcunix.com.             7200    IN      NS      NS40.WORLDNIC.com.

;; Query time: 106 msec
;; SERVER: 10.1.36.249#53(10.1.36.249)
;; 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 64.226.42.29.

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
Address: 216.168.225.170#53
Aliases: 

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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