nslookup and dig - query Internet name servers interactively.

$ nslookup
>chirico.org
Server:        68.80.0.6
Address:       68.80.0.6#53

Name: chirico.org
Address: 66.35.250.210
>

The nslookup command will query the dns server is "/etc/resolve.conf"
However, you can force a certain dns with "- server".  For example the
command below goes to the server named dilbert

$ nslookup - dilbert
>

dig:

dig gives you more information. You should probably use dig instead
of nslookup.

Below I am forcing the lookup from DNS 68.80.0.6 of the name chirico.org, and
note that the query time is return too.

$ dig @68.80.0.6  +qr chirico.org

; <<>> DiG 9.2.1 <<>> @68.80.0.6 +qr chirico.org
;; global options:  printcmd
;; Sending:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55908
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;chirico.org.                   IN      A

;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55908
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

;; QUESTION SECTION:
;chirico.org.                   IN      A

;; ANSWER SECTION:
chirico.org.            5538    IN      A       66.35.250.210

;; AUTHORITY SECTION:
chirico.org.            30599   IN      NS      ns78.worldnic.com.
chirico.org.            30599   IN      NS      ns77.worldnic.com.

;; ADDITIONAL SECTION:
ns78.worldnic.com.      16022   IN      A       216.168.225.218
ns77.worldnic.com.      7       IN      A       216.168.228.41

;; Query time: 155 msec
;; SERVER: 68.80.0.6#53(68.80.0.6)
;; WHEN: Thu Dec 23 07:48:23 2004
;; MSG SIZE  rcvd: 127

So what if you wanted to know what name the IP address 66.35.250.210
resolves to, when using dns 68.80.0.12.

$ dig @68.80.0.12 -x 66.35.250.210
...
;; ANSWER SECTION:
210.250.35.66.in-addr.arpa. 3600 IN   CNAME   210.0/24.250.35.66.in-addr.arpa.
210.0/24.250.35.66.in-addr.arpa. 3600 IN PTR  vhost.sourceforge.net.

Above you can see it resolved to "vhost.sourceforge.net"

Reference ( http://www.tldp.org/HOWTO/DNS-HOWTO-5.html )