Hello, you can use dig or nslookup,
dig -x 123.123.123.123
Where 123.123.123.123 is the ip number. dig show to you the domain name that the ip have. Here is an example:
dig -x 200.93.220.18
; <<>> DiG 9.2.2-P3 <<>> -x 200.93.220.18
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41002
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 2
;; QUESTION SECTION:
;18.220.93.200.in-addr.arpa. IN PTR
;; ANSWER SECTION:
18.220.93.200.in-addr.arpa. 86400 IN PTR srv.eth0.www.manta.telconet.net.
;; AUTHORITY SECTION:
220.93.200.in-addr.arpa. 86400 IN NS srv1.telconet.net.
220.93.200.in-addr.arpa. 86400 IN NS ns1.manta.telconet.net.
220.93.200.in-addr.arpa. 86400 IN NS uio.telconet.net.
;; ADDITIONAL SECTION:
uio.telconet.net. 42196 IN A 200.93.216.2
srv1.telconet.net. 86400 IN A 200.93.192.148
;; Query time: 23 msec
;; SERVER: 200.93.220.2#53(200.93.220.2)
;; WHEN: Fri Jun 11 09:47:04 2004
;; MSG SIZE rcvd: 176
The nslookup use is similar,
nslookup 200.93.220.18
Note: nslookup is deprecated and may be removed from future releases.
Consider using the `dig' or `host' programs instead. Run nslookup with
the `-sil[ent]' option to prevent this message from appearing.
Server: 200.93.220.2
Address: 200.93.220.2#53
18.220.93.200.in-addr.arpa name = srv.eth0.www.manta.telconet.net.
Hope this help.