IP Whois Tool fetches the registered data for the IP address from the global whois servers.
Which server does it use?
IP Whois tool uses the whois server provide by ARIN (whois.arin.net)
What or Who is ARIN?
Each IP address is registered with a Regional Internet Registry (RIR). Internet Assigned Numbers Authority (IANA) delegates IP addresses to RTRs and they in turn provide then to ISPs. ARIN is one such regional authority.
How many RTRs are there?
Currently there are five of them.
African Network Information Center (AfriNIC) for Africa
American Registry for Internet Numbers (ARIN) for US, Canada and several parts of Caribbean
Asia-Pacific Network Information Center (APNIC) for Asia, Australia and neighbouring countries
Latin America and Caribbean Network Information Center (LACNIC) for Latin America and parts of the Caribbean region
RIPE NCC for Europe, the Middle East, and Central Asia
Does this tool work for all RTRs?
Yes, this tool recursively fetches records from the whois until it reaches the correct authority.