In the real world, users do not interface directly with a DNS resolver - they interface with programs like web browsers (Mozilla Firefox, Safari, Opera, Internet Explorer etc.) and mail clients (Outlook Express, Mozilla Thunderbird etc.). When users make a request which requires a DNS lookup (in effect, virtually any request that uses the Internet), such programs send a request to the DNS resolver built into their operating system.
In the context of the Internet Protocol and the Domain Name System, a reverse lookup is often referred to simply as reverse resolving, or more specifically reverse DNS lookups. Typically, DNS is used to determine what IP address is associated with a given hostname; so to reverse resolve a known IP address is to lookup what the associated hostname for it is.
The Get Country option will attempt to determine the country the specified host is located in, and should work with almost any host, although it may not be foolproof.
Whois (IP) and Whois (Domain)
Whois is a TCP-based query/response protocol which is widely used for querying a database in order to determine the owner of a domain name, an IP address, or an autonomous system number, on the Internet. The Whois (IP) server field can also accept a port. If you need to specify a port, just add a colon to the end of the server followed by the port number.
NS Lookup
The NS Lookup option can be used to find the IP addresses of a particular computer. The name means 'name server lookup'.
Dig (ANY, A, IN, MX, NS, SOA, HINFO, AXFR, IXFR)
Dig lookups will show the DNS records for the given host or domain. This gateway allows lookups for network address, mail exchanger, name servers, host information, arbitrary strings and zone of authority records.
Html code
This function retrieves the html code of the page that is specified in the pagename field (don't forget to enter a host or ip as well).
Tracepath
This function is quite similar to the so-called traceroute feature that is found in many operating systems. It send a request to the specified host, and shows all servers that the request passes. Please, be patient - the tracepath algorithm may take a while to complete.
Portscan
Portscan determines if the specified ports on the host computer are open. Use commas (,) to separate ports. Use a dash (-) to indicate a range of ports. You can mix commas and dashes. Example: '21-23,80' will scan ports 21,22,23,80.