Iptools.com is a site which gives you free information about various issues related to IP address. It is even more better a site of Network Administrators who need to have access to various critical information related to Internet Protocol (IP) address.
Some of the services (free) provided by the site are as follows:-
(b) Domain information of an IP address
(c) Displays country of origin of an IP address
(d) Calculate the CIDR (Classless Inter-Domain Routing) range
(e) Find IP address from a hostname.
(f) Whois lookup information etc...
I think everyone especially the Network Administrators will benefit tremendously from the site.