Whatmask is a small C program that will help you with network settings.

It displays the following information given IP address and/or netmask:
- The netmask in the following formats: CIDR, Netmask, Hex, Wildcard Bits
- The Network Address
- The Broadcast Address
- The number of Usable IP Addresses
- The First Usable IP Address
- The Last Usable IP Address

WWW: http://www.laffeycomputer.com/whatmask.html