ipcalc takes an IP address and netmask and calculates the resulting broadcast,
network, Cisco wildcard mask, and host range. By giving a second netmask, you
can design sub- and supernetworks. It is also intended to be a teaching tool
and presents the results as easy-to-understand binary values. 

Enter your netmask(s) in CIDR notation (/25) or dotted decimals
(255.255.255.0). Inverse netmasks are recognized. 

WWW: http://jodies.de/ipcalc/