ipcalc

parameter calculator for IPv4 addresses
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.
.
Originally, ipcalc was intended for use from the shell prompt, but a
CGI wrapper is provided to enable colorful HTML display through a
webserver.