Package netmask

Utility for determining network masks

http://packages.debian.org/netmask

This is a handy tool for generating terse netmasks in several common
formats. If you've ever maintained a firewall with more than a few
rules in it, you might use netmask to clean up and generalize sloppy
rules left by the network administrator before you. It will also
convert netmasks from one format to another for the day you change
your firewall software.

General Commands
Command Description
netmask a netmask generation and conversion program