Net::Netmask parses and understands IPv4 CIDR blocks. It's built with an
object-oriented interface. Nearly all functions are methods that operate
on a Net::Netmask object.

There are methods that provide the nearly all bits of information about
a network block that you might want.

There are also functions to put a network block into a table and then
later lookup network blocks by IP address in that table. There are
functions to turn a IP address range into a list of CIDR blocks. There
are functions to turn a list of CIDR blocks into a list of IP addresses.

There is a function for sorting by text IP address.
