“In a previous article in this series, I talked about using
Linux-based systems for what could be a quasi-security purpose:
network packet monitoring. In this article I go “all the way” and
discuss how Linux can be used in areas where you need absolute
control over what happens on a network, a firewall.”
“Firewalls seem to be the stuff of legend in the IT
community. Everyone has one because they’re afraid of system
crackers, viruses, and other nefarious things, but very few people
know what a firewall is, let alone how to construct one. This
article will give you a good overview of what happens under the
hood, and how you might use Linux in other security applications
such as penetration-testing and intrusion detection.”
“In its most straightforward definition, a firewall is a process
that implements a set of policies that control the flow of
information between one area of interest and another. You might be
wondering why I defined “firewall” in such a non-technical way. …
It turns out that the concept of a firewall in the
information-management realm goes back long before the advent of
computers. Looking at what a firewall does outside the context of
computing can demystify what’s really going on.”