This chapter showed you the basics of firewalls and firewall systems. You were introduced to the various types of firewalls and their functions, and you learned how to design a good firewall system. The remainder of this book focuses on how to secure your Cisco IOS router and use it as a component in a firewall system. This can be something as simple as setting it up as a packet-filtering firewall, to something as complex as using stateful firewall features to implement security levels, authenticating user connections, inspecting traffic for network threats, authenticating user connections, and making use of many other features.

Next up is Part II, which shows you how to protect the router itself by securing access to it and disabling all unnecessary services.