One of the main purposes of this book is to discuss how to secure your Cisco IOS router?more specifically, how to use your Cisco IOS router to protect your network from threats. Basically, this entails using your router as a firewall solution. As you will see in this chapter and throughout the rest of the book, the Cisco IOS supports many technologies and features that will enable you to do this.
Before I start discussing the many security features that Cisco routers support, as well as when and how to deploy them, it is important to give you a basic understanding of firewall technologies?what they are and how they can be used to protect your network. That will make it easier to determine how you will use your router to protect your network infrastructure.
The beginning of this chapter covers what a firewall is and what its purpose is. As you will see, there are many definitions and many types of firewalls; this makes it difficult to put an exact definition on them or to place them into a specific category. One of the first things I do is discuss what a firewall is and how it operates. I also discuss some general design guidelines on using firewall products to protect your network infrastructure.
These subjects are discussed in this chapter:
Traffic control and the OSI reference model
Cisco IOS security