To be CCNA Security certified, you need to leverage your grasp of basic network fundamentals to achieve a broad-based understanding of network security concepts and ideas. This chapter introduces some of these concepts and points out key areas that will be tested on the CCNA Security exam. These concepts are crucial because they form a solid foundation for understanding the rest of this book. We explore network security basics and the need for network security, while also getting to know our adversaries and exploring the taxonomy of network attacks. This should definitely make you feel a bit of healthy network insecurity. Thankfully, there are ways to mitigate the effectiveness of attacks against our network’s confidentiality, integrity, and availability (CIA); thus, we finish off the chapter with Cisco’s recommendations for best practices for defense against the identified network attacks.