It provides a holistic view of modern network security including operating system hardening, Firewalls, intrusion-detection systems, VPNs and Encryption.Physical Security, Standards, System Security and Security Policies are also included. Before diving into how to protect a network, exploring what networks are,would probably be a good idea. For many readers this section will be a review, but for some it might be new material. Whether this is a review for you, or new information, having a thorough understanding of basic networking before attempting to study network security is critical. Also, be aware this is just a brief introduction of basic network concepts.