This chapter presents a collection of exercises designed to deepen understanding of fundamental topics in network security. The content is structured into four sections, each addressing an aspect of the field. The first section explores network threats and defenses, using examples based on the TCP/IP model to illustrate common vulnerabilities and attack vectors. It provides insights into both offensive techniques and defensive strategies to mitigate risks. The second section focuses on host discovery and network scanning, examining the methods used to identify devices and services within a network. Students will gain hands-on experience with reconnaissance techniques, understanding their role in both security assessment and potential misuse. The third section focuses on firewall configuration and analysis, emphasizing problem-solving through practical exercises using the widely adopted Linux iptables packet filter. Students will develop essential skills in designing, implementing, and troubleshooting firewall rulesets to enforce network security policies effectively. Finally, the fourth section covers the Transport Layer Security (TLS) protocol and its supporting technologies. This includes a look at the Web Public Key Infrastructure (PKI), trust models, and the real-world application of TLS in securing Internet communications.