This chapter provides a detailed tutorial on simulating denial-of-service (DoS) attacks in network-on-chip (NoC) environments using Gem5. First, we introduce the microarchitecture of NoC-based multiprocessor system-on-chip (MPSoC), highlighting fundamental components such as routers, network interfaces, communication protocols, and typical design scenarios. Next, we present an overview of security threats specific to NoC architectures, including common vulnerabilities and attack vectors such as flooding-based denial-of-service attacks. A comprehensive literature review summarizes state-of-the-art studies addressing NoC security, focusing on both threat modeling approaches and recent security countermeasures. Subsequently, we describe the implementation details of a flooding DoS attack threat model within the Gem5 Garnet simulator, including a step-by-step guide to reproducing and analyzing attack scenarios. Finally, the chapter concludes by examining recent methodologies and architectures proposed in the literature to enhance NoC security against emerging hardware threats.