The term internet of things (IoT) has gained much popularity in the last decade, which can be defined as various connected devices over the internet. IoT has rapidly spread to include all aspects of our lives. For instance, smart houses, smart cities, and variant wearable devices. IoT devices work to do their desired goals, which is to develop a person's living with his/her minimal involvement. At the same time, IoT devices have many weaknesses, which attackers exploit to affect these devices' security. Denial of Service (DoS) and Distributed Denial of Service (DDoS) are considered the most common attacks that strike IoT security. The main aim of these attacks is to make victim systems down and inaccessible for legitimate users by malicious malware. This paper's objective is to discuss and review security issues related to DoS/DDoS attacks and their countermeasures i.e. prevention based on IoT devices' layers structure.