## 4 Resource Constrained IoT and Vulnerability to Cyber-Attacks
The success rate of DDoS attacks over IoT devices is relatively higher as compared to conventional IT infrastructure, due to the limited resources associated with each IoT device. As a result, the Network and Application layers of IoT-based devices are highly prone to DDoS attacks that can easily knock out many IoT devices without generating a large volume of network traffic per IoT device. The largest known IoT-based DDoS attack occurred in 2016 by the malware known as Mirai botnets, where it created a massive data traffic that targeted several resources, including DNS servers, which had secondary effects on other extremely large service providers, including Sony PlayStation, Amazon, GitHub, Netflix, PayPal, Reddit, and Twitter [62; 63]. Other massive, non-IoT-based DDoS attacks also took place in recent years; in February 2020, Amazon experienced a 2.3 Tbps DDoS attack, the largest DDoS attack recorded by 2020 [64]. Moreover, a DDoS attack took place in November 2021 that targeted Microsoft Azure, where the attack hit a peak throughput of 3.47 Tbps and a packet rate of 340 million packets per second [65]. Though the last two attack incidents did not originate from IoT devices, the rapid proliferation of IoT deployments may lead to witnessing larger DDoS attack incidents originating from unprotected IoT devices being used as Botnets. In addition, the IoT devices themselves may become victims of DDoS and other cyber-attack incidents, resulting in knocking them out of service or compromising their operations. In summary, several unique features are exhibited by IoT networks and devices, where the main features are as follows:  
* IoT-based systems are typically constrained due to their devices having distinctive resource limitations, including processing power, memory, and energy sources. This \begin{table}
\begin{tabular}{c c c} \hline \hline
**Layer** & **Layer Description** & **Possible Attacks** \\ \hline \multirow{4}{*}{Perception} & This layer comprises IoT sensors, & \\  & devices, and actuators. The connected & \\  & devices at this layer enable the IoT & \\  & environment while compromising the & \\  & services over this layer would lead to & \\  & failure in data collection from the & \\  & environment. & \\ \hline \multirow{4}{*}{Network} & This layer acts as a bridge & \\  & encompassing all communication & \\  & technologies that carry and transmit & \\  & the data collected from different & \\  & sensors and toward the server, cloud, & \\  & or the internet. & \\ \hline \multirow{4}{*}{Application} & This layer comprises different & \\  & applications software for which the IoT & \\  & has been deployed, such as & \\  & applications for managing healthcare, & \\  & smart homes, and smart cities. & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Common Cyber-attacks on IoT Layers. consequently makes traditional resource-hungry security solutions unsuitable to be directly applied to such devices. * IoT applications are pervasive; hence, traditional centralized security solutions may prove to be inappropriate. Conversely, decentralized security solutions demand extra efforts to employ an efficient protection mechanism due to the diversity, heterogeneity, and large-scale deployment of nodes within the IoT ecosystem. * Since real-world IoT implementations require the physical deployment of sensors, actuators, and communication modules at locations that might be accessible to the public, such devices may also be prone to physical assaults. * Various devices in IoT systems communicate via both IP and non-IP-enabled devices. Therefore, its weak security configuration makes it a soft target, which may result in the leakage of important information or make it part of a bot army utilizable to launch attacks on other networks/devices. * In IoT systems, sensors continually generate and send data to the internet. Such a phenomenon can result in generating huge amounts of network traffic and unique network patterns as compared to the existing internet.