## 1 Introduction
Without such a critical orientation for a standardized IoT protocol such as RPL, it would be hard to effectively realize efficient and practical IoT security solutions. Therefore, there is a compelling need to investigate the impact of these types of internal routing attacks on the overall performance of RPL networks. A deep understanding of such critical situations is a vital step towards effectively developing efficient IoT attack mitigation solutions. This is more critical in the case of large-scale deployment scenarios which are common in different IoT applications including smart cities, e-healthcare, and industrial automation. In this research work, we carried out an extensive experimental study of a set of critical routing attacks in the context of RPL networks. Addressing the practical investigation of RPL networks during simple-to-complex routing attack scenarios while considering different attack types and varying-scale setups in a multidimensional performance study represents the novelty of this work. The major focus was on analyzing the effects of certain well-known internal routing attacks on RPL networks. These were namely the Version Number (VN), rank, Worst Parent (WP), and replay attacks. This research work provides a practical contribution toward experimentally studying the effectiveness of internal routing attacks on RPL-based IoT networks. It mainly contributes to the practical understanding of diverse routing attacks in varying-scale IoT network setups and simple-to-complex security attack scenarios. The main objective is to provide future research works with a practical research reference of the security efficiency and overall network performance of RPL networks under routing attacks. Accordingly, a set of critical security research questions were identified for this study to experimentally answer. These are as follows:What is the most adverse internal routing attack in RPL networks considering the rank, VN, WP, and replay attacks? What is the impact of composite internal routing attacks on the overall performance and topology stability of RPL networks? How adverse is it to have hybrid internal routing attacks initiated in RPL networks, compared to single and composite attacks? Would RPL internal routing attacks be more effective as the scale of the network increases? Systematic and practical experimentation was carried out to give in-depth answers to these research questions. The results indicate the adverse impacts of routing attacks on the overall performance of RPL networks. Even in simple attack scenarios, the networks experienced noticeable degradation of QoS performance and network stability in addition to noticeable increases in control traffic overhead and energy consumption. This was more evident in large-scale experimental setups and also under composite and hybrid attacks. The following section presents an overview of the standard RPL. Section 3 discusses RPL security and describes the RPL internal routing attacks of interest. In Section 4, the attack model and network assumptions are presented. Section 5 provides a research overview of the related work. In Section 6, the experimental methodology followed in this study is detailed. Section 7 presents the obtained experimental results whereas Section 8 provides insightful discussion. The conclusion is then provided in Section 9.