## 2 Research Selection Method
There is at least one proposal in each category, mitigating a set of attacks, and that is why there is no isolated set in the view diagram. In the case of the D2A theme, this attack is mitigated in five proposals, four of them mitigate only this attack, but, in one proposal, it is mitigated together with the WA, SA, and RSA themes. Finally, it can be noted that no proposal mitigates all the attacks detailed here, as seen in Figure 8.  
Tables and figures allow us to detail the following implications:  
Implication 1: RPL security is a topic highly associated with the industry since the highest percentage of publications are in proceedings of international conferences (see Table 8). Implication 2: The investigation takes strength in the field of security in RPL. Since its inception, its authors stated that this protocol did not manage security at the network layer. Therefore this has been a starting point for the investigation and implementation of mechanisms to mitigate attacks in this protocol (see Figure 3). Implication 3: 10 authors have more than one publication in this SLR. This shows a trend of the persistence of researchers in the area. On the other hand, according to Table 8, the collaboration index is 2.65, which shows temporary work among the authors. Implication 4: New Zealand is evidenced as a strong country at the level of technological research, according to Figure 5.  
Implication 5: Of the five proposals for 2020, only one of them belongs to a conference, and the rest are part of journals. This is deduced given the global crisis experienced due to the Covid-19 pandemic, for which mass gatherings of people have been restricted, including academic or research conferences. The statistics and taxonomy generated allow us to answer the research questions detailed in the introduction. RQ1: What are the development issues in IoT in RPL attacks. Development issues in the RPL attacks are presented in Table 5, where themes are detailed. Each one of these attacks is described in section II. Table 5 shows attacks on the RPL protocols in layer 3. Some attacks are inherited from the WSN, like SA or WA. Attacks like DNA or D2A are attacks that arise from the logic of the protocol. RQ2: What are the trends to solve the security problems of the RPL-protocol. Table 6 summarizes three principal groups into which this SLR divides the mechanisms to mitigate attacks on the RPL protocol. To mitigate attacks, the authors have designed strategies related to selecting a reliable parent in the design of the protocol topology, cryptography or authentication to change messages, and monitor the network for unusual behavior. RQ3: What is the trend of future research. There is a tendency to improve the metrics of the RPL protocol. One of these metrics is energy consumption, given the nature of WSN, and it is necessary to  
Figure 9: Correlation between mitigated attacks. maximize the lifetime to the sensors. In the protocol proposal [12], the authors affirm that they do not have security mechanisms implemented for the routing layer, leaving the line of investigation open to those who wish to improve the said protocol. In the first instance in the investigations, it was evidenced not to take into account the energy consumption, although, as a future trend, it is a metric that is intended to improve even so by implementing the security mechanisms.