# Preventing Black Hole Attacks in AODV Using RREQ Packets
## 1 Introduction  
Internet of Things (IoT) technologies and devices, in which various devices that were not previously connected to the internet connect to a network and exchange information with each other, have attracted increasing attention recently. According to IHS Technology, the number of IoT devices shipped in 2018 reached nearly 10 billion units per year, with a cumulative installed base of 30 billion units. The forecast for 2025 is just over 20 billion units shipped annually, with a cumulative installed base of 80 billion units. IoT devices communicate wirelessly, and in many cases connect to base stations called access points to achieve internet connectivity. However, the increase in the number of wireless communication devices has increased the load on access points; accordingly, the degradation of communication quality due to congestion has become a major concern. Mobile ad hoc networks are a representative technology for infrastructure-less communication that does not involve base stations such as access points. Consequently, ad hoc networks are expected to be implemented under various situations, and have become a topic of active research recently [1]. For example, by applying this network technology to automobiles, information on traffic congestion, accidents, and nearby vehicles can be shared between vehicles. Examples include vehicular ad hoc networks (VANETs) [2], which can improve transportation, off-grid rescue, and disaster support operations [3]. Thus far, various protocols derived from this routing protocol have been proposed. Numerous Mobile Ad Hoc Network (MANET) routing protocols have been proposed recently. The routing used in such applications primarily includes flat routing protocols; however proactive, reactive, and hybrid protocols have been considered as well, depending on the implemented routing table management methods [4]. A proactive protocol is a method in which a route table is created even before a communication request is initiated. Although communication can start as soon as a communication request is made, packets are exchanged with neighboring nodes to keep the route list up-to-date, which may result in excessive use of bandwidth and radio waves. In a reactive protocol, on the otherhand, the route is created when a communication request occurs. Although starting a communication is time-consuming when using this approach, it is effective in networks that include battery-powered mobile devices, as there is no need to use extra bandwidth or radio waves. One of the most potent reactive routing protocols is the so-called Ad hoc On-demand Distance Vector (AODV) routing [5, 6]. Experiments comparing the performance of AODV, DSR, and DSDV have concluded that AODV is the best protocol in terms of throughput and performance when there are large numbers of implemented nodes in an environment where data is exchanged regularly [7]. Ad hoc networks can rarely use existing infrastructure. Because there is no authentication infrastructure that functions as a trusted third party, distinguishing between malicious terminals and other terminals is not possible. As a result, there is a risk of unauthorized participation in the network by malicious terminals, leading to unauthorized reception or falsification of data. Such security problems are an important barrier to the development of ad hoc networks [8, 9]. In the AODV protocol, black hole attacks have been reported to take advantage of this vulnerability [10, 11] In such attacks, an unauthorized terminal impersonates a real destination for packets that are used by the source to route destinations. As a result, data are absorbed and discarded as if they had fallen into a \"black hole\" in the network. Consequently, the performance of such networks can degrade considerably.