# Analysing the Performance of a Trust-Based AODV in the Presence of a Flooding Attack
## 2 Related Work
The evidence of trustworthiness in this model is collected efficiently from direct interactions with the neighbouring nodes and through recommendations from other nodes. This mechanism contains two components: detection and reaction. Inthe detection phase, evidence of the malicious behaviour of neighbouring nodes is collected and in the reaction phase, the source node uses this evidence to accept or reject a newly discovered route. Also, in the reaction stage, the source node can predict the future behaviour of a cretin node by using the evidence collected. [PERSON] et al. [19] proposed an improved trust-based version of the DSR routing protocol. Each node in the MANET has a trust table that stores the trust values of the neighbouring nodes. The amended DSR selects the routing path with the highest trust values and least delay, unlike the standard DSR, which chooses the routing path that has the lowest hop count. The trust values are calculated and updated individually by the nodes. A trust value ranges between \(-1\) and \(+1\), where \(-1\) means distrust and \(+1\) absolute trust. Implementing this mechanism in the DSR protocol showed a better PDR under selfish attacks. [PERSON] et al. [20] proposed a trust algorithm based on packet forwarding ratio (PFR). PFR is calculated using the ratio of the number of packets forwarded to the number of packets received. Trust values are assigned based on the PFR results. The trust value of any node can increase or decrease based on its behaviour in forwarding packets. When the PFR increases, the trust value increases, and when it decreases, the trust value decreases. The trust value in this model is between 0 and 1, where 0 means distrust and 1 means absolute trust. A trust value between 0 and 0.5 indicates the node is malicious, 0.5 to 0.75 indicates the node is suspect, 0.75 to 0.9 suggests the node might be not entirely trustworthy and 0.9 to 1 means the node is trustworthy. Nodes with low trust values are isolated and not allowed to participate in new routes. [PERSON] et al. [21] suggested a scheme called Flooding Attack Prevention (FAP), which aims to monitor the RREQ packets received from neighbouring nodes. The FAP algorithm assumes that there is less of a risk of a node that sends fewer RREQ packets being a malicious node running a flooding attack. Thus, if a node sends fewer RREQ packets, it is assigned a higher priority for selection. When a node broadcasts a high rate of RREQ packets, the neighbouring nodes will observe this and reduce the responding priority for this node. [PERSON] et al. [22] added a fixed threshold to the FAP. The modified algorithm assumes that if the RREQ packets received by a neighbouring node exceeds the threshold, it is launching a flooding attack. Any RREQ packets from this node will be ignored in the future. The disadvantage of this modification is that if the attacker guesses the fixed threshold, it is possible simply to make the number of RREQ packets less than the threshold. This way a flooding attack will not be detected. [PERSON] et al. [23] proposed a filtering mechanism that has two thresholds: the rate limit and the blacklist limit. The source node only accepts RREQ packets from nodes that have not reached the rate limit. After receiving the RREQ packet, the source node compares the sequence number of the packet with the one stored in the blacklist. If it is greater than the sequence numbers in the blacklist, the RREQ packet is discarded and the node will be added to the blacklist. The disadvantage of this mechanism is that the attacker can run the attack by reducing the flooding rate and sequence number if they discover the values of the thresholds. [PERSON] et al. [24] proposed a trust management solution to mitigate the impact of flooding attacks on MANETs. The algorithm of the solution classifies neighbours based on their given trust values under three categories: friend, stranger and acquaintance. A friend node is trusted, a stranger is not trusted and an acquaintance is neutral.