# Analysing the Performance of a Trust-Based AODV in the Presence of a Flooding Attack
## 2 Related Work  
Since the AODV routing protocol was introduced, many schemes and solutions have been proposed to improve its performance in the presence of network attacks. Some of these schemes use techniques that require high computational power, such as cryptography. Although many of these solutions improve the performance of MANETs by detecting and isolating malicious nodes, the cooperative nodes suffer from the high computational load required. This may not fit the special characteristics of MANETs. Other solutions rely on the assumption that the first RREP packet received and the RREP packet with the highest sequence number are sent by a malicious node. This assumption is true in the case of black-hole and grey-hole attacks, but not in the case of selfish attack. Various solutions have been suggested to improve the performance of MANETs black-hole, grey-hole and selfish attacks and these are reviewed in the following subsections. Several solutions and algorithms have been suggested to deal with flooding attacks. The flooding attack model is completely different from the black-hole, grey-hole and selfish attacks. In flooding, the attackers use the RREQ packet to launch the attack, unlike black-hole, grey-hole and selfish attackers, who use the RREP packet. They flood the network with RREQ packets to non-existing destinations to keep the nodes processing these packets for the longest possible time. The solutions previously outlined concentrated on the RREP packets to detect black-hole, grey-hole and selfish attacks. In contrast, flooding attack solutions need to focus on and analyse RREQ packets. [PERSON] et al. [9] suggested an observation mechanism to calculate a trust value for neighbouring nodes. This mechanism aims to detect malicious nodes and isolate them. The trust value is calculated dynamically after every time interval using three parameters: (i) the RREP packet sequence number; (ii) the routing table sequence number; (iii) the number of replies received over the time interval. This algorithm is designed to detect and isolate malicious nodes in the route discovery phase. When sending the RREQ packet in the discovery phase, the source node broadcasts a list of malicious nodes. When the intermediate nodes receive this list, they update their routing tables. This trust-based mechanism was found to improve the packet delivery ratio (PDR) under black-hole and grey-hole attacks. [PERSON] and [PERSON] [10] implemented a trust-based distributed algorithm in the AODV protocol to detect and separate grey-hole attackers from other nodes. Each node in the network monitors the behaviour of its neighbours; when it senses the existence of a grey-hole node, it stores it in a grey-hole attacker list. To confirm the decision, it sends RREQ packets to the other neighbouring nodes to see if the suspected node will still behave maliciously. Based on the responses received from the neighbours, it can decide whether the suspected node is a grey-hole attacker or not. When it is confirmed that the suspected node is malicious, the source will avoid any future communication with it. This algorithm shows a better throughput in the presence of a grey-hole attack. [PERSON] et al. [11] proposed a trust-based mechanism to improve MANET performance under black-hole and grey-hole attacks. The mechanism detects malicious nodes by filtering their RREP packets at the source and intermediate nodes. The mechanism ignores the RREP packets with very high sequence numbers and also ignores the first RREP packet received. The malicious nodes will be added to a blacklist to prevent any communication with them in the future. The mechanism consists of two stages: prevention and detection. Both stages run while transmitting data between the source and destination nodes. [PERSON] [12] proposed an algorithm to detect and separate multiple black-hole and grey-hole attackers during the routing discovery phase. They suggested modifying the functionality of receiving RREP packets.