# Preventing Black Hole Attacks in AODV Using RREQ Packets
## 6 Discussion  
First, we discuss the experimental results. With attacks present, the packet arrival rate of the proposed method increases dramatically compared to that of standard AODV. This is because the detection of black hole nodes by dummy RREQ packets and route reconstruction in the proposed method functions well. In contrast, when no attacks are present, the performance of the proposed method is inferior to that of standard AODV.  
Figure 5: Packet arrival rate (PAR).  
Figure 6: Round-trip time (RTT).  
Without attacks, the round-trip time is higher when using the proposed method, indicating that delays occur in sending and receiving data. The round-trip time is affected by the number of relay nodes along the route. The increase in the round-trip time when using the proposed method is due to the additional time required for processing when a black hole node is detected. From the above, it can be observed that although the proposed method can prevent the occurrence of black hole attacks, it affects performance to a limited extent in terms of both data transmission and reception. In the proposed method, a normal node that detects a black hole node discards its routing information and searches for a new route that does not pass through the black hole node. During this search, no data are transmitted, and the packets that exceed the survival time of the data packet buffer held by the node are discarded. Therefore, such events occur more frequently when the environment in which normal nodes detect black hole nodes becomes more dense, leading to a reduced packet arrival rate in the experiment.  
In addition, in the scenario without attacks, the total amount of control packets circulating in the network when using the proposed method is larger than when using standard AODV, which is due to the dummy RREQ packets used to detect black hole nodes and RERR packets used to reconstruct routes. Clearly, these packets cause collisions and loss of data packets. Therefore, although the proposed method is able to reliably detect black hole nodes, there is room for improvement in terms of ensuring route construction that avoids black hole nodes. Finally, we consider the practical feasibility of our proposed approach. The proposed method often uses existing AODV mechanisms to defend against black hole attacks. For example, the dummy RREQ packets are simply an application of the normal RREQ packet-issuing mechanism, and the process of route destruction and reconstruction when a black hole node appears in the route follows the same process relating to existing RERR packets. The only newly added parts are the list that manages node information and the mechanism that controls communication using this information. Therefore, the proposed method consists of a simple algorithm. The advantage of this design is that the algorithm can be easily incorporated into many AODV-derived routing protocols. If a routing protocol uses RREQ, RREP, or RERR packets for routing, those packets can easily be used in the proposed approach. There is no need to create new packet types to improve security.  
Furthermore, the algorithm is backwards-compatible. As mentioned above, the proposed method uses the existing AODV packet mechanism. Therefore, terminals that do not apply the proposed method can process dummy RREQ packets in the same way as when receiving normal RREQ packets. Because no RREP packet is returned for dummy RREQ packets, they are not mistakenly registered in the blacklist. Therefore, the routing process need not vary between the terminals to which the proposed method is applied and those to which it is not, enabling straightforward communication between the two. However, if a black hole node exists in the environment, a terminal could be mistakenly registered in the blacklist. This point is discussed further below.