  The wireless ad hoc networks are highly vulnerable to distributed denial of
service(DDoS) attacks because of its unique characteristics such as open
network architecture, shared wireless medium and stringent resource
constraints. These attacks throttle the tcp throughput heavily and reduce the
quality of service(QoS) to end systems gradually rather than refusing the
clients from the services completely. In this paper, we discussed the DDoS
attacks and proposed a defense scheme to improve the performance of the ad hoc
networks. Our proposed defense mechanism uses the medium access control (MAC)
layer information to detect the attackers. The status values from MAC layer
that can be used for detection are Frequency of receiving RTS/CTS packets,
Frequency of sensing a busy channel and the number of RTS/DATA retransmissions.
Once the attackers are identified, all the packets from those nodes will be
blocked. The network resources are made available to the legitimate users. We
perform the simulation with Network Simulator NS2 and we proved that our
proposed system improves the network performance.
