  A mobile ad hoc network (MANET) is a collection of autonomous nodes that
communicate with each other by forming a multi-hop radio network and
maintaining connections in a decentralized manner. Security remains a major
challenge for these networks due to their features of open medium, dynamically
changing topologies, reliance on cooperative algorithms, absence of centralized
monitoring points, and lack of clear lines of defense. Protecting the network
layer of a MANET from malicious attacks is an important and challenging
security issue, since most of the routing protocols for MANETs are vulnerable
to various types of attacks. Ad hoc on-demand distance vector routing (AODV) is
a very popular routing algorithm. However, it is vulnerable to the well-known
black hole attack, where a malicious node falsely advertises good paths to a
destination node during the route discovery process but drops all packets in
the data forwarding phase. This attack becomes more severe when a group of
malicious nodes cooperate each other. The proposed mechanism does not apply any
cryptographic primitives on the routing messages. Instead, it protects the
network by detecting and reacting to malicious activities of the nodes.
Simulation results show that the scheme has a significantly high detection rate
with moderate network traffic overhead and computation overhead in the nodes.
