  With the evolution of wireless technology and use of mobile devices, Mobile
Ad-hoc Network has become popular among researchers to explore. A mobile ad-hoc
network (MANET) is a self-configuring network of mobile routers (and associated
hosts) connected by wireless links. The routers and hosts are free to move
randomly and organize themselves arbitrarily. It allows mobile nodes to
communicate directly without any centralized coordinator. Such network
scenarios cannot rely on centralized and organized connectivity, and can be
conceived as applications of Mobile Ad-Hoc Networks. Thus, MANET is vulnerable
due to its dynamic network topology, as any node become untrusted at any time.
The Black hole attack is one kind of security risk in which malicious node
advertises itself to have a shortest path for any destination, to forge data or
for DOS attack. In this paper, to detect such nodes effectively, we propose a
Permutation based Acknowledgement for most widely used reactive protocol ad-hoc
on demand distance vector routing AODV. This mechanism is enhancement of
Adaptive Acknowledgement (AACK) and TWO-ACK, here we have tried to show the
efficiency increment by decreasing number of messages routed in the network.
