Mobile ad hoc networks (MA configure, a highly dynamic network chang infrastructure less. The MANETs don't infrastructure or central access points and the backbone infrastructure, and it contains se information. The MANET is use for designin applications. The providing security on that a of the major tasks for researchers. In this pap network vulnerabilities of a pro-active rou analyzing attack on optimized link state routin which is proactive, we propose a reputation b prevention attacks. The mechanism is usefu OLSR protocol against the denial of service isolation attack). Our mechanism is capable of node is presenting correct network topology i by confirming its HELLO message. The exper results show the protocol is able to achiev mechanism with increasing throughput, frequency and control overhead. Our propo light weight because the protocol doesn't computational complexity for securing OLSR the node isolation attacks in MANETs. This few modifications and still compatible with th In order to evaluate network parameters simulator (NS-2) tool. Keywords-Mobile Ad hoc Networks (MANEAttack; Multipoint Relay (MPR); Optimized Link 978-1-4799-8792-4/15/$31.00 c 2015 IEEE