Role of ad-hoc networks has become vital in ubiquitous computing. Ad-hoc On-demand Distance Vector (AODV) is such a routing protocol which is susceptible to a variety of security threats against ad-hoc networks. Black hole and Gray hole attacks are such attacks that drop significant number of packets by performing packet forwarding misbehavior and breach the security to cause denial of service in Mobile Ad-hoc Networks (MANETs). In this paper, we discuss our previous work, R-AODV, to detect and isolate multiple Black hole and Gray hole nodes during route discovery process and propose a modified version to improve the performance of MANET. We analyze the proposed solution and evaluate its performance using Network Simulator-2 (NS-2) under different network parameters.