Dynamic Source Routing (DSR) is a reactive routing protocol designed for mobile ad-hoc networks. It is based on two mechanisms including route discovery and route maintenance. In highly dynamic networks, the surplus use of expired routes in the cache of DSR increases the latency and the frequent diffusion of route request packets consumes bandwidth. Consequently, DSR presents handicap in terms of end-to- end delay and overhead. In this paper, we propose a new routing protocol, called Ant-DSR, which implements a distributed topology discovery mechanism through mobile agents to maintain DSR cache. Implemented and simulated on ns-2, Ant-DSR shows a better resistance in high mobility and huge load environments in comparison to DSR.