A Group Dynamic Source Routing (GDSR) protocol that employs the passive clustering technique is proposed in order to improve overhead related to the formation and maintenance of clusters. This approach does not use any additional message to build and maintain a cluster topology. A route request message establishes a disjoint set of clusters and at the same time, explores group path which is expressed as a sequence of cluster labels or clusterheads' IDs. All data packets and control messages contribute to the formation and/or maintenance of clusters, thus significantly reducing control overhead. The nodes with the same label collaborate to deliver packets to a node with next label on the group path. Since there does exist multiple links that connect two adjacent clusters, the group path is highly robust. Simulation results show that the proposed GDSR with the passive clustering far outperforms its predecessors DSR and CBRP in various simulation scenarios.