Abstract-- Many clustering protocols for mobile ad hoc networks (MANETs) have been proposed in the literature. With only one exception so far [1], all these protocols are proactive, thus wasting bandwidth when their function is not currently needed. To reduce the signalling traffic load, reactive clustering may be employed. We have developed a clustering protocol named "OnDemand Group Mobility-Based Clustering" (ODGMBC) which is reactive. Its goal is to build clusters as a basis for address autoconfiguration and hierarchical routing. The design process especially addresses the notion of group mobility in a MANET. As a result, ODGMBC maps varying physical node groups onto logical clusters. In this paper, ODGMBC is described. It was implemented for the ad hoc network simulator GloMoSim [2] and evaluated using several performance indicators. Simulation results are promising and show that ODGMBC leads to stable clusters. This stability is advantageous for autoconfiguration and ro...