Routing protocols are the main issue of ad hoc networks. Because flat propositions (reactive, proactive) are not sufficient and suffer from a lack of performance, new solutions should he investigated and proposed. On the other hand, virtual topologies propose to structure the network and to give a hierarchy between the strongest and the weakest nodes. We propose a new routing protocol, virtual structure routing (VSR), based on a virtual topology including both a backbone and clusters. The backbone is used to collect control traffic and to reduce overhead for route discovery. VSR uses clusters to define a route as a list of cluster IDs. This cluster topology is more stable than the physical topology. Hence, routes are more robust. VSR combines the assets of both flat approaches; intra-cluster routing is proactive while inter-cluster routing is reactive. Finally, routes are computed dynamically and a mechanism for route repair is proposed.