Multi-hop wireless ad-hoc networks are drawing more and more attention from both academic and industrial research. The lack of infrastructure makes those networks easy to deploy, thus they can potentially include a large number of nodes. Consequently, the scalability issue of the routing protocol used should be addressed. The simulation of large and highly dense networks, with thousands of nodes, can take a long time to complete when using simulators like NS-2. In this paper, we propose a simple analytical model to study the scalability of the OLSR routing protocol. We focus on the protocol overhead and show that OLSR with the Fish-Eye extension can suppport large and dense networks. Our results show a good accuracy.