Abstract. PlanetLab testbed is widely used to evaluate protocols and applications under realistic Internet conditions, but this realism comes at the cost of uncontrolled topology and traffic behavior. The use of overlay networks on PlanetLab can solve this problem by giving more control to the experimenter. However, manually creating such overlays is far from simple, and existing solutions are either not available for all PlanetLab nodes, or lack support for low level overlays. Deployment and customization of overlay architectures are also poorly supported. In this paper we present a flexible solution to support overlay networks on PlanetLab, providing deployment automation, tunneling, routing, and traffic shaping capabilities. By building our solution into NEPI, a general framework for network experimentation, which automates design, deployment, and management of experiments, we simplify the complexity of building overlays on PlanetLab, and foster reusability and extensibility though NEPI's modular structure.