Evaluating the performance of MANET-specific communication protocols is essential to build robust mobile ad hoc applications. Unfortunately, most existing evaluation results are either based on simulations - which makes it difficult to draw conclusions beyond confined lab settings - or they are based on custom testbed results - which makes it difficult to reproduce them. In order to overcome this challenge, we introduce ManetLab, a modular and configurable software framework for creating and running testbeds to evaluate MANET-specific protocols. With ManetLab, one can easily configure and automate reproducible protocol executions on standard computer hardware, and thus provides both the accuracy of testbed-based evaluations and the reproducibility of simulation-based evaluations. After presenting ManetLab's extensible architecture, based on the notion of modular protocol stack, we show how it helps evaluate the performance of different broadcast protocols in real MANETs and how its results compare with simulation-based results.