Discrete Event Simulation (DES) is one of the major experimental methodologies in several scientific and engineering domains. Parallel Discrete Event Simulation (PDES) constitutes a very active research field for at least three decades, to surpass speed and size limitations. In the context of Peer-to-Peer (P2P) protocols, most studies rely on simulation. Surprisingly enough, none of the mainstream P2P discrete event simulators allows parallel simulation although the tool scalability is considered as the major quality metric by several authors. This paper revisits the classical PDES methods in the light of distributed system simulation and proposes a new parallelization design specifically suited to this context. The constraints posed on the simulator internals are presented, and an OS-inspired architecture is proposed. In addition, a new thread synchronization mechanism is introduced for efficiency despite the very fine grain parallelism inherent to the target scenarios. This new architecture was implemented into the general-purpose open-source simulation framework SimGrid. We show that the new design does not hinder the tool scalability. In fact, the sequential version of SimGrid remains orders of magnitude more scalable than state of the art simulators, while the parallel execution allows to save up to 33% of the execution time on Chord simulation.