Recent advances in symbolic execution have proposed a number of promising solutions to automatically achieve high-coverage and explore non-determinism during testing. This attractive testing technique of unmodified software assists developers with concrete inputs and deterministic schedules to analyze erroneous program paths. Being able to handle complex systems' software, these tools only consider single software instances and not their distributed execution which forms the core of distributed systems. The step to symbolic distributed execution is however steep, posing two core challenges: (1) additional state growth and (2) the state intra-dependencies resulting from communication. In this paper, we present SDE - a novel approach enabling scalable symbolic execution of distributed systems. The key contribution of our work is two-fold. First, we generalize the problem space of SDE and develop an algorithm significantly eliminating redundant states during testing. The key idea is to benefit from the nodes' local communication minimizing the number of states representing the distributed execution. Second, we demonstrate the practical applicability of SDE in testing with three sensor net scenarios running Contiki OS.