Interoperability testing for ad hoc routing protocols is crucial to the reliability of wireless mobile ad hoc networks. Nevertheless, most of the works in this area are devoted to simulations analyzing the performance of such protocols without taking into account their formal requirements and specifications. Our works deal with formal methods to test the interoperability of a MANET routing protocol, DSR. From previous works, many inconclusive verdicts were obtained on some test cases. We present therefore in this paper, a node self-similarity approach in order to improve the interoperability testing by reducing the number of these in conclusive verdicts