This paper presents a method to evaluate iBGP topologies with route reflection, and to measure their performances compared to the full-mesh, in order to choose the best one. First, we describe the procedure and the criteria used for the comparison. After that, we briefly present the result of an application of this method to the GEANT network [3]. This analysis allows us then to isolate some of the factors that are influencing the quality of an iBGP topolog