Measuring robustness of SDN control layers

The controller placement problem remains a key aspect of Software Defined Networking (SDN). The selection of a suboptimal controller may impact severely the performance of the control layer and, in consequence, cause a substantial degradation in the data layer. Different approaches for controller placement have been proposed with various objectives in mind, but most of them do not consider the characteristics of the resulting control layer in terms of robustness. In this paper we propose and formalize a complete metric for estimating robustness of a SDN control layer, and we evaluate two heuristics for controller selection and control layer construction: Fast Failover and a simplified version of k-Critical. The results of the performed evaluation indicate that the control layer topology induced by k-Critical is less prone to failures, more robust and more homogenous than those computed by Fast Failover.