On reliable controller placements in Software-Defined Networks

In order to deploy fault-tolerant Software-Defined Networks (SDNs), a logically centralized controller must be physically distributed among different devices. In this paper, we focus on determining how many controllers need to be instantiated, where they must be deployed, and what network nodes are under control of each of them, in order to achieve high reliability in the southbound interface between controllers and nodes. For this, we define the fault tolerant controller placement problem and develop a heuristic algorithm that computes placements with (at least) the required reliability. We run such algorithm on a set of 124 publicly available network topologies. The results are thoroughly analyzed and provide insight on the feasibility of achieving fault tolerant SDNs by carefully determining the placement of controllers.