Loop Free Clusters in Layer 2 Hybrid Software Defined Networks

Software defined networking (SDN) is a new architecture for computer networks in which control plane is decoupled from data plane and implemented centrally. The transition to SDN in companies requires upgrade of legacy network equipment which will have high cost implications for the company. The solution to this problem is a gradual deployment of SDN in form of hybrid networks. Hybrid networks necessitate communication between control plane of legacy switches and the SDN controller. In legacy networks, spanning tree protocol (STP) is used to prevent loop in layer 2. The loop problem can be solved in a better way by using the global view of SDN controller in the hybrid network. In this paper, we studied and evaluated three ways to prevent loop in hybrid networks. In first method OpenFlow switches use STP and in the other two methods instead of STP, the global view of SDN controller is used to prevent the loop. As a result, we reached better convergence time and link recovery time and performance in these two method.