Consistent and fault-tolerant SDN with unmodified switches

Motivation. In a reliable SDN environment, different controllers coordinate different switches and backup controllers can be set in place to tolerate faults. This approach increases the challenge to maintain a consistent network view. Indeed, if this global view is not consistent with the actual network state, applications will operate on a stale state and potentially lead to incorrect behavior. These anomalies can degrade network performance and introduce problems such as network loops or security breaches [1].