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Current approaches to tackle the single point of failure in SDN entail a distributed operation of SDN controller instances. Their state synchronization process is reliant on the assumption of a correct decision-making in the controllers. Successful introduction of SDN in the critical infrastructure networks also requires catering to the issue of <italic>unavailable</italic>, <italic>unreliable</italic> (e.g. buggy), and <italic>malicious</italic> controller failures. We propose MORPH, a framework tolerant to unavailability and Byzantine failures, which distinguishes and localizes faulty controller instances and appropriately reconfigures the control plane. Our controller-switch connection assignment leverages the awareness of the source of failure to optimize the number of active controllers and minimize the controller and switch reconfiguration delays. The proposed re-assignment executes dynamically after each successful failure identification. We require <inline-formula> <tex-math notation="LaTeX">$2F_{M}+F_{A}+1$ </tex-math></inline-formula> controllers to tolerate <inline-formula> <tex-math notation="LaTeX">$F_{M}$ </tex-math></inline-formula> malicious and <inline-formula> <tex-math notation="LaTeX">$F_{A}$ </tex-math></inline-formula> availability-induced failures. After a successful detection of <inline-formula> <tex-math notation="LaTeX">$F_{M}$ </tex-math></inline-formula> malicious controllers, MORPH reconfigures the control plane to require a <italic>single</italic> controller message to forward the system state. Moreover, we outline and present a solution to the practical correctness issues related to the <italic>statefulness</italic> of the distributed SDN controller applications, previously ignored in the literature. We base our performance analysis on a resource-aware routing application, deployed in an emulated testbed comprising up to 16 controllers and up to 34 switches, so to tolerate up to 5 unique Byzantine and additional 5 availability-induced controller failures (a total of 10 unique controller failures). We quantify and highlight the dynamic decrease in the packet and CPU load and the response time after each successful failure detection.

MORPH: An Adaptive Framework for Efficient and Byzantine Fault-Tolerant SDN Control Plane