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We propose a Fast Controller Failover for Multidomain Software-Defined Networks (SDNs) (FCF-M) to handle SDN controller failures. The proposed FCF-M is composed of controller failure detection and switch reassignment. In the controller failure detection, each controller checks the timestamp of its preceding controller. If a controller is failed, its succeeding controller will check its preceding controller. Because a failed controller does not prevent its preceding controller from healthy check, the proposed FCF-M can prevent a single point of failure (SPOF) for healthy check. We also make use of an adaptive timeout delay to reduce failure detection time. In the switch reassignment, when a controller is failed, we need to reassign the switches under the failed controller to an alternative controller. We consider controller load and distance between a switch and a controller to choose an alternative controller for reducing delay. The proposed FCF-M can achieve intra-domain controller failover and interdomain controller failover. Using EstiNet, simulation results show that the proposed FCF-M outperforms the Devolved controller (DC) in terms of average end-to-end delay and failover time.