Solving The Backup Controller Placement Problem In SDN Under Simultaneous Targeted Attacks Targeted attacks on software defined networks (SDN) can heavily disrupt the network connectivity and thus service continuity. One of the worst disruptions occurs when a targeted attack on network nodes is able to divide the network into different components (islands). Since the network is usually managed by a limited number of controllers, such attacks can result in isolating a significant proportion of nodes from the surviving controllers, causing major disruptions in service availability. In the paper we study the issue of adding a number of additional controllers to the network in order to increase its resilience to targeted attacks. For that we introduce an original optimization model for solving the related controller placement problem, based on a novel measure of network service availability called average network resilience (ANR). Additionally, we analyse two strategies to generate simultaneous targeted attack scenarios used in the numerical study illustrating the model effectiveness.

Minimizing MultiController Deployment Cost in SoftwareDefined Networking Aiming at various issues, such as performance, loadbalance and robustness, of SoftwareDefined Networking (SDN) controller cluster, several deployment strategies have been proposed. As a supplement, our work delivers a costeffective multicontroller deployment strategy in terms of economic benefits. In this paper, we formalize a Costoptimized MultiController Deployment (COMCD) problem by concerning the controllerxe2x80x99s deployment cost and the network servicexe2x80x99s delay cost. Meanwhile, we characterize the communication between the controller and the switch using a queuing system, and design an algorithm to determine the optimal deployment in the specified environment. Simulation results validate that the proposed algorithm can always obtain a deployment solution which minimizes the economic cost of the entire SDN network. This work aims at being a useful primer to provide insights regarding the economic impact of multiple controllers in the realistic SDN deployment, so that network owners plan their investments more rationally.