Improving Resiliency of SoftwareDefined Networks with Network Codingbased Multipath Routing Traditional network routing protocol exhibits high statics and singleness, which provide significant advantages for the attacker. There are two kinds of attacks on the network: active attacks and passive attacks. Existing solutions for those attacks are based on replication or detection, which can deal with active attacks; but are helpless to passive attacks. In this paper, we adopt the theory of network coding to fragment the data in the SoftwareDefined Networks and propose a network codingbased resilient multipath routing scheme. First, we present a new metric named expected eavesdropping ratio to measure the resilience in the presence of passive attacks. Then, we formulate the network codingbased resilient multipath routing problem as an integerprogramming optimization problem by using expected eavesdropping ratio. Since the problem is NPhard, we design a Simulated Annealingbased algorithm to efficiently solve the problem. The simulation results demonstrate that the proposed algorithms improve the defense performance against passive attacks by about 20% when compared with baseline algorithms.

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.