Distributed Software Defined Networking federates multiple controllers In a network to solve the problems In single controller networks, e.g., to improve network reliability and reduce the delay between controllers and switches. However, in the current distributed SDN schemes, the mapping between SDN switches and controllers is statically configured, which may result in uneven load distribution among controllers. These schemes cannot fully benefit from the distributed SDN architecture. In order to address this issue, this paper proposes an adaptive elastic distributed SDN architecture. The architecture dynamically selects a minimum. number of active controllers that switches attached to, and changes the mapping between switches and controllers according to the network load. Specially, a switch can migrate from one controller domain to another so that the mapping is adaptive to the network load. We formalize the controller selection problem as an optimization problem, and prove that the problem is NP-Hard. We solve the problem by using greedy algorithms. With the algorithms, controllers In a network are dynamically changed with respect to the network load and the number of active controll0ers is close to the optimal value. We validate the algorithms and evaluate the performance by simulations. In particular, the simulation results show that the number of active controllers is reduced by 60% when the whole network load decreases.
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