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Software-defined networks have many benefits such as more control over the control plane and reduced operating costs through separating the control plane from the data plane in network equipment. One of the most critical problems in software-defined networks is a controller placement problem, which significantly influences its overall performance. The purpose of this problem is to determine the number of controllers required and how to assign switches. This paper attempts to solve this problem, aiming to reduce the network's operational cost and to improve their survivability and load balancing. Hence, we have tried to divide the network into several subdomains using segmentation. Then, we used multi-criteria decision-making methods to solve the controller placement in each subdomain. For this purpose, we considered criteria such as reliability rate, cost, delay, and processing capacity. To assign switches to controllers, we used the proposed mathematical model to minimize the objective function while observing the defined constraints. Furthermore, according to the proposed architecture, we used distance to the central controller, adjacent neighborhood, and controller memory to select the cluster head controller for each subdomain to communicate with the central controller. Finally, we performed experiments on topologies Uran, SwitchL3, and Sinet of the Internet Topology Zoo to evaluate the proposed method. In these experiments, we compared the results of the proposed method with our work-related methods, including Controller Placement Analytic Hierarchy Process (CPAHP) and Controller Placement Modified Density Peak (CPMDP), in terms of criteria such as cost, survivability, number of controllers, connection failure probability, average delay, and controller load-balancing rate. The results show that the proposed method outperforms CPMDP and CPAHP. Thus, the proposed method has a 24.97% and 19.76% improvement in reducing network implementation costs than CPMDP and CPAHP, respectively. [ABSTRACT FROM AUTHOR]

Software‐defined networks are a modern architecture in computer networks where traffic transfer is separated from network control. In software‐defined networks, all decisions are made in the controller, and the necessary commands are injected into the network equipment. With the advent of software‐defined networks and the introduction of a new concept called controller in these types of networks, it becomes important to find an appropriate location for the controller and its number in the network. This problem aims to find the location and the optimal number of controllers needed in the network, and how to assign switches to the controllers declined certain constraints. In this article, a method to determine the appropriate location for controllers is proposed, so that the cost of network implementation would be reduced and thus its survivability is improved. Finally, we analyzed the proposed method in terms of evaluation criteria. [ABSTRACT FROM AUTHOR]