Software Defined Networking (SDN) is the most recent, evolving, and emerging technology nowadays in computer networks. It has replaced the traditional networks in which the control and data planes were tightly coupled with decoupling the control and data planes. SDN provides complete network visibility, centralized management, a global view of the network, the programmability of the network devices, and dynamic updates of forwarding rules. Although SDN has provided a great advantage, there are many security issues like data modification, data leakage, configuration issues, denial of service (DoS), distributed denial of service (DDoS) attacks, and unauthorized access to network devices. DDoS is the most lethal, restricting authorized users from gaining access. In this paper, a high-rate DDOS attack is detected by using an entropy-based approach. Mininet emulator used for creating topology and defining rules. Furthermore, attack traffic was generated from different sources on a single destination. In the future, attack traffic will be blocked by turning off the incoming port on the switch, and attack traffic rules will be deleted from the flow table using a suitable algorithm.