Denial of Service (DDoS) attack has been used as a weapon by many hackers to cause a network failure thereby preventing the users from using the network service. This attack is perpetrated to create a financial loss, to gain money, to seek revenge, etc. Software-Defined Network (SDN) has grown widely to gain the hope of many researchers and network administrators to meet the need for maintenance of the data centers. Today’s world mostly prefers SDN due to its flexibility, cost-efficient, manageability, etc. SDN has a network architecture that changes its traffic pattern every time whenever a change is done in its central architecture. The separation of the planes in SDN ensures the security of entire network devices and their functions thereby protecting the network. So, the attackers target the controller to bring it down leading to a network failure. In the existing methods, there are many mitigation schemes that help to mitigate the attack. But still, the attacker tries a new way to perpetrate the DDoS attack. The proposed approach uses Flow entry-based OpenFlow methodology to mitigate the DDoS attack at the early stage.