Mitigating Denial of Service (DoS) attacks in OpenFlow networks Software Defined Networking (SDN) is a promising step towards the future network. But, it still has some issue regarding the security. One of the security issues is the augmented impact of Denial of Service (DoS) attacks. In this paper, we create an application on the top of Beacon controller to mitigate the DoS attacks in the OpenFlow networks. The attacks include IP/MAC Spoofing and Bulky/Garbage Message. We launch the DoS attacks towards the network and analyze the performance of the application. All of these attacks, Beacon, and OpenFlow are implemented in the network simulation environment Mininet. At the end of this paper, we also discuss about another strategy and supplementary method to mitigate the DoS attacks.