Network virtualization brings remarkable evolution for networking, and it breaks through the resource boundaries originated from the physical network devices. Software-defined network (SDN), on the other hand, makes operational management more flexible for virtual network. DHCP is one of the most common protocols in the network. However, it becomes unsafe if misused by hackers. In this paper, we develop an SDN-based defensive solution against three kinds of severe DHCP attacks or misconfiguration. Besides, we also launch attacks in our environment to ensure the solution can be practically used.