Abstract: With the rise and development of cloud computing, people have a requirement of taking on demand and charging on quantity demanded to cyber resources. Although the available types of IaaS(Infrastructure as a Service) suppliers provides the corresponding virtual cyber resources in the platform, but there is still a big difference between the performance of the virtual network purely based on cloud plaform and the performance of the actual hardware network. In order to improve the performance of the virtual network on the cloud platform, the combination of SDN (Software Define Network) and virtual network is particularly important, and has become the most popular and important project in cloud computing network research field. This paper firstly introduces Neutrons virtual network implementation principle in OpenStack, then introduces the implementation principle of plug-in DVR which solves some problems of North-South traffic concentration, and at last, analyzes and studies the implementation principle of distributed SDN controller plug-in Dragonflow, which is devoted to solving the North-South traffic concentration problem.

Key words: cloud computing, distributed routing, OpenStack, SDN