中文摘要：

随着软件定义网络的发展，可扩展性成为软件定义网络面临的重要问题之一。主要研究由于SDN的自身特征导致应用于大规模网络时面临的可扩展性问题。首先，讨论了导致SDN可扩展问题的3个主要方面原因：控制平面和数据平面分离、逻辑集中的控制以及细粒度的流管控。其次，从性能可扩展、地理位置可扩展、管控可扩展3个方面介绍了当前SDN可扩展性问题的研究进展。再次，讨论了SDN可扩展性评价方面的进展。最后，展望了SDN可扩展性的未来研究方向。

英文摘要：

With the development of software-defined networking(SDN),its scalability has become one of the most important issues of SDN.The features of SDN was studied which lead to its scalability problem when SDN was applied to large-scale network.The three main causes leading to scalability problem were discussed:control plane and data plane separation,logical centralized control and fine-grained flow control.Meanwhile,the studies which focus on the scalability of SDN from three aspects:scalability of performance,scalability of geographic and scalability of control was presented.Further,the studies on the performance evaluation of the scalability of SDN were introduced.Finally,the future work was discussed.