—Currently, the architecture of network device is closed. This is detrimental to the network innovation. Software defined networking (SDN) [1] decouples the vertically coupled architecture, and reconstructs the Internet as a modular structure. The idea of SDN is widely accepted by both of the academic and industry researchers, and is considered as a promising way to re-architect the Internet. OpenFlow as a typical instance of the SDN has been deployed by many universities and research institutions all over the world. However, the research and technologies on transitioning the existing networks to SDN are not mature. So this paper takes the instance OpenFlow for example and proposes a simple and practical BGP (Border Gateway Protocol) based transition solution named BTSDN. BTSDN fully explores the characteristics of OpenFlow network, proposes to continue using the current BGP protocol, and retains the legacy BGP border routers to connect the OpenFlow network with the rest of Internet....