Abstract: The current Internet architecture based on TCP/IP is facing with many unprecedented challenges, including scalability, security, mobility and controllability. New clean-slate architecture designs are expected to address these challenges and provide better evolvability. As such, they have been attracting great attention in recent years. Before deployment in production networks, the future Internet architectures, protocols and algorithms should be comprehensively validated, evaluated and optimized in large-scale and realistic testbeds. The testbeds for network innovation should closely simulate the real network, and provide more flexibility. These requirements make it critical to study architectures and key technologies of testbeds. Although there have been long-term interests in network testbeds, a comprehensive survey is still missing. In this paper, we first analyze the requirements of network innovation testbeds based on four common problems of network experiments, namely cost, feasibility, credibility and controllability. We then summarize technical challenges of testbeds design and development from the perspectives of virtualization and programmability of network, federate management/control of resources, as well as monitor/measurement of infrastructures and experiments. In particular, we summarize the state-of-the-art technologies and architectures that aim at addressing the aforementioned challenges. Finally, we present some representative testbeds, and discuss the future trends and open questions.