Existing network architectures fall short when handling networking trends, e.g., mobility, server virtualization, and cloud computing, as well as market requirements with rapid changes. Software-defined networking (SDN) is designed to transform network architectures by decoupling the control plane from the data plane. Intelligence is shifted to the logically centralized controller with direct programmability, and the underlying infrastructures are abstracted from applications. The wide adoption of SDN in network industries has motivated development of large-scale, high-fidelity testbeds for evaluation of systems that incorporate SDN. We leverage our prior work on a hybrid network testbed with a parallel network simulator and a virtual-machine-based emulation system. In this paper, we extend the testbed to support OpenFlow-based SDN simulation and emulation; show how to exploit typical SDN controller behavior to deal with potential performance issues caused by the centralized controller in parallel discrete-event simulation; and investigate methods for improving the model scalability, including an asynchronous synchronization algorithm for passive controllers and a two-level architecture for active controllers. The techniques not only improve the simulation performance, but also are valuable for designing scalable SDN controllers.