Modern virtualization technologies provides an optimal use of underused hardware resources by sharing them among virtual machines hosted on the same physical machine. These technologies hence have been broadly adopted in many areas, such as server consolidation, virtualized network testbeds, etc. A large-scale network testbed is considered one of the useful tools for evaluating or verifying advanced networking technologies. To construct a network testbed that matches as much as a real setup, the testbed should meet requirements of isolation, fidelity, repeatability, scalability, containment and extensibility. Among these requirements, scalability can be realized by the modern virtualization technology, whereas vulnerability and security weakness brought along with virtualization can also be harmful to the other requirements of a network testbed, like isolation and fidelity. This paper reviews the modern virtualization technologies, their resource management mechanisms, and the known attacks of these virtualization technologies. Then, we discuss the requirements of existing network testbeds and the security impacts when introducing such modern virtualization technologies into a network testbed.