Network testbeds are useful for protocol performance evaluation. They overcome most challenges commonly involved in live network experimentation, retaining fair realism and repeatability under controllable conditions. However, large-scale testbeds are difficult to set up due to limited resources available to most experimenters. In this paper, we explore the use of hardware virtualisation as an experimental tool to improve resource efficiency, allowing to boost the effective number of nodes available for network testing. By virtualising network routers and links, a cluster environment with off-the-shelf equipment can host hundreds of virtual routers for large-scale network testing. We apply this technique to construct a 800-node Cognitive Packet Networks (CPN) testbed that provides insight into the benefits and limitations of the approach. © 2013 Springer-Verlag London.