Software routers are an alternative low-cost and moderate-performance router solutions implemented with general-purpose workstations able to host two or more network interface cards (NICs). Workstations can be programmed to forward packets between different NICs and to participate in routing functions. The value of software routers lies on their low cost and on the flexibility to modifying routing and switching functions. Machine virtualization can be used to model novel protocols or hardware systems, however, implemented in software and without modifications to the host's kernel. This virtualization allows the implementation of not only one but also multiple (and independent) virtual systems. Virtualization of software routers, called virtual software routers, is then a possible application of this technology. However, because of the software platforms, virtualized machines are expected to suffer from performance degradation. In this paper, we investigate the switching performance of a virtual software router and compare it to that of a software router. We present the performance of virtual software routers hosted by different workstations, with single and multiple processing cores.