In recent decade network virtualization has become a popular topic in research papers, white papers, and text books. Network virtualization allows coexistence of multiple virtual network on the same physical network/substrate. Popular commercial provider for operating system (OS) virtualization solutions are VMware, Microsoft, Citrix and Oracle. One important aspects of such a virtualization platforms is sharing of hardware resources among many virtual machine created over OS. For instance one important task in such a platform is sharing of the Network Interface Card (NICS, at the network edge) which is shared by many instances of the virtual machine. In this regard review different research articles, or IEEE or ACM reputed conference papers and write critical review, reflection and critical observation on the following aspect of the network virtualization. a) Review the spectrum of network virtualization technologies b) Discuss the limitations of the network devices virtualization