Network virtualization is a relatively new research topic. A number of articles propose that certain benefits can be realized by virtualizing links between network elements as well as adding virtualization on intermediate network elements. In this article we argue that network virtualization may bring nothing new in terms of technical capabilities and theoretical performance, but it provides a way of organizing networks such that it is possible to overcome some of the practical issues in today?s Internet. We strengthen our case by an analogy between the concept of network virtualization as it is currently presented in research, and machine virtualization as proven useful in deployments in recent years. First we make an analogy between the functionality of an operating system and that of a network, and identify similar concepts and elements. Then we emphasize the practical benefits realized by machine virtualization, and we exploit the analogy to derive potential benefits brought by network virtualization. We map the established applications for machine virtualization to network virtualization, thus identifying possible use cases for network virtualization. We also use this analogy to structure the design space for network virtualization.