The interest in network virtualization has been growing steadily among the networking community in the last few years. Network virtualization opens up new possibilities for the evolution path to the Future Internet by enabling the deployment of different architectures and protocols over a shared physical infrastructure. The deployment of network virtualization imposes new requirements and raises new issues in relation to how networks are provisioned, managed and controlled today. The starting point for this paper is the network virtualization reference model conceived in the framework of the EU funded 4WARD project. In this paper we look at network virtualization mainly from the perspective of the network infrastructure provider, following the 4WARD network virtualization architecture and evaluate the main issues and challenges to be faced in commercial operator environments. Categories and Subject Descriptors C.2.3 [Computer-Communication Networks]: Network Architecture and Design Ge...