Abstract. Cloud computing is an emerging paradigm to provide Infrastructure as a Service (IaaS). In this paper we present NEPTUNE-IaaS, a software system able to support the whole lifecycle of IaaS provisioning in a Virtual Cluster environment. Our system allows interactive design of complex system topologies and their efficient mapping onto the available physical resources of a cluster. It also provides transparent VM migration features across geographically distributed datacenters, thanks to the adoption of the Service Switching paradigm. We also evaluate the effectiveness of the VM mapping procedures and compare our solution against other existing IaaS solutions. Key words: Cloud Computing, IaaS, Xen, Virtual Networking.