This paper addresses the provisioning of virtual resources in future networks relying on the Infrastructure as a service principle. Exact and heuristics optimization algorithms for the provisioning of virtual networks involving multiple infrastructure providers are presented. The study assumes the emergence of new actors such as virtual network providers acting as brokers requesting virtual resources on behalf of users. Resource matching, splitting, embedding and binding steps required for virtual network provisioning are proposed and evaluated. Splitting of the virtual network provisioning request across multiple infrastructure providers is solved using both max-flow min-cut algorithms and linear programming techniques. Virtual network embedding is formulated and solved as a mixed integer program with the aim of decreasing embedding cost for infrastructure providers while increasing the acceptance ratio of requests. Performance of the splitting and embedding algorithms is reported