The interconnection of the different geographically dispersed cloud and fog infrastructures is a key issue for the development of the fog technology. Although most existing cloud providers and platforms offer some kind of connectivity services to allow the interconnection with external networks, these services exhibit many limitations and they are not suitable for fog computing environments. In this work we present a hybrid fog and cloud interconnection framework, which allows the automatic provision of cross-site virtual networks to interconnect geographically distributed cloud and fog infrastructures. This framework provides a scalable and multi-tenant solution, and a simple and generic interface for instantiating, configuring and deploying Layer 2 and Layer 3 overlay networks across heterogeneous fog and cloud platforms, with abstraction from the underlying cloud/fog technologies and network virtualization technologies.