This document discusses network service in OpenStack clouds. It introduces SDN and network virtualization technologies like OpenFlow, VXLAN, and NVGRE. It describes how OpenStack's Quantum project provides network as a service and supports various plug-ins for different virtual network implementations. The author then outlines their work on a virtual cube (vCube) network service that provides quality of service, visibility, and a transition between VLAN and GRE virtual network solutions in OpenStack.