Hierarchical SDN for the hyper-scale, hyper-elastic data center and cloud.

ABSTRACTWith the explosive growth in the demand for cloud services, the Data Center and Data Center Interconnect have to achieve hyper-scale and provide unprecedented elasticity and resource availability. The underlay network infrastructure has to scale to support tens of millions of physical endpoints at low cost; the virtualized overlay layer has to scale to millions of Virtual Networks connecting hundreds of millions of Virtual Machines (VMs) and Virtualized Network Functions (VNFs), and provide seamless VM and VNF mobility. In this paper, we present Hierarchical SDN (HSDN), an architectural solution that achieves hyper scale using surprisingly small forwarding tables in the network nodes. HSDN introduces a new paradigm for the forwarding and control planes, in that all paths in the network are pre-established in the forwarding tables and the labels identify entire paths rather than simply destinations. These properties of HSDN dramatically simplify establishing tunnels, and thus enable optimal handling of both ECMP and any-to-any end-to-end TE, which in turn yields extremely high network utilization with small buffers in the switches. The pre-established tunnels make HSDN the ideal underlay infrastructure to enable seamless and lossless VM and VNF overlay mobility, and achieve excellent elasticity. HSDN is suitable for a full SDN implementation, using a scalable SDN controller to configure all forwarding tables in the network nodes and in the endpoints, as well as a hybrid approach, using conventional routing protocols in conjunction with a SDN controller.