Virtual Switches and Network Overlays: The Foundation of Modern SDNs

Abstract

Software-Defined Networking (SDN) has radically redefined the network architecture of the XXI century by decoupling the control plane and the data plane, allowing unprecedented centralization, control, and automation. This technical article explores two foundational building blocks that underlie modern SDN deployments: virtual switches and network overlays. Virtual switches are software-defined Layer 2 devices deployed inside hypervisors, which deliver connectivity to virtualized workloads and have programmable forwarding tables that are responsive to centralized controllers. Multi-tenancy Network overlay technologies, such as VXLAN and GENEVE, address multi-tenancy issues by applying an encapsulation of Ethernet frames into IP packets to form logical network topologies that have no physical boundaries. A combination of these technologies provides a highly scalable architecture in which thousands of isolated virtual networks may co-exist on the shared physical infrastructure. It discusses the internal layouts of these components and how they integrate with each other, and design principles are employed that facilitate cloud-scale deployments. Through analysis of the interaction between distributed elements of forwarding and centralized control, the article gives network engineers the necessary information to design and operate modern cloud infrastructure.