Which API type does a controller use to interact with edge devices?

A southbound API is used by a controller to communicate with and manage network devices (like switches, routers, and access points) at a lower level of the network hierarchy. This allows the controller to push configurations, retrieve telemetry, and control the data plane of these edge devices. Northbound APIs, conversely, are used by the controller to communicate with higher-level applications or orchestration systems, providing an abstract view of the network. Overlay and underlay refer to network architectures where an overlay network runs on top of an underlying physical (underlay) infrastructure.