The SDN controller's interfaces connect to various components: Northbound to applications, Southbound to network devices, and Eastbound/Westbound to other controllers for distributed control.
The four interfaces of an SDN controller connect different components within a software-defined networking architecture. The Northbound interface connects the SDN controller to the application layer, which includes the network services and applications utilizing the network.
The Southbound interface links the SDN controller to the network devices, such as switches and routers, enabling the controller to communicate with and manage the network infrastructure. The Eastbound and Westbound interfaces are less commonly discussed and generally refer to interfaces that facilitate communication between different SDN controllers, potentially allowing for a distributed SDN control plane.