What is the primary function of southbound APIs?

The primary function of southbound APIs is to facilitate communication between the network controller and the data plane. In a software-defined networking (SDN) architecture, the network controller acts as the central management point, overseeing and controlling the various aspects of the network. The data plane, on the other hand, is responsible for the actual data forwarding and processing that takes place within the network devices.

Southbound APIs serve as the means through which the network controller can send instructions to and receive information from the data plane, enabling dynamic and centralized control over network resources. This interaction is crucial for implementing policies, managing network traffic, and orchestrating services within the network.

The other choices revolve around different aspects of networking and application communication but do not specifically pertain to the distinct role of southbound APIs in the context of SDN. For instance, communication between management software and applications reflects a different layer and is not strictly related to the interaction between the controller and the data plane.