SDN Controller Communication Protocol

C.

An SDN (Software Defined Networking) controller is a central management entity that manages the network by controlling the flow of data. It is responsible for creating and managing the network's forwarding rules, and it uses a southbound API (Application Programming Interface) to communicate with the network's data forwarding devices, such as switches and routers.

The southbound API is used by the SDN controller to communicate with the forwarding devices and to provide instructions on how to forward traffic. To relay forwarding changes to the southbound API, the SDN controller uses a communication protocol. This protocol defines the rules and procedures for exchanging information between the controller and the forwarding devices.

Out of the given options, OpenFlow is the communication protocol used by the SDN controller to relay forwarding changes to the southbound API. OpenFlow is a standardized protocol that is used by SDN controllers to communicate with the forwarding devices. It defines how the SDN controller can configure the forwarding devices to forward traffic in the network.

Java, REST, and XML are not communication protocols used by the SDN controller to relay forwarding changes to the southbound API. Java is a programming language, REST (Representational State Transfer) is an architectural style for building web services, and XML (Extensible Markup Language) is a markup language used for encoding documents in a format that is both human-readable and machine-readable.

In summary, the correct answer is C. OpenFlow.