On which SDN plane does CDP function?

The Cisco Discovery Protocol (CDP) functions on the management plane of the SDN model. It helps with management of the routers and switches and does not directly impact the data plane. The data plane is responsible for switching and routing data. Any data that is destined for endpoints is switched or routed on the data plane. Network plane is not a term normally used to describe data types; therefore, option C is an invalid answer. The management plane is any mechanism that helps in the management of a router or switch.