Which component of the SDN architecture automatically ensures that application traffic is routed according to policies established by network administrators?

The SDN controller sits between the application plane and the data plane, receiving policy intent via northbound APIs and automatically pushing forwarding rules to all network devices via southbound APIs. This centralized enforcement guarantees that application traffic is routed consistently according to administrator policies across the entire network without per-device manual configuration.

The packet forwarding engine simply executes forwarding decisions that have already been pushed to it by the controller - it has no awareness of policies and cannot enforce them autonomously.

The southbound API is only the communication channel between the controller and data plane devices - it transmits instructions but has no decision-making or policy-enforcement capability of its own.

The northbound API is the interface through which applications and orchestration systems express intent to the controller - it carries policy requests upward but does not itself enforce routing behavior.