Explain Software-Defined Networking (SDN) architecture.

SDN separates control plane (decision making) from data plane (forwarding). Components: SDN controller (centralized brain, network-wide view), northbound APIs (applications interact with controller), southbound APIs (controller to switches - OpenFlow), data plane (programmable switches). Benefits: centralized management, programmable network, dynamic configuration, vendor-agnostic. Use cases: data center networking, network virtualization, traffic engineering. Compare with traditional networking where control and data planes are integrated in each device.