Software-Defined Networking

Software-Defined Networking, or SDN, separates network control from packet forwarding. The forwarding plane still moves, drops, or changes packets. A software control plane decides what that forwarding behavior should be.

The key change is the interface between those responsibilities. Software can initialize, inspect, and change network behavior through defined interfaces. That makes network behavior programmable without requiring every decision to live inside each forwarding device.

The mental model

Think in planes.

• The application plane holds applications and services that request network behavior.
• The control plane decides how packets should be forwarded.
• The management plane monitors, configures, and maintains network devices.
• The forwarding plane, also called the data plane, handles packets according to installed instructions.
• The operational plane exposes device state such as ports and resources.