SDN

Software Defined Networking separates the control plane from the data plane so that a central controller can program the forwarding behavior of many devices.

Key Ideas

• A logically centralized controller maintains a global view of the network.
• Switches become simple forwarding devices managed via southbound APIs like OpenFlow.
• Applications communicate with the controller using northbound APIs to implement policies or automation.

SDN enables rapid innovation because new features can be rolled out in software without replacing hardware. Operators gain fine‑grained control over traffic flows and can automate configuration at scale.

Flow Tables and Rules

Switches in an SDN network store flow tables programmed by the controller. Each flow rule contains match criteria, actions (like forward or drop), and a priority. By updating these rules, the controller adapts the forwarding behavior in real time.