Software-Defined Networking (SDN) Controller & OpenFlow Engine

What is Software-Defined Networking (SDN)?

Software-Defined Networking (SDN) decouples the network's Control Plane (which decides where traffic is sent) from the underlying Data Plane (which forwards traffic according to control instructions). By centralizing network intelligence into a logical software controller, SDN enables dynamic, programmatically configured network management.

Core SDN Architectural Layers & Interfaces

• Application Plane: Contains network applications and services (e.g., Load Balancers, Firewalls, QoS Policies, Topology Viewers) communicating intent to the controller.
• Northbound APIs (REST/RESTCONF): Interfaces connecting applications to the SDN Controller, allowing soft-programmatic abstraction.
• Control Plane (SDN Controller): The centralized "brain" maintaining a global view of network state, topology, and flow rules (e.g., OpenDaylight, ONOS, Ryu).
• Southbound APIs (OpenFlow / gRPC / NETCONF): Standardized protocols allowing the controller to dynamically program state and rules into Data Plane forwarding elements.
• Data Plane (Infrastructure Layer): Hardware or software switches (e.g., Open vSwitch) executing rule matches, actions, and counter updates across packet streams.

Key SDN Operational Concepts

• Flow Table: A set of match criteria, counters, and actions programmed in switches to handle matching network packets.
• Table-Miss: Occurs when an incoming packet matches no entries in a flow table, triggering a PACKET_IN event sent to the central controller.
• Reactive vs. Proactive Flow Installation: Reactive installs entries dynamically upon initial unknown packet arrivals, whereas Proactive pre-populates switch flow tables prior to traffic flow creation.