Method of handling SDN protocol messages in a modular and partitioned SDN switch

A method involves a Software-Defined Networking (SDN) switch that includes multiple Network Flow Switch (NFX) integrated circuits, a Network Flow Processor (NFP) circuit, and a controller processor. The controller processor is coupled to the NFP circuit by a serial bus. A flow table is maintained on each of the NFX integrated circuits. A SDN flow table is maintained on the NFP circuit. A copy of each of the flow tables is maintained on the NFP circuit. Another SDN flow table is maintained on the controller processor. A SDN protocol stack is executed on the controller processor. A SDN protocol message is received onto the SDN switch via one of the NFX integrated circuits. The SDN protocol message is communicated across a network link to the NFP circuit, and across the serial bus from the NFP circuit to the controller processor such that the SDN protocol message is received and processed by the SDN protocol stack executing on the controller processor.