OpenFlow

• Open flow is to define both the communications protocol between the SDN data plane and SDN control plan and part of the behavior of the data plan.
• The Open Network Foundation (ONF) was created for the express purpose of accelerating the delivery and commercialization of SDN.
• Three fundamental packet paths are (1) A. Forward the packet out a local port, possibly modifying certain header fields first (2) B. Drop the packet (3) C. Pass the packet to the controller.
• Openflow switch implementation is either OpenFlow only or OpenFlow-hybrid. OpenFlow only switch is one that forwards packets only according to the OpenFlow logic. An OpenFlow hybrid is a switch that can also switch packets its legacy mode as an Ethernet switch or IP router, it requires a preprocessing classification mechanism that directs packets to either OpenFlow processing or the traditional packet processing.
• The OpenFlow control plane differs from the legacy control plan in three key ways.

      (a) It supports to program different data plan elements with a common, standard language.
      (b) it exists on a separate hardware device than the forwarding plan. Administrator can program data plan elements remotely over the Internet.
     (c) controller can program multiple data plan elements from a single control plan instance.

• OpenFlow controller is responsible for programming all the packet-matching and forwarding rules in the switch.