SDN Overview
Traditionally, every switch and router in a network has its own control and data plane, which means all routing decisions are made on the switch itself.
The idea behind SDNs is to abstract that control plane from the switches and routers and run it on a central controller. That leaves the switches with just the data plane that actually ships packets in and out; the decisions on where the packets will go is based on instructions coming from that central controller.
The central controller helps in automatically adjusting the network architecture to deliver the fastest and most efficient data paths at the right time.
OpenFlow Overview
OpenFlow is a new protocol implemented on an Ethernet switch that allows its forwarding plane to be managed by an external OpenFlow controller.
OpenFlow exposes a switch’s forwarding plane as a set of Ethernet ports, flow tables, counters, queues, and capabilities. A flow table entry consists of a set of L2/L3/L4 match conditions, which may be variously wildcarded or masked. Associated with each flow table rule is a set of one or more actions, including Forwarding (to a physical or virtual port, to the controller, or flooded), Enqueueing, and Packet Modification.
By default, packets arriving at an OpenFlow-managed port which do not match a flow entry are encapsulated and sent to the controller, which as a result may send a flow installation command to the switch and return the packet back to the switch for forwarding.
OpenFlow exposes a switch’s forwarding plane as a set of Ethernet ports, flow tables, counters, queues, and capabilities. A flow table entry consists of a set of L2/L3/L4 match conditions, which may be variously wildcarded or masked. Associated with each flow table rule is a set of one or more actions, including Forwarding (to a physical or virtual port, to the controller, or flooded), Enqueueing, and Packet Modification.
By default, packets arriving at an OpenFlow-managed port which do not match a flow entry are encapsulated and sent to the controller, which as a result may send a flow installation command to the switch and return the packet back to the switch for forwarding.
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