Southbound APIs such as OpenFlow provide the forwarding tables to network devices such as switches and routers. SDN controllers have an abstraction of the network topology based on discovery and provisioning information provided by management and orchestration systems.
The SDN controllers use the concept of flows to identify network traffic based on predefined rules that can be statically or dynamically programmed by the SDN control software. With the network topology abstraction, they are able to determine how traffic should flow through network devices based on application data, business policy, bandwidth, and path availability. If the SDN-enabled network elements do not provide updated link state information, the SDN controller is not able to reconverge the network to verify there is reachability to all destinations. |