7.7 Describe network programmability in enterprise network architecture
7.7.a Function of a controller
A SDN controller’s function is to concentrate the control plane of the entire network and attached routers into a single device. This means that the whole network can be orchestrated and controlled from a single point.
7.7.b Separation of control plane and data plane
The control plane represent policy management and the data plane represents policy implementation.
Traditionally routers and switches had a unit specific control plane and data plane which meant each device had to be hand configured. The separation of control planes and data planes means that devices can be orchestrates, automated and remotely administrated.
7.7.c Northbound and southbound APIs
A northbound API is an API that is on the control plane side, this allows for general control of the entire network. A southbound APIs is something that typically communicates policy to the individual routers/switches under control of the network controller.
Cisco doesn’t believe is the complete separation of control planes and data planes and recommends a hybrid approach that they believe increases reliability.