planes from each network device and consolidate all of
them in the network controller. The network controller
can then communicate with the network elements, and
the network elements can send management data to the
controller. Because you now have one controller, this
architecture is called a centralized control plane. Figure
17-22 shows how a network controller can be used to
programmatically manage and control various
networking elements using the northbound and
southbound APIs.
Figure 17-22 Centralized Control Plane with a
Network Controller
Communication between the network controller and the
network elements is bidirectional. Both sides use
application programming interfaces (APIs), which allow
the network controller and the network devices to
communicate programmatically. The network controller
interacts with the network devices via southbound APIs,
and the network elements interact with the network
controller via northbound APIs.
SDN Controllers
An SDN controller is often considered the “brain” in a
modern network. The Open Networking Foundation