PROGRAMMABLE CONTROL PLANE
Now that the control plane is centralized in a
central controller, it is easy for the network manager
to implement control changes by simply
changing the control program. In effect, with a
suitable API, one can implement a variety of
policies and change them dynamically as the system
states or needs change.
This programmable control plane is the most
important aspect of the SDN. A programmable
control plane in effect allows the network to be
divided into several virtual networks that have
very different policies and yet reside on a shared
hardware infrastructure. Dynamically changing
the policy would be very difficult and slow with a
totally distributed control plane.