SDN Control and Data Separation
What is the control/data plane separation?
The control plan is logic that controls the forwarding behavior in the network.
Examples of the control plane are routing protocols, network box configuration such as firewall configuration or load balancer configuration, and so forth. One can think of it in some ways as the brain of the network.
The data plane on the other hand forwards traffic according to the control plane logic.
Examples of data planes are IP forwarding layered to switching and so forth.
Why we need the control/data plane separation?
One reason of the control/data plane separation is that control plane and data plane can evolve and be developed independently. In particular the software control of the network can evolve independently of the hardware. That means one can buy a router, switches, middle boxes, and so forth deploy them in the network and not be bound by capabilities of software that ship with the hardware at that particular time.
The second reason to separate the control and data planes is that it allows the network to be controlled from a single high level software program. The higher order programs could easily control or debug the behavior of the entire network instead of reconfigure/check each network component one by one.
The opportunities and challenges of control/data plane separation
The first opportunity of separating the data and control plane can help in data centers and in routing. The second advantage of the control and data plane separation can help make certain applications in enterprise networks easier to manage.
There are also challenges to make the control and data plane separation being a reality.
The first is scalability, once we separate the control elements from the forwarding elements. The other challenge is reliability or security what happens if a controller fails or is compromised?
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