Quiz Entry - updated: 2026.10.15
How does software-defined networking (SDN) change where the control plane lives?
Traditionally each switch has its own control plane (distributed control). In SDN the control plane moves to a central controller, and the switches keep only the data plane and become programmable.
* Traditionally every switch decides for itself; in SDN one controller decides and the switches only forward. *
Every network device does two jobs:
- Control plane: decides where traffic should go (routing protocols, spanning tree, building forwarding tables).
- Data plane: actually forwards each packet according to those tables, fast, in hardware.
| Traditional networking | Software-defined networking | |
|---|---|---|
| Control plane | On every device (distributed) | In one central controller |
| Data plane | On every device | On every device |
| How you change behaviour | Configure each box | Program the controller |
Centralising the control plane is what makes the network programmable as a whole: an application tells the controller what it wants, and the controller works out and pushes the forwarding behaviour to every device.
Go deeper:
Control plane — Wikipedia — what the control plane computes and how it feeds forwarding.- Data plane — Wikipedia — the fast path that actually moves packets.