What is the difference between controller-based networks and traditional networks as they relate to control-plane and/or data-plane functions?

Controller-based networks primarily centralize the *control plane* for network intelligence, while the data plane, responsible for forwarding actual traffic, remains distributed across the individual network devices.

Traditional networks distribute control-plane functions across each individual network device, where each device independently makes routing and forwarding decisions, rather than centralizing them.

Traditional networks keep the data plane functions distributed on individual devices for local packet forwarding; they do not centralize data-plane functions.

In controller-based networks, often associated with Software-Defined Networking (SDN), the control plane, which is responsible for making forwarding decisions, routing logic, and network intelligence, is decoupled from the data plane and centralized in a software controller. Conversely, traditional networks feature a distributed control plane where each network device (router, switch) independently runs its own routing protocols and maintains its own forwarding tables, making its own forwarding decisions.