SDN

Software-Defined Networking decouples the control plane — the logic that decides where traffic goes — from the data plane, which actually forwards packets. Traditional routers and switches bundle both functions inside one device; SDN moves control to a centralized software controller that has a global view and programs forwarding rules down to individual devices via southbound APIs such as OpenFlow. For the N10-009 exam, the key distinction is SDN versus SD-WAN: SDN applies this model to a local or data-center network, while SD-WAN applies it specifically to wide-area connectivity, optimizing traffic across multiple internet or MPLS links. Confusing the two scopes is a common exam trap.