A software-defined networking (SDN) controller learns network topology information by using BGP link-state sessions with the route reflectors of an MPLS-enabled network. The controller then uses the…

SDN centralized removes the distributed control plane entirely and has the controller directly program all forwarding entries; in this design routers maintain their own RIBs, which is not a fully centralized model.

SDN traffic engineering describes a use case or application of SDN rather than a recognized architectural model classification.

SD-WAN is a specific overlay architecture for branch WAN connectivity and is not an SDN control-plane model applicable to MPLS core networks.

SDN hybrid combines a centralized controller - which uses BGP-LS sessions with route reflectors to learn the full MPLS topology - with a distributed forwarding plane where each router independently maintains its own RIB and processes locally installed policy entries. The controller pushes policies through a standard protocol such as BGP understood by all Layer 3 devices, preserving per-router autonomy while still enabling centralized orchestration, which is the defining characteristic distinguishing hybrid from fully centralized SDN.