In an SDN architecture, which network-node function is centralized on the controller?

In an SDN (Software-Defined Networking) architecture, the control plane, which includes making routing decisions, is centralized on the controller. This contrasts with traditional networking where each device makes independent routing decisions. The controller gathers network-wide information and computes optimal paths, then pushes these forwarding instructions to the data plane devices (switches and routers). "Creates the IP routing table" is incorrect because while the controller dictates the entries in the forwarding tables, the individual devices still create and maintain their local tables based on controller instructions. "Discards a message due filtering" is a data plane function performed by the network devices themselves based on policies pushed by the controller. "Provides protocol access for remote access devices" is a function of network access devices, not the core centralized SDN controller.