2.8.1. SDN and SD-WAN

Software-Defined Networking (SDN): Separates the control plane (decision-making) from the data plane (packet forwarding). A central controller makes routing and policy decisions; switches/routers just execute instructions.

SD-WAN (Software-Defined WAN): Applies SDN principles to wide-area networking:

• Application-aware routing: Routes traffic based on application requirements (VoIP over low-latency path, backups over high-bandwidth path)
• Zero-touch provisioning: Devices auto-configure when connected
• Transport-agnostic: Works over MPLS, internet, LTE—whatever's available
• Central policy management: Define policies once, apply everywhere