What's changed: Initial version
4.3Network virtualization
Covers SDN, which separates the control and data-forwarding functions (via OpenFlow), SD-WAN, which centrally controls a multi-site WAN in software, NFV, which turns dedicated appliance functions into software, and VXLAN (VNI), which builds an L2 network as an overlay on top of L3, building the judgment needed to decide when to migrate from a traditional network.
In a traditional network appliance, the control plane that decides routing and the data plane that actually forwards packets are integrated into a single device, requiring individual configuration per device. Network virtualization technologies separate this integration and turn it into software, raising operational efficiency in multi-site, large-scale environments subject to frequent change. This section teaches network designers to judge whether to migrate from a traditional network to SDN/SD-WAN, based on scale, rate of change, and operating structure.
4.3.1SDN (control plane / data plane separation)
- SDN (Software-Defined Networking) is a design philosophy that separates the control plane, which decides routing, from the data plane, which actually forwards packets, consolidating the control plane into an SDN controller managed centrally in software. This removes the need to configure each switch or router individually, letting network-wide policy be changed and applied from a single point.
- OpenFlow is the representative protocol used between the SDN controller and the switches (data-plane devices) to exchange flow tables (forwarding rules). The controller distributes rules such as "for this packet pattern, take this action (forward/drop/rewrite)" to the switches, giving a clear division of labor in which the switch merely forwards mechanically according to the rules (decision-making is consolidated in the controller).
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