How do STP and dynamic routing relate to SD-WAN overlays?

• A. Underlay networks may use dynamic routing; overlay routing is managed by the SD-WAN controller, allowing selective path choices independent of STP; STP is less central to overlay fabrics.
• B. STP is essential to overlay.
• C. Dynamic routing is not used in underlay.
• D. SD-WAN disables all STP.

Answer: (A)

SD-WAN overlays separate the transport network (underlay) from the virtual network (overlay). In the underlay, devices can run dynamic routing to keep connectivity between sites. The overlay, however, is steered by the SD-WAN controller, which makes path choices across multiple transport links (for example Internet, MPLS) based on policies, quality, and cost, rather than relying on STP to determine routes. This means the overlay fabric can select and switch paths independently of how the underlay handles layer-2 loop prevention, making STP less central to how the overlay operates.

That’s why the statement about underlay dynamic routing existing and the overlay routing being managed by the SD-WAN controller is the best fit. STP isn’t the mechanism that governs overlay traffic, and dynamic routing in the underlay doesn't disappear or become irrelevant—it supports reachability while the overlay handles path selection. The idea that STP is essential to overlay or that SD-WAN disables STP everywhere isn’t accurate, since the overlay and underlay can coexist with STP where appropriate and with the overlay providing its own routing decisions on top.