The suggested answer is D.
When a WAN edge router connects to the Cisco SD-WAN fabric, it establishes a DTLS or TLS tunnel with the vSmart controller to ensure secure and reliable control plane connections. Additionally, the WAN edge router forms IPsec tunnels with other WAN edge routers to secure the data plane traffic passing between the branches. Hence, DTLS or TLS tunnels are used for control plane communication with controllers like vSmart, while IPsec tunnels are used for data plane communication among WAN edge routers.