Which control plane protocol is used between Cisco SD-WAN routers and vSmart controllers?

 The control plane protocol used between Cisco SD-WAN routers and vSmart controllers is the Overlay Management Protocol (OMP). OMP is a proprietary protocol of Cisco SD-WAN that facilitates the exchange of routing, policy, and management information across the network. It operates within the secure environment provided by the Datagram Transport Layer Security (DTLS) or Transport Layer Security (TLS) control connection, ensuring that the communication between the routers and controllers is encrypted and authenticated1.

References := Cisco 300-415: Cisco SD-WAN vSmart-WAN Edge Router Control Plane Protocol