The correct answer is B. TLS.
In Cisco Catalyst SD-WAN, the architecture separates:
* Control Plane # Secure communication between controllers and edge devices
* Data Plane # Encrypted tunnels carrying user traffic
* The control plane (between vSmart, vBond, vManage, and WAN Edge routers) uses:
* TLS (Transport Layer Security)
* In some cases also DTLS, depending on configuration
* These protocols provide:
* Authentication
* Encryption
* Integrity protection
Thus, TLS is used to establish secure control plane adjacencies.
* A. IPsec Used for data plane encryption (IPsec tunnels), not control plane.
* C. IKE Used for key exchange in IPsec, not for SD-WAN control plane adjacencies.
* D. ESP Part of IPsec (data plane encryption), not control plane.
Memorize this SD-WAN separation:
* Control Plane # TLS / DTLS
* Data Plane # IPsec (ESP encapsulation)
This distinction is frequently tested in ENCOR exams.