Which encryption algorithm is used to encrypt SD-WAN data-plane traffic?

AES-256 GCM (Advanced Encryption Standard with 256-bit key in Galois/Counter Mode) is the correct answer because it is the industry-standard, highly secure, and efficient encryption algorithm used in Cisco SD-WAN for data-plane traffic. It provides both confidentiality and integrity for the data. Triple DES (3DES) is an older, less secure, and computationally intensive algorithm that is largely deprecated. AES-128 is a valid AES variant but is less secure than AES-256 and not the primary choice for maximum security in SD-WAN. IPsec (Internet Protocol Security) is a suite of protocols that uses encryption algorithms like AES, but it is not an encryption algorithm itself.