D. IPSec. IPSec provides authenticated and encrypted communication at the network layer and is the standard, most secure method for site-to-site connectivity over untrusted networks. It ensures confidentiality, integrity, and authenticity of traffic between sites. Why The Other Options Are Incorrect A. VXLAN. VXLAN is an overlay tunneling protocol used to extend Layer 2 networks over Layer 3 infrastructure. It does not provide encryption or security by default. B. IKE. IKE is a key management an