OCI Site-to-Site VPN connections use Internet Protocol Security (IPsec) to secure data transmission, providing encryption and authentication over the tunnel. SSL (Option A) and TLS (Option C) are typically used for web traffic, not VPNs, while DTLS (Option B) is designed for datagram-based applications, not standard VPNs. Oracle’s VPN documentation specifies IPsec as the protocol, aligning with industry standards for secure VPNs. The original question incorrectly listed SSL as the answer; IPsec is correct per OCI standards.