Which of the following is the most common VPN security protocol?

The most common VPN security protocol is SSL (Secure Sockets Layer). SSL is widely utilized because it secures internet connections by encrypting data transmitted between the user and the server, protecting against eavesdropping and tampering. Many modern VPN solutions leverage SSL to create a secure tunnel for data transmission over the Internet, providing users with a reliable method to protect their communications.

SSL's popularity stems from its ease of use and implementation. It works seamlessly with existing web infrastructure, allowing users to connect through web browsers without the need for additional software installations. This accessibility has made SSL-based VPNs a go-to choice for both corporate environments and individual users seeking secure remote access.

In contrast, while IPSec and SSTP are robust protocols that also provide strong security, SSL's wide compatibility with web applications and straightforward configuration often gives it the edge in common usage scenarios. Similarly, although DTLS (Datagram Transport Layer Security) offers certain advantages like low latency for real-time applications, it is not as widely adopted as a primary VPN protocol as SSL.

Therefore, SSL stands out as the most common VPN security protocol due to its broad application, user-friendliness, and strong encryption capabilities that help secure a wide range of online activities.