Question: Which VPN protocol is best for the highest security and performance?

A.  PPTP

B.  L2TP

C.  OpenVPN

D.  IPsec

Correct Answer: C

Explanation:

A. PPTP (Point-to-Point Tunneling Protocol)
PPTP is a legacy protocol that should be avoided in modern security architectures.

The Vulnerability: It uses MS-CHAPv2 for authentication, which is notoriously easy to crack. Furthermore, it relies on MPPE (Microsoft Point-to-Point Encryption), which has significant cryptographic weaknesses.

The Verdict: While it is very fast (due to low encryption overhead), its security is virtually non-existent by today's standards. It is often blocked by modern firewalls because it relies on GRE (Generic Routing Encapsulation) tunnels.

B. L2TP (Layer 2 Tunneling Protocol)
L2TP is a "tunneling" protocol, not an "encryption" protocol.

The Dependency: Because L2TP provides no confidentiality on its own, it is almost always paired with IPsec (L2TP/IPsec).

Performance Impact: Because L2TP/IPsec encapsulates data twice, it is typically slower than more streamlined protocols. While it is more secure than PPTP, its complexity and lack of native "firewall-friendly" features (it uses specific UDP ports that are easily blocked) make it less ideal than OpenVPN.

C. OpenVPN
OpenVPN is a modern, open-source solution that utilizes the OpenSSL library to provide encryption.

Security Strength: It supports the highest levels of encryption, including AES-256, and uses custom security protocols based on SSL/TLS. Being open-source means the code is constantly scrutinized by the global security community, making it highly trustworthy.

Performance and Flexibility: OpenVPN can run over either TCP or UDP. Running it over UDP provides the best performance for streaming and low-latency tasks. Additionally, it can be configured to run on Port 443 (HTTPS), allowing it to bypass strict firewalls that block other VPN types.

D. IPsec (Internet Protocol Security)
IPsec is a suite of protocols used to secure IP communications at the Network Layer (Layer 3).

The Use Case: IPsec is the gold standard for Site-to-Site VPNs (connecting two offices together). It is incredibly robust and provides strong authentication and encryption (via AH and ESP headers).

The Trade-off: While extremely secure, client-side IPsec can be difficult to configure and can sometimes struggle with NAT-Traversal (NAT-T) issues when users are connecting from home routers. Compared to OpenVPN’s ease of use and ability to navigate various network environments, IPsec is often viewed as more rigid for remote access.

Key Takeaway for the CISSP Exam

VPN Comparison at a Glance:

• PPTP: Fast but broken. Avoid.
• L2TP/IPsec: Secure but slow/clunky. Good for mobile device compatibility.
• IPsec: The "King" of Site-to-Site connections. Operates at Layer 3.
• OpenVPN: Best all-around for security, speed, and bypassing firewalls.
• TLS/SSL VPNs: Operates at the Application Layer (Layer 7). Great for "clientless" browser-based access.