Which protocol provides authentication, integrity, and confidentiality services as a type of VPN?

IPsec, or Internet Protocol Security, is the correct answer because it is specifically designed to provide comprehensive security services, which include authentication, integrity, and confidentiality for data being transmitted over networks, particularly those using the Internet Protocol (IP). By utilizing encryption and authentication protocols, IPsec ensures that data packets are securely communicated between two endpoints.

This is particularly vital for virtual private networks (VPNs), as it creates a secure tunnel for transferring sensitive data over public networks. IPsec works at the network layer, which allows it to protect all IP traffic, and can operate in two modes: transport mode, which encrypts only the payload of the IP packet, and tunnel mode, which encrypts the entire IP packet.

While other protocols mentioned also have roles in establishing VPNs, they do not provide the same level of combined security services as IPsec. For instance, SSL is primarily used for secure web communications and does not natively include IP-level protection. PPTP and L2TP are older protocols that may not offer the same strength of encryption and are often paired with IPsec to enhance security. Thus, IPsec stands out as the robust choice for VPN implementations requiring comprehensive security measures.