Final answer:
IPSec is not a tunneling protocol but is often used to secure L2TP and other tunneling protocols, ensuring private communications over IP networks.
Step-by-step explanation:
The question is asking which option is not a tunneling protocol itself, but is used in conjunction with tunneling protocols. Out of the options provided, IPSec (Internet Protocol Security) is the correct answer. IPSec is a suite of protocols for ensuring private, secure communications over IP networks through the use of cryptographic security services. It is not a tunneling protocol on its own, but it is often used to secure L2TP (Layer Two Tunneling Protocol) and other tunneling protocols.
On the other hand, PPTP (Point-to-Point Tunneling Protocol), L2TP, and L2F (Layer 2 Forwarding) are actual tunneling protocols designed to support the creation of VPNs (Virtual Private Networks) by allowing a secure tunnel for transporting packets across an IP network.