L2F (Layer 2 Forwarding) provides no authentication or encryption. It is a Protocol that supports the creation of secure virtual private dial-up networks over the Internet.
At one point L2F was merged with PPTP to produce L2TP to be used on networks and not only on dial up links. IPSec is now considered the best VPN solution for IP environments.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, Chapter 8: Cryptography (page 507).