Which of the following protocols works at the LOWEST layer of the OSI model?

A.
L2TP

B.
PPTP

C.
ISAKMP

D.
IPSec

Explanation:
Layer Two Tunneling Protocol (L2TP) is an extension of the Point-to-Point
Tunneling Protocol (PPTP) used by an Internet service provider (ISP) to enable the operation of a
virtual private network (VPN) over the Internet.