One of the following statements about the differences between PPTP and L2TP is NOT true

A.
PPTP can run only on top of IP networks.

B.
PPTP is an encryption protocol and L2TP is not.

C.
L2TP works well with all firewalls and network devices that perform NAT.

D.
L2TP supports AAA servers

Explanation:
L2TP is not compatible with NAT.
Incorrect Answers:
A: PPTP was designed to provide a way to tunnel PPP connections through an IP network.
B: PPTP uses PPP data packets that encrypted using Microsoft Point to Point Encryption (MPPE), while L2TP
on the other hand does not provide any encryption or confidentiality by itself.
D: Radius AAA servers can be configured to use L2TP tunnels.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, pp. 702-703