Which of the following remote access authentication systems is the MOST robust?

A.
TACACS+

B.
RADIUS

C.
PAP

D.
TACACS

Explanation:
TACACS+ is more secure compared to TACACS, RADIUS, and PAP.
Incorrect Answers:
B: TACACS+ encrypts all of this data between the client and server and thus does not have the vulnerabilities
inherent in the RADIUS protocol.
C: PAP transmits unencrypted ASCII passwords over the network and is therefore considered insecure.
D: TACACS uses fixed passwords for authentication, while TACACS+ allows users to employ dynamic (onetime) passwords, which provides more protection. TACACS+ is XTACACS with extended two-factor user
authentication.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, New York, 2013, p. 234