A technician has deployed a new VPN concentrator. The device needs to authenticate users based on a
backend directory service.
Which of the following services could be run on the VPN concentrator to perform this authentication?

A.
Kerberos

B.
RADIUS

C.
GRE

D.
IPsec

Explanation:
https://security.stackexchange.com/questions/130095/what-is-the-difference-between-a-radius-server-andactive-directory