An Internet Service Provider (ISP) has a need to authenticate users connecting using analog modems, Digital
Subscriber Lines (DSL), wireless data services, and Virtual Private Networks (VPN) over a Frame Relay
network.
Which AAA protocol is most likely able to handle this requirement?

A.
RADIUS

B.
DIAMETER

C.
Kerberos

D.
TACACS+

Explanation:
Because of the broad support and the ubiquitous nature of the RADIUS protocol, it is often used by ISPs and
enterprises to manage access to the Internet or internal networks, wireless networks, and integrated e-mail
services. These networks may incorporate modems, DSL, access points, VPNs, network ports, web servers,
etc.
https://en.wikipedia.org/wiki/RADIUS