What type of authentication does the Cisco 3000 Series Concentrator use?

A.
RADIUS

B.
TACACS+

C.
CHAP

D.
PAP

Explanation:
Full support of current and emerging security standards, including RADIUS, NT Domain Authentication, RSA SecurID, and digital certificates, allows for integration of external authentication systems and interoperability with third-party products
Ref:
Cisco VPN 3000 Series Concentrators – Cisco VPN 3000 Series Concentrator Overview