Which of the following protocols provides for mutual authentication of the client and server?

A.
Two-factor authentication

B.
Radius

C.
Secure LDAP

D.
Biometrics

Explanation:
C: The LDAP directory service is based on a client-server model. The function of LDAP is to enable access to an existing directory. Because it is a client-server
model it makes provision for mutual authentication between the two parties.
Incorrect Answers:
A: Two-factor authentication refers to an authentication method used to gain access, not a protocol.
B: Remote Authentication Dial-In User Service (RADIUS) is a mechanism that allows authentication of remote and other network connections. You should use
RADIUS when you want to improve network security by implementing a single service to authenticate users who connect remotely to the network.
D: Biometrics is a physical security measure which makes use of some kind of unique biological trait as a means of identification. It is not a protocol.

Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, Sixth Edition, Sybex, Indianapolis, 2014, pp 154, 147, 375.
https://msdn.microsoft.com/en-us/library/aa367008%28v=vs.85%29.aspx