In a network that requires multilayer switches to use authentication via RADIUS/TACACS+, which of the
following access control models will the switches need to utilize?

A.
802.1q

B.
802.3af

C.
PKI

D.
802.1x

Explanation:
http://www.cisco.com/c/en/us/td/docs/ios/12_4t/12_4t11/ht_8021x.html#wp1258507