Which command is used to enable CHAP authentication whit PAP as the fallback method on a serial interface?
A.
(config-if)# authentication ppp chap fallback ppp
B.
(config-if)# authentication ppp chap pap
C.
(config-if)# ppp authentication chap pap
D.
(config-if)# ppp authentication chap fallback ppp
Explanation
Router(config-if)#ppp authentication chap pap
Defines that the link will use CHAP authentication, but will try PAP if CHAP fails or is rejected by other side.