Which command is used to enable CHAP authentication, with PAP as the fallback method, on a serial interface?
Click on the arrows to vote for the correct answer
A. B. C. D.Explanation
The correct answer is C. Router(config-if)# ppp authentication chap pap.
The Point-to-Point Protocol (PPP) is used to establish a connection between two devices over a serial interface. PPP supports several authentication protocols, including Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).
To enable CHAP authentication with PAP as the fallback method on a serial interface, the "ppp authentication chap pap" command is used. This command specifies that the router should first attempt CHAP authentication. If CHAP authentication fails, the router falls back to PAP authentication.
Option A, "Router(config-if)# ppp authentication chap fallback ppp," is incorrect because it specifies the use of CHAP as the primary authentication method and PAP as the fallback method, which is the opposite of what the question is asking.
Option B, "Router(config-if)# authentication ppp chap fallback ppp," is incorrect because it uses the incorrect command syntax. The correct syntax is "ppp authentication," not "authentication ppp."
Option D, "Router(config-if)# authentication ppp chap pap C," is incorrect because it also uses the incorrect command syntax. Additionally, the "C" at the end of the command is not a valid option or argument.