Refer to the exhibit. Routers R1 and R2 have been configured with PPP. CHAP authentication is configured, but for some reason communication cannot be established between them.

The command: "debug ppp authentication" is executed on router R1. What is most likely to be the issue?

R2 is configured with PAP authentication.

R1 is using a different authentication algorithm.

The serial interface on R2 is administratively down.

There is an encapsulation mismatch.

There is no username with matching password.

Explanation

For CHAP authentication to happen on both sides, a local username with matching passwords must configured on both side. The output of the command "debug ppp authentication" shows one line "using hostname from unknown source" and means that there is not known name, hostname or username and no password is set. For more information refer to: http://www.ciscopress.com/articles/article.asp?p=2202412&seqNum=7 /- - - - - - - - - - - - - - - - - - - - - I can't verify this answer through the source given, but figured it out logically, which is something you'll have to do on Cisco exams from time to time/ - - - (1)Neither interface is down, and there is no encapsulation mismatch, otherwise, we wouldn't be getting any output at all/- - - - - - (2) In the debug lines it goes {Timestamp} {INT Se1/0} {CHAP / PPP} {Direction: I=inbound, O=outbound}; we have "CHAP lines inbound and going outbound from "us", so R1 isn't using a different algorithm,/ - - - - - (3) The messages indicate that the 2 routers are attempting to perform CHAP authentication, but it's not working, it's stuck in a loop, where the "CHALLENGE" -and- "RESPONSE" "id"numbers just keep incrementing, the actual messages you might see will probably vary by system & IOS version, but you should see something on the order of: "SUCCESS", but the "hostname from unknown source" is definitely a problem.