Practice Quiz

Advanced Networking Administrator Test Prep

Category - CCNA

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The following shows the configuration files for routers A and B:

hostname A hostname B
! !
Username B password king username A password king
! !
interface serial 0 interface serial 0
ip address 14.4.4.8 255.255.0.0 ip address 12.3.6.3 255.255.0.0
encapsulation ppp encapsulation ppp
clockrate 56000 ppp authentication chap

In this situation, if you enter the “show interface serial 0” command on router A, which of the following will be displayed?
  1. Serial 0 is down, line protocol is down
  2. Open: IPCP, CDPCP
  3. Serial 0 is up, line protocol is up
  4. LCP closed
Explanation
Answer: C - The router A console shows that the Serial 0 is up and line protocol is up, too.

Key Takeaway: The possible cause of this message is that a loop exists in the circuit. The sequence number in the keep-alive packet changes to a random number when a loop is first detected. If the same random number is returned over the line, a loop exists. To fix this, you should check to see whether the DSU/CSU is configured in manual loopback mode and disable it. You can also try reseating the DSU/CSU.
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