CCNA And CCENT Cisco Certification Exam Training Questions:
10 Questions On HDLC, PPP, And Point-To-Point Connections
By Chris Bryant, CCIE #12933
With point-to-point WAN links, we have two options for encapsulation - the High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP). They're both used every day in production networks, and you'll no doubt see questions concerning both on your CCNA and CCENT exams!
To help you pass the CCNA and CCENT exams and be prepared for real-world success, here are 10 free Cisco certification exam training questions dealing with these protocols and directly connected Serial interfaces.
Answers are on the bottom of the page. Enjoy, and no peeking!
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1. Identify the correct statements regarding HDLC and PPP running on a point-to-point connection.
A. If HDLC is running on one end, HDLC must be running on the other end as well.
B. If HDLC is running on one end, the other end can run HDLC or PPP.
C. If PPP is running on one end, PPP must be running on the other end as well.
D. If PPP is running on one end, the other end can run HDLC or PPP.
2. If a point-to-point connection is physically fine but there is a timer or encapsulation mismatch issue, which of the following will appear in the output of show interface serial?
A. Serial0 is up, line protocol is up
B. Serial0 is up, line protocol is down
C. Serial0 is down, line protocol is up
D. Serial0 is down, line protocol is down
3. Which of the following cannot appear in the output of show interface serial?
A. Serial0 is up, line protocol is up
B. Serial0 is up, line protocol is down
C. Serial0 is down, line protocol is up
D. Serial0 is down, line protocol is down
4. Which of the following is offered by PPP but not by HDLC?
A. PAP
B. multilink capabilities
C. dialer callback
D. CHAP
5. Name both debug commands that could produce the following output.
2d04h: Se1 CHAP: O CHALLENGE id 82 len 23 from "R3"
2d04h: Se1 CHAP: I CHALLENGE id 222 len 23 from "R1"
2d04h: Se1 CHAP: O RESPONSE id 222 len 23 from "R3"
2d04h: Se1 CHAP: I RESPONSE id 82 len 23 from "R1"
2d04h: Se1 CHAP: O SUCCESS id 82 len 4
2d04h: Se1 CHAP: I SUCCESS id 222 len 4
6. What is the net result of the following command?
R3(config-if)#ppp authentication chap pap
A. CHAP authentication will be attempted before PAP.
B. CHAP and PAP authentication attempts will be made at the same time.
C. If the CHAP authentication attempt results in a failed authentication, a PAP attempt will be made.
D. If the remote router isn't running CHAP, a PAP authentication attempt will be made.
E. The password for CHAP authentication has been set to "pap".
7. What protocol is sometimes referred to as the manager of a PPP connection?
8. PPP allows you to select one of two compression techniques. What are they?
9. Identify the true statements.
A. PAP sends a clear-text password across the WAN.
B. PAP sends a hash result across the WAN rather than a password.
C. CHAP sends a clear-text password across the WAN.
D. CHAP sends a hash result across the WAN rather than a password.
10. What is the default encapsulation for a Cisco router serial interface?
Answers are at the bottom of this page. In the meantime...
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Here are the answers....
1. (A, C) Whether you're running PPP or HDLC, the encapsulation type must match on both ends of the point-to-point connection.
2. (B) If the connection is physically fine, we'd expect to see Serial0 is up. A timing issue such as a missing clockrate command or a PPP / HDLC mismatch would result in a line protocol is down message.
3. (C) If the interface is physically down, the line protocol cannot be up.
4. (A,B,C,D). PPP has the capability to run PAP and CHAP, can be configured to run PPP Multilink, and PPP does have dialer callback capability. HDLC offers none of these.
5. You would see that output in both the debug ppp negotiation and debug ppp authentication commands. The debug ppp negotiation command will give you much more output, so if you're just beginning troubleshooting on a PPP connection, run debug ppp authentication first - you'll see immediately if there's a problem with the passwords.
6. When you list multiple ppp authentication methods, the methods are tried in the order in which they're listed from left to right. If the remote router isn't running that particular method, the next method is tried. However, if the remote router is running that first method and authentication fails, the second method is not used.
7. The Link Control Protocol (LCP) is the "manager" of PPP connections. PPP gets all the glory, LCP does all the work!
8. PPP allows you to configure stacker or predictor.
9. (A, D). PAP sends the password in clear text, making it easy for anyone intercepting the packets during transmission to read the pw. CHAP runs a hash algorithm against the password, and it's that hash value that is actually sent across the wire.
10. The default encapsulation for a Cisco router Serial interface is HDLC.
Look for other CCNA, CCENT, and CCNP certification question sets coming soon, along with Network+ and Server 2008 questions coming in July and August. You'll find new sets on the Cisco Tutorials page, and they'll also be announced in my Cisco certification blog and in my newsletter as well.
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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