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Foundation Summary 317
Table 9-8 lists the important comparison points between HDLC and PPP.
Table 9-8 |
Point-to-Point Data-Link Protocol Attributes |
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Architected Type |
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Protocol |
Error Correction |
Field |
Other Attributes |
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HDLC |
No |
No |
HDLC serves as Cisco’s default on |
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serial links. Cisco uses a Proprietary |
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Type field to support multiprotocol |
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traffic. Supports synchronous links |
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only. |
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PPP |
Supported but not |
Yes |
PPP was meant for multiprotocol |
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enabled by default |
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interoperability from its inception, |
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unlike HDLC. PPP also supports |
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asynchronous communication. |
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Figure 9-6 outlines the different PAP and CHAP flows.
Figure 9-6 PAP and CHAP Messages
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PAP |
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Waiting |
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Dialing |
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for Dial |
I Am Barney |
Router |
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Password = Betty |
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Fred |
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Ack. |
Barney |
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CHAP |
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Waiting |
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Challenge! |
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Dialing |
for Dial |
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Router |
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I Am #$%#$@ |
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Fred |
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Barney |
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Accepted |
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318 Chapter 9: Point-to-Point Leased Line Implementation
Q&A
As mentioned in the Introduction, you have two choices for review questions. The following questions give you a bigger challenge than the exam because they are open-ended. By reviewing with this more-difficult question format, you can exercise your memory better and prove your conceptual and factual knowledge of the topics covered in this chapter. The answers to these questions are found in Appendix A.
For more practice with exam-like question formats, including multiple-choice questions and those using a router simulator, use the exam engine on the CD.
1.Define the terms DCE and DTE in the context of the physical layer and a point-to-point serial link.
2.Identify the command used to set the clock rate on an interface in which a DCE cable has been inserted. Compare and contrast the two styles of the command that may be entered in configuration mode versus which style shows up in the configuration.
3.Name one WAN data-link protocol used on point-to-point leased lines that defines a method of announcing the interface’s IP addresses to other devices attached to the WAN.
4.Can PPP dynamically assign IP addresses? If so, is this feature always enabled?
5.Create a configuration to enable PPP on serial 0 for IP. Make up IP Layer 3 addresses as needed.
6.Define the terms PAP and CHAP. Which one sends passwords in clear-text format?
7.CHAP configuration uses names and passwords. Given Routers A and B, describe what names and passwords must match in the respective CHAP configurations.
8.What field has Cisco added to the HDLC header, making it proprietary?
9.List the types of packet switching mentioned in this chapter. Identify the one for which all traffic is segmented into smaller pieces.
10.Two-wire leased circuits are seldom used today, and certainly not between two routers. What problem was solved with the advent of four-wire leased circuits versus two-wire?
11.Define “synchronous” in relation to leased lines.
12.Create a CHAP configuration between two routers. Make up specific details as needed.
This chapter covers the following subjects:
■ISDN Protocols and Design
■ISDN Configuration and Dial-on- Demand Routing