The document describes the Point-to-Point Protocol (PPP) and its use in establishing serial connections over WAN links. It discusses PPP concepts like its layered architecture, frame structure, session establishment process, and support for multiple network layer protocols. The document also covers configuring PPP encapsulation on serial interfaces, verifying the PPP connection, troubleshooting encapsulation issues, and configuring PPP authentication using PAP and CHAP protocols.

1. Point-to-Point Protocol
(PPP)
Accessing the WAN – Chapter 2
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2. Objectives
 Describe the fundamental concepts of point-to-point serial
communication including TDM, demarcation point, DTE-DCE
functions, HDLC encapsulation, and serial interface
troubleshooting.
 Describe PPP concepts including PPP layered architecture, PPP
frame structure, PPP session establishment, multiprotocol
encapsulation support, link control protocol (LCP), network
control protocol (NCP), and Internet Protocol Control Protocol
(IPCP).
 Configure PPP on a serial interface including enabling PPP
encapsulation, verifying the PPP connection and troubleshooting
encapsulation problems.
 Configure PPP authentication including explaining PAP and
CHAP authentication protocols, configuring PPP authentication
using PAP and CHAP, and troubleshooting PPP authentication
problems.
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3. Fundamental Concepts of Point-to-Point
Serial Communication
 Concept of serial communication as the basis of WAN
technologies – Which is faster?
Two wires to
carry 2 bits
Eight data-
carrying wires
to carry 8 bits –
1 byte
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4. Serial Communication Standards
 Serial connections commonly used – why?
•cost of cable and synchronization
•simpler wiring
•longer than parallel cables
•much less interaction (crosstalk)
 There are three key serial communication
standards
•RS-232 - pc to modem
•V.35 - modem-to-multiplexer - DSU
•HSSI - High-Speed Serial Interface – Token
Ring
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5. RS-232
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6. Fundamental Concepts of Point-to-Point
Serial Communication
 Htwo or more data streams are transported across a
single physical connection using TDM
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7. Fundamental Concepts of Point-to-Point
Serial Communication
 Define the location of the demarcation point relative to
customer and service provider networks
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8. Fundamental Concepts of Point-to-Point
Serial Communication
 Explain the terms DTE and DCE with relative to the
location of devices in a network
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9. Fundamental Concepts of Point-to-Point
Serial Communication
 Describe how high-level data link control (HDLC) uses
one of three frame types to encapsulate data
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10. Fundamental Concepts of Point-to-Point
Serial Communication
 Explain when and how to configure HDLC
encapsulation on a router
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11. Describe the Fundamental Concepts of
Point-to-Point Serial Communication
 Describe the procedure to follow when troubleshooting
a serial connection
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12. Point-to-Point Concepts
 Describe PPP in terms of its use in WAN links
•The link quality
management feature
monitors the quality of
the link. If too many
errors are detected, PPP
takes the link down.
•PPP supports PAP and
CHAP authentication.
This feature is explained
and practiced in a later
section.
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13. Point-to-Point Concepts
 Describe the general function of each layer of PPP
architecture
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14. Point-to-Point Concepts
 Describe the purpose and format of each of the fields in
a PPP frame
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15. Point-to-Point Concepts
 Define the three phases of PPP session establishment
LCP must first open the
connection and negotiate
configuration options.
The LCP tests the link to
determine whether the link
quality is sufficient to bring
up network layer protocols.
NCP can separately
configure the network
layer protocols, and
bring them up and take
them down at any
time.
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16. Point-to-Point Concepts
 Explain the role of the LCP in PPP
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17. Point-to-Point Concepts
 Describe the characteristics of NCP
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18. Configure PPP on a Serial Interface
 Describe how configuration options are communicated
in the LCP frame
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19. Configure PPP on a Serial Interface
 Explain the purpose of the commands used to
configure and verify PPP connections
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20. Configure PPP on a Serial Interface
 Explain the output of the show interfaces serial
command
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21. Configure PPP on a Serial Interface
 Explain the output of the debug ppp command
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22. Configuring PPP with Authentication
 Differentiate between PAP and CHAP
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23. Configuring PPP with Authentication
 Describe how to use PAP to authenticate a PPP
connection
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24. Configuring PPP with Authentication
 Describe how to use CHAP to authenticate a PPP
connection
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25. Configuring PPP with Authentication
 Outline the PPP encapsulation and authentication
process on a flow chart
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26. Configuring PPP with Authentication
 Explain how to configure a PPP connection with
authentication
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27. Configuring PPP with Authentication
 Explain the output of the debug ppp authentication
command
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28. Summary
 PPP is a widely used WAN protocol
 PPP provides multi-protocol LAN to WAN connections
 PPP session establishment – 4 phases
Link establishment
Link quality determination
Network layer protocol configuration negotiation
Link termination
 WAN Encapsulation
–HDLC default encapsulation
–PPP
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29. Summary
 PPP authentication
–PAP
•2 way handshake
–CHAP
•3 way handshake
–Use debug ppp authentication to confirm authentication
configuration
 PPP configuration
–Done on a serial interface
 After PPP configuration, use show interfaces command
to display:
–LCP state
–NCP state
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