Exploration_Accessing_WAN_Chapter2

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© 2006 Cisco Sy stems, Inc. All rights reserv ed.

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ITE I Chapter 6

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Point
-
to
-
Point Protocol
(PPP)

Accessing the WAN



Chapter 2

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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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2.1 Serial Point to Point links

Accessing the WAN



Chapter 2

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Serial and Parallel communications.

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Time Division Multiplexing

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TDM Examples


SONET (SDH)

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Demarcation Point


Demarcation point defines the end of customer and
start of service provider network.


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DTE and DCE

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Parallel to Serial Conversion

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HLDC Frame Format

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WAN Encapsulation Protocols

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Configuring HDLC Encapsulation

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Troubleshooting a serial connection

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2.2 Introducing PPP

Accessing the WAN



Chapter 2

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Point
-
to
-
Point Concepts


HDLC

protocol for encapsulating
datagrams over point
-
to
-
point links.



Extensible
Link Control Protocol

(LCP) to establish, configure, and test the
data link connection.


Family of
Network Control Protocols

(NCPs) for establishing and configuring
different network layer protocols.

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PPP architecture

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PPP architecture

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PPP architecture

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PPP Frame Structure

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Three phases of PPP session establishment


Phase 1:


Link establishment and configuration negotiation




Before PPP exchanges any network layer datagrams
(for example, IP), the LCP must first open the
connection and negotiate configuration options.


This phase is complete when the receiving router sends
a configuration
-
acknowledgment frame back to the
router initiating the connection.

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Three phases of PPP session establishment


Phase 2:


Link quality determination (optional)




The LCP tests the link to determine whether the link
quality is sufficient to bring up network layer protocols.
The LCP can delay transmission of network layer
protocol information until this phase is complete.

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Three phases of PPP session establishment


Phase 3:


Network layer protocol configuration negotiation




After the LCP has finished the link quality determination
phase, the appropriate NCP can separately configure
the network layer protocols, and bring them up and take
them down at any time.


If the LCP closes the link, it informs the network layer
protocols so that they can take appropriate action.

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Three phases of PPP session establishment

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LCP Operation

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NCP Operation

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PPP Configuration Options

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2.3 Configuring PPP

Accessing the WAN



Chapter 2

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Configure PPP on a Serial Interface

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Verifying and Troubleshooting

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Configure PPP on a Serial Interface


Explain the output of the debug ppp command

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2.4 PPP Authentication Protocols

Accessing the WAN



Chapter 2

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PAP and CHAP

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PAP

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CHAP

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Authentication process

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Configuring PPP with Authentication

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PAP example

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CHAP example

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Explain the output of the debug ppp authentication
command

Debuging ppp authentication

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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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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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