Exploration Accessing WAN Chapter2 Enhan

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2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE I Chapter 6 1

Point-to-Point Protocol

(PPP)

Accessing the WAN Chapter 2


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2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE 1 Chapter 6 2

Point-to-Point Protocol (PPP)

PPP connections are used to connect LANs to service

providers or to connect LAN segments within anetwork.

Provides connectionacross protocols(TCP/IP, IPX,

AppleTalk).

Works over copper,fiber, or satellite.

Works through ATM,

Frame Relay, or ISDN. Uses Password Authentication Protocol (PAP) or ChallengeHandshake Authentication Protocol (CHAP) for security.


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How Does Serial Communications Work?

Serial sends data 1 bit at a time & Parallel sends data

over multiple wires simultaneously.Parallel may be faster but factors like clock skew (bits dont

arrive at same time) & interference (crosstalk across wirescauses dropped bits) make parallel communications impracticalacross long distances.


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Serial Communication Standards

All long-haul communications & most networks useserial connections.

RS-232 (serialport on a PC)

V.35: Used bymost routers/DSUs toconnect to T1carriers.

HSSI: ConnectLANs to WANsover high speed(T3 lines).


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Time-Division Multiplexing (TDM)

TDM is a signaling method that divides the bandwidth

of a single link into separate channels.

TDM shares available transmission time on a mediumby assigning timeslots to users.

Multiplexer (MUX) combines 3 data streams into single stream

of a never ending pattern. Examples of Synchronous TDM are T1 & ISDN.


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Statistical Time Division Multiplexing (STDM)

This form of TDM overcomes the inefficiency caused by

empty time slots.

STDM uses a variable time slot, allowing channels tocompete for any free slot space.


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Demarcation Point

The demarcation point is the point in the network where

the responsibility of the service provider ends. This figure shows the difference between the U.S. and

the International community.

Customer Premises Equipment (CPE)

CPE



Data Terminal Equipment (DTE) & DataCommunications Equipment (DCE)

DTE refers to the devices at the user end & serves as adata source or destination.

DCE provides the physical connection to the network.

It provides the clocking signal for synchronize data

transmission.

We use the Smart Serial Connector in this class (p. 70).

When you make a serial connection between2 routers, you must set 1 to DCE & 1 to DTE!



Layer 2 WAN Encapsulation Protocols

The choice of protocol depends on the WAN technology

and the communicating equipment.

Examples of common WAN protocols and where theyare used areshown

in thefigure.



High-Level Data Link Control (HDLC)

HDLC is the default encapsulation type point-to-point connections, dedicated links, & circuit-switched connections between Cisco devices.

HDLC uses synchronous serial transmission to

provide error-free communication between two points. HDLC defines a Layer 2 framing structure that allows

for flow control and error control through the use ofacknowledgments.



Configuring HDLC Encapsulation

This is a tough one (want to see it again?).



Troubleshooting Serial Interfaces

Show interfaces serial command returns 6 possible

states (1st part is serial/2nd part is line protocol):UP/UP. Everything o.k.

DOWN/DOWN. Cable or hardware failure.

UP/DOWN. Timing problem (DCE/DTE) or router

failed/misconfigured.UP/UP (looped). Loop exists in the circuit.

UP/DOWN (disabled). High error rate, CSU or DSU hardwareproblem, or router hardware bad.

Administratively DOWN/DOWN. Interface is shutdown or

duplicate IP address exists.

For the full list, see p. 77-81



Point-to-Point (PPP)

When you need to connect to a non-Cisco router, you

should use PPP encapsulation.PPP encapsulates data frames for transmission over Layer 2

physical links.

PPP contains 3 main components:

HDLC protocol for encapsulating datagrams over point-to-pointlinks.

Extensible Link Control Protocol (LCP) to establish,configure, and test the data link connection.

Family of Network Control

Protocols (NCPs) forestablishing and configuringdifferent Network layerprotocols.



PPP Layered Architecture: Physical Layer

At this layer, PPP can be configured for a range of

interfaces:Asynchronous serial. Voice/video/data conveyed in fix length

cells.

Synchronous serial. Bit oriented, full duplex.

High-Speed Serial Interface (HSSI).ISDN. Offered by telephone companies.



PPP Frame Structure

A PPP frame has 6 fields:

Flag. Indicates the beginning or end of a frame.

Address. Standard broadcast address.

Control. In PPP this field is set to 0xFF (broadcast).

Protocol. Identifies encapsulated protocol.

Data. Max is 1500 bytes.

Frame Check Sequence (FCS). Error detection.



Establishing a PPP Session Using LCP

Link Control Protocol (LCP) does the talking.



LCP Link Negotiation Process

See the process flowchart detailing the negotiationprocess.



Internet Protocol Control Protocol (IPCP)

IPCP is a network control protocol for establishing and

configuring IP over a PPP link.After LCP establishes the link, IPCP (red) negotiates 2

options: 1) Compression. 2) IP address for PPP routing.



PPP Configuration Commands

Examples ofCompress (slows performance) & Quality(checks link if suitable for Layer 3 protocols) commands.



Verifying Serial PPP Encapsulation

Use show interfaces to verify proper configuration.

Use debug command to troubleshoot in real-time.

Remember to use the undebug command because debugconsumes lots of device resources.

Youll get lots of practice on these commands in thisweeks lab.



Debug PPP

The table explains the debug PPP command

parameters. See p. 104-7 for printout examples.



PPP Authentication Protocols

Youll get some PAP/CHAP questions on the CCNA

exam. Know that CHAP (3-way exchange of a shared secret,

Message Digest 5) is more secure than PAP (sends passwordin plain text).

Router R3 initiates a 3-way handshake & sends a challenge message to router R1.



PPP Encapsulation & Authentication Process

Visual example of the logic decisions that PPP makes.

See p. 113-115 for PPP authentication steps.


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Configuring PPP with Authentication

The PPP Authentication command specifies the order

in which the CHAP or PAP protocols are requested onthe interface (you can specify CHAP or PAP or both).

Note: AAA/TACACS is a dedicated server used to authenticate users.AAA stands for "authentication, authorization and accounting.


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Troubleshooting PPP with Authentication

The following is an interpretation of the output:

Line 1. The router is unable to authenticate on interface Serial0because the peer did not send a name.

Line 2. The router was unable to validate the CHAP responsebecause USERNAME 'pioneer' was not found.

Line 3. No password was found for 'pioneer'. Other possibleresponses at this line might have been no name received toauthenticate, unknown name, no secret for given name, shortMD5 response received, or MD5 compare failed.


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Other commands

Interface s0/0/0

Encapsulation ppp

PPP multilink

Hostname Jmac-Router

Username Freak password cisco

Int S0/0/0Encap PPP

Ppp authentication CHAP


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Exploration Accessing WAN Chapter2 Enhan

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