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CCNA Semester 4

Chapter 03Chap

ter 03

POINTTO-POINTPOINTTO-POINT

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ObjectivesObjectives

Explain serial communication Identify the demarcation point in a WAN

Describe the functions of the DTE and DCE

Identify the advantages of using PPP

Explain the functions of the Link Control Protocol(LCP) and the Network Control Protocol (NCP)components of PPP

Identify the three phases of a PPP session Explain the difference between PAP and CHAP

List the steps in the PPP authentication process

Configure PPP encapsulation

Configure CHAP and PAP authentication

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Table of ContentTable of Content

1 Serial Point-to-point links

2 PPP Authentication

3 PPP configuration

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SERIAL POINT-TO-POINT LINKSERIAL POINT-TO-POINT LINK

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Introduction To Serial CommunicationIntroduction To Serial Communication

WAN technologies are based on serial

transmission at the physical layerThe signaling methods include Nonreturn to

Zero Level (NRZ-L), High Density Binary 3,(HDB3), and Alternative Mark Inversion (AMI).

011111100110 ..11110 011111100110 ..11110

Transmissionsystem

Transmissionsystem

Physical medium

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Time-division MultiplexingTime-division Multiplexing

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Demarcation PointDemarcation Point

The demarcation point is the point in thenetwork where the responsibility of the service

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DTE-DCEDTE-DCE

The DCE, commonly a modem or CSU/DSU, is thedevice used to convert the user data from the DTEinto a form acceptable to the WAN serviceprovider transmission link.

The DTE-DCE interface for a particular standarddefines the following specifications:

Mechanical/physical Number of pins and connectortype

Electrical Defines voltage levels for 0 and 1

Functional Specifies the functions that are performedby assigning meanings to each of the signaling lines in

Procedural Specifies the sequence of events fortransmitting data

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DTE-DCE (cont.)DTE-DCE (cont.)

The synchronous serial port on a router isconfigured as DTE or DCE depending on the

attached cable

The router end of the shielded serialtransition cable may be a DB-60 connector

The serial end of the smart serial cable is a26-pin connector significantly more compactthan the DB-60 connector.

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HDLC EncapsulationHDLC Encapsulation

HDLC uses synchronous serial transmissionproviding error-free communication betweentwo points.

HDLC defines a Layer 2 framing structure that

allows for flow control and error control usingacknowledgments and a windowing scheme.

Each frame has the same format, whether itis a data frame or a control frame

Standard HDLC does not inherently supportmultiple protocols on a single link

The Cisco HDLC frame allows multiplenetwork layer protocols to share the sameserial link

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Supports only single-protocol environments

HDLC Frame FormatHDLC Frame Format

Uses a proprietary data field to supportmultiprotocol environments

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HDLC Encapsulation (cont.)HDLC Encapsulation (cont.)

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Configuring HDLC EncapsulationConfiguring HDLC Encapsulation

Enter the interface configuration mode of theserial interface.

Then enter the encapsulation hdlccommand to specify the encapsulationprotocol on the interface.

When communicating with a non-Ciscodevice, synchronous PPP is a more viableoption.

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Router(config-if)#encapsulation hdlc

Enables HDLC encapsulation

Uses the default encapsulation on synchronous

serial interfaces

Configuring HDLC EncapsulationConfiguring HDLC Encapsulation

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Troubleshooting A Serial InterfaceTroubleshooting A Serial Interface

show interfaces serial

Serial x is down, line protocol is down

Serial x is up, line protocol is down Serial x is up, line protocol is up (looped)

Serial x is up, line protocol is down (disabled)

Serial x is administratively down, line protocol is

down

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Troubleshooting A Serial InterfaceTroubleshooting A Serial Interface

show controllers

debug serial interface debug frame-relay lmi

debug frame-relay events

debug ppp negotiation

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PPP AUTHENTICATION

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PPP Layered ArchitecturePPP Layered Architecture

PPP uses a layered architecture. A layeredarchitecture is a logical model, design, or blueprintthat aids in communication betweeninterconnecting layers.

PPP provides a method for encapsulating multi-protocol datagrams over a point-to-point link, anduses the data link layer for testing the connection.

PPP is made up of two sub-protocols: Link Control Protocol Used for establishing thepoint-to-point link.

Network Control Protocol Used for configuring thevarious network layer protocols.

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PPP can carry packets from several protocol suitesusing NCP.

PPP controls the setup of several link options using LCP.

PPP Layered ArchitecturePPP Layered Architecture

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PPP Layered Architecture (Cont.)PPP Layered Architecture (Cont.)

- Asynchronous serial- Synchronous serial- High-Speed Serial Interface (HSSI)

- Integrated Services Digital Network (ISDN)

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Authentication Compression Error detection

Multilink PPP Callback

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For every network layer protocol used, aseparateNetwork Control Protocol (NCP) is provided.

NCP includes functional fields containing

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Flag Indicates the beginning or end of aframe

and consists of the binary sequence01111110.

Address Consists of the standard broadcast

address, which is the binary sequence11111111.

Control 1 byte that consists of the binarysequence 00000011,

Protocol 2 bytes that identify the protocol

encapsulated in the data field of the frame. Data 0 or more b tes

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PPP LCP Configuration OptionsPPP LCP Configuration Options

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PPP Session EstablishmentPPP Session Establishment

Two PPP authentication protocols:PAP and CHAP

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Establishing A PPP SessionEstablishing A PPP Session

Link-establishment frames are used to

establish and configure a link. Link-termination frames are used to

terminate a link.

Link-maintenance frames are used to manageand debug a link.

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Establishing A PPP Session: Link-establishment phaseEstablishing A PPP Session: Link-establishment phase

In this phase each PPP device sends LCP framesto configure and test the data link.

LCP frames contain a configuration option fieldthat allows devices to negotiate the use ofoptions such as

maximum transmission unit (MTU),

compression of certain PPP fields,

link-authentication protocol.

If a configuration option is not included in an LCPpacket, the default value for that configurationoption is assumed

This phase is complete when a configurationacknowledgment frame has been sent andreceived.

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Establishing A PPP Session:Establishing A PPP Session: Authentication phaseAuthentication phase

Authentication phase (optional) Afterthe link has been established and theauthentication protocol decided on, the peermay be authenticated.

Authentication, if used, takes place before thenetwork layer protocol phase is entered.

LCP also allows for an optional link-quality

determination test.

The link is tested to determine whether thelink quality is good enough to bring up

network layer protocols

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Establishing A PPP Session:Network layer phaseEstablishing A PPP Session:Network layer phase

In this phase the PPP devices send NCPpackets to choose and configure one or morenetwork layer protocols, such as IP.

Once each of the chosen network layerprotocols has been configured, packets fromeach network layer protocol can be sent over

the linkThe show interfaces command reveals the

LCP and NCP states under PPP configuration

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Passwords sent in clear text

Peer in control of attempts

PPP Authentication ProtocolsPPP Authentication Protocols

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Hash values, not actual passwords, are sent acrosslink.

The local router or external server is in control ofattempts.

Challenge Handshake Authentication ProtocolChallenge Handshake Authentication Protocol

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PPP Authentication Protocols:CHAP OperationPPP Authentication Protocols:CHAP Operation

Sydney Hongkong

Challenge

01IDRandomSydneyUsername PasswordSysney cisco

Melbourne sanhinoon

MD5

Hash #

Response

02IDHash#Hongkong

Username PasswordHongkong cisco

Melbourne sanhinoon

MD5

Hash #

Is Equal?

03IDAck/NackSydney

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PPP Encapsulation And Authentication ProcessPPP Encapsulation And Authentication Process

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CONFIGURING PPP

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Configuring PPPConfiguring PPP

Enable PPP

Router(config)#interface serial 0/0Router(config-if)#encapsulation ppp

To configure compression over PPP, enter the followingcommands:

Router(config-if)#compress [predictor | stac]

Enter the following to monitor the data dropped on thelink, and avoid frame looping:

Router(config-if)#ppp qualitypercentage

The following commands perform load balancing acrossmultiple links:

Router(config-if)#ppp multilink

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Configuring PPP authenticationConfiguring PPP authentication

Step 1: Define username and password to expectfrom remote router

Router(config)#username remote password secret

Secret must be the same at both ends

Step 2: Enable PPP Router(config-if) encapsulation ppp

Step 3: Configure authentication

Router(config-if) Ppp authentication { pap|chap|pap-

chap|chap-pap}

Step 4: if IOS 11.1 or later, PAP must be enableon interface

Router(config-if)ppppap sent-username user

passwordpass

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Configuring PPP and AuthenticationConfiguring PPP and Authentication

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Configuring PPP authentication - PAPConfiguring PPP authentication - PAP

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Configuring PPP authentication - CHAPConfiguring PPP authentication - CHAP

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Verifying The Serial PPP Encapsulation ConfigurationVerifying The Serial PPP Encapsulation Configuration

Houston#sh int serial 1/0:1

Serial1/0:1 is up, line protocol is up

Hardware is DSX1

Internet address is 10.10.10.3/24

MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation PPP, loopback not setKeepalive set (10 sec)

LCP Open

Open: IPCP, CDPCP

Last input 00:00:09, output 00:53:17, output hang never

Last clearing of "show interface" counters 01:09:05Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 164

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/1/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)--More--

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Troubleshooting The Serial Encapsulation ConfigurationTroubleshooting The Serial Encapsulation Configuration

right#debug ppp negotiation00:02:28: %LINK-3-UPDOWN: Interface Serial0/0, changed state to

up

00:02:28: Se0/0 PPP: Using default call direction

right(config-i8: Se0/0 PPP: Phase is AUTHENTICATING, by both [0sess, 0 load]

00:02:28: Se0/0 CHAP: O CHALLENGE id 14 len 26 from "right"

00:02:28: Se0/0 CHAP: I CHALLENGE id 17 len 25 from "left"

00:02:28: Se0/0 CHAP: O RESPONSE id 17 len 26 from "right"

00:02:28: Se0/0 CHAP: I RESPONSE id 14 len 25 from "left"

00:02:28: Se0/0 CHAP: O SUCCESS id 14 len 4

00:02:28: Se0/0 CHAP: I SUCCESS id 17 len 4

leftright

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SummarySummary

Explain serial communication Identify the demarcation point in a WAN

Describe the functions of the DTE and DCE

Identify the advantages of using PPP

Explain the functions of the Link Control Protocol(LCP) and the Network Control Protocol (NCP)components of PPP

Identify the three phases of a PPP session

Explain the difference between PAP and CHAP

List the steps in the PPP authentication process

Configure PPP encapsulation

Configure CHAP and PAP authentication

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