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Establishing Serial Point-to-PointConnection

Chapter 9

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Chapter 9 2

Chapter Objectives

Explain wide area network Explain data-link protocols of point-to-point

leased linesExplain HDLC Explain PPP

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Chapter 9 3

Recall - IA CL are the statements, which are grouped together by using a name or number A CLs supports the following types:

Standard A CLExtended A CL

You can use the access-list command to create anA CL. The syntax to create an A CL is:

access-listA

CL_# permit|deny conditions

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Chapter 9 4

Recall - II

W ildcard masks can be used for matching a rangeof IP addresses in A CL, instead of manuallyentering itA wildcard is similar to an inverted subnet maskthe extended A CL filters the source and destinationIP address, IP protocols such as IP, TCP, UDP ,ICMP etc. and protocol information such as portnumbers or message types

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Chapter 9 5

Wide Area Network

The terms and components of WAN are:Data Communications Equipment (DCE)Data Terminal Equipment (DTE)

Customer Premises Equipment (CPE)Demarcation pointToll networkCentral Office (CO) switchLocal loop

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Chapter 9 6

Wide Area Network (WAN)

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Chapter 9 7

Types of WAN

WAN s are available in four types, based on thedistance covered and the equipment usedThe four types of WAN are:

Leased-Lines ConnectionCircuit-Switched ConnectionPacket-Switched ConnectionsCell-Switched Connections

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Chapter 9 8

Selecting WAN

W hile connecting a L AN to a WAN , you should beaware of the connection requirementsSome of the major factors that help to select a WANare:

FrequencyTransfer ratesTraffic load

Cost

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Chapter 9 9

Data-Link Protocols

Data-link layer protocols are commonly called thedata link protocolsThese protocols communicate between two devicessuch as, routers, and bridgesData packets are sent over the link created by theprotocolsData-link protocols consist of:

High Level Data Link Control (HDLC) protocolPoint-to-Point protocol (PPP)

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Chapter 9 10

HDLC Frames

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Chapter 9 11

HDLC Frame Fields

Field Name Description

Flag Contains a single byte which indicatesthe beginning or end of a frame

A ddress Contains the broadcast address whichis a binary sequence

Control Contains a single byte of binarysequence. This calls for transmissionof user data in a non-sequence frame

Proprietary Contains information about the way tocarry multiple protocols on a single link

Data Contains encapsulated data. Therange if this field is variable

FCS Contains 2 to 4 bytes. Improves error detection

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Chapter 9 12

Types of HDLC Frames

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Chapter 9 13

Configuring HDLC

The encapsulation on a Cisco synchronous serialinterface is HDLCHDLC needs to be configured if the data linkprotocol is change to some other protocol, andHDLC has to be set back to defaultTo configure the HDLC protocol to be set as default,use the router CLI

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Chapter 9 14

Output of HDLC Verification

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Chapter 9 15

PPP

The PPP allows computers to connect to theInternet using a dial-up telephone line and ISD N

PPP was originally designed to transport IP trafficover point-to-point linksPPP can transfer data over synchronous andasynchronous linksIt supports a transfer of data over different network

protocols

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Chapter 9 16

PPP Frame

The frame format of PPP is similar to the HDLCFrameThe only difference is that, PPP includes a ProtocolfieldThe PPP frame is made up of six fields as shown inFigure

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Chapter 9 17

PPP Stack

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Chapter 9 18

Link Control Protocol (LCP)

The PPP Link Control Protocol can establish,configure, maintain and terminate point-to-pointconnection between the devicesLCP uses following three classes of frames for establishing, configuring, maintaining andterminating connection between the devices:

Link Configuration frames

Link Maintenance framesLink Termination frames

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Chapter 9 19

Communication Between Devices

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Chapter 9 21

PPP Session Establishment

Point-to-Point protocol is used to transmit datapackets over serial point-to-point linksThe three phases of session establishment aregiven as follows:

Link establishment phaseA uthentication phaseN etwork layer protocol phase

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Chapter 9 22

PPP Authentication - I

Point-to-Point protocol supports authentication of devicesOnce a link is established between nodes theprocess of authentication startsPPP supports two authentication protocolsPassword A uthentication Protocol (P A P) andChallenge Handshake A uthentication Protocol(CH A P)

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Chapter 9 23

PPP Authentication - II

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Chapter 9 24

CHAP Authentication

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Chapter 9 25

Configuring PPP

Cisco allows you to configure the PPP to be used onWAN interfaceYou can configure the PPP using encapsulation andinterface commands in the configuration modeThe syntax of the command to configure PPP is:encapsulation ppp

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Chapter 9 26

Configuring PPP Authentication

Once the serial interface is configured to support thePPP encapsulation, you must configure PPPauthentication on the routersBefore authentication process, it is required to set ahostname for the router if not already assignedA lso, you must set username and password for theremote router to which the router is connectedA fter the hostname, username and password is set ,select the appropriate authentication for the router such as P A P or CH A P

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Chapter 9 27

Verifying PPP Encapsulation

PPP does not begin authentication until the LinkControl Protocol (LCP) process is completed andopenPPP authentication needs to be set up on both endsfor the authentication process to workUsing commands, such as show and debug you cansolve problems for PPP

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Chapter 9 28

Mismatched WAN Encapsulations

R outers can communicate in a network only if their encapsulation methods are sameIf you connect two routers in the network usingpoint-to-point link but the encapsulation methods aredifferent on each router, the connection between therouters is not establishedIn this case, if one router sends request to the other,it will never receive a response from that router

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Chapter 9 29

Mismatched IP Addresses

R outers configured with same WAN encapsulationmethod such as PPP, HDLC or Frame R elayconnected in different subnets will have connectionestablished between themHowever, the data packets do not transfer betweenthe routers. It becomes very difficult to identify thisproblem, as the link appears to be functioningproperlyTo resolve the problem, you can use the showrunning-config and show interface command oneach router

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Chapter 9 30

Case Study

The Blue Diamond steel company, Gujarat branch hasall Cisco routers connected in the network. The router of the Business Development department isdamaged. The computers in this department cannotexchange data with the other departments in thenetwork. The network administrator R obert replacesthe damaged router with a new non-Cisco router.

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Chapter 9 31

Problem

The Business Development department still cannot

have transaction with the other departments

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Chapter 9 32

Suggested Solution

Cisco routers by default use HDLC as the serialencapsulation method on Cisco serial links. If youconnect a non-Cisco router to a Cisco router in thenetwork, data transfer does not occur between them.To enable communication between the routers,implement the Point-to-Point encapsulation method.You must configure PPP on all the serial interfaces of both the routers

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Chapter 9 33

Comparing HDLC and PPP - I

H DLC PPP

Fails to provide a method of detectingerrors

Uses FCS to detect errors whiletransmitting data

Consist of two types; ISO HDLC andCisco HDLC

Based on ISO's HDLC frame format

Supports synchronous andasynchronous links

Supports synchronous, asynchronous,High-Speed Serial Interface (HSSI),and ISD N links

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Chapter 9 34

Comparing HDLC and PPP - II

Used to perform encapsulation of datawithout using other encapsulationprotocols

Used to transfer data. PPP cannotencapsulate data without the help of other encapsulation protocols, suchas, HDLC and Synchronous Data LinkControl (SDLC)

Fails to provide authenticationbetween two nodes or devices

Provides authentication usingprotocols, such as, PPP A uthenticationProtocol (P A P), and ChallengeHandshake A uthentication Protocol

(CH A P)

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Chapter 9 35

Comparing HDLC and PPP - III

Provides a frame format that containsa proprietary field. The other six fieldsare similar to the PPP frame field.N ote, the ISO HDLC frame containsonly six fields, as the proprietary fieldis not present

Provides a frame format that containsa protocol field. The other six fields aresimilar to the HDLC frame field

Fails to check for quality of a linkestablished

Uses Link Control Protocol (LCP) tothe check for quality of an establishedlink

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Chapter 9 36

Summary - I

WAN is a network that spans a large geographicalareaLeased lines are a transmission line, which is provided

by telephone companies to a particular customer Frequency, usage, traffic and cost are factors thatneed to considered when selecting a WAN connectionData-Link layer protocols are commonly called thedata link protocols, which communicate between twodevices

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Chapter 9 37

Summary - II

Configuring HDLC only needs to be done only if the datalink protocol is change to some other protocolThe two types of HDLC:

ISO HDLCCisco HDLCThe Cisco HDLC contains proprietary field, whichdefines carrying a multiple protocols across a link

PPP enables computers to connect to the internet usinga dial-up telephone line and ISD N

Configuring the PPP is to specify that PPP is to be usedon the WAN

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Chapter 9 38

Summary - III

Features of PPP are:A uthenticationLink testError-detection

CompressionComponents of PPP are:

HDLCLCP

N CPsA uthentication protocols supported by PPP are:

P A PCH A P

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Chapter 9 39

Summary - IV

By default the authentication is not mandatory butmust be specified toP A P is a insecure protocol because the username

and password is sent in plain textUsing CH A P protocol the server sends challengemessages to the node. The node calculates andsends the results back to the server