Ppt in Chapter 16

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Troubleshooting WAN

Implementation Issues

Chapter 16


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Chapter Objectives

At the end of this Chapter you will be able to:Configure and verify a PPP connection between Cisco routersConfigure and verify Frame Relay on Cisco routers


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High-Level Data-Link Control (HDLC) Protocol

Introduction

The High-Level Data-Link Control (HDLC) protocol is a popular ISO-

standard, bit-oriented, Data Link layer protocol. It specifies an

encapsulation method for data on synchronous serial data links using

frame characters and checksums.

HDLC is a point-to-point protocol used on leased lines. No

authentication can be used with HDLC.

HDLC is the default encapsulation used by Cisco routers over

synchronous serial links. And Ciscos HDLC is proprietaryit wont

communicate with any other vendors HDLC implementation.

Figure below shows the Cisco HDLC format.


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Cisco HDLC format

Cisco HDLC Frame Format


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Point-to-Point Protocol (PPP)

When would you choose to use PPP?

Basic purpose of PPP is to transport layer 3 packets across a Data

Link layer point-to-point link,

its nonproprietary. So unless you have all Cisco routers, you needPPP on your serial interfacesthe HDLC encapsulation is Cisco

proprietary.

since PPP can encapsulate several layer 3 routed protocols and

provide authentication, dynamic addressing, and callback.


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PPP Authentication Methods

PPP Authentication MethodsThere are two methods of authentication that can be used with PPP

links:

Password Authentication Protocol (PAP)

The Password Authentication Protocol (PAP) is the less secure of

the two methods. Passwords are sent in clear text, and PAP is only

performed upon the initial link establishment. When the PPP link is

first established, the remote node sends the username and

password back to the originating router until authentication is

acknowledged.


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Conti..

Challenge Handshake Authentication Protocol (CHAP)

The Challenge Handshake Authentication Protocol (CHAP) is used

at the initial startup of a link and at periodic checkups on the link to

make sure the router is still communicating with the same host.

After PPP finishes its initial link-establishment phase, the local

router sends a challenge request to the remote device. The remote

device sends a value calculated using a one-way hash function

called MD5. The local router checks this hash value to make sure it

matches. If the values dont match, the link is immediately

terminated.


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Configuring PPP Encapsulation

Configuring PPP encapsulation on an interface is straightforward.

To configure it from the CLI, follow these simple router commands:

Router#config t

Router(config)#int s0

Router(config-if)#encapsulation ppp

Router(config-if)#^Z

Router#


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Configuring PPP Authentication

After you configure your serial interface to support PPP

encapsulation, you can configure authentication using PPP between

routers. First, you need to set the hostname of the router, if its not

already. Then you set the username and password for the remote

router that will be connecting to your router:

Router#config t

Router(config)#hostname RouterA

RouterA(config)#username RouterB password cisco


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Now, after youve set the hostname, usernames, and passwords,choose the authentication type, either CHAP or PAP:

RouterA#config t

Enter configuration commands, one per line. End with CNTL/Z.

RouterA(config)#int s0

RouterA(config-if)#ppp authentication chap pap

RouterA(config-if)#^Z

RouterA#


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Frame Relay

What is Frame Relay?

Frame Relay is still one of the most popular WAN services deployed

over the past decade, and theres a good reason for thiscost.

By default, Frame Relay is classified as a non-broadcast multi-

access (NBMA) network, meaning it doesnt send any broadcasts

like RIP updates across the network.


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Explaining Frame Relay Technology

Frame Relay is a packet-switched technology. You wont be using theencapsulation hdlc or encapsulation ppp command to configure it.

Frame Relay doesnt work like a point-to-point leased line.

Before Frame Relay


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Conti..

After Frame Relay


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Committed Information Rate (CIR)

CIR: The maximum bandwidth of data guaranteed to be delivered.In reality, its the average amount that the service provider will allow

you to transmit.

Heres an example: Lets say that you buy an access rate of T1

(1.544Mbps) and a CIR of 256Kbps. By doing this, the first 256Kbps

of traffic you send is guaranteed to be delivered. Anything beyond

that is called a burst a transmission that exceeds your

guaranteed 256Kbps rate, and can be any amount up to the T1

access rate (if that amount is in your contract). If your combined

committed burst (the basis for your CIR) and excess burst sizes,

known as the MBR or maximum burst rate


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Virtual Circuits

Permanent virtual circuits (PVCs) are by far the most common

type in use today. What permanent means here is that the telco

creates the mappings inside their gear and as long as you pay the

bill, theyll remain in place.

Switched virtual circuits (SVCs) are more like a phone call. The

virtual circuit is established when data needs to be transmitted, then

its taken down when the data transfer is complete.


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Data Link Connection Identifiers (DLCIs)

Frame Relay PVCs are identified to DTE end devices by Data LinkConnection Identifiers (DLCIs). A Frame Relay service provider

typically assigns DLCI values, which are used on Frame Relay

interfaces to distinguish between different virtual circuits. Because

many virtual circuits can be terminated on one multipoint Frame

Relay interface

DLCI on a local computer


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Conti..

RouterA(config-if)#frame-relay interface-dlci ? Define a DLCI as part of the current

RouterA(config-if)#frame-relay interface-dlci 16


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Local Management Interface (LMI)

Local Management Interface (LMI) is a signaling standard usedbetween your router and the first Frame Relay switch its connected

to. It allows for passing information about the operation and status of

the virtual circuit between the providers network and the DTE (your

router).

RouterA(config-if)#frame-relay lmi-type ?

cisco

ansi

q933a


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Frame Relay Implementation

RouterA#config t

RouterA(config)#int s0/0

RouterA(config-if)#encapsulation frame-relay

RouterA(config-if)#ip address 172.16.20.1 255.255.255.0

RouterA(config-if)#frame-relay lmi-type ansi

RouterA(config-if)#frame-relay interface-dlci 101

RouterA(config-if)#^Z

RouterA#


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Configuring PPP with Authentication Using SDM

Create New Connection Wizard


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Conti..

Serial WAN Configuration Wizard


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Configure HDLC

Conti..


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IP Address Dialogue Box

Conti..


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Authentication Dialogue Box

Conti..


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Conti..


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Configuring Frame Relay with SDM

Configuration Encapsulation Wizard


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Configuring Static IP

Conti..


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Configure LMI & DLCI

Conti..


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Configuration Summary

Conti..


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THANK YOU

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