Troubleshooting WAN Implementation Issues

Chapter 16

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Chapter ObjectivesAt 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 Cisco’s HDLC is proprietary—it won’t communicate with any other vendor’s HDLC implementation.

Figure below shows the Cisco HDLC format.

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Cisco HDLC format

Cisco HDLC Frame Formatpowered by DJ 4

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,

it’s nonproprietary. So unless you have all Cisco routers, you need PPP on your serial interfaces—the 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 MethodsPPP Authentication Methods

There 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 don’t 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 it’s 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 you’ve 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 there’s a good reason for this—cost.

By default, Frame Relay is classified as a non-broadcast multi-access (NBMA) network, meaning it doesn’t 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 won’t be using the encapsulation hdlc or encapsulation ppp command to configure it.

Frame Relay doesn’t work like a point-to-point leased line.

Before Frame Relaypowered by DJ 12

Conti..

After Frame Relay

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Committed Information Rate (CIR)

CIR: The maximum bandwidth of data guaranteed to be delivered. In reality, it’s the average amount that the service provider will allow you to transmit.

Here’s an example: Let’s 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, they’ll 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 it’s 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 Link

Connection 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 computerpowered by DJ 16

Conti.. RouterA(config-if)#frame-relay interface-dlci ?

<16-1007> 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 used

between your router and the first Frame Relay switch it’s connected to. It allows for passing information about the operation and status of the virtual circuit between the provider’s 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 Wizardpowered by DJ 20

Conti..

Serial WAN Configuration Wizardpowered by DJ 21

Conti..

Configure HDLCpowered by DJ 22

Conti..

IP Address Dialogue Boxpowered by DJ 23

Conti..

Authentication Dialogue Boxpowered by DJ 24

Conti..

Configuration Summarypowered by DJ 25

Configuring Frame Relay with SDM

Configuration Encapsulation Wizardpowered by DJ 26

Conti..

Configuring Static IPpowered by DJ 27

Conti..

Configure LMI & DLCIpowered by DJ 28

Conti..

Configuration Summarypowered by DJ 29

THANK YOU

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