instructor & todd lammle

Sybex CCNA 640-802 Chapter 14: Wide Area Networks

Instructor & Todd Lammle

Chapter 14 Objectives

The CCNA Topics Covered in this chapter include:

• Introduction to WAN’s• HDLC• PPP• Frame Relay• Introduction to VPN’s

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Defining WAN Terms

• Customer Premises Equipment (CPE)

• Demarcation (demarc)

• Local loop

• Central Office (CO)

• Toll network

WAN Connection Types

DTE-DCE-DTE

Channel Service Unit (CSU) is a device that converts a digital data frame from the communications technology used on a local area network (LAN) into a frame appropriate to a wide-area network (WAN) and vice versa. The Data Service Unit (DSU) is a device that performs protective and diagnostic functions for a telecommunications line.

WAN Support

• Frame Relay• ISDN: Integrated Services Digital

Network• LAPB: Link Access Procedure,

Balanced• LAPD: Link Access Procedure, D-

channel• HDLC: High-level Data Link Control• PPP• ATM: Asynchronous Transfer Mode

HDLC Protocol

• Bit-oriented Data Link layer ISO standard protocol, i.e., control information is encoded by bits

• Specifies a data encapsulation method on synchronous serial data links

• A point-to point protocol used on leased lines

• No authentication can be used

HDLC Frame Format

Point-to-Point Protocol (PPP)

• Purpose:– Transport layer-3 packets across a

Data Link layer point-to-point link

• Can be used over asynchronous serial (dial-up) or synchronous serial (ISDN) media– Uses Link Control Protocol (LCP)

• Builds & maintains data-link connections

Point-to-Point Protocol Stack

PPP Main Components

• EIA/TIA-232-C– Intl. Std. for serial communications

• HDLC– Serial link datagram encapsulation method

• LCP– Used in P-t-P connections:

• Establishing• Maintaining• Terminating

• NCP– Method of establishing & configuring Network

Layer protocols– Allows simultaneous use of multiple Network

layer protocols

LCP Configuration Options

• Authentication– PAP: Password Authentication Protocol– CHAP: Challenge Handshake

Authentication Protocol• Compression

– Stacker– Predictor

• Error detection– Quality– Magic Number

• Multilink– Splits the load for PPP over 2+ parallel

circuits; a bundle

PPP Session Establishment

• Link-establishment phase

• Authentication phase

• Network-layer protocol phase

PPP Session Establishment

PPP Authentication Methods

• Password Authentication Protocol (PAP)– Passwords sent in clear text– Remote node returns username & password– Only performed in initial link establishment

• Challenge Handshake Authentication Protocol (CHAP)– Done at start-up & periodically– Challenge & Reply

• Remote router sends a one-way hash ~ MD5

Configuring PPP• Step #1: Configure PPP on RouterA & RouterB:

Router__#config t

Router__(config)#int s0

Router__(config-if)#encapsulation ppp

Router__(config-if)#^Z

• Step #2: Define the username & password on each router:– RouterA: RouterA(config)#username RouterB password cisco– RouterB: RouterB(config)#username RouterA password cisco

NOTE: (1) Username maps to the remoteremote router

(2) Passwords must match

• Step #3: Choose Authentication type for each router; CHAP/PAP

Router__(Config)#int s0

Router__(config-if)#ppp authentication chap

Router__(config-if)#ppp authentication pap

Router__(config-if)#^Z

PPP Example 1

PPP Example 2: Failed PPP authentication

PPP Example 3:Mismatched WAN Encapsulations

PPP Example 4:Mismatched IP Address

Frame Relay

• Background– High-performance WAN encapsulation

method– OSI Physical & data Link layer– Originally designed for use across ISDN

• Supported Protocols– IP, DECnet, AppleTalk, Xerox Network

Service (XNS), Novell IPX, Banyan Vines, Transparent Bridging, & ISO

Before Frame Relay

After Frame Relay

Frame Relay

• Purpose– Provide a communication interface

between DTE & DCE equipments– Connection-oriented Data Link

layer communication• Via virtual circuits: PVC, SVC• Provides a complete path from the

source to destination before sending the first frame

Frame Relay Terminology

Frame Relay Encapsulation

• Specified on serial interfaces• Encapsulation types:

– Cisco (default encapsulation type)– IETF (used between Cisco & non-

Cisco devices)

RouterA(config)#int s0

RouterA(config-if)#encapsulation frame-relay ?

ietf Use RFC1490 encapsulation

<cr>

Data Link Connection Identifiers (DLCIs)

• Frame Relay PVCs are identified by DLCIs• IP end devices are mapped to DLCIs

– Mapped dynamically or mapped by IARP

• Global Significance: – Advertised to all remote sites as the same PVC, need

LMI extensions

• Local Significance: – DLCIs do not need to be unique

• ConfigurationRouterA(config-if)#frame-relay interface-dlci ?

<16-1007> Define a DLCI as part of the current

subinterface

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

DLCI’s are Locally Significant

Local Management Interface (LMI)

• Background: a signaling standard between a router and the first connected frame relay switch

• Purpose: passing information about the operation and status of the VC between the DTE and switch

• LMI Messages– Keepalives– Multicasting– Global addressing– Status of virtual circuits

LMI Types

• Configuration:RouterA(config-if)#frame-relay lmi-type ? cisco ansi q933a

– Beginning with IOS ver 11.2+ the LMI type is auto-sensed

– Default type: cisco• Virtual circuit status:

– Active: everything is up, routers can exchange information

– Inactive: router interface is up and connected with the switch, but the remote router is not up

– Deleted: no LMI info is being received on the interface from the switch

Single interfacesRouterA(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

Sub-interfaces

• Definition– Multiple virtual circuits on a single

serial interface: multiplexing– Enables the assignment of different

network-layer characteristics to each sub-interface

• IP routing on one sub-interface• IPX routing on another

– Mitigates difficulties associated with:• Partial meshed Frame Relay networks• Split Horizon protocols

Creating Sub-interfaces

Configuration:#1: Set the encapsulation on the serial

interface

#2: Define the subinterfaceRouterA(config)#int s0

RouterA(config)#encapsulation frame-relay

RouterA(config)#int s0.?

<0-4294967295> Serial interface number

RouterA(config)#int s0.16 ?

multipoint Treat as a multipoint link

point-to-point Treat as a point-to-point link

Sub-interfaces

– Point-to-point: a single virtual circuit connects one router to another. Each p-t-p subinterface requires its own subnet.

– Multipoint: when the router is the center of a star of virtual circuits that are using a single subnet for all routers’ serial interfaces connected to the switch.

Mapping Frame Relay

Necessary to IP end devices to communicate– Addresses must be mapped to

the DLCIs– Methods:

• Frame Relay map command• Inverse-arp function

Using the map command

RouterA(config)#int s0

RouterA(config-if)#encap frame

RouterA(config-if)#int s0.16 point-to-point

RouterA(config-subif)#no inverse-arp

RouterA(config-subif)#ip address 172.16.30.1 255.255.255.0

RouterA(config-subif)#frame-relay map ip 172.16.30.17 16 ietf broadcast

Using the inverse arp command

RouterA(config)#int s0.16 point-to-point

RouterA(config-subif)#encap frame-relay ietf

RouterA(config-subif)#ip address 172.16.30.1 255.255.255.0

RouterA(config-subif)#frame-relay interface-dlci 200

Committed Information Rate (CIR)

• Definition: Provision allowing customers to purchase amounts of bandwidth lower than what they might need– Cost savings– Good for bursty traffic– Not good for constant amounts of

data transmission

Congestion Control• Discard Eligibility (DE):

– Transmit packets beyond the CIR, the packets exceeding the CIR are to be discarded if network is congested at that time. These excessive bits are marked with a DE bit.

• Forward-Explicit Congestion Notification (FECN)– When the frame relay network recognizes

congestion in the cloud, the FECN bit will be set to 1 to notify the destination DTE that the path the frame just traversed is congested.

• Backward-Explicit Congestion Notification (BECN)– When the switch detects congestions, it’ll set the

BECN bit in a frame that’s destined for the source router.

Monitoring Frame Relay

RouterA>sho frame ?

ip show frame relay IP statistics

lmi show frame relay lmi statistics

map Frame-Relay map table

pvc show frame relay pvc statistics

route show frame relay route

traffic Frame-Relay protocol statistics

RouterA#sho int s0

RouterB#show frame map

Router#debug frame-relay lmi

Troubleshooting Frame Relay

Why can’t RouterA talk to RouterB?Why can’t RouterA talk to RouterB?You need to use your own DLCI number 100 instead of the remoteYou need to use your own DLCI number 100 instead of the remoteDLCI number to communicate with the switch. DLCI number to communicate with the switch.

Troubleshooting Frame Relay

Why is RIP not sent across the PVC?Why is RIP not sent across the PVC?Because frame relay is a non-broadcast multi-access network, i.e., no Because frame relay is a non-broadcast multi-access network, i.e., no broadcast across the PVC. So it’s necessary to add broadcast in the broadcast across the PVC. So it’s necessary to add broadcast in the mapping statement.mapping statement.

Introduction to VPN’s

• VPNs are used daily to give remote users and disjointed networks connectivity over a public medium like the Internet instead of using more expensive permanent means.

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Types of VPN’s

• REMOTE ACCESS VPNSRemote access VPNs allow remote users like

telecommuters to securely access the corporate network wherever and whenever they need to.

• SITE-TO-SITE VPNSSite-to-site VPNs, or, intranet VPNs, allow a company to

connect its remote sites to the corporate backbone securely over a public medium like the Internet instead of requiring more expensive WAN connections like Frame Relay.

• EXTRANET VPNSExtranet VPNs allow an organization’s suppliers,

partners, and customers to be connected to the corporate network in a limited way for business-to-business (B2B) communications.

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Written Labs and Review Questions

– Open your books and go through all the written labs and the review questions.

– Review the answers in class.

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