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Establishing Frame Relay Connection

Chapter 11

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Chapter 11 2

Chapter Objectives

Discuss the Frame Relay componentsExplain virtual circuit Explain LMI configuration and EncapsulationExplain DLCI addressing detailsExplain concerns of network layer and frame layer

Troubleshoot LMI Configure Frame Relay

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Chapter 11 3

Recall - I

S peed, Multiple Device S upport, Inexpensive areThe features of I S DN areNetwork Termination Device 1 (NT1), NetworkTermination Device 2 (NT2), I S DN Router, TerminalEquipment 1 (TE1), Terminal Equipment 2 (TE2),Terminal Adapter (TA) are e I S DN devicesIS DN is a channelized service. A channelizedservice splits a wire into many logical channels or time slots

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Chapter 11 4

Recall - II

IS DN supports two types of connections such as theBasic Rate Interface (BRI) and Primary RateInterface (PRI)You can verify the I S DN connections using twocommands:

show interface commandshow isdn status command

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Chapter 11 5

Frame Relay

F eatures of F rame RelayOperates at a higher speed (44.3 Mbps)Operates only in physical and data link layers

Is less expensive than other WAN connectionsuch as X.25Has error detection at the data link layer onlyProvides faster transmission for media that are

more reliable and protocols that have flow anderror control at the higher layers

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Chapter 11 6

Frame Relay Components - I

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Chapter 11 7

Frame Relay Components - II

The basic terms associated with the F rame Relaynetwork are as follows:

Data Terminal Equipment (DTE)

Data Communications Equipment (DCE)Access linkLocal access rateDLCI

LMICommitted Information (CIR)

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Chapter 11 8

Frame Relay Components - III

Committed burst (Bc)Excess Burst (Be)F orward explicit congestion notification ( F ECN)

Backward explicit congestion notification (BECN)Discard Eligibility (DE) indicator

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Chapter 11 9

Logical Connectivity of Frame Relay

Network

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Chapter 11 10

Committed Information Rate (CIR)

F rame Relay allows multiple users to use the packetswitched network at the same timeThe only limitation of F rame Relay is that not allusers can transmit the data at the same timeF rame Relay provides dedicated bandwidths to allthe users for data transmissionThe F rame Relay can function as a leased line if the

access rate and CIR values are same

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Chapter 11 11

Standard Frame Relay Frame Structure

The frame format allows you to understand thefunctionality of F rame RelayEach frame has flags that indicate the start and end

of the frame

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Chapter 11 12

Frame Relay Encapsulation Types

The F rame Relay has two types of encapsulationsthat you can view using the encapsulation frame-relay ? command:

CiscoInternet Engineering Task F orce (IET F )

The devices in a network can communicate only if their F rame Relay encapsulation types are same

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Chapter 11 13

Virtual Circuit

A Virtual Circuit (VC) represents the path on whichthe frame travels. Virtual circuits enable you tocompare F rame Relay to leased physical circuitThere are two types of virtual circuits, such as:

Permanent Virtual Circuit (PVC)S witched Virtual Circuit ( S VC)

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Chapter 11 14

Virtual Circuits

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Chapter 11 15

Partial Mesh Network

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Chapter 11 16

LMI Configuration and Encapsulation

LMI is the signaling standard used between theF rame Relay DTE and F rame Relay DCELMI is the communication between the router andthe nearest F rame Relay switchThe LMI performs the following functions:

Implements a keepalive function to verify the flowof data between the DTE and DCE

Informs whether Permanent Virtual Circuit (PVC)is active or not

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Chapter 11 17

LAPF Header

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Chapter 11 18

Identifying the type of protocol

If the F rame Relay is using the LAP F header thenthe DTEs cannot support multiprotocol trafficbecause there is no way to identify the type of protocolTo solve this problem. Cisco Encapsulation andRF C 1490 Encapsulation is used

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Chapter 11 19

Cisco Encapsulation

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Chapter 11 20

RFC 1490 Encapsulation

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Chapter 11 21

DLCI Addressing

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Chapter 11 22

DLCI Addressing Details

The exact number of DLCI is dependent on thefollowing factors:

Protocols being routed

Broadcast trafficS peed of lineS tatic RoutesS ize of routing protocol and S AP updates

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Chapter 11 23

F rame Relay involves following issues related to thetransmission of data packets from the layer 3 across

the network:Layer 3 addressing with F rame RelayBroadcast handling

Concerns of Network Layer and

Frame Relay

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Chapter 11 24

Frame Relay Layer 3 Addressing

The F rame Relay implementation of Cisco providesthree different options to assign subnets and IPaddress on the F rame Relay interfaces. The optionsare:

A subnet that contains all the F rame Relay DataTerminal Equipments (DTE)A subnet for each virtual circuitHybrid of the above two options

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Chapter 11 25

Full Mesh Network

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Chapter 11 26

Partial Mesh Network

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Chapter 11 27

Hybrid Network

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Chapter 11 28

Broadcast Handling

The F rame Relay can send copies of broadcast over all the virtual circuitsThe F rame Relay does not have the capability toreplicate and deliver across multiple virtual circuitsto several destinationsThe routers need to send broadcast for certainfeatures to activate their functioning

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Chapter 11 29

Frame Relay Service Internetworking

F rame Relay networks use Asynchronous Transfer Mode (ATM) in the core of the F rame Relay networkThe working of ATM is similar to a F rame Relay.However, ATM has certain features that make itmore effective than F rame RelayThe service provider uses the ATM to build the coreof the F rame Relay networks as shown in figure

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Chapter 11 30

Frame Relay Network

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Chapter 11 31

Network as it Appears to Routers

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Chapter 11 32

Configuration Steps for Remote

Router routes

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Chapter 11 33

Steps to Change DLCI Status

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Chapter 11 34

Frame Configuration Command - I

Commands Description

encapsulation frame-relay[ieft|cisco]

Defines the F rame Relayencapsulation which is preferred over HDLC and PPP

frame-relay lmi-type{ansi|q933a|cisco]

Defines the type of LMI messages thatare sent to the switch

bandwidth num Enables to set the interface speed of the router

frame-relay map [protocolprotocol-addressdlci}payload-compressionfrf9 stac caim [element-number][broadcast][ieft|cisco]

Defines statically the mappingbetween the network layer and DLCI

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Chapter 11 35

Frame Configuration Command - II

k eepalive sec Enables to configure the way and timeinterval that the LMI messages aresent and received

interface serial number.sub

[point-to-point|multipoint]Enables to create a subinterface or reference a subinterface that isalready created

frame-relay interface-dlcidlci [ieft|cisco] [voice-circir] [ppp virtual-template-

name]

Links the DLCI to the subinterface

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Chapter 11 36

Frame Configuration Commands in

the Privileged Mode - ICommand Description

show interfaces Displays the status of the physicalinterface

show frame-relay lmi [typenumber]

Displays LMI status information

show frame-relay pvc Displays a list of all the configuredPVCs and DLCI numbers

show frame-relay map Provides a list of network layer

addresses mapped to DLCI numbersshow ip route Displays the available routes for the

packets to travel from one router toanother

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Chapter 11 37

Basic Frame Relay Network

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Chapter 11 38

Verification of Frame Relay

Encapsulation on Router1

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Chapter 11 39

Output of show ip route Command

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Output of show frame-relay lmi

Command

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Output of show frame-relay pvc

Command

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Chapter 11 42

Output of show frame-relay map

Command

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Chapter 11 43

Configuring Frame Relay

SubinterfacesF rame Relay subinterfaces provide a solution to theproblem of split horizon on the partially meshedF rame Relay networksCisco routers support two types of subinterfacesgiven as follows:

Point-to-point subinterface

Multipoint subinterfaces

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Chapter 11 44

Frame Relay Point-to-Point

Subinterfaces

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Output of show frame-relay lmi

Command

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Chapter 11 46

Output of show frame-relay pvc

Command

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Output of show frame-relay map

Command

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Frame Relay Multipoint Subinterfaces

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Output of show frame-relay lmi

Command

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Output of show frame-relay pvc

Command

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Output of show frame-relay map

Command

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Hub-and-Spoke Frame Relay Network

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Output of show frame-relay lmi

Command

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Output of show frame-relay pvc

Command

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Output of show frame-relay map

Command

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Fully Meshed Network

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Output of show frame-relay lmi

Command

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Output of show frame-relay pvc

Command

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Chapter 11 59

Output of show frame-relay map

Command

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Chapter 11 60

Frame Relay Congestion Control

F rame Relay reduces the network overhead byimplementing congestion-control mechanismF rame Relay implements two congestion-notificationmechanisms such as F orward-explicit congestion

notification ( F ECN) and Backward-explicit congestionnotification (BECN)The F rame Relay frame includes following three bitsthat allow congestion control:

Discard Eligibility (DE)F orward-explicit congestion notification ( F ECN)Backward-explicit congestion notification (BECN)

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Chapter 1161

Frame Relay Error Checking

F rame Relay uses cyclic redundancy check (CRC)error checking mechanismThe CRC compares two derived values from the twomathematical functions computed at the source andthe destination devicesThis determines whether an error occurred duringthe transmission of data from source to destination

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Chapter 1162

Case Study

At the Gujarat branch of the Blue Diamond S teelorganization, all Cisco routers are implemented on thenetwork. The routers use HDLC as the defaultencapsulation method for data transmission. All the

transaction between the departments of the companyis carried out over the network. However,unfortunately, some important information of F inancedepartment regarding policies could not reach to the

S oftware Management departments destinationcomputer because it was lost in transit.

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Chapter 1163

Problem

Information was lost due to network congestion

in network

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Chapter 1164

Suggested Solution

All the branches should be integrated using theF rame Relay technology. F rame Relay provides a

congestion control mechanism that can prevent theloss of critical data

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Chapter 1165

Frame Relay Backup using ISDN

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Chapter 1166

Output of show frame-relay lmi

Command

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Chapter 1167

Output of show frame-relay pvc

Command

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Chapter 1168

Output of show frame-relay map

Command

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Chapter 1169

Output of show ip route Command

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Chapter 1170

Troubleshooting Frame Relay

The commons issues in the F rame Relay can beresolved using the debug commandThis command enables you to troubleshoot theF rame Relay connectionsYou can use the router console to enter thesecommands:

debug frame-relay events Commanddebug F rame Relay packet Command

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Chapter 1171

Summary - I

F rame Relay networks are multi-access networks wheremore than two devices can be attached to the networkA Virtual circuit (VC) represents the path on which theframe travels. Virtual circuits enable you to compareF rame Relay to leased physical circuit. There two typesof virtual circuits are:

Permanent virtual circuit (PVC)S witched virtual circuit ( S VC)

LMI is the definition used between the F rame Relay DTEand F rame Relay DCE, which means that the data sendby the DTE is processed between them

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Chapter 1172

Summary - II

S ometimes you might face problems with theconnection to the carrier switch. The commandsavailable are to troubleshoot LMI are:

show interfacesshow frame-relay lmidebug frame-relay lmi

The DLCI identifies a virtual circuit for the F rame

Relay to forward the frames to appropriate remotesite when multiple access list use the same accesslist

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Summary - III

The F rame Relay implementation of Cisco provideswith three different options to assign subnets and IPaddress on the F rame Relay interfaces. The optionsare:

A subnet that contains all the F rame Relay dataterminal equipments (DTE)A subnet for each virtual circuit

Hybrid of the above twoF rame Relay networks use Asynchronous Transfer Mode (ATM) in the core of the F rame Relay network