robert e. meyers ccna, ccai youngstown state university manager, cisco regional academy cisco...

Robert E. Meyers CCNA, CCAIYoungstown State UniversityManager, Cisco Regional Academy

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Semester 4, v.2.1.2 Semester 4, v.2.1.2

Chapter 6: Frame RelayChapter 6: Frame Relay

Curriculum ReviewCurriculum Review

Youngstown State University Youngstown State University Cisco Regional AcademyCisco Regional Academy


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DisclaimerDisclaimer

This presentation is intended for review purposes by Cisco Networking Academy Program teachers and students only.This presentation is not a substitute for careful study of the Cisco Academy curriculum.Most of the text and graphics have been copied directly from the on-line curriculum, and remain the copyrighted property of Cisco Systems.CCNA 640-507 objectives are used for reviews.


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ContentsContents

Part 1: Frame Relay TechnologyPart 2: LMI: Cisco’s Frame RelayPart 3: LMI FeaturesPart 4: Frame Relay

Subinterfaces.Part 5: Configuration of

Basic Frame Relay


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Chapter Learning ObjectivesChapter Learning Objectives

– List and describe the commands necessary for configuring basic and extended Frame Relay on subinterfaces.

– List the commands for verifying Frame Relay operation.


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Part 1Part 1

Frame Relay Technology


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Frame Relay OverviewFrame Relay Overview

Frame Relay provides WAN connectivity.– High performance industry-standard.– Switched data link-layer protocol.– Handles multiple virtual circuits.– Operates at the physical and data link layers of OSI.– Uses High-Level Data Link Control

(HDLC) encapsulation.– Relies on upper-layer protocols,

like TCP, for error correction.


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Frame Relay OverviewFrame Relay Overview

Can be a carrier-provided public network or a single network of privately owned equipment:– Data is divided into packets.– Each packet travels through a series of switches to

reach its destination.– Uses virtual circuits to

establish a connection-orientedconnection-oriented service.


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Important Frame Relay TermsImportant Frame Relay Terms

Access Rate– Port speed of the local loop connection.

Data-Link Connection Identifier (DLCI)– A number that identifies the FR end point.– Significant for the local network only.– Identifies logical circuits.


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Important Frame Relay TermsImportant Frame Relay Terms

Local Management Interface (LMI)– A signaling standard between the CPE and the

frame relay switch.– Responsible for managing the connection.

Committed Interface Rate (CIR)– The rate of service, in

bits per second, the service provider guarantees.


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Frame Relay OperationFrame Relay Operation

Public FR uses carrier-provided services.– Economic benefits:

• Traffic-sensitive charging rates• Telco maintains the switching equipment.

– Speeds between 56 kbps and 2 Mbps are typical.• Can support lower or

higher speeds as required.


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Frame Relay OperationFrame Relay Operation

Provides a method for multiplexing many data conversations.– Each is called a “virtual circuit.”– All are shared through one physical connection.– Multiplexing provides

high flexibility and efficient use of bandwidth.

– Users can share BW at reduced cost.


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Frame Relay DLCI’sFrame Relay DLCI’s

Permanent Virtual Circuits (PVC)– Administratively configured and managed.– Each is Identified using a DLCI number.– Significant as a local number only; are not unique in

the WAN.– Service provider's switch constructs a table mapping

DLCI values to outbound ports.


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Frame Relay FramesFrame Relay Frames

Frame format:– Flags indicate beginning and end of frame.– Address contains:

• DLCI address (first 10 bits)• Congestion control (last 3 bits)

– Data – FCS (Frame Check Sequence) for data integrity.


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Frame Relay AddressingFrame Relay Addressing

DLCI address space is only 10 bits.– Possible 1024 DLCI addresses. – Usable portion of these addresses are determined

by the LMI type used.

– Cisco LMI type supports DLCI addresses from DLCI 16 to 1007 for user-data.


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Part 2Part 2

LMI: Cisco’s Implementation of Frame Relay


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LMI OperationLMI Operation

Cisco and 3 others extended the Frame Relay protocol capabilities to include Local Management Interface (LMI):– Determines the operational status of various PVC’s.– Transmits “keep alive” packets to ensure the PVC

does not shut down.– Tells the router what

PVC’s are available.


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LMI ExtensionsLMI Extensions

Eases support of large complex networks.– Virtual Circuit status messages, commoncommon:

• Synchronization between network and service.• Periodically report new or deleted PVCs.• Report on PVC integrity.

– Multicasting, optional:• Single frame multicast to numerous recipients

– Global Addressing, optional:• Gives DLCI’s global significance.• Address resolution mimics LAN method.


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LMI Frame FormatLMI Frame Format

LMI messages are sent in frames– After the flags and DLCI there are four

mandatory bytes:• Unnumbered information indicator.• Protocol discriminator.• Call reference (always all zeroes.)• Message-type field.


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Part 3Part 3

LMI Features


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LMI Global AddressingLMI Global Addressing

Basic (non-extended) Frame Relay supports DLCI’s that identify locally significant PVCs.– Static maps must be created to tell routers which

DLCIs to use to find a remote device.

LMI allows routers to make address translations between the DLCI and the actual device interface.– This permits routing in complex environments. – The Frame Relay network now appears to the

routers on its periphery like any LAN.


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MulticastingMulticasting

Multicast groups are designated by a series of four reserved DLCI values.– 1019 to 1022

– Frames sent using these DLCIs are replicated by the network and sent to all exit points in the set.

– Routing messages can be sent.


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Inverse ARPInverse ARP

Allows router to dynamically build a Frame Relay Map.– Learns DLCIs during LMI exchange.– Sends an Inverse ARP request to each DLCI for each

protocol configured on the interface.

– Return information is used to build the Frame Relay map.


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Frame Relay MapFrame Relay Map

Bind next router hop IP addresses to DLCI’s.– Static (configured by network administrator.)– Dynamic (built by router using Inverse ARP.)– Provides outgoing traffic with next-hop protocol

address, or the DLCI.


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Frame Relay Switching TablesFrame Relay Switching Tables

Consists of 4 entries:– Incoming port and DLCI.– Outgoing port and DLCI.


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Part 4Part 4

Frame Relay Subinterfaces


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Frame Relay SubinterfacesFrame Relay Subinterfaces

Configure the router with logically assigned interfaces called “subinterfaces.” – Logical “subdivisions” of a physical interface.– Each can be configured as a separate PVC.– Allows subinterface to act as a dedicated line.– Significantly reduces the cost of implementation by

reducing the actual number of router interfaces.– Subinterfaces resolve routing loops using split

horizon.• “If you learn a protocol’s route on an interface, do not send

information about that route back out that interface.”


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Subinterface: Point to PointSubinterface: Point to Point

Point to Point– A single interface is used to set up one PVC to

another on a remote router.• Both are on same subnet.

– Each point-to-point connection is its own subnet.– This solves broadcast problems.


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Subinterface: MultipointSubinterface: Multipoint

One subinterface is used for multiple PVC connections on multiple physical interfaces or subinterfaces on a remote router.– All participating interfaces are on the same subnet.– Each interface has its own local DLCI.– Routing updates subject to split horizon rules.


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Part 5Part 5

Configuration of Basic Frame Relay


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Basic Frame Relay ConfigurationBasic Frame Relay Configuration

Assumes that the configuration is:– On one or more physical interfaces.

– LMI and inverse ARP are supported on the remote routers.


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IOS Command SequenceIOS Command Sequence

1. Select the interface: router(config)#interface serial 0

2. Configure the layer 3 address:router(config-if)#ip address [ip|sm]

3. Select the encapsulation type:router(config-if)#encapsulation frame-relay [cisco|ietf]– Use ietf when the remote router is not a Cisco router!

4. For IOS 11.1 or earlier, specify the LMI type used: router(config-if)#frame-relay lmi-type[ansi|cisco|q933a]

IOS 11.2 and later autosenses the type.

5. Configure the link bandwidth:router(config-if)#bandwidth kilobits

6. Enable Inverse ARP(default):router(config-if)#frame-relay inverse-arp {protocol} {dlci}


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Verifying Frame Relay OperationsVerifying Frame Relay Operations

Use the following show commands:show interface

• Verifies traffic on interface.

show interfaces serial• Displays the multicast DLCI, and the LMI.

show frame-relay pvc• Status of each configured connection with traffic statistics.

show frame-relay map• Displays network-layer address and associated DLCI for

each remote device connected to the local router.

show frame-relay lmi• LMI traffic statistics.


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Configuring SubinterfacesConfiguring Subinterfaces

1. Select the interface.

2. Remove any network-layer addresses.

3. Configure Frame Relay encapsulation.router(config-if)#encapsulation frame-relay

4. Select the subinterface:router(config-if)#interface serial number.subinterface-number

[multipoint|point-to-point]

– Multipoint allows the router to forward broadcasts and updates.

5. Configure local DLCI for subinterface:router(config-f)#frame-relay interface-dlci [number]


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Frame Relay SummaryFrame Relay Summary

Flexible packet-switching WAN capability. Uses virtual circuits to establish connections (PVCs.) LMI’s

– Determine the operational status of the various PVCs. – Transmit keep-alive packets to ensure that the PVC does not

shut down due to inactivity. – Tell the router what PVCs are available. – Uses Inverse ARP so the router can build a Frame Relay map.– Router next-hop address determined from the routing table

must be resolved to a Frame Relay DLCI.

Can divide a single physical WAN interface into multiple subinterfaces.


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End

robert e. meyers ccna, ccai youngstown state university manager, cisco regional academy cisco...

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