chapter 6- semester4

8/7/2019 Chapter 6- Semester4

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Chapter 6Chapter 6-- Semester4Semester4

Carl MarandolaCarl Marandola

CCRI


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What is Frame Relay?What is Frame Relay?

Frame Relay is an industryFrame Relay is an industry--standard, switched datastandard, switched datalinklink--layer protocol thatlayer protocol thathandles multiple virtualhandles multiple virtual

circuits using Highcircuits using High--LevelLevelData Link Control (HDLC)Data Link Control (HDLC)encapsulation betweenencapsulation betweenconnected devices.connected devices.Frame Relay uses virtualFrame Relay uses virtual

circuits to makecircuits to makeconnections through aconnections through aconnectionconnection--orientedorientedservice.service.


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Frame Relay FeaturesFrame Relay FeaturesCCITT and ANSI standard that defines a process forCCITT and ANSI standard that defines a process forsending data over a public data network (PDN).sending data over a public data network (PDN).

high performance, efficient data technology used inhigh performance, efficient data technology used in

networks throughout the world.networks throughout the world.

Sends information over a WAN by dividing data intoSends information over a WAN by dividing data intopackets.packets.

Operates at the physical and data link layers of the OSIOperates at the physical and data link layers of the OSI

reference model.reference model.

Relies on upperRelies on upper--layer protocols such as TCP for errorlayer protocols such as TCP for errorcorrection.correction.

Frame Relay interface can be either a carrierFrame Relay interface can be either a carrier--providedprovided

public network or a network of privately ownedpublic network or a network of privately owned

equipment, serving a single enterprise.equipment, serving a single enterprise.


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Terms used in Frame RelayTerms used in Frame RelayAccess rateAccess rate ---- The clockThe clockspeed (port speed) of thespeed (port speed) of theconnection (local loop) toconnection (local loop) tothe Frame Relay cloud. Itthe Frame Relay cloud. Itis the rate at which datais the rate at which datatravels into or out of thetravels into or out of the

network.network.DataData--link connectionlink connectionidentifier (DLCI)identifier (DLCI) A DLCIA DLCIis a number that identifiesis a number that identifiesthe end point in a Framethe end point in a FrameRelay network. ThisRelay network. This

number has significancenumber has significanceonly to the local network.only to the local network.The Frame Relay switchThe Frame Relay switchmaps the DLCIs betweenmaps the DLCIs betweena pair of routers to createa pair of routers to createa permanent virtuala permanent virtualcircuit.circuit.


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Terms used in Frame RelayTerms used in Frame Relay-- ContinueContinueLocal management interface (LMI)Local management interface (LMI) ---- A signaling standard betweenA signaling standard between

the customer premises equipment (CPE) device and the Framethe customer premises equipment (CPE) device and the FrameRelay switch that is responsible for managing the connection andRelay switch that is responsible for managing the connection andmaintaining status between the devices.maintaining status between the devices.

LMIs can include support forLMIs can include support for

1.1. a keepalive mechanism, which verifies that data is flowing.a keepalive mechanism, which verifies that data is flowing.

2.2. a multicast mechanism, which can provide the network server with itsa multicast mechanism, which can provide the network server with its

local DLCI.local DLCI.3.3. multicast addressing, providing a few DLCIs to be used as multicastmulticast addressing, providing a few DLCIs to be used as multicast

addresses and the ability to give DLCIs global (whole Frame Relayaddresses and the ability to give DLCIs global (whole Frame Relaynetwork) significance, rather than just local significance (DLCIs usednetwork) significance, rather than just local significance (DLCIs usedonly to the local switch);only to the local switch);

4.4. a status mechanism, which provides an ongoing status on the DLCIsa status mechanism, which provides an ongoing status on the DLCIsknown to the switch.known to the switch.

There are several LMI types, and routers need to be told which LMI typeThere are several LMI types, and routers need to be told which LMI typeis being used. Three types of LMIs are supported: cisco, ansi, andis being used. Three types of LMIs are supported: cisco, ansi, andq933a.q933a.


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Terms used in Frame RelayTerms used in Frame Relay-- ContinueContinue

Committed information rate (CIR)Committed information rate (CIR) ---- The CIR is theThe CIR is theguaranteed rate, in bits per second, that the serviceguaranteed rate, in bits per second, that the serviceprovider commits to providing.provider commits to providing.

Committed burstCommitted burst ---- The maximum number of bits that theThe maximum number of bits that theswitch agrees to transfer during a time interval. (It isswitch agrees to transfer during a time interval. (It isnoted Bc)noted Bc)

Excess burstExcess burst ---- The maximum number of uncommittedThe maximum number of uncommittedbits that the Frame Relay switch attempts to transferbits that the Frame Relay switch attempts to transferbeyond the CIR. Excess burst is dependent on thebeyond the CIR. Excess burst is dependent on theservice offerings available by the vendor, but is typicallyservice offerings available by the vendor, but is typicallylimited to the port speed of the local access loop.limited to the port speed of the local access loop.

Forward explicit congestion notification (FECN)Forward explicit congestion notification (FECN) ---- A bitA bitset in a frame that notifies a DTE that congestionset in a frame that notifies a DTE that congestionavoidance procedures should be initiated by theavoidance procedures should be initiated by thereceiving device. When a Frame Relay switchreceiving device. When a Frame Relay switchrecognizes congestion in the network, it sends a FECNrecognizes congestion in the network, it sends a FECNpacket to the destination device, indicating thatpacket to the destination device, indicating thatcongestion has occurred.congestion has occurred.


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Backward explicit congestion notification (BECN)Backward explicit congestion notification (BECN) ---- A bitA bitset in a frame that notifies a DTE that congestionset in a frame that notifies a DTE that congestionavoidance procedures should be initiated by the receivingavoidance procedures should be initiated by the receivingdevice. As shown in Figure when a Frame Relay switchdevice. As shown in Figure when a Frame Relay switch

recognizes congestion in the network, it sends a BECNrecognizes congestion in the network, it sends a BECNpacket to the source router, instructing the router to reducepacket to the source router, instructing the router to reducethe rate at which it is sending packets. If the router receivesthe rate at which it is sending packets. If the router receivesany BECNs during the current time interval, it decreasesany BECNs during the current time interval, it decreasesthe transmit rate by 25%.the transmit rate by 25%.


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Forward explicit congestionForward explicit congestionnotification (FECN)notification (FECN) ---- A bit set in aA bit set in aframe that notifies a DTE thatframe that notifies a DTE thatcongestion avoidance procedurescongestion avoidance proceduresshould be initiated by the receivingshould be initiated by the receivingdevice.When a Frame Relay switchdevice.When a Frame Relay switchrecognizes congestion in the network,recognizes congestion in the network,

it sends a FECN packet to theit sends a FECN packet to thedestination device, indicating thatdestination device, indicating thatcongestion has occurred.congestion has occurred.

Backward explicit congestionBackward explicit congestionnotification (BECN)notification (BECN) ---- A bit set in aA bit set in aframe that notifies a DTE thatframe that notifies a DTE thatcongestion avoidance procedurescongestion avoidance procedures

should be initiated by the receivingshould be initiated by the receivingdevice. when a Frame Relay switchdevice. when a Frame Relay switchrecognizes congestion in the network,recognizes congestion in the network,it sends a BECN packet to the sourceit sends a BECN packet to the sourcerouter, instructing the router to reducerouter, instructing the router to reducethe rate at which it is sending packets.the rate at which it is sending packets.If the router receives any BECNsIf the router receives any BECNs

during the current time interval, itduring the current time interval, itdecreases the transmit rate by 25%.decreases the transmit rate by 25%.


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Frame Relay operationFrame Relay operation

You deploy a public Frame Relay service by puttingYou deploy a public Frame Relay service by puttingFrame Relay switching equipment in the central office ofFrame Relay switching equipment in the central office ofa telecommunications carrier. In this case, users geta telecommunications carrier. In this case, users geteconomic benefits from trafficeconomic benefits from traffic--sensitive charging rates,sensitive charging rates,

and don't have to spend the time and effort to administerand don't have to spend the time and effort to administerand maintain the network equipment and service.and maintain the network equipment and service.

The lines that connect user devices to the networkThe lines that connect user devices to the networkequipment can operate at a speed selected from a broadequipment can operate at a speed selected from a broadrange of data rates. Speeds between 56 kbps and 2range of data rates. Speeds between 56 kbps and 2Mbps are typical, although Frame Relay can supportMbps are typical, although Frame Relay can supportlower and higher speedslower and higher speeds


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Frame Relay DLCIFrame Relay DLCI

Frame Relay provides aFrame Relay provides ameans for multiplexingmeans for multiplexingmany logical datamany logical dataconversations, referred toconversations, referred toas virtual circuits, through aas virtual circuits, through ashared physical medium byshared physical medium byassigning DLCIs to eachassigning DLCIs to eachDTE/DCE pair of devices.DTE/DCE pair of devices.

Frame Relay's multiplexingFrame Relay's multiplexingprovides more flexible andprovides more flexible andefficient use of availableefficient use of available

bandwidth. Therefore,bandwidth. Therefore,Frame Relay allows usersFrame Relay allows usersto share bandwidth at ato share bandwidth at areduced cost.reduced cost.


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Frame Relay DLCIFrame Relay DLCI

Frame Relay standardsFrame Relay standardsaddress permanent virtualaddress permanent virtualcircuits (PVCs) that arecircuits (PVCs) that areadministratively configured andadministratively configured andmanaged in a Frame Relaymanaged in a Frame Relaynetwork. Frame Relay PVCsnetwork. Frame Relay PVCsare identified by DLCIsare identified by DLCIs

The service provider'sThe service provider'sswitching equipmentswitching equipmentconstructs a table mappingconstructs a table mappingDLCI values to outbound ports.DLCI values to outbound ports.When a frame is received, theWhen a frame is received, the

switching device analyzes theswitching device analyzes theconnection identifier andconnection identifier anddelivers the frame to thedelivers the frame to theassociated outbound port. Theassociated outbound port. Thecomplete path to thecomplete path to thedestination is establisheddestination is establishedbefore the first frame is sent.before the first frame is sent.


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Frame Relay Frame FormatFrame Relay Frame Format

The Frame Relay frame formatThe Frame Relay frame formatis shown in the Figure. Theis shown in the Figure. Theflag fields indicate theflag fields indicate thebeginning and end of thebeginning and end of theframe. Following the leadingframe. Following the leadingflag field are 2 bytes offlag field are 2 bytes ofaddress information. 10 bits ofaddress information. 10 bits ofthese 2 bytes make up thethese 2 bytes make up theactual circuit ID (that is, theactual circuit ID (that is, theDLCI).DLCI).

Congestion ControlCongestion Control ---- The lastThe last3 bits in the address field,3 bits in the address field,

which control the Frame Relaywhich control the Frame Relaycongestion notificationcongestion notificationmechanisms. These are themechanisms. These are theFECN, BECN, and discardFECN, BECN, and discardeligible (DE) bits.eligible (DE) bits.


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Frame Relay addressingFrame Relay addressing

DLCI address space is limited to 10 bits. This creates aDLCI address space is limited to 10 bits. This creates apossible 1024 DLCI addresses. The usable portion ofpossible 1024 DLCI addresses. The usable portion ofthese addresses are determined by the LMI type used.these addresses are determined by the LMI type used.The remaining DLCI addresses are reserved for vendorThe remaining DLCI addresses are reserved for vendor

implementation. This includes LMI messages andimplementation. This includes LMI messages andmulticast addresses.multicast addresses.

Examples:Examples:

The Cisco LMI type supports a range of DLCI addressesThe Cisco LMI type supports a range of DLCI addressesfrom DLCI 16from DLCI 16--1007 for carrying user1007 for carrying user--data.data.

The ANSI/ITU LMI type supports the range of addressesThe ANSI/ITU LMI type supports the range of addressesfrom DLCI 16from DLCI 16--992 for carrying user992 for carrying user--data.data.


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LMI operation & extensionsLMI operation & extensionsIn addition to the basic FrameIn addition to the basic Frame

Relay protocol functions forRelay protocol functions fortransferring data, the Frametransferring data, the FrameRelay specification includes LMIRelay specification includes LMIextensions that make supportingextensions that make supportinglarge, complex internetworkslarge, complex internetworks

easier.easier.

A summary of the LMI extensionsA summary of the LMI extensionsfollows:follows:

Virtual circuit status messagesVirtual circuit status messages(common)(common) ---- ProvideProvidecommunication andcommunication andsynchronization between thesynchronization between thenetwork and the user device,network and the user device,periodically reporting theperiodically reporting theexistence of new PVCs and theexistence of new PVCs and thedeletion of already existingdeletion of already existingPVCs, and providing generalPVCs, and providing generalinformation about PVC integrity.information about PVC integrity.


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Multicasting (optional)Multicasting (optional) ---- Allows a sender to transmit a singleAllows a sender to transmit a singleframe but have it delivered by the network to multipleframe but have it delivered by the network to multiplerecipients.recipients.

Global addressing (optional)Global addressing (optional) ---- Gives connection identifiersGives connection identifiers

global rather than local significance, allowing them to beglobal rather than local significance, allowing them to beused to identify a specific interface to the Frame Relayused to identify a specific interface to the Frame Relaynetwork. Global addressing makes the Frame Relay networknetwork. Global addressing makes the Frame Relay networkresemble a localresemble a local--area network (LAN) in terms of addressing;area network (LAN) in terms of addressing;

Simple flow control (optional)Simple flow control (optional) ---- Provides for an XON/XOFFProvides for an XON/XOFFflow control mechanism that applies to the entire Frameflow control mechanism that applies to the entire FrameRelay interface. It is intended for devices whose higherRelay interface. It is intended for devices whose higherlayers cannot use the congestion notification bits and thatlayers cannot use the congestion notification bits and thatneed some level of flow controlneed some level of flow control

LMI extensionsLMI extensions --ContinueContinue


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LMI frame FormatLMI frame Format

The Frame RelayThe Frame Relay

specificationspecification

includes the LMIincludes the LMI

procedures. LMIprocedures. LMI

messages aremessages are

sent in framessent in frames

distinguished bydistinguished by

an LMIan LMI--specificspecific

DLCI (defined inDLCI (defined inthe consortiumthe consortium

specification asspecification as

DLCI = 1023).DLCI = 1023).


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LMI FeatureLMI Feature-- Global addressingGlobal addressing

In normal Frame Relay there are no addresses that identifyIn normal Frame Relay there are no addresses that identifynetwork interfaces, or nodes attached to thesenetwork interfaces, or nodes attached to theseinterfaces. Because these addresses do not exist, theyinterfaces. Because these addresses do not exist, theycannot be discovered by traditional address resolutioncannot be discovered by traditional address resolution

and discovery techniques.and discovery techniques.So, static maps must be created to tell routers which DLCIsSo, static maps must be created to tell routers which DLCIs

to use to find a remote device and its associatedto use to find a remote device and its associatedinternetwork address.internetwork address.

Global addressing provides significant benefits in a large,Global addressing provides significant benefits in a large,complex network. The Frame Relay network nowcomplex network. The Frame Relay network nowappears to the routers on its periphery like any LAN.appears to the routers on its periphery like any LAN.


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LMI FeaturesLMI Features-- MulticastingMulticasting

Multicast groups are designated by a series of fourMulticast groups are designated by a series of fourreserved DLCI values (1019 to 1022). Framesreserved DLCI values (1019 to 1022). Framessent by a device using one of these reservedsent by a device using one of these reserved

DLCIs are replicated by the network and sent toDLCIs are replicated by the network and sent toall exit points in the designated set. Theall exit points in the designated set. Themulticasting extension also defines LMImulticasting extension also defines LMImessages that notify user devices of themessages that notify user devices of theaddition, deletion, and presence of multicastaddition, deletion, and presence of multicast

groups.groups.


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LMI FeaturesLMI Features-- Inverse ARPInverse ARP

The Inverse ARP mechanismThe Inverse ARP mechanismallows the router toallows the router toautomatically build the Frameautomatically build the FrameRelay map, as shown in theRelay map, as shown in theFigure. The router learns theFigure. The router learns the

DLCIs that are in use from theDLCIs that are in use from theswitch during the initial LMIswitch during the initial LMIexchange. The router thenexchange. The router thensends an Inverse ARP requestsends an Inverse ARP requestto each DLCI for each protocolto each DLCI for each protocolconfigured on the interface ifconfigured on the interface if

the protocol is supported. Thethe protocol is supported. Thereturn information from thereturn information from theInverse ARP is then used toInverse ARP is then used tobuild the Frame Relay map.build the Frame Relay map.


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LMI FeaturesLMI Features-- Frame Relay mappingFrame Relay mapping

The router nextThe router next--hop addresshop addressdetermined from the routingdetermined from the routingtable must be resolved to atable must be resolved to aFrame Relay DLCI, as shownFrame Relay DLCI, as shownin the Figure. The resolution isin the Figure. The resolution is

done through a data structuredone through a data structurecalled a Frame Relay map.called a Frame Relay map.The routing table is then usedThe routing table is then usedto supply the nextto supply the next--hop protocolhop protocoladdress or the DLCI foraddress or the DLCI foroutgoing traffic. This dataoutgoing traffic. This data

structure can be staticallystructure can be staticallyconfigured in the router, or theconfigured in the router, or theInverse ARP feature can beInverse ARP feature can beused for automatic setup of theused for automatic setup of themap.map.


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LMI FeaturesLMI Features-- Frame Relay switching tableFrame Relay switching table

The router nextThe router next--hop addresshop addressdetermined from the routingdetermined from the routingtable must be resolved to atable must be resolved to aFrame Relay DLCI, as shownFrame Relay DLCI, as shownin the Figure. The resolution isin the Figure. The resolution is

done through a data structuredone through a data structurecalled a Frame Relay map.called a Frame Relay map.The routing table is then usedThe routing table is then usedto supply the nextto supply the next--hop protocolhop protocoladdress or the DLCI foraddress or the DLCI foroutgoing traffic. This dataoutgoing traffic. This data

structure can be staticallystructure can be staticallyconfigured in the router, or theconfigured in the router, or theInverse ARP feature can beInverse ARP feature can beused for automatic setup of theused for automatic setup of themap.map.


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LMI FeaturesLMI Features-- Frame Relay SwitchingFrame Relay Switching

The Frame Relay switchingThe Frame Relay switchingtable consists of four entries:table consists of four entries:two for incoming port andtwo for incoming port andDLCI, and two for outgoingDLCI, and two for outgoingport and DLCI, as shown in theport and DLCI, as shown in the

Figure. The DLCI could,Figure. The DLCI could,therefore, be remapped as ittherefore, be remapped as itpasses through each switch;passes through each switch;the fact that the port referencethe fact that the port referencecan be changed is why thecan be changed is why theDLCI does not change evenDLCI does not change even

though the port referencethough the port referencemight change.might change.


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Frame Relay SubinterfacesFrame Relay Subinterfaces

Subinterfaces are logicalSubinterfaces are logical

subdivisions of a physicalsubdivisions of a physical

interface.interface.

By logically dividing aBy logically dividing asingle physical WANsingle physical WAN

serial interface intoserial interface into

multiple virtualmultiple virtual

subinterfaces, the overallsubinterfaces, the overall

cost of implementing acost of implementing aFrame Relay network canFrame Relay network can

be reduced.be reduced.


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Spilt Horizon Use in Frame RelaySpilt Horizon Use in Frame Relay

if a remote routerif a remote routersends an update tosends an update tothe headquartersthe headquartersrouter that isrouter that isconnecting multipleconnecting multiplePVCs over a singlePVCs over a singlephysical interface,physical interface,the headquartersthe headquartersrouter cannotrouter cannotadvertise that routeadvertise that route

through the samethrough the samephysical interface tophysical interface toother remoteother remoteroutersrouters


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SubinterfacesSubinterfaces

You can configure subinterfaces to support theYou can configure subinterfaces to support thefollowing connection types:following connection types:

PointPoint--toto--pointpoint ---- A single subinterface is used toA single subinterface is used toestablish one PVC connection to anotherestablish one PVC connection to anotherphysical interface or subinterface on a remotephysical interface or subinterface on a remoterouter.router.

MultipointMultipoint ---- A single subinterface is used toA single subinterface is used toestablish multiple PVC connections to multipleestablish multiple PVC connections to multiplephysical interfaces or subinterfaces on remotephysical interfaces or subinterfaces on remoterouters.routers.


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Writing the IOS command sequence toWriting the IOS command sequence to

completely configure Frame Relaycompletely configure Frame Relay

Select the interface and go into interface configuration modeSelect the interface and go into interface configuration mode

Router(config) # interface serial 0Router(config) # interface serial 0

Configure a networkConfigure a network--layer address, for examlple, an IP addresslayer address, for examlple, an IP address

Router(configRouter(config--if) # ip address 212.14.249.197 255.255.255.0if) # ip address 212.14.249.197 255.255.255.0

Select the encapsulation type used for data traffic endSelect the encapsulation type used for data traffic end--toto--endendRouter(configRouter(config--if) # encapsulation frameif) # encapsulation frame--relay [cisco|ietf]relay [cisco|ietf]

For Cisco IOS 11.1 or earlier specify the LMI type used in the FrameFor Cisco IOS 11.1 or earlier specify the LMI type used in the Frame

Relay Switch,Relay Switch, Router(configRouter(config--if) # frameif) # frame--relay lmirelay lmi--type {ansi|cisco|q933i}type {ansi|cisco|q933i}

for later versions of the Cisco IOS LMI type is autosensedfor later versions of the Cisco IOS LMI type is autosensed

Configure the bandwidth of the linkConfigure the bandwidth of the linkRouter(configRouter(config--if) # bandwidthif) # bandwidth kilobitskilobits

If the inverse ARP was disabled on the router, reIf the inverse ARP was disabled on the router, re--enable itenable it

Router(configRouter(config--if) # frameif) # frame--relay inverserelay inverse--arp [protocol] [dlci]arp [protocol] [dlci]


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Configuring subinterfacesConfiguring subinterfaces

Select the interfaceSelect the interface

Remove any network layer address assigned to the physicalRemove any network layer address assigned to the physicalinterfaceinterface

Configure Frame Relay encapsulation as stated perviuslyConfigure Frame Relay encapsulation as stated perviusly

Select the subinterface you want to configureSelect the subinterface you want to configureRouter(configRouter(config--if)# interface serial number.subinterfaceif)# interface serial number.subinterface--number {multipoint|pointnumber {multipoint|point--toto--point}point} Interface number 1Interface number 1--42949672934294967293

Multipoint is used when you want the router to forward broadcasts and routingMultipoint is used when you want the router to forward broadcasts and routingupdates it receivesupdates it receives

PointPoint--toto--point is used when you do not want the router to forward broadcasts andpoint is used when you do not want the router to forward broadcasts androuting updates it receives.routing updates it receives.

Configure the network layer address on the subinterfaceConfigure the network layer address on the subinterface

If you configured the subinterface as multipoint or pointIf you configured the subinterface as multipoint or point--toto--point youpoint youmust configure a local DLCImust configure a local DLCI

Router(configRouter(config--if)# frameif)# frame--relay interfacerelay interface--dlcidlci dlcidlci--numbernumber


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Router(configRouter(config--if)#if)# frameframe--relay maprelay map protocolprotocol protocolprotocol

address dlciaddress dlci[[broadcastbroadcast] [] [ietf|cisco|payloadietf|cisco|payload--compresscompress

packetpacket--byby--packetpacket]]


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GOOD LUCK Carl MGOOD LUCK Carl M

chapter 6- semester4

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