ccna exp4 - chapter03 - frame-relay

8/3/2019 CCNA Exp4 - Chapter03 - Frame-Relay

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Chapter 3 Frame-Relay

CCNA Ex loration 4.0

Please purchase apersonal license.


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Introduction

Hc vin mng Bach Khoa - Website: www.bkacad.com 2


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Basic Frame Relay Concepts



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Introducing Frame Relay


Frame Relay: An Efficient and Flexible WAN Technology

Frame Relay has become the most widely used WAN technology in the world.

Large enterprises, governments, ISPs, and small businesses use FrameRelay, primarily because of its price and flexibility.

Moreover, Frame Relay provides greater bandwidth, reliability, and resiliencythan private or leased lines

Frame Relay reduces network costs by using less equipment, less complexity,

and an easier implementation.


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In the example shown in the figure, Span Engineering has fivecampuses across North America.

The bandwidth requirement of each site:



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The first Solution Leased line

Using leased lines, each Span site is connected through a switch at the localtelephone company's central office (CO) through the local loop, and then

across the entire network. These lines are truly dedicated in that the network provider reserves that line

for Span's own use. There is no sharing, and Span is paying for the end-to-endcircuit regardless of how much bandwidth it uses.



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The second Solution Frame Relay

Frame Relay is a more cost-effective option for two reasons. First, with dedicated lines, customers pay for an end-to-end connection. That

includes the local loop and the network link.

With Frame Relay, customers only pay for the local loop, and for the bandwidththey purchase from the network provider.

The second reason for Frame Relay's cost effectiveness is that it shares bandwidthacross a larger base of customers.



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The table shows a representative cost comparison for comparableISDN and Frame Relay connections.



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The Flexibility of Frame Relay A virtual circuit provides considerable flexibility in network design. In Frame Relay, the end of each connection has a number to identify it

called a Data Link Connection Identifier (DLCI).

Any station can connect with any other simply by stating the address of

that station and DLCI number of the line it needs to use.


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The Frame Relay WAN

In the late 1970s and into the early 1990s, the WAN technology joining the endsites was typically using the X.25 protocol. However, X.25 have much

overhead to the protocol. Frame Relay has lower overhead than X.25 because it has fewer capabilities.

For example, Frame Relay does not provide error correction, modern WANfacilities offer more reliable connection services and a higher degree ofreliabilit than older facilities.



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Frame Relay Operation

The connection between a DTE device and a DCE device consists of both a physicallayer component and a link layer component:

The physical component defines the mechanical, electrical, functional, andprocedural specifications for the connection between the devices.

The link layer component defines the protocol that establishes the connectionbetween the DTE device, such as a router, and the DCE device, such as a switch.



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Virtual Circuits

The connection through a Frame Relay network between two DTEs is called avirtual circuit (VC). The circuits are virtual because there is no direct electricalconnection from end to end.

There are 2 ways to establish VCs: SVCs, switched virtual circuits, are established dynamically by sending

signaling messages to the network (CALL SETUP, DATA TRANSFER,IDLE, CALL TERMINATION).

PVCs, permanent virtual circuits, are preconfigured by the carrier, and after


, .


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Virtual Circuits

Local Significance

VCs provide a bidirectional communication path from one device to another.VCs are identified by DLCIs. DLCI values typically are assigned by the Frame

Relay service provider (for example, the telephone company). Frame Relay DLCIs have local significance, which means that the values

themselves are not unique in the Frame Relay WAN.



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Virtual Circuits

Idenfiying VCs

Frame Relay labels each VC with a DLCI. The DLCI is stored in the address field of every frame transmitted to tell the network how

the frame should be routed.

The Frame Relay service provider assigns DLCI numbers. Usually, DLCIs 0 to 15 and1008 to 1023 are reserved for special purposes. Therefore, service providers typicallyassign DLCIs in the range of 16 to 1007.



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Virtual Circuits

Multiple VCs

Frame Relay is statistically multiplexed, meaning that it transmits only oneframe at a time, but that many logical connections can co-exist on a single

physical line. The Frame Relay Access Device (FRAD) or router connected to the FrameRelay network may have multiple VCs connecting it to various endpoints.

Multiple VCs on a single physical line are distinguished because each VC has


.


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Virtual Circuits

For example, Span Engineering has five locations, with its headquarters inChicago. Chicago is connected to the network using five VCs and each VC isgiven a DLCI.



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Frame Relay Encapsulation

Frame Relay takes data packets from a network layer protocol, such asIP or IPX, encapsulates them as the data portion of a Frame Relayframe, and then passes the frame to the physical layer for delivery on

the wire.



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Frame Relay Topologies

There are three topology types: star, full mesh, or partial mesh.



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A fully meshed topology means that each node on the periphery of agiven packet-switching network has a direct path to every other node

on the cloud.



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A partially meshed topology reduces the number of routers within aregion that have direct connections to all other nodes in the region.



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DLCI


A data-link connection identifier (DLCI) identifies the logical VC between the CPE andthe Frame Relay switch.

The Frame Relay switch maps the DLCIs between each pair of routers to create a PVC.

DLCIs have local significance, although there some implementations that use globalDLCIs. DLCIs 0 to 15 and 1008 to 1023 are reserved for special purposes. Service providers assign DLCIs in the range of 16 to 1007.

DLCI 1019 - 1022: Multicasts DLCI 1023: Cisco LMI

DLCI 0: ANSI LMI


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Frame Relay Address Mapping


Cisco routers support all network layer protocols over Frame Relay, such asIP, IPX, and AppleTalk. This address-to-DLCI mapping can be accomplishedeither by static or dynamic mapping:

Manual

Manual: Administrators use a frame relay map statement.

Dynamic

Inverse Address Resolution Protocol (I-ARP) provides a given DLCIand requests next-hop protocol addresses for a specific connection.

The router then updates its mapping table and uses the information inthe table to forward packets on the correct route.


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Inverse ARP

12


Once the router learns from the switch about available PVCs and theircorresponding DLCIs, the router can send an Inverse ARP request to theother end of the PVC. (unless statically mapped)

For each supported and configured protocol on the interface, the router sendsan Inverse ARP request for each DLCI. (unless statically mapped)

In effect, the Inverse ARP request asks the remote station for its Layer 3address.

At the same time, it provides the remote system with the Layer 3 address ofthe local system.

The return information from the Inverse ARP is then used to build the FrameRelay map.


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Inverse ARP


Inverse Address Resolution Protocol (Inverse ARP) was developed toprovide a mechanism for dynamic DLCI to Layer 3 address maps.

Inverse ARP works much the same way Address Resolution Protocol(ARP) works on a LAN.

However, with ARP, the device knows the Layer 3 IP address andneeds to know the remote data link MAC address.

With Inverse ARP, the router knows the Layer 2 address which is theDLCI, but needs to know the remote Layer 3 IP address.


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Inverse ARP


On a Cisco router, Inverse ARP is on by default when an interface isconfigured to use Frame Relay encapsulation.

If static mapping for a specific DLCI is configured, Inverse ARP isautomatically disabled for the specified protocol on the specifiedDLCI.

Use static mapping if the router at the other end either does notsupport Inverse ARP or does not support Inverse ARP for a specificprotocol being used over Frame Relay.


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Inverse ARP Limitations

Inverse ARP only resolves network addresses of remote Frame-Relay

Frame RelayNetwork

Headquarters

Hub City

Satellite Office 1

Spokane

172.16.1.1172.16.1.2

DLCI 101 DLCI 102


connections that are directly connected.

Inverse ARP does not work with Hub-and-Spoke connections. When using dynamic address mapping, Inverse ARP requests a next-hop

protocol address for each active PVC.

Once the requesting router receives an Inverse ARP response, it updates itsDLCI-to-Layer 3 address mapping table.

Dynamic address mapping is enabled by default for all protocols enabled on aphysical interface.

If the Frame Relay environment supports LMI autosensing and Inverse ARP,dynamic address mapping takes place automatically.

Therefore, no static address mapping is required.


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Local Management Interface (LMI)

LMI is a signaling standard between the DTE and the Frame Relay switch. LMI is responsible for managing the connection and maintaining the status

between devices.

LMI Extensions: VC status messages Multicasting

Global addressing


Simple flow control


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Starting with Cisco IOS software release 11.2, the default LMI

autosense feature detects the LMI type supported by the directlyconnected Frame Relay switch. Based on the LMI status messages itreceives from the Frame Relay switch, the router automaticallyconfigures its interface with the supported LMI type acknowledged bythe Frame Relay switch.


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Using LMI and Inverse ARP to Map Addresses



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Activity 3.1.5.5



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Configuring Frame Relay



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Frame Relay Configuration Tasks



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Enable Frame Relay Encapsulation

Step 1. Setting the IP Address on the Interface Step 2. Configuring Encapsulation

R(config-if)# encapsulation frame-relay [cisco | ietf]

Step 3. Setting the Bandwidth Step 4. Setting the LMI Type (optional)



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Configuring a Static Frame Relay Map


Static mapping is manually configured on a router. Establishing static mappingdepends on your network needs.

Router(config-if)# frame-relay map protocol protocol-address dlci

[broadcast] [ietf | cisco] Note:

(config-if)# no frame-relay inverse-arp Disables the sending of InverseARP requests.

(config-if)# no arp frame-relay Disables Inverse ARP responses.


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By default,cisco is thedefault

Example


Remote IPAddress

Local DLCIUses ciscoencapsulation forthis DLCI (not

needed, default)

encapsu a on


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Applies to all DLCIs unlessconfigured otherwise


If the Cisco encapsulation is configured on a serial interface, then bydefault, that encapsulation applies to all VCs on that serial interface. If the equipment at the destination is Cisco and non-Cisco, configure

the Cisco encapsulation on the interface and selectively configure IETFencapsulation per DLCI, or vice versa.

C S


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Case study: Hub and Spoke Topology

HeadquartersHub City

172.16.1.2

DLCI 101 DLCI 112

Hub Router


Frame RelayNetwork

Satellite Office 1Spokane

Satellite Office 2Spokomo

172.16.1.1 172.16.1.3

DLCI 102 DLCI 211

Spoke

Routers



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HubCity

interface Serial0

ip address 172.16.1.2 255.255.255.0

encapsulation frame-relay

Spokane

Frame RelayNetwork



172.16.1.1 172.16.1.3

172.16.1.2

DLCI 101

DLCI 102

DLCI 112

DLCI 211

Configuration using Inverse ARP


n er ace er a

ip address 172.16.1.1 255.255.255.0encapsulation frame-relay

Spokomo

interface Serial0

ip address 172.16.1.3 255.255.255.0


Headquarters

Hub City

C


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HubCity# show frame-relay map

Frame Relay

Network

Satellite Office 1

Spokane

Satellite Office 2

Spokomo

172.16.1.1 172.16.1.3

172.16.1.2

DLCI 101

DLCI 102

DLCI 112

DLCI 211



status defined, active

Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast,


Spokane# show frame-relay map



Spokomo# show frame-relay map



C fi i i I ARP


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Inverse ARP resolved the ip addresses for HubCity for bothSpokane and Spokomo Inverse ARP resolved the ip addresses for Spokane for HubCity Inverse ARP resolved the ip addresses for Spokomo for HubCity

What about between Spokane and Spokomo?

,




R

Headquarters

Hub City


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Inverse ARP Limitations

Can HubCity ping both Spokane and Spokomo? Yes!

Frame Relay

Network

Satellite Office 1

Spokane

Satellite Office 2

Spokomo

172.16.1.1 172.16.1.3

172.16.1.2

DLCI 101

DLCI 102

DLCI 112

DLCI 211


Can Spokane and Spokomo ping HubCity? Yes

Can Spokane and Spokomo ping each other? No! The Spokerouters serial interfaces (Spokane and Spokomo) drop the ICMPpackets because there is no DLCI-to-IP address mapping for thedestination address.

Solutions to the limitations of Inverse ARP1. Add an additional PVC between Spokane and Spokomo (FullMesh)

2. Configure Frame-Relay Map Statements

3. Configure Point-to-Point Subinterfaces.

HubCityFrame Relay Map Statements


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172.16.1.2

DLCI 101 DLCI 112

y

interface Serial0

ip address 172.16.1.2

255.255.255.0encapsulation frame-relay

(Inverse-ARP still works here)

Spokane

interface Serial0


255.255.255.0


frame-relay map ip 172.16.1.3 102

Frame-Relay Map Statements


Network



172.16.1.1 172.16.1.3

DLCI 102 DLCI 211

rame-re ay map p . . .

Spokomo

interface Serial0


255.255.255.0


frame-relay map ip 172.16.1.1 211frame-relay map ip 172.16.1.2 211

Notice that the routers are configured to use either IARP or Frame Relay

maps. Using both on the same interface will cause problems.

HeadquartersHub CityMixing Inverse ARP and Frame Relay


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Frame RelayNetwork

y

172.16.1.2

DLCI 101

DLCI 102

DLCI 112

DLCI 211

Inverse ARP

Map Statements

Frame Relay




172.16.1.1 172.16.1.3

The previous configuration works fine and all routers can ping eachother.

What if we were to use I-ARP between the spoke routers and the hub,and frame relay map statements between the two spokes?

There would be a problem!

maps

Mixing Inverse ARP and Frame Relay Map Statements


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HubCity

interface Serial0


255.255.255.0


Spokane

interface Serial0



172.16.1.2

DLCI 101 DLCI 112



255.255.255.0

encapsulation frame-relayframe-relay map ip 172.16.1.3 102

Spokomo

interface Serial0


255.255.255.0



Network



172.16.1.1 172.16.1.3

DLCI 102 DLCI 211



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Serial0 (up): ip 172.16.1.1 dlci 101, dynamic,broadcast, status defined, active





. . . , ,

broadcast, status defined, activeSerial0 (up): ip 172.16.1.3 dlci 102, static, CISCO,




Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO,




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Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active




Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active





Good News:

Everything looks fine! Now all routers can ping each other!Bad News:

Problem when using Frame-Relay map statements AND InverseARP.

This will only work until the router is reloaded, here is why...



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Frame-Relay Map Statement Rule:

When a Frame-Relay map statement is configured for a particular

protocol (IP, IPX, ) Inverse-ARP will be disabled for that specificprotocol, only for the DLCI referenced in the Frame-Relay mapstatement.



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The previous solution worked only because the Inverse ARP had taken












place between Spokane and HubCity, and between Spokomo and HubCity,

before the Frame-Relay map statements were added. (The Frame-Relaymap statement was added after the Inverse ARP took place.)

Both the Inverse-ARP and Frame-Relay map statements are in effect. Once the router is reloaded (rebooted) the Inverse-ARP will never occur

because of the configured Frame-Relay map statement. (assuming the

running-config is copied to the startup-config)

Rule: Inverse-ARP will be disabled for that specific protocol, for theDLCI referenced in the Frame-Relay map statement.



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HubCity# show frame-relay map (after reload)

Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status

defined, active


defined, active


NOW MISSING: Serial0 (up): ip 172.16.1.2 dlci 102, dynamic,



broadcast, status defined, active

Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, statusdefined, active


NOW MISSING: Serial0 (up): ip 172.16.1.2 dlci 211, dynamic,

broadcast, status defined, active

Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status

defined, active



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HubCity# show frame-relay map (after reload)


defined, active


defined, active





defined, active



defined, active

Spokane and Spokomo can no longer ping HubCity because they do nothave a dlci-to-IP mapping for the others IP address!

HubCity

interface Serial0Frame-Relay Map Statements


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172.16.1.2

DLCI 101 DLCI 112

interface Serial0


255.255.255.0encapsulation frame-relay

(Inverse-ARP still works here)

Spokane

interface Serial0


255.255.255.0



y p


Network



172.16.1.1 172.16.1.3

DLCI 102 DLCI 211

rame-re ay map p . . .

Spokomo

interface Serial0


255.255.255.0


frame-relay map ip 172.16.1.1 211frame-relay map ip 172.16.1.2 211

Solution: Do not mix IARP with Frame Relay maps statements. If needbe use Frame-Relay map statements instead of IARP.


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Advanced Frame Relay Concepts


Solving Reachability Issues


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By default, a Frame Relay network provides NBMA connectivitybetween remote sites. NBMA clouds usually use a hub-and-spoke

topology. Unfortunately, a basic routing operation based on the split horizon

principle can cause reachability issues on a Frame Relay NBMAnetwork.



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g y

Router(config-if)#no ip split-horizon [EIGRP {AS_number}]

Split Horizon prohibits routing updatesreceived on an interface from exiting thatsame interface.


To remedy preview situation, turn off split horizon for IP. When configuring a serial interface for Frame Relay encapsulation,

split horizon for IP is automatically turned off.

Of course, with split horizon disabled, the protection it affords againstrouting loops is lost.

Split horizon is only an issue with distance vector routing protocols likeRIP, IGRP and EIGRP. It has no effect on link state routing protocolslike OSPF and IS-IS.



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g y


Frame Relay can partition a physical interface into multiple virtual interfacescalled subinterfaces.

A subinterface is simply a logical interface that is directly associated with aphysical interface. Therefore, a Frame Relay subinterface can be configuredfor each of the PVCs coming into a physical serial interface.



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g y


Each point-to-point subnetwork can be assigned a unique network address,

which allows packets received on a physical interface to be sent out the samephysical interface because the packets are forwarded on VCs in different

subinterfaces.This allows each subinterface to act similar to a leased line.

Each point-to-point subinterface is treated as a separate physical interface.

Key Terminology


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y gy


Access rate or port speed - This is the clock speed or port speed of the connection orlocal loop to the Frame Relay cloud.

It is the rate at which data travels into or out of the network, regardless of othersettings.

Committed Information Rate (CIR) This is the rate, in bits per second, at which theFrame Relay switch agrees to transfer data.

The rate is usually averaged over a period of time, referred to as the committedrate measurement interval (Tc).

In general, the duration of Tc is proportional to the "burstiness" of the traffic.

Key Terminology


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Oversubscription Service providers sometimes sell more capacity than they have on the

assumption that not everyone will demand their entitled capacity all of thetime.

This oversubscription is analogous to airlines selling more seats than they

have in the expectation that some of the booked customers will not showup.

Bursting


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A great advantage of Frame Relay is that any network capacity that is beingunused is made available or shared with all customers, usually at no extracharge.

Because the physical circuits of the Frame Relay network are shared betweensubscribers, there will often be time where there is excess bandwidth available.Frame Relay can allow customers to dynamically access this extra bandwidthand "burst" over their CIR for free.

A device can burst up to the access rate and still expect the data to getthrough. The duration of a burst transmission should be short, less than 3 or 4

seconds.

Bursting


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Committed Burst Information Rate (CBIR) - The CBIR is a negotiated rateabove the CIR which the customer can use to transmit for short burst. It allowstraffic to burst to higher speeds, as available network bandwidth permits.

However, it cannot exceed the port speed of the link. Excess Burst Size (BE) is the term used to describe the bandwidth available

above the CBIR up to the access rate of the link. Unlike the CBIR, it is notnegotiated. Frames may be transmitted at this level but will most likely be

dropped.

Frame Relay Flow Control


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Forward Explicit Congestion Notification (FECN) When a Frame Relayswitch recognizes congestion in the network, it sends an FECN packet to thedestination device.

This indicates that congestion has occurred.

Backward Explicit Congestion Notification (BECN) When a Frame Relay

switch recognizes congestion in the network, it sends a BECN packet to thesource router.

This instructs the router to reduce the rate at which it is sending packets.

With Cisco IOS Release 11.2 or later, Cisco routers can respond to BECNnotifications.



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Discard eligibility (DE) bit When the router or switch detectsnetwork congestion, it can mark the packet "Discard Eligible".

The DE bit is set on the traffic that was received after the CIR was

met. These packets are normally delivered. However, in periods of

congestion, the Frame Relay switch will drop packets with the DEbit set first.



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Frames arriving at a switch are queued or buffered prior to forwarding. As inany queuing system, it is possible that there will be an excessive buildup offrames at a switch.

This causes delays. Delays lead to unnecessary retransmissions that occurwhen higher level protocols receive no acknowledgment within a set time. Insevere cases, this can cause a serious drop in network throughput. To avoidthis problem, Frame Relay incorporates a flow control feature.

e er o . . .



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Activity 3.3.3.2



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Confi urin Advanced Frame Rela


Configuring Frame Relay Subinterfaces


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There are two types of Frame Relay subinterfaces: Point-to-point

Multipoint



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Mulitpoint


Physical interfaces: With a hub and spoke topology Split Horizon willprevent the hub router from propagating routes learned from one spokerouter to another spoke router.

Point-to-point subinterfaces: Each subinterface is on its own subnet.

Broadcasts and Split Horizon not a problem because each point-to-point connection is its own subnet.

Multipoint subinterfaces: All participating subinterfaces would be inthe same subnet. Broadcasts and routing updates are also subject tothe Split Horizon Rule and may pose a problem.

Point-to-point

Configuring Subinterfaces Example


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Step 1. Remove any network layer address assigned to the physical interface.If the physical interface has an address, frames are not received by the local

subinterfaces. Step 2. Configure Frame Relay encapsulation on the physical interface using

the encapsulation frame-relay command.

Ste 3. For each of the defined PVCs create a lo ical subinterface. S ecif


the port number, followed by a period (.) and the subinterface number. To

make troubleshooting easier, it is suggested that the subinterface numbermatches the DLCI number.

Step 4. Configure an IP address for the interface and set the bandwidth.At this point, we will configure the DLCI. Recall that the Frame Relay serviceprovider assigns the DLCI numbers.

Step 5. Configure the local DLCI on the subinterface using the frame-relayinterface-dlci command.

Configuring Subinterfaces Example


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show frame-relay map


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Point-to-point subinterfaces are listed as a point-to-point dlci

Router#show frame-relay map

Serial0.1 (up): point-to-point dlci, dlci 301 (0xCB, 0x30B0),broadcast status defined, active


mu po n su n er aces, ey are s e as an nverse

entry, dynamic

Router#show frame-relay map

Serial0 (up): ip 172.30.2.1 dlci, 301 (0x12D, 0x48D0),

dynamic,, broadcast status defined, active

Point-to-point Subinterfaces


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Mulitpoint

Point-to-point


Point-to-point subinterfaces are like conventional point-to-point interfaces (PPP,) and have no concept of (do not need): Inverse-ARP

mapping of local DLCI address to remote network address (frame-relaymap statements)

Frame-Relay service supplies multiple PVCs over a single physical interfaceand point-to-point subinterfaces subdivide each PVC as if it were a physicalpoint-to-point interface.

Point-to-point subinterfaces completely bypass the local DLCI to remotenetwork address mapping issue.



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Mulitpoint

Point-to-point


With point-to-point subinterfaces you: Cannot have multiple DLCIs associated with a single point-to-

point subinterface

Cannot use frame-relay map statements

Cannot use Inverse-ARP Can use theframe-relay interface dlcistatement (for both

point-to-pointandmultipoint)



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Each subinterface is on a separate

network or subnet with a single remoterouter at the other end of the PVC.


172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

S0 S1 S2

172.30.1.1/24 172.30.2.1/24 172.30.3.1/24


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Point-to-point subinterfaces are equivalent to using multiple physicalpoint to point interfaces.

Site A Site B Site C

172.30.1.2/24 172.30.2.2/24 172.30.3.2/24



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physical or subinterface on a remote router.

In this case, the interfaces would be:

In the same subnet

Each interface would have a single DLCI

Each point-to-point connection is its own subnet.

In this environment, broadcasts are not a problem because the routers arepoint-to-point and act like a leased line.



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Point-to-point subinterface configuration, minimum of twocommands:

Router(config)# interface Serial0.1point-to-point

Router(config-subif)# frame-relay interface-dlci dlci

Rules:


1. No Frame-Relay map statements can be used with point-to-point

subinterfaces.2. One and only one DLCI can be associated with a single point-to-pointsubinterface

By the way, encapsulation is done only at the physical interface:interface Serial0no ip address


Point-to-Point Subinterfaces at the Huband Spokes

Each subinterface on Hub router requires aseparate subnet (or network) Each subinterface on Hub router is treatedlike a regular physical point-to-point


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g p y p p

interface, so split horizon does not need tobe disabled.Interface Serial0 (for all routers)


no ip address

HubCityinterface Serial0.1point-to-point

ip address 172.16.1.1 255.255.255.0


-

Headquarters

Hub City

Serial 0.1

172.16.1.1/24

DLCI 301 DLCI 302

Serial 0.2

172.16.2.1/24


interface Serial0.2point-to-pointip address 172.16.2.1 255.255.255.0


frame-relay interface dlci 302

Spokane

interface Serial0.1point-to-point

ip address 172.16.1.2 255.255.255.0


Spokomo


ip address 172.16.2.2 255.255.255.0


Frame Relay

Network

Satellite Office 1

Spokane

Satellite Office 2

Spokomo

Serial 0.1

172.16.1.2/24

Serial 0.1

172.16.2.2/24

DLCI 103 DLCI 203

Two subnets

Multipoint Subinterfaces


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Mulitpoint

Point-to-point


Share many of the same characteristics as a physical Frame-Relay interface

With multipoint subinterface you: can have multiple DLCIs assigned to it.

can use frame-relay map & interface dlci statements

can use Inverse-ARP

Remember, with point-to-point subinterfaces you:

cannot have multiple DLCIs associated with a single point-to-point subinterface cannot use frame-relay map statements

cannot use Inverse-ARP

(can use theframe-relay interface dlcistatement for bothpoint-to-pointandmultipoint)

Multipoint subinterfaces


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Each subinterface is on a separatenetwork or subnet but may have

multiple connections, with a differentDLCI for each connection.


172.30.1.0/24172.30.2.0/24

172.30.3.0/24

Split horizon still an issue on each Multipoint subinterface.

S0 S1 S2

172.30.1.1/24 172.30.2.1/24 172.30.3.1/24


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Multipoint subinterfaces are equivalent to using multiple physical hubto spoke interfaces.

Site A1

Site B1

Site C2

172.30.1.2/24

172.30.2.2/24

172.30.3.3/24

Site A2

172.30.1.3/24

Site B2

172.30.2.3/24

Site C1

172.30.3.2/24

Notes

Multipoint subinterface at the Hub andPoint-to-Point Subinterfaces at theSpokes


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Serial 0

172.16.3.3

DLCI 301 DLCI 302

Highly scalable solution Disable Split Horizon on Hub router whenrunning a distance vector routing protocol

Interface Serial0 (for all routers)


no ip address

HubCity

interface Serial0.1mulitpoint

ip address 172.16.3.3 255.255.255.0


Frame Relay

Network

Satellite Office 1

Spokane

Satellite Office 2

Spokomo

Serial 0

172.16.3.1

Serial 0

172.16.3.2

DLCI 103 DLCI 203

frame-relay interface-dlci 301


no ip split-horizon [EIGRP{AS_number}]

Spokane


ip address 172.16.3.1 255.255.255.0


Spokomo


ip address 172.16.3.2 255.255.255.0


One subnet

Verifying Frame Relay Operation


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Troubleshooting Frame Relay Configuration


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When an Inverse ARP request is made, the router updates its map table withthree possible LMI connection states. These states are active state, inactivestate, and deleted state ACTIVE States indicates a successful end-to-end (DTE to DTE) circuit. INACTIVE State indicates a successful connection to the switch (DTE to

DCE) without a DTE detected on the other end of the PVC. This can occurdue to residual or incorrect configuration on the switch.

DELETED State indicates that the DTE is configured for a DLCI the switchdoes not recognize as valid for that interface.



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The possible values of the status field are as follows: 0x0 - The switch has this DLCI ro rammed but for some reason it


is not usable. The reason could possibly be the other end of the

PVC is down. 0x2 - The Frame Relay switch has the DLCI and everything is

operational.

0x4 - The Frame Relay switch does not have this DLCIprogrammed for the router, but that it was programmed at some

point in the past. This could also be caused by the DLCIs beingreversed on the router, or by the PVC being deleted by the serviceprovider in the Frame Relay cloud.



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Extra: Configure a Router as a FR Switch


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Enable frame-relay switching on the router acting as theservice provider Frame Relay cloud as follows:

FRswitch(config)#frame-relay switching



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The remaining configurations on the Frame Relay switch are specific tothe interfaces. On each serial interface, configure the encapsulation toFrame Relay, define the interface as a Frame Relay DCE, and set theclockrate (if the serial interface connects to DCE cable).

The following is an example:

FRswitch(config-if)#encapsulation frame-relayFRswitch(config-if)#frame-relay intf-type dceFRswitch(config-if)#clock rate 56000



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Frame Relay switches identify inbound frames by their data-link connectionidentifier (DLCI). The DLCI is then referenced in a switching table to determinethe outbound port.

Statically define an end-to-end PVC between SanJose1 and London. A staticroute needs to be configured for each serial interface, as shown in thefollowing:

FRswitch(config)#interface serial 0/0FRswitch(config-if)#frame-relay route 102 interface serial 0/1 201FRswitch(config-if)#interface serial 0/1FRswitch(config-if)#frame-relay route 201 interface serial 0/0 102



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Verifying:

Labs


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Summary


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ccna exp4 - chapter03 - frame-relay

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