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Chapter 5Chap
ter 5
FRAME RELAYFRAME RELAY
Semester 4
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ObjectiveObjective
Learn about another type of WAN technology,Frame Relay, that can be implemented to solve
connectivity issues for users who need access togeographically distant locations.
Learn about Frame Relay services, standards,components, and operation.
Describes the configuration tasks for Frame Relayservice, along with the commands for monitoringand maintaining a Frame Relay connection.
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ContentContent
#Day Topic Duration
Frame Relay Technology
LMI: Ciscos Implementation of FR
LMI Features
Frame Relay Sub-Interfaces
Configuration of Basic Frame Relay
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FRAME RELAY TECHNOLOGYFRAME RELAY TECHNOLOGY
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IntroductionIntroduction
Frame Relay is a Consultative Committee forCCITT and ANSI standard.
Defines a process for sending data over apublic data network (PDN).
A way of sending information over a WAN bydividing data into packets.
It operates at the physical and data linklayers of the OSI reference model.
It relies on upper-layer protocols such as TCPfor error correction.
Frame Relay uses virtual circuits to make
connections.
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OverviewOverview
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Frame Relay devicesFrame Relay devices
The network providing the Frame Relay
interface can be either: A carrier-provided public network
A network of privately owned equipment, servinga single enterprise.
Frame Relay network devices such asswitches, routers, CSU/DSUs, or multiplexers.
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Connection oriented servicesConnection oriented services
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Frame Relay terminologiesFrame Relay terminologies
Access rate
Local management interface (LMI)
Committed information rate (CIR) Committed burst (Bc)
Committed rate measurement interval (Tc)
Excess burst (Be)
Forward explicit congestion noti. (FECN)
Backward explicit congestion noti.(BECN)
Discard eligibility (DE) indicator
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Frame Relay technologyFrame Relay technology
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Terminologies:Terminologies: Access RateAccess Rate
The clock speed of the connection (local loop) to theFrame Relay cloud.
It is the rate at which data travels into or out of thenetwork
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Terminologies:Terminologies: DLCIDLCI
Data-link connection identifier.
A number that identifies the end point in a FrameRelay network.
Significance only to the local network.
The Frame Relay switch maps the DLCIs between apair of routers to create a permanent virtual circuit.
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Terminologies:Terminologies: LMILMI
Local management interface.
A signaling standard between the CPE device and theFrame Relay switch
Responsible for managing the connection andmaintaining status btw the devices.
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Terminologies:Terminologies: CIRCIR
Committed information rate.
The CIR is the guaranteed rate, that the serviceprovider commits to providing.
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Terminologies:Terminologies: BcBc
Committed Burst
The maximum number of bits that the switch agreesto transfer during a interval.
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Terminologies:Terminologies: TcTc
Committed Rate Measurement Interval.
The time interval shouldnt exceed 125 ms, almostalways 125 ms
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Terminologies:Terminologies: Excess burstExcess burst
The maximum number of uncommitted bits that theswitch attempts to transfer beyond the CIR.
Dependent on the service offerings available by the
vendor, but is typically limited to the port speed ofthe local access loop.
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Terminologies:Terminologies: FECNFECN
Forward explicit congestion notification.
When a switch recognizes congestion in the network,it sends a FECN packet to the destination device.
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Terminologies:Terminologies: BECNBECN
Backward explicit congestion notification.
When a switch recognizes congestion in the network,it sends a BECN packet to the source router,instructing the router to reduce the rate at which it issending packets.
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Frame Relay congestionFrame Relay congestion
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Terminologies:Terminologies: DEDE
Discard eligibility indicator.
A set bit that indicates the frame may be discardedin preference to other frames if congestion occurs
The DE bit is set on the oversubscribed traffic.
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Frame Relay operationFrame Relay operation
A public FR service is deployed by putting FRswitching equipment in the central office of acarrier.
Economic benefits are got by from trafficsensitive charging rates and lack ofequipment and service maintenance.
The lines that connect user devices to theprovider can operate at a speed selected
from a broad range of data rates. Speeds between 56 kbps and 2 Mbps are
typical, although Frame Relay can supportlower and higher speeds.
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Frame Relay operationFrame Relay operation
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Frame Relay multiplexingFrame Relay multiplexing
Frame Relay provides a means formultiplexing many logical data
conversations, as virtual circuits, through ashared physical medium
Frame Relay's multiplexing provides moreflexible and efficient use of available
bandwidth. Frame Relay allows users to share bandwidth
at a reduced cost.
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Frame Relay multiplexingFrame Relay multiplexing
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Frame Relay DLCIFrame Relay DLCI
FR standards address PVCs that areconfigured and managed in a FR network.
FR PVCs are identified by DLCIs, that have
LOCAL significance. Multiplexing many virtual circuit through a
physical medium.
FR switches constructs a table mapping DLCIvalues to outbound ports.
The complete path to the destination isestablished before the first frame is sent.
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Frame Relay DLCI (cont.)Frame Relay DLCI (cont.)
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Frame Relay frame formatFrame Relay frame format
DLCI: Indicates the DLCI value. Consists of
the first 10 bits of the Address field. Congestion Control: The last 3 bits in the
address field. These are the FECN, BECN, anddiscard eligible (DE) bits.
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Frame Relay addressingFrame Relay addressing
DLCI address space is limited to 10 bits. possible 1024 DLCI addresses.
The usable portion of these addresses aredetermined by the LMI type: The Cisco LMI type supports a range of DLCI
addresses from DLCI 16-1007.
The ANSI/ITU LMI type supports the range ofaddresses from DLCI 16-992.
The remaining DLCI addresses are reservedfor vendor implementation.
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Frame Relay addressingFrame Relay addressing
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LMI: CISCOS IMPLEMENTATION OFLMI: CISCOS IMPLEMENTATION OF
FRAME RELAYFRAME RELAY
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LMI functionsLMI functions
To determine the operational status of thevarious PVCs that the router knows about
To transmit keepalive packets to ensure thatthe PVC stays up and does not shut downdue to inactivity
To tell the router what PVCs are available
Three LMI types can be invoked by therouter: ansi, cisco, and q933a
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LMI operationLMI operation
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LMI extension functionsLMI extension functions
In addition to the basic Frame Relay protocolfunctions for transferring data, the Frame
Relay specification includes LMI extensionsthat make supporting large, complexinternetworks easier. Virtual circuit status messages
Multicasting Global addressing
Simple flow control
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LMI FEATURESLMI FEATURES
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Frame Relay SignalingFrame Relay Signaling
Cisco supports three LMI standards: Cisco
ANSI T1.617 Annex D
ITU-T Q.933 Annex A
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Frame Relay mapFrame Relay map
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Frame Relay mappingFrame Relay mapping
Network address DLCI
The routing table is then used to supply thenext-hop protocol address or the DLCI foroutgoing traffic.
The resolution is done through a datastructure called a Frame Relay map.
This data structure can be staticallyconfigured in the router, or the Inverse ARPfeature can be used for automatic setup ofthe map.
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Frame Relay mappingFrame Relay mapping
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Inverse ARPInverse ARP
The Inverse ARP mechanism allows therouter to automatically build the Frame
Relay map.1. The router learns the DLCIs that are in use fromthe switch during the initial LMI exchange.
2. The router then sends an Inverse ARP request toeach DLCI for each protocol configured on theinterface.
3. The return information from the Inverse ARP isthen used to build the Frame Relay map.
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Frame Relay Inverse ARP and LMI SignalingFrame Relay Inverse ARP and LMI Signaling
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Stages of Inverse ARP and LMI OperationStages of Inverse ARP and LMI Operation
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Frame Relay switching tableFrame Relay switching table
The Frame Relay switching table consists offour entries: two for incoming port and DLCI,and two for outgoing port and DLCI.
The DLCI could, therefore, be remapped as itpasses through each switch; the fact that theport reference can be changed is why theDLCI does not change even though the portreference might change.
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Frame Relay switching tableFrame Relay switching table
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Frame Relay default: nonbroadcast, multiaccess (NBMA)
Selecting a Frame Relay TopologySelecting a Frame Relay Topology
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FRAME RELAY SUBINTERFACESFRAME RELAY SUBINTERFACES
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What are Frame Relay subinterfacesWhat are Frame Relay subinterfaces
Subinterfaces are logical subdivisions of aphysical interface.
In a subinterface configuration, each PVC canbe configured as a point-to-point connection,which allows the subinterface to act as adedicated line.
By using multiple virtual subinterfaces, theoverall cost of implementing a Frame Relaynetwork can be reduced.
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FR without subinterfaceFR without subinterface
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FR with subinterfaceFR with subinterface
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SubinterfaceSubinterface
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Split horizon routing environmentsSplit horizon routing environments
Split horizon reduces routing loops by notallowing a routing update received on onephysical interface to be sent back out that
same interface. As a result, if a remote router sends an
update to the headquarters router that isconnecting multiple PVCs over a singlephysical interface, the headquarters routercannot advertise that route through the samephysical interface to other remote routers.
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Split horizon and reachability problemSplit horizon and reachability problem
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Reachability issues:Reachability issues: Point-to-pointPoint-to-point
A single subinterface is used to establish one
PVC connection to another physical interfaceor subinterface on a remote router.
Each point-to-point connection is its ownsubnet. In this environment, broadcasts are
not a problem because the routers are point-to-point and act like a leased line.
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Reachability issues:Reachability issues: MultipointMultipoint
A single subinterface is used to establishmultiple PVC connections to multiple physical
interfaces or subinterfaces on remote routers. All the participating interfaces would be inthe same subnet, and each interface wouldhave its own local DLCI.
Because the subinterface is acting like aregular Frame Relay network, routing updatesare subject to split horizon.
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FRAME RELAY CONFIGURATIONFRAME RELAY CONFIGURATION
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Basic Frame Relay configurationBasic Frame Relay configuration
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Basic Frame Relay configurationBasic Frame Relay configuration
A basic Frame Relay configuration assumesthat:
you want to configure Frame Relay on onephysical interface and that LMI and Inverse ARPare supported by the remote routers.
The LMI notifies the router about the
available DLCIs. Inverse ARP is enabled by default, so it does
not appear in configuration output.
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Basic configuration:Basic configuration: Step 1Step 1
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Basic configuration:Basic configuration: Step 2Step 2
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Basic configuration:Basic configuration: Step 3Step 3
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Basic configuration:Basic configuration: Step 4Step 4
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Basic configuration:Basic configuration: Step 5Step 5
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Basic configuration:Basic configuration: Step 6Step 6
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Verifying Frame Relay operationVerifying Frame Relay operation
if i i
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Verifying Frame Relay operationVerifying Frame Relay operation
C fi F R l S i h
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Configure Frame Relay SwitchConfigure Frame Relay Switch
Enable Frame Relay Switching
FRSW(conf)# frame-relay switching
Configure interface
FRSW(conf-if)#Encapsulation frame-relay
FRSW(conf-if)#frame-relay intf-type dce|dte
FRSW(conf-if)#clock rate 56000
FRSW(conf-if)#frame-relay lmi-type cisco|ansi|q933a
FR route (create PVC - Switching Table)
FRSW(conf-if)#frame-relay route interface
C fi i i fC fi ti bi t f
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Configuration subinterfacesConfiguration subinterfaces
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Configuring SubinterfacesConfiguring Subinterfaces
Point-to-point Subinterfaces act like leased lines.
Each point-to-point subinterface requires its own subnet.
Point-to-point is applicable to hub and spoke topologies.
Multipoint Subinterfaces act like NBMA networks, so they do not resolve the
split-horizon issues.
Multipoint can save address space because it uses a single subnet.
Multipoint is applicable to partial mesh and full mesh topologies.
C fi ti bi t fC fi ti bi t f
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Configuration subinterfacesConfiguration subinterfaces
C fi ti bi t fC fi ti bi t f
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Configuration subinterfacesConfiguration subinterfaces
M lti i t bi t f lM lti i t bi t f l
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Multipoint subinterfaces exampleMultipoint subinterfaces example
P i t t i t bi t f lP i t t i t bi t f l
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Point-to-point subinterfaces examplePoint-to-point subinterfaces example
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FRAME RELAY CONFIGURATIONFRAME RELAY CONFIGURATIONEXAMPLESEXAMPLES
C fi tiC fi ti ith t bi t fith t bi t f
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Configuration:Configuration: without subinterfacewithout subinterface
#interface serial 0
#encapsulation frame-relay
#ip address 9.0.0.1 255.0.0.0
#router igrp 1
#network 1.0.0.0
#network 9.0.0.0
LMI type is automatically sensed
The encapsulation is Cisco
DLCI is learned via LMI status messages
Inverse ARP is enable (by default)
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FR Cloud
C fi tiConfiguration: S ifi d l tiSpecified encapsulation
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Configuration:Configuration: Specified encapsulationSpecified encapsulation
#interface serial 0
#ip address 9.0.0.1 255.0.0.0#encapsulation frame-relay ietf
#frame-relay lmi-type ansi
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FR CloudDLCI 41 DLCI 42
C fi tiConfiguration: ith bi t fwith subinterface
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Configuration:Configuration: with subinterfacewith subinterface
#interface serial 0
#encapsulation frame-relay
#frame-relay lmi-type ansi
#interface serial 0.1 point-to-point
#frame-relay interface-dlci 41
#ip address 9.0.0.1 255.0.0.0
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FR CloudDLCI 41 DLCI 42
Configuration:Configuration: with subinterfacewith subinterface
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Configuration:Configuration: with subinterfacewith subinterface
#interface serial 0
#encapsulation frame-relay
#interface serial 0.1 multipoint#ip address 9.0.0.1 255.0.0.0
#frame-relay interface-dlci 41
#frame-relay interface-dlci 43 ietf
DLCI 41 DLCI 42
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FR Cloud
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Intel
DLCI 44
DLCI 43
Configuration:Configuration: disabled inverse ARPdisabled inverse ARP
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Configuration:Configuration: disabled inverse ARPdisabled inverse ARP
#interface serial 0.1 multipoint
#ip address 9.0.0.1 255.0.0.0
#frame-relay interface-dlci 41#frame-relay interface-dlci 43 ietf
#frame-relay map ip 9.0.0.2 41 broadcast
#frame-relay map ip 9.0.0.3 43 broadcast
DLCI 41 DLCI 42
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FR Cloud
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DLCI 44
DLCI 43
Configuring a Static Frame Relay MapConfiguring a Static Frame Relay Map
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Configuring a Static Frame Relay MapConfiguring a Static Frame Relay Map
Configuring Point to Point SubinterfacesConfiguring Point to Point Subinterfaces
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Configuring Point-to-Point SubinterfacesConfiguring Point-to-Point Subinterfaces
Multipoint Subinterfaces ConfigurationMultipoint Subinterfaces Configuration
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p gp g
ExampleExample
Q&AQ&A
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Q&AQ&A
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