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Frame Relay. CCNA4 Chapter 6. Frame Relay Overview. Layer 2 Connection-oriented Packet switched Virtual Circuits: Permanent (and Switched) Links two DTE devices through DCE Originally designed for operation over ISDN Faster than X.25 Encapsulation can be Cisco or IETF.

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frame relay

Frame Relay

CCNA4 Chapter 6

frame relay overview
Frame Relay Overview
  • Layer 2
  • Connection-oriented
  • Packet switched
  • Virtual Circuits:

Permanent (and Switched)

  • Links two DTE devices through DCE
  • Originally designed for operation over ISDN
  • Faster than X.25
  • Encapsulation can be Cisco or IETF

RouterA(config-if)#encapsulation frame-relay ?

ietf Use RFC1490 encapsulation

frame relay dlci
Frame Relay - DLCI
  • Data Link Connection Identifier
  • IP addresses must be resolved to DLCI
  • Logical Virtual Circuits are distinguished by DLCI
  • Only locally significant
  • DLCI do not need to match end to end, though the may do if connected to different switches
  • DLCI are assigned by the service provider.
  • FR switch maps DLCI numbers to outgoing ports
slide5
DLCI

C

DLCI=100

E

DLCI=101

DLCI=102

A

DLCI=16

B

DLCI=100

D

DLCI=100

DLCI=101

DLCI=201

dlci mapping
DLCI Mapping
  • The FR switch uses DLCI numbers to communicate
  • Network layer addresses must be mapped

Static mapping:

RouterA(config-if)#frame-relay map ip 172.16.30.19 18

Dynamic mapping uses Inverse ARP:

  • Router learns DLCI from switch during initial LMI exchange
  • Router sends IARP request for each DLCI
  • 3. The return information is then used to build the map

DLCI = 100

What’s the next hop address for DLCI 100?

My IP address:172.16.1.2

frame relay rates
Frame Relay Rates

Network performance at the router level is affected by:

Access Rate

Line speed of connection to the provider

CIR

Guaranteed bandwidth

Bursting

Faster than CIR for a short time period

(Tc) Committed Rate measurement interval

(Bc) Committed Burst

(Be) Excess Burst – maximum transfer attempted

DE = Discard Eligibility bit. Set on oversubscribed traffic

lmi local management interface
LMI -Local Management Interface
  • Signalling between router and frame switch
  • Determine which PVCs are available and their status
  • LMI DLCI=1023
  • Extensions to basic frame relay protocol:

Common: Status of virtual circuits (Keepalives)

Optional: Multicasting (DLCI 1019-1022)

Global Addressing

Simple Flow Control

  • Cisco IOS 11.2 and later uses auto-detection
  • Cisco routers support three versions of LMI:

RouterA(config-if)#frame-relay lmi-type ?

cisco

ansi

q933a

frames
Frames

Frame Relay Format

LMI Frame

Mandatory bytes

1023

Status-enquiry message (from user device)

Status message:keepalives and PVC status

frame relay subinterfaces
Frame Relay Subinterfaces

FR can divide a single physical WAN interface into multiple subinterfaces.

Subinterfaces are logical subdivisions of the physical interface.

Split-Horizon issues can be resolved.

RouterA(config)#int s0

RouterA(config-if)#encapsulation frame-relay

RouterA(config-if)#int s0.1 ?

multipoint Treat as a multipoint link

point-to-point Treat as a point-to-point link

Point to Point is used when each PVC is a separate subnet.

Multipoint is used when the PVCs use the same subnet.

slide11

Frame Relay Subinterfaces

Configure the local DLCI for the subinterface to distinguish it from the physical interface:

RouterA(config-if)#frame-relay interface-dlci ?

<16-1007> Define a DLCI as part of the current

subinterface

RouterA(config-if)#frame-relay interface-dlci 16

Example configuration:

RouterA(config)#interface Serial0

RouterA(config-if)# no ip address

RouterA(config-if)# encapsulation frame-relay

RouterA(config-if)# interface Serial0.102 point-to-point

RouterA(config-if)# ip address 10.1.12.1 255.255.255.0

RouterA(config-if)# frame-relay interface-dlci 102

verifying frame relay
Verifying Frame Relay

show interface s0

show frame-relay pvc

show frame-relay map

show frame-relay lmi

questions
Questions

Q- What is the first step in configuring Frame-Relay on an interface?

A- Setting the encapsulation

Q- What are the possible types of LMI?

A- Cisco, ANSI and Q.933a

Q- What is the solution to the issue of split-horizon when configuring multiple VCs on a single physical interface?

A- Sub-interfaces

Q- What command can you issue to see your PVCs?

A- show frame-relay pvc

Q- What three bits does frame-relay use for congestion control?

A- FECN, BECN, DE

Q- What DLCI value defines an LMI frame?

A- 1023

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