1. Frame Relay
CCNA4 Chapter 6

2. 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

3. Frame Relay Operation

4. 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

5. DLCI C DLCI=100 E DLCI=101 DLCI=102 A DLCI=16 B DLCI=100 D DLCI=100

6. 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
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:

7. 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

8. 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 )
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

9. Frames Frame Relay Format LMI Frame Mandatory bytes 1023
10 bit address (0-1023)
8th bit of each byte indicates address length (currently 2 bytes)
Forward Explicit Congestion Notification
Backward Explicit Congestion Notification
Discard Eligibility
LMI Frame
Mandatory bytes
1023
Status-enquiry message (from user device)
Status message:keepalives and PVC status

10. 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.

11. Frame Relay Subinterfaces
Configure the local DLCI for the subinterface to distinguish it from the physical interface:
RouterA(config-if)#frame-relay interface-dlci ?
< > 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
RouterA(config-if)# frame-relay interface-dlci 102

12. Verifying Frame Relay Command Description
Encapsulation, Layer 1 and 2 status, DLCIs in use on the interface, LMI DLCI and LMI type.
The status of each configured connection and traffic statistics,DLCI, BECN, FECN, DE
Displays the interface, network layer address and DLCI mapping
Statistics for the interface including LMI type and status enquiries sent and recieved
show interface s0
show frame-relay pvc
show frame-relay map
show frame-relay lmi

13. 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