2. Frame Relay Overview
Frame Relay defines the interconnection process between the DTE and the DCE (the Frame Relay network switch, not the CSU/DSU).
It does not define the way the data is transmitted within the service provider’s Frame Relay cloud.

3. What Is Frame Relay?
Frame Relay defines the interconnection process between a
router and the service provider’s local access switching equipment.

4. NBMA - Non-Broadcast Multiple Access
Frame Relay networks are known as NBMA, Nonbroadcast Multi-Access networks.
NBMA networks allow a router to set up and maintain several logical connections over a single physical serial interface.
The “cloud” is a single network to which multiple devices are attached.
Unlike Ethernet and Token Ring, which are broadcast networks, non-broadcast networks means a packet sent into the network might not be seen by all other routers attached to the network.

5. Frame Relay Terminology #1
Local access rate (LAR)
The maximum physical media speed of the link used by the Frame Relay interface. Frame Relay may or may not use this full bandwidth, but cannot exceed it
Common local access rates include T1 (1.544 Mbps) and could be up to T3 ( Mbps).
Committed information rate (CIR)
The transmission rate that the frame relay provider guarantees without frame drops
Any frames sent above this rate has the DE bit set to one allowing them to be dropped if congestion occurs.
Monthly service charge is based heavily on this rate.

6. Frame Relay Terminology #2
Excess burst
The maximum bits that the Frame Relay switch will attempt to transfer beyond the CIR. Can not exceed the local access rate .

7. Frame Relay Operation

8. DLCIs
A data-link connection identifier (DLCI) identifies the logical VC between the CPE and the Frame Relay switch.
The Frame Relay switch maps the DLCIs between each pair of routers to create a PVC.
DLCIs have local significance
Your Frame Relay provider sets up the DLCI numbers to be used by the routers for establishing PVCs.

9. DLCI Mapping to Network Address
Manual
Manual: Administrators use a frame relay map statement.
Dynamic:
Inverse Address Resolution Protocol (I-ARP) provides a given DLCI and requests next-hop protocol addresses for a specific connection.
The router then updates its mapping table and uses the information in the table to forward packets on the correct route.

11. Inverse ARP
The Inverse ARP mechanism allows the router to automatically build the Frame Relay map.
The router learns the DLCIs that are in use from the switch during the initial LMI exchange and then sends an Inverse ARP request to each DLCI for each protocol configured on the interface if the protocol is supported.
The return information, the remote network address, from the Inverse ARP is then used to build the Frame Relay map.

12. Minimum Frame Relay Configuration
HubCity(config)# interface serial 0
HubCity(config-if)# ip address
HubCity(config-if)# encapsulation frame-relay
Spokane(config)# interface serial 0
Spokane(config-if)# ip address
Spokane(config-if)# encapsulation frame-relay

13. Router(config-if)#encapsulation frame- relay [cisco | ietf]
cisco is the default. Use this if connecting to another Cisco router.
ietf—Select this if connecting to a non- Cisco router. - RFC 1490

14. Cisco Router is now ready to act as a Frame-Relay DTE device.
The following process occurs:
1. The interface is enabled.
2. The Frame-Relay switch announces the configured DLCI(s) to the router.
3. Inverse ARP is performed to map remote network layer addresses to the local DLCI(s).
The routers can now ping each other!

15. Inverse ARP HubCity# show frame-relay map
Serial0 (up): ip dlci 101, dynamic, broadcast, status defined, active
(dynamic refers to the router learning the ip address via Inverse ARP)

16. Inverse ARP Limitations
Limitation of Inverse ARP
Inverse ARP only resolves network addresses of remote Frame-Relay connections that are directly connected.

17. NBMA Topologies

18. A Frame-Relay Configuration Supporting Multiple Sites
Hub Router
This is known as a Hub and Spoke Topology, where the Hub router relays information between the Spoke routers.
Limits the number of PVCs needed as in a full-mesh topology (coming).
Spoke Routers

19. Configuration using Inverse ARP:
HubCity
interface Serial0
ip address
encapsulation frame-relay
Spokane
ip address
Spokomo
ip address

20. HubCity# show frame-relay map
Serial0 (up): ip dlci 101, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 112, dynamic, broadcast, status defined, active
Spokane# show frame-relay map
Serial0 (up): ip dlci 102, dynamic, broadcast, status defined, active
Spokomo# show frame-relay map
Serial0 (up): ip dlci 211, dynamic, broadcast, status defined, active

21. Notice:
Inverse ARP resolved the ip addresses for HubCity for both Spokane and Spokomo
Inverse ARP resolved the ip addresses for Spokane for HubCity
Inverse ARP resolved the ip addresses for Spokomo for HubCity

22. Inverse ARP Limitations
Can HubCity ping both Spokane and Spokomo? Yes!
Can Spokane and Spokomo ping HubCity? Yes!
Can Spokane and Spokomo ping each other? No! The router’s serial interface (spoke routers) drops the ICMP packet because there is no DLCI-to-IP address mapping for the destination address.
Solutions to the limitations of Inverse ARP
1. Add an additional PVC between Spokane and Spokomo (Full Mesh)
2. Configure Frame-Relay Map Statements
3. Configure Point-to-Point Subinterfaces.

23. Full Mesh Solution Does Not Scale Well
Full Mesh Topology (n*(n-1)) / 2
Number of Number of
Connections PVCs

24. Frame Relay Map Statements
Instead of using additional PVCs, Frame-Relay map statements can be used to:
Statically map local DLCIs to an unknown remote network layer addresses.
Also used when the remote router does not support Inverse ARP

25. Router(config-if)# frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco | payload-compress packet-by-packet]
broadcast (Optional) Forwards broadcasts to this address when multicast is not enabled. Use this if you want the router to forward routing updates. If not enabled, you must define static routes, and if using IPX, static SAPs.
ietf | cisco (Optional) Select the Frame Relay encapsulation type for use. Use ietf only if the remote router is a non-Cisco router. Otherwise, use cisco

26. Frame-Relay Map Statements
HubCity
interface Serial0
ip address
encapsulation frame-relay
(Inverse-ARP still works here)
Spokane
ip address
frame-relay map ip
frame-relay map ip
Spokomo
ip address
frame-relay map ip
frame-relay map ip

27. Mixing Inverse ARP and Frame Relay Map Statements
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!

28. HubCity
interface Serial0
ip address
encapsulation frame-relay
Spokane
ip address
frame-relay map ip
Spokomo
ip address
frame-relay map ip

29. HubCity# show frame-relay map
Serial0 (up): ip dlci 101, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 112, dynamic, broadcast, status defined, active
Spokane# show frame-relay map
Serial0 (up): ip dlci 102, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 102, static, CISCO, status defined, active (static = learned via fr map statement)
Spokomo# show frame-relay map
Serial0 (up): ip dlci 211, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 211, static, CISCO, status defined, active (static = learned via fr map statement)

30. Good News:
Everything looks fine!
Now all routers can ping each other!
Bad News:
Problem when using Frame-Relay map statements AND Inverse ARP.
This will only work until the router is reloaded, here is why...

31. 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 specific protocol, only for the DLCI referenced in the Frame-Relay map statement.

32. 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-Relay map 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 the DLCI referenced in the Frame-Relay map statement.

33. HubCity# show frame-relay map (after reload)
Serial0 (up): ip dlci 101, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 112, dynamic, broadcast, status defined, active
Spokane# show frame-relay map
NOW MISSING: Serial0 (up): ip dlci 102, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 102, static, CISCO, status defined, active
Spokomo# show frame-relay map
NOW MISSING: Serial0 (up): ip dlci 211, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 211, static, CISCO, status defined, active

34. HubCity# show frame-relay map (after reload)
Serial0 (up): ip dlci 101, dynamic, broadcast, status defined, active
Serial0 (up): ip dlci 112, dynamic, broadcast, status defined, active
Spokane# show frame-relay map
Serial0 (up): ip dlci 102, static, CISCO, status defined, active
Spokomo# show frame-relay map
Serial0 (up): ip dlci 211, static, CISCO, status defined, active
Spokane and Spokomo can no longer ping HubCity!

35. Solution: Wherever there are Inverse-ARP statements, replace them with Frame-Relay map statements.

36. Frame-Relay Map Statements - Solution
HubCity
interface Serial0
ip address
encapsulation frame-relay
(Inverse-ARP still works here)
Spokane
ip address
frame-relay map ip
frame-relay map ip
Spokomo
ip address
frame-relay map ip
frame-relay map ip

37. Local Management Interface

38. LMI
LMI is a signaling standard between the CPE device and the Frame Relay switch that is responsible for managing the connection and maintaining status between the devices. LMI includes:
A keepalive mechanism, which verifies that data is flowing
A multicast mechanism, which provides the network server (router) with its local DLCI
A status mechanism, which provides an ongoing status on the DLCIs known to the switch

39. The router must be programmed to choose which LMI type encapsulation will be used.
If using Cisco IOS Release 11.1 or earlier, specify the LMI-type used by the FR switch:
Router(config-if)#frame-relay lmi-type {ansi | cisco | q933a}
cisco is the default.
With IOS Release 11.2 or later, the LMI-type is autosensed so no configuration is needed.

40. LMI Autosensing
Beginning in Cisco IOS Release 11.2, the router tries to autosense which LMI type the Frame Relay switch is using by sending one or more full status requests to the Frame Relay switch.
The Frame Relay switch responds with the LMI type.
The router configures itself with the LMI type received.

41. FR Configuration Example
For routing metric information

42. FR Configuration
The following example shows a case in which most destinations use Cisco encapsulation, but one site requires IETF encapsulation:
Router(config-if)#encapsulation frame-relay Router(config-if)#frame-relay map ip broadcast Router(config-if)#frame-relay map ip broadcast ietf Router(config-if)#frame-relay map ip broadcast

43. Early Implementations of Frame Relay Required that a router (DTE device) must have a WAN serial interface for every permanent virtual circuit (PVC)

44. Early Implementations of Frame Relay
Early implementation of Frame Relay Technology required that a router (DTE device) must have a WAN serial interface for every permanent virtual circuit (PVC).
This was effective but increased the cost because of the increased number of interfaces, WAN connections, at the hub router.

45. Multipoint Physical Interface (and multipoint subinterfaces) and Split Horizon
A single physical interface works, but Split Horizon prohibits distance vector routing updates from propagating out the same physical interface that it received the update.

46. Solution: No Split Horizon with Point-to-point Subinterfaces

47. FR and Subinterfaces

48. FR and Subinterfaces
Two types of subinterfaces are available on Cisco routers:
1. point-to-point subinterfaces
2. multipoint subinterfaces
By using point-to-point subinterfaces, Cisco routers can treat each PVC as if it were a separate point-to-point interface on the router.

49. Hub 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 in the same subnet. Broadcasts and routing updates are also subject to the Split Horizon Rule and may pose a problem.

50. Frame Relay and Split Horizon
Physical interfaces: With a hub and spoke topology Split Horizon will prevent the hub router from propagating routes learned from one spoke router 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 in the same subnet. Broadcasts and routing updates are also subject to the Split Horizon Rule and may pose a problem.

51. Point-to-point Subinterfaces
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-relay map statements)
Frame-Relay service supplies multiple PVCs over a single physical interface and point-to-point subinterfaces subdivide each PVC as if it were a physical point-to-point interface.
Point-to-point subinterfaces completely bypass the local DLCI to remote network address mapping issue.

52. Point-to-point Subinterfaces
With physical and multipoint subinterface you:
can have multiple DLCIs assigned to it.
can use frame-relay map & interface dlci statements
can use Inverse-ARP
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 the frame-relay interface dlci statement for both point-to-point and multipoint)

53. Point-to-point subinterfaces
Each subinterface is on a separate network or subnet with a single remote connection (I.e. point-to-point)
/24
/24
/24

54. Point-to-point subinterfaces are equivalent to using multiple physical “point to point” interfaces

55. Point-to-point subinterface
A single subinterface is used to establish one PVC connection to another physical or subinterface on a remote router.
In this case, the interfaces would be:
in the same subnet and
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 are point-to- point and act like a leased line.

56. Point-to-point subinterface configuration, minimum of two commands:
(config)# interface Serial0.1 point-to-point
(config-subif)# frame-relay interface-dlci dlci-number
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-point subinterface
By the way, encapsulation is done only at the physical interface:
interface Serial0
no ip address
encapsulation frame-relay

57. frame-relay interface-dlci
Router(config-if)#frame-relay interface-dlci dlci-number
Used to assign specific DLCIs to specific subinterfaces.
This command is required for all point-to-point subinterfaces.
It is also required for multipoint subinterfaces for which inverse ARP is enabled.
It is not required for multipoint subinterfaces that are configured with static route maps.
Do not use this command on physical interfaces.

58. frame-relay interface-dlci and the show frame map
point-to-point subinterfaces: listed as a “point-to-point dlci”
Serial0.1 (up): point-to-point dlci, dlci 301 (0xCB, 0x30B0), broadcast status defined, active
With multipoint subinterfaces, the it lists it an inverse ARP entry, “dynamic”
Serial0 (up): ip dlci, 301 (0x12D, 0x48D0), dynamic,, broadcast status defined, active

59. Point-to-Point Subinterfaces at the Hub and Spokes
Each subinterface on Hub router requires a separate subnet (or network)
Each subinterface on Hub router is treated like a regular physical point-to-point interface, so split horizon does not need to be disabled.
Interface Serial0 (for all routers)
encapsulation frame-relay
no ip address
HubCity
interface Serial0.1 point-to-point
ip address
frame-relay interface dlci 301
interface Serial0.2 point-to-point
ip address
frame-relay interface dlci 302
Spokane
ip address
frame-relay interface dlci 103
Spokomo
ip address
frame-relay interface dlci 203
Point-to-Point Subinterfaces at the Hub and Spokes

60. Multipoint Subinterfaces
Share many of the same characteristics as a physical Frame-Relay interface
With multipoint subinterface you can have:
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 the frame-relay interface dlci statement for both point-to-point and multipoint)

61. Multipoint subinterfaces
Each subinterface is on a separate network or subnet but may have multiple connections, with a different DLCI for each connection.
/24
/24
/24
Split horizon still an issue on each Multipoint subinterface.

62. Multipoint subinterfaces are equivalent to using multiple physical “hub to spoke” interfaces.

63. Multipoint subinterface at the Hub and Point-to-Point Subinterfaces at the Spokes
Notes
Highly scalable solution
Disable Split Horizon on Hub router when running a distance vector routing protocol
Interface Serial0 (for all routers)
encapsulation frame-relay
no ip address
HubCity
interface Serial0.1 mulitpoint
ip address
frame-relay interface-dlci 301
frame-relay interface-dlci 302
no ip split-horizon
Spokane
interface Serial0.1 point-to-point
ip address
frame-relay interface-dlci 103
Spokomo
ip address
frame-relay interface-dlci 203

64. BECN and FECN
A Frame Relay switch sends FECN and BECN packets to reduce congestion.
FECN packets are sent to the destination device, BECN packets are sent to
the source device.

65. Verifying and Troubleshooting Frame Relay
The show interface serial Command
The show frame-relay lmi Command
The show frame-relay pvc [interface interface [dlci#]] Command
The show frame-relay map Command
The debug frame-relay Command

66. The show interfaces serial Command
Lab-B#show interfaces serial
Serial 2 is up, line protocol is up
Hardware type is MCI Serial
Internet address is , subnet mask is
MTU 1500 bytes, BW 1544 Kbit, DLY usec, rely 255/255,load 1/255
Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec)
multicast DLCI 1022, status defined, active
source DLCI 20, status defined, active
LMI DLCI 1023, LMI sent 10, LMI stat recvd 10, LMI upd recvd 2
Last input 7:21:29, output 0:00:37, output hang never

67. The show frame-relay lmi Command
Router#show frame-relay lmi
LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = ANSI
Invalid Unnumbered info Invalid Prot Disc 0
Invalid dummy Call Ref Invalid Msg Type 0
Invalid Status Message Invalid Lock Shift 0
Invalid Information ID Invalid Report IE Len 0
Invalid Report Request Invalid Keep IE Len 0
Num Status Enq. Sent Num Status msgs Rcvd 0
Num Update Status Rcvd Num Status Timeouts 9

68. The show frame-relay pvc Command
Router#show frame-relay pvc 100
PVC Statistics for interface Serial5/1 (Frame Relay DTE)
DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1
input pkts output pkts in bytes 154
out bytes dropped pkts in FECN pkts 0
in BECN pkts out FECN pkts out BECN pkts 0
in DE pkts out DE pkts 0
out bcast pkts out bcast bytes 0
pvc create time 00:35:11, last time pvc status changed 00:00:22
Bound to Virtual-Access1 (up, cloned from Virtual-Template5)

69. The show frame-relay map Command
Router#show frame-relay map
Serial 1 (up): ip
dlci 177 (0xB1,0x2C10), static, broadcast, CISCO

70. The debug frame-relay Command
Serial0(i): dlci 500(0x7C41), pkt type 0x0800, datagramsize 24
Serial0(i): dlci 1023(0xFCF1), pkt type 0x309, datagramsize 13

71. Labs Configuring Hub and Spoke Frame Relay
Configuring Full-Mesh Frame Relay
Configuring Full-Mesh Frame Relay With Sub Interfaces