CCNA Guide to Cisco Networking

1. CCNA Guide to Cisco Networking Chapter 12 : Frame Relay

2. Objectives Understand Frame Relay standards and equipment Describe the role of virtual circuits and performance parameters in Frame Relay Understand the Frame Relay topologies Understand the difference between multipoint and point-to-point configurations Configure and monitor Frame Relay

3. Frame Relay Standards And Equipment Packet switching technology Encapsulation technology Physical and Data Link layers 56 kbps to 44.736 mbps Does not perform error correction like X.25

4. Frame Relay Standards And Equipment (continued) Connect to multiple sites using one physical interface Equipment DCE Frame relay switch Public data network (PDN) Frame relay network device (FRND) DTE Custom premise equipment (CPE) CSU/DSU Customer owned router Frame relay access device (FRAD)

5. Frame Relay Standards And Equipment (continued) Equipment (continued) CSU/DSU Encoding Filtering Translating communications

6. Frame Relay Standards And Equipment (continued)

7. Frame Relay Standards And Equipment (continued)

8. Frame Relay Standards And Equipment (continued)

9. Virtual Circuits Frame relay operates with nearly any serial interface Logical connections (software-maintained) Multiplexing Two types of virtual circuits Switched virtual circuits Permanent virtual circuits

10. DLCI Data link connection identifier (DLCI) identify virtual circuits Map virtual circuits to layer 3 protocol addresses Only have local significance Are not unique identifiers on the global network (basic configuration only)

11. Frame Relay Map DLCI numbers are mapped or assigned to a specific interface Frame relay map table is active in RAM Can be built automatically or statically Service provider FRND will have a frame relay switching table

12. Frame Relay Map (continued)

13. Subinterfaces Single physical interface may service multiple PVCs Referenced as Serial 0/0.3, serial 0/0.4 Router(config)# interface serial 0/0.5

14. LMI Local Management Interface (LMI) Makes the DLCIs globally significant rather than locally significant Creates a signaling mechanism between the router and the Frame Relay switch, which could report on the status of the link Supports multicasting Makes auto configuration of the frame relay map possible Keepalive packets Sent every 10 seconds by default Verify the frame relay link

15. LMI (continued) LMI provides the following states of the virtual circuits Active: The connection is working and routers can use it to exchange data Inactive: The connection from the local router to the switch is working, but the connection to the remote router is not available Deleted: No LMI information is being received from the Frame Relay switch Without LMI the frame relay map must be built statically

16. Inverse ARP Send a query using the DLCI number to find the remote IP address Inverse ARP responses build the frame relay map automatically Inverse ARP exchanges every 60 seconds On by default LMI is required for inverse ARP to function

17. Encapsulation Types Three types of LMI encapsulations cisco ansi q933a “Autosense” the LMI type Three information elements of LMI Report type Keepalive PVC status

18. Encapsulation Types (continued) DLCI status messages New: Used if a new DLCI connection has been configured Active: Used to indicate whether the virtual circuit is available for data transfer Receiver not ready: Used for flow control Minimum bandwidth: Indicates the minimum available bandwidth

19. Encapsulation Types (continued) DLCI status messages (continued) Global addressing: Used to give DLCI global significance Multicasting: Make DLCI numbers globally significant by advertising them across the Frame Relay network Provider-Initiated Status Update: Allows the provider to initiate a status inquiry

20. Split Horizon Reduces the chances of routing loops Routing updates arrived on an interface can not be sent back out the same interface Nonbroadcast multiaccess (NBMA) network A problem for multipoint configuration Single subnet configuration for all VCs Broadcast multiaccess topology

21. Split Horizon (continued) Solution to the split horizon problem Point-to-point subinterfaces

22. Split Horizon (continued)

23. Split Horizon (continued)

24. Split Horizon (continued)

25. Performance Parameters Telecommunications provider contract specs Access rate: Physical speed of the interface Committed information rate (CIR): The minimum transfer rate Committed burst size (Bc): Maximum amount of data bits to transfer in a set period under normal conditions Excess Burst Size (Be): Amount of excess traffic over Bc which is discard eligible

26. Congestion Frame relay congestion management Forward explicit congestion notification (FECN) Message to destination router Backward explicit congestion notification (BECN) Message to source router Discard eligible (DE)

27. Frame Format

28. Frame Format (continued) Flag: An eight-bit binary sequence (01111110) that indicates the start of the data frame Address: Two to four bytes that contain several pieces of Frame Relay information Ethertype: Identifies the type of higher-layer protocol being encapsulated (IP, IPX, or AppleTalk) Data: A variable-length field that contains the information from the higher layers encapsulated in the Frame Relay frame

29. Frame Format (continued) FCS: Frame check sequence (FCS) or cyclical redundancy check (CRC) used to ensure that the frame was not corrupted during transmission Flag: An eight-bit binary sequence (01111110) that indicates the end of the data frame Frame Relay Address Field descriptions CR: A command or response bit that is used for sending connection management and frame acknowledgment information between stations FECN: Setting used to alert receiving devices if the frame experiences congestion

30. Frame Format (continued) Frame Relay Address Field descriptions (continued) BECN: Setting used on frames traveling away from the congested area to warn source devices that congestion has occurred on that path DE: Discard eligible bit that is used to identify frames that are first to be dropped when the CIR is exceeded EA: Extension address bits that are used to extend the Address field from two bytes to either three or four bytes

31. Frame Relay Topologies

32. Frame Relay Configuration

33. Frame Relay Configuration (continued)

34. Frame Relay Configuration (continued)

35. Frame Relay Configuration (continued)

36. Frame Relay Configuration (continued)

37. Frame Relay Configuration (continued)

38. Frame Relay Configuration (continued) Frame relay static mapping Define DLCI numbers manually Reasons to statically configure DLCI numbers Remote router doesn’t support Inverse ARP Assign specific subinterfaces to specific DLCI connections Reduce broadcast traffic Open Shortest Path First (OSPF) over Frame Relay

39. Frame Relay Configuration (continued) Non-Cisco Routers Do not support the Cisco frame relay encapsulation IETF setting RouterA(config-if)# encapsulation frame-relay ietf Keepalive configuration Default setting of every 10 seconds Maintain connection Connection status Setting can be 0 to 30 seconds RouterA(config-if)# keepalive 15

40. Monitoring Frame Relay

41. Monitoring Frame Relay (continued)

42. Monitoring Frame Relay (continued)

43. Monitoring Frame Relay (continued)

44. Summary Frame Relay is a flexible WAN technology that can be used to connect two geographically separate LANs Frame Relay is both a service and type of encapsulation The service parameters must be discussed with the Frame Relay provider (telecommunications company) Service parameters for Frame Relay include the access rate, Committed Information Rate (CIR), Committed Burst Size (Bc), and Excess Burst Size (Be) Frame Relay connections employ virtual circuits that can be either permanent or switched

45. Summary (continued) Virtual circuit connections across Frame Relay connections are defined by Data Link Connection Identifier (DLCI) numbers The DLCI numbers can be associated with remote Network layer addresses; however, they are only locally significant unless the Local Management Interface (LMI) is available Most Frame Relay providers support LMI, which allows Frame Relay maps to be dynamically created via Inverse ARP Static mappings of DLCI numbers to remote IP addresses can be configured when routers do not support Inverse ARP Inverse ARP is on by default for multipoint configurations

46. Summary (continued) Inverse ARP is not enabled on point-to-point links because only one path is available Frame Relay circuits can be established over serial interfaces or subinterfaces on Cisco routers