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CAPÍTULO III Frame Relay

CAPÍTULO III Frame Relay. M. En C. Juan Antonio Guerrero Ibáñez. Objectives. Describe the operation of Frame Relay Describe the functions of DLCIs in Frame Relay Describe Cisco’s implementation of Frame Relay Describe the process for configuring and verifying Frame Relay

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CAPÍTULO III Frame Relay

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  1. CAPÍTULO IIIFrame Relay M. En C. Juan Antonio Guerrero Ibáñez M.C. Juan Antonio Guerrero Ibáñez

  2. Objectives • Describe the operation of Frame Relay • Describe the functions of DLCIs in Frame Relay • Describe Cisco’s implementation of Frame Relay • Describe the process for configuring and verifying Frame Relay • Describe the Frame Relay subinterfaces • Describe how Frame Relay uses subinterfaces to solve the problem of split horizon M.C. Juan Antonio Guerrero Ibáñez

  3. Frame Relay Technology Overview • Frame Relay Terminology • Frame Relay Operation • Frame Relay Multiplexing • Frame Relay Frame Format • Frame Relay Addressing M.C. Juan Antonio Guerrero Ibáñez

  4. What Is Frame Relay? Frame Relay is a packet-switched, connection-oriented, WAN service. FR defines the interconnection process between a router and the service provider’s local access switching equipment. M.C. Juan Antonio Guerrero Ibáñez

  5. What Is Frame Relay? • Frame Relay uses a subnet of the HDLC protocol called LAPF (Link Access Procedure for Frame Relay) • Originally FR was designed to allow ISDN equipment to have access to a packet-switched service on a B channel • FR is now a stand-alone technology M.C. Juan Antonio Guerrero Ibáñez

  6. Connection-Oriented Service Connection-oriented protocols use an acknowledgement process between source and destination. M.C. Juan Antonio Guerrero Ibáñez

  7. Frame Relay stack layered support • Takes data packets from a network layer protocol, such as IP or IPX • Encapsulates them as the data portion of a Frame Relay frame • Passes them to the physical layer for delivery on the wire M.C. Juan Antonio Guerrero Ibáñez

  8. Terminology • VC can be: • established dynamically by sending signaling messages to the network. (SVC) • Preconfigured by the carrier (PVC) • The switching information for a VC is stored in the memory of the switch. • FR provides no error recovery mechanism because it was designed to operate on high-quality digital lines. • The FRAD or router connected to FR network may have multiple virtual circuits connecting it to various end points. M.C. Juan Antonio Guerrero Ibáñez

  9. LMI and Local Access The DLCI (Data Link Channel Identifier)value identifies the logical connection that is multiplexed into the physical channel. LMI (Local Management Interface) M.C. Juan Antonio Guerrero Ibáñez

  10. M.C. Juan Antonio Guerrero Ibáñez

  11. Frame Relay Terminology #1 • Local access rate • 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 56 Kbps – could be up to T3 (44.476 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. M.C. Juan Antonio Guerrero Ibáñez

  12. Frame Relay Terminology #2 • Committed burst • The maximum number of bits per second that the Frame Relay provider agrees to transmit during any CIR measurement time interval. • While in most contracts, generally isn’t used very much . • Excess burst • The maximum bits that the Frame Relay switch will attempt to transfer beyond the CIR. Can not exceed the local access rate . M.C. Juan Antonio Guerrero Ibáñez

  13. Frame Relay Terminology #3 • Oversubscription • A link is oversubscribed when the combined traffic rate of all VCs (often customers) exceeds the local access link speed. The bursty nature of data traffic allows some VCs to burst while others are idle. • Port speed • The maximum burst rate in bits per second. Basically, CIR is what you’re guaranteed, port speed is what you can burst up to, and local access rate is the capacity of the physical interface to the cloud. M.C. Juan Antonio Guerrero Ibáñez

  14. 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. M.C. Juan Antonio Guerrero Ibáñez

  15. Frame Relay Traffic-Control Functions • Error Control with Frame Relay • Relies on upper-layer protocols to provide retransmission of damaged or missing frames. This is a concession to increase speed, but it works only because the quality and reliability of the underlying circuits. • Flow/Congestion Control with Frame Relay • Pseudo flow-control capability via the FECN, BECN, and DE bits in the protocol frame’s address field. Not true flow control because upper-layer protocols are still required to actually carry out the task of reducing transmission rates M.C. Juan Antonio Guerrero Ibáñez

  16. Frame Relay Operation Interconnection of Frame Relay switches and routers. M.C. Juan Antonio Guerrero Ibáñez

  17. Frame Relay DLCIs The end devices at two different ends of a connection can use different DLCI numbers to the same connection. DLCIs are locally significant. M.C. Juan Antonio Guerrero Ibáñez

  18. Frame Relay Frame Format • Flag - Beginning and the end of the Frame Relay frame (01111110) • Address - Contains the following information: • DLCI VALUE – First 10 bits: Indicates the DLCI value. • Congestion CONTROL - Last 3 bits control congestion-notification mechanisms. These bits are: • FECN (forward explicit congestion notification) • BECN (backward explicit congestion notification) • DE (discard eligible) • Data - Contains encapsulated upper-layer data • FCS - Frame check sequence M.C. Juan Antonio Guerrero Ibáñez

  19. Frame Relay Addressing M.C. Juan Antonio Guerrero Ibáñez

  20. LMI Operation LMI provides for management of connections. Includes operational status of PVCs, transmit keepalives, and tell the router the available PVCs. M.C. Juan Antonio Guerrero Ibáñez

  21. LMI Frame Format • Flag • DLCI - Defined in the specification as DLCI = 1023. • Unnumbered information indicator - Same format as LAPB unnumbered information (UI) frame indicator, with the poll/final bit set to 0. • Protocol discriminator - Value indicates LMI. • Call reference - Always filled with 0s. • Message type - Two message types: • Status messages (respond to status-enquiry messages). Examples: • Keepalives • Status message of each DLCI defined for the link • Status-enquiry messages • Together help verify the integrity of logical and physical links • Information element (IE) - Consists of one or more: 1-byte IE identifier, an IE length field, and 1 or more bytes containing actual data. M.C. Juan Antonio Guerrero Ibáñez

  22. LMI States • LMI Connection States. There are three: • Active–Connection between two end routers is up and capable of transmitting data. • Inactive–Connection between the local router and local Frame Relay switch is operational, but the remote router’s link is not operational. • Deleted–Indicates a failed link between the local router and local Frame Relay switch. M.C. Juan Antonio Guerrero Ibáñez

  23. Multicasting and Inverse ARP The router learns the DLCIs from the Frame Relay switch and sends an Inverse ARP request to each DLCI. M.C. Juan Antonio Guerrero Ibáñez

  24. Multicasting and Inverse ARP • Multicast groups are designated by a series of four reserved DLCI values (1019 to 1022). Frames sent by a device using one of these reserved DLCIs are replicated by the network and sent to all exit points in the designated set. • The Inverse ARP allows the router to automatically build the Frame Relay map. The router learns the DLCIs from the switch during the initial LMI exchange. The router then sends an Inverse ARP request to each DLCI. The return information is used to build the Frame Relay map. M.C. Juan Antonio Guerrero Ibáñez

  25. Frame Relay Mapping Responses to Inverse ARP requests are entered in an address-to-DCLI mapping table on the router or access server. M.C. Juan Antonio Guerrero Ibáñez

  26. Frame Relay Switching Tables Routers use Inverse ARP to find the remote IP address and create a mapping of local DLCIs and their associated remote IP addresses. M.C. Juan Antonio Guerrero Ibáñez

  27. Basic Frame Relay Configuration • Verifying Frame Relay Operation • Configuring the Serial Interface for a Frame Relay Connection • Verifying Frame Relay Configuration • Configuring Subinterfaces • Configuring Optional Commands M.C. Juan Antonio Guerrero Ibáñez

  28. Frame Relay Configuration Steps • Enabling Frame Relay Encapsulation • Router(config-if)#encapsulation frame-relay [cisco|ietf] • Default is Cisco; IETF is the standard. • Specifying the LMI Type • Router(config-if)#frame-relay lmi-type [ansi|cisco|q933a] • Not necessary since Cisco IOS Release 11.2. • Configuring the Link Bandwidth (Optional) • Router(config-if)#bandwidth Num kbps • Default on serial links is 56 kbps. • Enabling Inverse ARP • Router(config-if)#frame-relay inverse-arp [protocol] [dlci] M.C. Juan Antonio Guerrero Ibáñez

  29. Configuring a Static Map (Parameters) • When not using inverse ARP to dynamically map DLCIs to protocol addresses, you must create a static mapping. The syntax: • Router(config-if)#frame-relay map protocol protocol-address dlci# [broadcast] [ietf|cisco] • Protocol - Protocol used on the interface • protocol-address - Protocol address of remote router interface • dlci# - Local DLCI used to reach the remote router • Broadcast - Permits the forwarding of broadcasts • ietf|cisco - Frame Relay encapsulation type • Overrides the encapsulation frame-relay command choice • Cisco is the default • Examples • RTA(config-if)#frame-relay map ip 192.168.4.1 16 broadcast • RTA(config-if)#frame-relay map ip 192.168.4.3 16 broadcast M.C. Juan Antonio Guerrero Ibáñez

  30. Basic Configuration Example M.C. Juan Antonio Guerrero Ibáñez

  31. 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 M.C. Juan Antonio Guerrero Ibáñez

  32. 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 131.18.79.1, subnet mask is 255.255.255.0 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 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 M.C. Juan Antonio Guerrero Ibáñez

  33. 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 0 Invalid Prot Disc 0 Invalid dummy Call Ref 0 Invalid Msg Type 0 Invalid Status Message 0 Invalid Lock Shift 0 Invalid Information ID 0 Invalid Report IE Len 0 Invalid Report Request 0 Invalid Keep IE Len 0 Num Status Enq. Sent 9 Num Status msgs Rcvd 0 Num Update Status Rcvd 0 Num Status Timeouts 9 M.C. Juan Antonio Guerrero Ibáñez

  34. 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 9 output pkts 16 in bytes 154 out bytes 338 dropped pkts 6 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 0 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) M.C. Juan Antonio Guerrero Ibáñez

  35. The show frame-relay map Command Router#show frame-relay map Serial 1 (up): ip 131.108.177.177 dlci 177 (0xB1,0x2C10), static, broadcast, CISCO M.C. Juan Antonio Guerrero Ibáñez

  36. The debug frame-relay Command #debug frame-relay Serial0(i): dlci 500(0x7C41), pkt type 0x0800, datagramsize 24 Serial0(i): dlci 1023(0xFCF1), pkt type 0x309, datagramsize 13 Serial0(i): dlci 500(0x7C41), pkt type 0x0800, datagramsize 24 Serial0(i): dlci 1023(0xFCF1), pkt type 0x309, datagramsize 13 M.C. Juan Antonio Guerrero Ibáñez

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