Introduction to Analog Telephony

The "Big show" and "Big D" for Frame Relay

The show and debug commands for Frame Relay are some of the most useful Cisco commands. They allow you to quickly isolate most problems, and they don't seem to provide excess data that doesn't help you troubleshoot or verify whether the service is running. The "Big show " and "Big D" commands for Frame Relay are as follows :

  show frame-relay pvc  [  dlci   interface  ]  show frame-relay lmi   show frame-relay map   debug frame-relay lm  i 

NOTE

For a complete list of the show and debug commands for Frame Relay, see the IOS WAN Configuration Guide .

show frame-relay pvc Command

The show frame-relay pvc command displays the statistics about all PVCs on the router, or an optional keyword can be used to display information on a specific DLCI or interface. Most of this command's information is self-explanatory ”it shows traffic rates in the form of packets and bytes. It also displays any forward-explicit congestion notification/backward-explicit congestion notification (FECN/BECN) information along with DE packets. The section "Configuring Frame Relay Traffic Shaping (FRTS)" discusses FECN/BECN in more details and gives some additional information that the show frame pvc command displays.

One of the key fields to look for is the PVC status. As mentioned previously, the PVC status can be one of the following:

• ACTIVE ” Indicates that the PVC is active and that information can be exchanged

• INACTIVE ” Indicates that the local connection to the frame switch is working but that the remote router's connection to the frame switch is not working

• DELETED ” Indicates that no LMI is being received from the frame switch or that the physical layer is not established

Example 5-9 lists the output from the show frame pvc command from the marlin router in the previous example. Notice that traffic is passing on the link, and the PVC status is ACTIVE.

Example 5-9 show frame pvc Output from the marlin Router

 marlin#  show frame-relay pvc  PVC Statistics for interface Serial0 (Frame Relay DTE)  DLCI = 110, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1  input pkts 500           output pkts 250          in bytes 62900   out bytes 29762          dropped pkts 2           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 250        out bcast bytes 29762  pvc create time 05:31:58, last time pvc status changed 05:29:46   DLCI = 120, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1  input pkts 498           output pkts 249          in bytes 27132   out bytes 29670          dropped pkts 0           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 249        out bcast bytes 29670  pvc create time 05:31:59, last time pvc status changed 05:29:47   DLCI = 130, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.2  input pkts 585           output pkts 590          in bytes 107506   out bytes 118208         dropped pkts 0           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 590        out bcast bytes 118208  pvc create time 05:32:00, last time pvc status changed 05:31:07  marlin# 

The PVC Create Time and the Last Time PVC Status Changed fields are also important. These times should be relatively close if your PVC has not dropped since the interface was brought up. Example 5-10 lists the output of the marlin router with a problem on the PVC. Can you guess where the problem might be just by this one command?

Example 5-10 Output of show frame pvc Command on the marlin Router with a PVC Down

 marlin#  show frame pvc  PVC Statistics for interface Serial0 (Frame Relay DTE)  DLCI = 110, DLCI USAGE = LOCAL, PVC STATUS = INACTIVE, INTERFACE = Serial0.1  input pkts 508           output pkts 255          in bytes 63860   out bytes 30362          dropped pkts 2           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 255        out bcast bytes 30362  pvc create time 05:38:00, last time pvc status changed 00:00:19  DLCI = 120, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1   input pkts 508           output pkts 254          in bytes 27632   out bytes 30270          dropped pkts 0           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 254        out bcast bytes 30270   pvc create time 05:38:01, last time pvc status changed 05:35:49 DLCI = 130, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.2   input pkts 595           output pkts 601          in bytes 109422   out bytes 120372         dropped pkts 0           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 601        out bcast bytes 120372   pvc create time 05:38:01, last time pvc status changed 05:37:09 marlin# 

Notice that the PVC 110 status has changed. The PVC status is now INACTIVE. Because the other PVC, DLCI 120 on interface Serial0.1, is up and the status of 110 is inactive, it indicates a problem at the remote end. In this example, the glock router's serial interface was shut down, again proving that even in a lab setting, "carrier gremlins" do exist.

show frame-relay lmi Command

Everything that rides over Frame Relay rides over the LMI. If the LMI is not working properly, your frame service will not work. When using the show frame-relay lmi command, look for the Num Status Enq. Sent xx to increment with the Num Status msgs Rcvd xx field. If you are sending LMI but are not receiving it, the problem is likely to be with the frame switch or an LMI mismatch. Ensure that the LMI for the interface is the same as what the carrier has the switch set for. Example 5-11 lists the output from the glock router demonstrating an LMI mismatch. Observe how the LMI is being sent, and notice that timeouts are increasing.

Example 5-11 LMI Mismatch Demonstrated with the show frame lmi Command

 glock#  show frame lmi  LMI Statistics for interface Serial0 (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 82               Num Status msgs Rcvd 18   Num Update Status Rcvd 0              Num Status Timeouts 63  glock#  show frame lmi  LMI Statistics for interface Serial0 (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 117               Num Status msgs Rcvd 18   Num Update Status Rcvd 0              Num Status Timeouts 98  glock# 

After changing the LMI to Cisco and performing a clear counters command, you can see what a proper running line looks like. Notice this time in Example 5-12 that the Num Status Enq. Sent messages are incrementing with the Num Status Msgs Rcvd field.

Example 5-12 show frame lmi Command Output

 glock#  show frame lmi  LMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = CISCO   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 1                Num Status msgs Rcvd 1  Num Update Status Rcvd 0              Num Status Timeouts 0 glock# glock#  show frame lmi  LMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = CISCO   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 8                Num Status msgs Rcvd 8  Num Update Status Rcvd 0              Num Status Timeouts 0 glock# 

show frame-relay map Command

The show frame-relay map command displays the network layer address and associated DLCI for each remote destination that the local router is connected to. It also displays whether the association is dynamic or static. Use this command to verify your frame-relay map statements and to check the operation of Inverse ARP. Example 5-13 demonstrates sample output from this command.

Example 5-13 show frame-relay map Command Output

 marlin#  show frame-relay map  Serial0.1 (up): ip 172.16.1.3 dlci 110(0x6E,0x18E0), static,               broadcast,               CISCO, status defined, active Serial0.1 (up): ip 172.16.1.5 dlci 120(0x78,0x1C80), static,               broadcast,               CISCO, status defined, active Serial0.2 (up): point-to-point dlci, dlci 130(0x82,0x2020), broadcast           status defined, active marlin# 

debug frame-relay lmi Command

Although many debug commands are available for Frame Relay, most of them are for specific configuration types and don't apply to a majority of general frame configurations. Debugging LMI, however, can be helpful for many, if not all, Frame Relay configurations.

The debug frame-relay lmi command is useful in displaying LMI exchanges. It allows you to quickly determine whether the router is properly exchanging LMIs. When using this command, look for the yourseq and the myseq numbers to increment. When the router receives a sequence number, it adds 1 to it and sends it back out on the next update as its current sequence number. If three of these LMI messages, or keepalives , are missed consecutively, the link will be reset.

If the output from this command shows only one number changing, it is a strong indication of an LMI mismatch. If no messages appear, there is poor connection between the router and the frame switch. Example 5-14 demonstrates a properly working frame circuit.

Example 5-15 exhibits what happens to a link after carrier gremlins cause an LMI mismatch.

Example 5-14 debug frame-relay lmi Command Output on an Operational Frame Circuit

 sig#  debug frame-relay lmi  Frame Relay LMI debugging is on Displaying all Frame Relay LMI data sig#  18:48:30: Serial0(out): StEnq, myseq 38, yourseen 37, DTE up  18:48:30: datagramstart = 0xE23E94, datagramsize = 13 18:48:30: FR encap = 0xFCF10309 18:48:30: 00 75 01 01 01 03 02 26 25 18:48:30:  18:48:30: Serial0(in): Status, myseq 38  18:48:30: RT IE 1, length 1, type 1 18:48:30: KA IE 3, length 2, yourseq 38, myseq 38  18:48:40: Serial0(out): StEnq, myseq 39, yourseen 38, DTE up  18:48:40: datagramstart = 0xE23E94, datagramsize = 13 18:48:40: FR encap = 0xFCF10309 18:48:40: 00 75 01 01 01 03 02 27 26 18:48:40:  18:48:40: Serial0(in): Status, myseq 39  18:48:40: RT IE 1, length 1, type 1 18:48:40: KA IE 3, length 2, yourseq 39, myseq 39 

Example 5-15 debug frame-relay lmi Command Output Demonstrating an LMI Mismatch

 sig#  debug frame-relay lmi  Frame Relay LMI debugging is on Displaying all Frame Relay LMI data sig#  18:59:26: Serial0(out): StEnq, myseq 7, yourseen 5, DTE up  missed one LMI  18:59:26: datagramstart = 0xE23E94, datagramsize = 13 18:59:26: FR encap = 0xFCF10309 18:59:26: 00 75 01 01 01 03 02 07 05 18:59:26:  18:59:36: Serial0(out): StEnq, myseq 8, yourseen 5, DTE up  missed two LMIs  18:59:36: datagramstart = 0xE23E94, datagramsize = 13 18:59:36: FR encap = 0xFCF10309 18:59:36: 00 75 01 01 01 03 02 08 05 18:59:36:  18:59:46: Serial0(out): StEnq, myseq 9, yourseen 5, DTE up  Strike three, link   down  18:59:46: datagramstart = 0xE23E94, datagramsize = 13 18:59:46: FR encap = 0xFCF10309 18:59:46: 00 75 01 01 01 03 02 09 05 18:59:46:  18:59:56: %FR-5-DLCICHANGE: Interface Serial0 - DLCI 121 state changed to INACTIVE   18:59:56: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0.1, changed state   to down   18:59:56: %FR-5-DLCICHANGE: Interface Serial0 - DLCI 121 state changed to DELETED   18:59:56: Serial0(out): StEnq, myseq 1, yourseen 5, DTE down  18:59:56: datagramstart = 0xE23E94, datagramsize = 13 18:59:56: FR encap = 0xFCF10309 18:59:56: 00 75 01 01 01 03 02 01 05 18:59:56: 18:59:57: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state           to down