Troubleshooting Frame Relay Connectivity

Now that your Frame Relay is configured, there might come a time when you need to ensure that it is working correctly. Fortunately, Cisco provides many different ways to verify configurations. Two easy ways to accomplish this through a CLI are the show and debug suite of commands available in Cisco IOS.

Becoming familiar with the show and debug commands available for Frame Relay allows you to quickly troubleshoot and correct most problems without becoming overloaded with a lot of excess information. In this chapter, only commands that relate to the information already covered are explored. For a complete list of available show and debug commands, refer to the IOS WAN Configuration Guide for the IOS version you will be using.

show frame-relay lmi Command

Because all traffic crossing a Frame Relay circuit rides over the LMI configured for that circuit, the show frame-relay lmi command can provide you with valuable information. The output of this command contains a lot of information. When you start to troubleshoot a connectivity problem or verify that the circuit is operational, two fields, Num Status Enq. Sent and Num Update Status Rcvd, give you an idea of the circuit's health. Example 9-1 shows the output of this command as issued on the R4 router.

Example 9-1. Output of the show frame-relay lmi Command

R4#show frame-relay 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 296              Num Status msgs Rcvd 293
  Num Update Status Rcvd 0              Num Status Timeouts 0

Looking at Example 9-1, you can see that the circuit is sending and receiving Status messages without any timeouts, which are vital to the operation of Frame Relay. This output also supplies the LMI type that the circuit is using for operationin this case, ANSI. If you were experiencing a problem with the configured LMI type, you would see output similar to Example 9-2.

Example 9-2. Mismatched LMI

R4#show frame-relay 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 96               Num Status msgs Rcvd 3
  Num Update Status Rcvd 0              Num Status Timeouts 93

As you can see, your Num Status Timeouts are increasing, indicating a misconfigured circuit.

show frame-relay pvc Command

After you have confirmed that your LMI matches the service provider's, you can verify that you have the proper PVC(s) configured. Use the show frame-relay pvc [dlci | interface] command to display information about the DLCIs that the router is aware of. Example 9-3 shows output from this command.

Example 9-3. Output of the show frame-relay pvc Command

R4#show frame-relay pvc

PVC Statistics for interface Serial0 (Frame Relay DTE)

              Active     Inactive      Deleted       Static
  Local          3            0            0            0
  Switched       0            0            0            0
  Unused         0            0            0            0

DLCI = 110, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1

  input pkts 78            output pkts 78           in bytes 21770
  out bytes 22404          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 63        out bcast bytes 20844
  pvc create time 01:00:23, last time pvc status changed 00:59:45

DLCI = 120, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.2

  input pkts 10            output pkts 20           in bytes 1040
  out bytes 2080           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 0         out bcast bytes 0
  pvc create time 01:00:17, last time pvc status changed 00:59:47

DLCI = 130, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.2

  input pkts 15            output pkts 16           in bytes 1560
  out bytes 1620           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 0         out bcast bytes 0
  pvc create time 01:00:19, last time pvc status changed 00:59:49

NOTE

Notice that the output of the show frame-relay pvc command displays information about all the PVCs the router knows about. If you want more-specific information about a specific interface or DLCI, you can supply the proper keyword with the command and receive only that information.

If you analyze the output of the show frame-relay pvc command in Example 9-3, you will notice that all the configured PVCs are in an active state. PVCs are in one of three states at any given time:

ACTIVE Your PVC is active and can pass traffic.
INACTIVE Your local connection to Frame Relay is operational, but the remote router's connection is not operational.
DELETED You are not receiving LMIs, or the physical layer is encountering a problem.

Other areas of interest in this output include the pvc create time, which tells you when the PVC was created, and the last time pvc status changed time, which tells you the last time the PVC state time changed. Both of these items can provide invaluable troubleshooting information.

If you are looking for information about congestion, this is the command to use, because it shows the counters related to FECN and BECN packets the router has processed.

debug frame-relay lmi Command

Like most technologies supported by Cisco IOS, Frame Relay supports debugging of numerous configuration items. The one debug command this chapter examines, debug frame-relay lmi, is a useful command when you start troubleshooting (see Example 9-4). If you require the use of other debugging commands for Frame Relay, refer to the IOS WAN Configuration Guide for your IOS version.

Example 9-4. Output of the debug frame-relay lmi Command

R4#debug frame-relay lmi
Frame Relay LMI debugging is on
Displaying all Frame Relay LMI data
R4#
01:51:51: Serial0(out): StEnq, myseq 31, yourseen 31, DTE up
01:51:51: datagramstart = 0xE30BD8, datagramsize = 14
01:51:51: FR encap = 0x00010308
01:51:51: 00 75 95 01 01 01 03 02 1F 1F
01:51:51:
01:51:51: Serial0(in): Status, myseq 31
01:51:51: RT IE 1, length 1, type 1
01:51:51: KA IE 3, length 2, yourseq 32, myseq 31
01:52:01: Serial0(out): StEnq, myseq 32, yourseen 32, DTE up
01:52:01: datagramstart = 0xE30BD8, datagramsize = 14
01:52:01: FR encap = 0x00010308
01:52:01: 00 75 95 01 01 01 03 02 20 20
01:52:01:
01:52:01: Serial0(in): Status, myseq 32
01:52:01: RT IE 1, length 1, type 1
01:52:01: KA IE 3, length 2, yourseq 33, myseq 32
01:52:11: Serial0(out): StEnq, myseq 33, yourseen 33, DTE up
01:52:11: datagramstart = 0xE30BD8, datagramsize = 14
01:52:11: FR encap = 0x00010308
01:52:11: 00 75 95 01 01 01 03 02 21 21
01:52:11:
01:52:11: Serial0(in): Status, myseq 33
01:52:11: RT IE 1, length 1, type 1
01:52:11: KA IE 3, length 2, yourseq 34, myseq 33
R4#

You can see from this output that this router is successfully exchanging LMIs with the service provider's Frame Relay switch. You know this because the fields myseq and yourseq are increasing. The router adds 1 to the received sequence number with each successive message sent. If this field were not increasing, LMI exchanges would not be occurring. If three successive LMI messages are sent without a reply, where only one field is increasing, the link is reset, and the process restarts.

[ LiB ]