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Cisco Frame Relay Configurations

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Apr 30, 2004.

Chapter Description

Jonathan Chin dicussess basic Frame Relay operations on Cisco routers in a router-based Frame Relay network. He also explains how to configure a basic frame relay network involving Cisco equipment and how to perform basic monitoring and troubleshooting using relevant Cisco IOS show and debug commands.

Troubleshooting Frame Relay Connections with Cisco IOS debug Commands

This final section discusses the common issues and problems encountered on Frame Relay networks and how several IOS debug commands are used for troubleshooting Frame Relay connections.

In general, debug commands are used on a Cisco router only for diagnostic and troubleshooting purposes. During normal operation, all debug commands should be turned off. Debug commands generate massive overhead by taking up CPU cycles on the router. Enabling many debug commands at once can overwhelm the router and adversely affect its performance.

When using debug commands, the user has several options for logging the debug messages. The debug messages can be logged directly onto the router console, logged to a monitor if the router is accessed via Telnet, logged to a syslog server on the network, or stored in a buffer. Storing the debug messages inside the buffer is an attractive option because it creates less overhead. It is beyond the scope of this book to discuss the troubleshooting methodology of Cisco IOS in detail.

debug frame-relay events

The debug frame-relay events EXEC mode command can be used to identify the cause of end-to-end connection problems during installations of Frame Relay networks. When the router is using Frame Relay dynamic addressing, the debug frame-relay events displays information about Frame Relay Inverse ARP packets exchanged between the local router and the Frame Relay network.

Use the no form of the debug frame-relay events command to disable the debugging output. Example 4-35 shows a sample debug output of the debug frame-relay events command.

Example 4-35 Sample Output of debug frame-relay events Command

Router#debug frame-relay events
*Mar 1 01:16:39.235: Serial1/2: FR ARP input
*Mar 1 01:16:39.235: datagramstart = 0x7D0DE6E, datagramsize = 34
*Mar 1 01:16:39.235: FR encap = 0x64110300
*Mar 1 01:16:39.235: 80 00 00 00 08 06 00 0F 08 00 02 04 00 08 00 00 
*Mar 1 01:16:39.239: AC 10 01 04 18 51 00 00 00 00 01 02 00 00 
*Mar 1 01:16:39.239: 
*Mar 1 01:16:44.899: Serial1/2: FR ARP input
*Mar 1 01:16:44.899: datagramstart = 0x7D0E0EE, datagramsize = 34
*Mar 1 01:16:44.899: FR encap = 0x30910300
*Mar 1 01:16:44.899: 80 00 00 00 08 06 00 0F 08 00 02 04 00 09 00 00 
*Mar 1 01:16:44.899: AC 10 01 02 30 91 AC 10 01 01 01 02 00 00
*Mar 1 01:17:44.911: Serial1/2: FR ARP input
*Mar 1 01:17:44.911: datagramstart = 0x7D0CCEE, datagramsize = 34
*Mar 1 01:17:44.911: FR encap = 0x48D10300
*Mar 1 01:17:44.911: 80 00 00 00 08 06 00 0F 08 00 02 04 00 09 00 00 
*Mar 1 01:17:44.911: AC 10 01 02 48 D1 AC 10 01 01 01 02 00 00

debug frame-relay lmi

The debug frame-relay lmi EXEC mode command is used to display information on the LMI packets exchanged by the router and the Frame Relay switch. The information from the debugging output can be used to determine whether the router and the Frame Relay switch are sending and receiving LMI packets properly.

The no form of this command disables the debugging output. Example 4-36 shows the sample debugging output of the debug frame-relay lmi command.

Example 4-36 Sample Output of debug frame-relay lmi Command

Router#debug frame-relay lmi
*Mar 1 01:26:16.063: Serial1/2(out): StEnq, myseq 43, yourseen 42, DTE up
*Mar 1 01:26:16.063: datagramstart = 0x7B00E94, datagramsize = 13
*Mar 1 01:26:16.063: FR encap = 0xFCF10309
*Mar 1 01:26:16.063: 00 75 01 01 00 03 02 2B 2A 
*Mar 1 01:26:16.063: 
*Mar 1 01:26:16.071: Serial1/2(in): Status, myseq 43
*Mar 1 01:26:16.071: RT IE 1, length 1, type 0
*Mar 1 01:26:16.071: KA IE 3, length 2, yourseq 43, myseq 43
*Mar 1 01:26:16.075: PVC IE 0x7 , length 0x6 , dlci 201, status 0x2 , bw 0
*Mar 1 01:26:16.075: PVC IE 0x7 , length 0x6 , dlci 301, status 0x2 , bw 0
*Mar 1 01:26:16.075: PVC IE 0x7 , length 0x6 , dlci 401, status 0x2 , bw 0
*Mar 1 01:26:16.075: PVC IE 0x7 , length 0x6 , dlci 501, status 0x2 , bw 0

The first line in the debugging output of debug frame-relay lmi is the LMI request the router has sent out to the switch. This is indicated by Serial1/2(out), which shows that the LMI request was sent out on serial1/2 to the switch. The sixth line in the debugging output shows the LMI response received from the switch, indicated by Serial1/2(in). The last four lines in the debugging output show the full LMI status message, which includes a description of the router's active PVCs.

debug frame-relay packet

The debug frame-relay packet EXEC command is used to analyze the packets sent on the Frame Relay interface. Because this debug command generates a large amount of debugging output, the command offers options to log the debugging output only to a specific interface or DLCI. Use the no form of the debug frame-relay packet command to disable the logging of the debugging output.

Example 4-37 shows the sample debugging output of the debug frame-relay packet command.

Example 4-37 Sample Output of debug frame-relay packet Command

Router#debug frame-relay packet
*Mar 1 01:37:25.195: Serial1/2(i): dlci 501(0x7C51), pkt type 0x800, datagramsize 53
*Mar 1 01:37:28.195: Serial1/2(i): dlci 501(0x7C51), pkt type 0x800, datagramsize 53
*Mar 1 01:37:31.203: Serial1/2(i): dlci 501(0x7C51), pkt type 0x800, datagramsize 53
*Mar 1 01:37:34.203: Serial1/2(i): dlci 501(0x7C51), pkt type 0x800, datagramsize 53

The debugging output shows that packets are received on Serial1/2 on DLCI 501. The packet type is 0x800 (IP on 10 MB net), and the size of the packets is 53 bytes.

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