Catalyst 3550 Multilayer Switch Software Configuration Guide, 12.1(9)EA1
Troubleshooting
Downloads: This chapterpdf (PDF - 270.0KB) The complete bookPDF (PDF - 10.01MB) | Feedback

Troubleshooting

Table Of Contents

Troubleshooting

Using Recovery Procedures

Recovering from Corrupted Software

Recovering from a Lost or Forgotten Password

Password Recovery with Password Recovery Enabled

Procedure with Password Recovery Disabled

Recovering from a Command Switch Failure

Replacing a Failed Command Switch with a Cluster Member

Replacing a Failed Command Switch with Another Switch

Recovering from Lost Member Connectivity

Preventing Autonegotiation Mismatches

GBIC Security and Identification

Diagnosing Connectivity Problems

Understanding Ping

Executing Ping

Understanding IP Traceroute

Executing IP Traceroute

Using Debug Commands

Enabling Debugging on a Specific Feature

Enabling All-System Diagnostics

Redirecting Debug and Error Message Output

Using the show forward Command

Using the crashinfo File


Troubleshooting


This chapter describes how to identify and resolve software problems related to the IOS software. Depending on the nature of the problem, you can use the command-line interface (CLI) or the Cluster Management Suite (CMS) to identify and solve problems.


Note For complete syntax and usage information for the commands used in this chapter, refer to the Catalyst 3550 Multilayer Switch Command Reference for this release and the Cisco IOS Command Summary for Release 12.1.


This chapter consists of these sections:

Using Recovery Procedures

Preventing Autonegotiation Mismatches

GBIC Security and Identification

Diagnosing Connectivity Problems

Using Debug Commands

Using the show forward Command

Using the crashinfo File


Note If after applying ACLs, you are experiencing packet performance problems or receiving messages about TCAM capacity, see the "Displaying ACL Resource Usage and Configuration Problems" section.


Using Recovery Procedures

These recovery procedures require that you have physical access to the switch:

Recovering from Corrupted Software

Recovering from a Lost or Forgotten Password

Recovering from a Command Switch Failure

Recovering from Lost Member Connectivity

Recovering from Corrupted Software

Switch software can be corrupted during an upgrade, by downloading the wrong file to the switch, and by deleting the image file. In all of these cases, the switch does not pass the power-on self-test (POST), and there is no connectivity.

This procedure uses the XMODEM Protocol to recover from a corrupt or wrong image file. There are many software packages that support the XMODEM protocol, and this procedure is largely dependent on the emulation software you are using.


Step 1 Connect a PC with terminal-emulation software supporting the XMODEM Protocol to the switch console port.

Step 2 Set the line speed on the emulation software to 9600 baud.

Step 3 Unplug the switch power cord.

Step 4 Press the Mode button, and at the same time, reconnect the power cord to the switch.

You can release the Mode button a second or two after the LED above port 1X goes off. Several lines of information about the software appear along with instructions:

The system has been interrupted prior to initializing the flash file system. The following 
commands will initialize the flash file system, and finish loading the operating system 
software:

flash_init
load_helper
boot

Step 5 Initialize the Flash file system:

switch: flash_init

Step 6 If you had set the console port speed to anything other than 9600, it has been reset to that particular speed. Change the emulation software line speed to match that of the switch console port.

Step 7 Load any helper files:

switch: load_helper

Step 8 Start the file transfer by using the XMODEM protocol.

switch: copy xmodem: flash:image_filename.bin

Step 9 After the XMODEM request appears, use the appropriate command on the terminal-emulation software to start the transfer and to copy the software image into Flash memory.


Recovering from a Lost or Forgotten Password

The default configuration for Catalyst 3550 switches allows an end user with physical access to the switch to recover from a lost password by interrupting the boot process during power-on and by entering a new password.


Note On Catalyst 3550 Fast Ethernet switches, a system administrator can disable some of the functionality of this feature by allowing an end user to reset a password only by agreeing to return to the default configuration. If you are an end user trying to reset a password on a Catalyst 3550 Fast Ethernet switch and password recover has been disabled, a status message shows this during the recovery process.


Follow the steps in this procedure if you have forgotten or lost the switch password.


Step 1 Connect a terminal or PC with terminal-emulation software to the switch console port.

Step 2 Set the line speed on the emulation software to 9600 baud.

Step 3 Unplug the switch power cord.

Step 4 Press the Mode button, and at the same time, reconnect the power cord to the switch.

You can release the Mode button a second or two after the LED above port 1X turns off. Several lines of information about the software appear with instructions, informing you if the password recovery procedure has been disabled or not.

If you see a message that begins with this:

The system has been interrupted prior to initializing the flash file system. The following commands will initialize the flash file system

proceed to the "Password Recovery with Password Recovery Enabled" section, and follow the steps.

If you see a message that begins with this:

	The password-recovery mechanism has been triggered, but

is currently disabled.

proceed to the "Procedure with Password Recovery Disabled" section, and follow the steps.

Password Recovery with Password Recovery Enabled

If the password-recovery mechanism is enabled, this message appears:

The system has been interrupted prior to initializing the flash file system. The following 
commands will initialize the flash file system, and finish loading the operating system 
software:

flash_init
load_helper
boot

Step 1 Initialize the Flash file system:

switch: flash_init

Step 2 If you had set the console port speed to anything other than 9600, it has been reset to that particular speed. Change the emulation software line speed to match that of the switch console port.

Step 3 Load any helper files:

switch: load_helper

Step 4 Display the contents of Flash memory:

switch: dir flash:

The switch file system is displayed:

Directory of flash:
   13  drwx         192   Mar 01 1993 22:30:48  c3550-i5q3l2-mz-121-0.0.53
   11  -rwx        5825   Mar 01 1993 22:31:59  config.text
   17  -rwx          27   Mar 01 1993 22:30:57  env_vars
    5  -rwx          90   Mar 01 1993 22:30:57  system_env_vars
   18  -rwx         720   Mar 01 1993 02:21:30  vlan.dat

16128000 bytes total (10003456 bytes free) 

Step 5 Rename the configuration file to config.text.old.

This file contains the password definition.

switch: rename flash:config.text flash:config.text.old

Step 6 Boot the system:

switch: boot

You are prompted to start the setup program. Enter N at the prompt:

Continue with the configuration dialog? [yes/no]: N

Step 7 At the switch prompt, enter privileged EXEC mode:

Switch> enable

Step 8 Rename the configuration file to its original name:

Switch# rename flash:config.text.old flash:config.text 

Step 9 Copy the configuration file into memory:

Switch# copy flash:config.text system:running-config 
Source filename [config.text]? 
Destination filename [running-config]?

Press Return in response to the confirmation prompts.

The configuration file is now reloaded, and you can change the password.

Step 10 Enter global configuration mode:

Switch# configure terminal

Step 11 Change the password:

Switch (config)# enable secret password

The secret password can be from 1 to 25 alphanumeric characters, can start with a number, is case sensitive, and allows spaces but ignores leading spaces.

Step 12 Return to privileged EXEC mode:

Switch (config)# exit 
Switch# 

Step 13 Write the running configuration to the startup configuration file:

Switch# copy running-config startup-config

The new password is now in the startup configuration.


Note This procedure is likely to leave your switch virtual interface in a shutdown state. You can see which interface is in this state by entering the show running-config privileged EXEC command. To re-enable the interface, enter the interface vlan vlan-id global configuration command, and specify the VLAN ID of the shutdown interface. With the switch in interface configuration mode, enter the no shutdown command.



Procedure with Password Recovery Disabled

If the password-recovery mechanism is disabled, this message appears:

The password-recovery mechanism has been triggered, but
is currently disabled.  Access to the boot loader prompt
through the password-recovery mechanism is disallowed at
this point.  However, if you agree to let the system be
reset back to the default system configuration, access
to the boot loader prompt can still be allowed.

Would you like to reset the system back to the default configuration (y/n)?


Caution Returning the switch to the default configuration results in the loss of all existing configurations. We recommend that you contact your system administrator to verify if there are backup switch and VLAN configuration files.

If you enter n (no), the normal boot process continues as if the Mode button had not been pressed; you cannot access the boot loader prompt, and you cannot enter a new password. You see the message:

Press Enter to continue........

If you enter y (yes), the configuration file in Flash memory and the VLAN database file are deleted. When the default configuration loads, you can reset the password.


Step 1 Elect to continue with password recovery and lose the existing configuration:

Would you like to reset the system back to the default configuration (y/n)? Y 

Step 2 Load any helper files:

Switch: load_helper

Step 3 Display the contents of Flash memory:

switch: dir flash:

The switch file system is displayed:

Directory of flash:
   13  drwx         192   Mar 01 1993 22:30:48  c3550-i5q3l2-mz-121-0.0.53
   17  -rwx          27   Mar 01 1993 22:30:57  env_vars
    5  -rwx          90   Mar 01 1993 22:30:57  system_env_vars

16128000 bytes total (10003456 bytes free) 

Step 4 Boot the system:

Switch: boot

You are prompted to start the setup program. To continue with password recovery, enter N at the prompt:

Continue with the configuration dialog? [yes/no]: N

Step 5 At the switch prompt, enter privileged EXEC mode:

Switch> enable

Step 6 Enter global configuration mode:

Switch# configure terminal

Step 7 Change the password:

Switch (config)# enable secret password

The secret password can be from 1 to 25 alphanumeric characters, can start with a number, is case sensitive, and allows spaces but ignores leading spaces.

Step 8 Return to privileged EXEC mode:

Switch (config)# exit 
Switch# 

Step 9 Write the running configuration to the startup configuration file:

Switch# copy running-config startup-config

The new password is now in the startup configuration.


Note This procedure is likely to leave your switch virtual interface in a shutdown state. You can see which interface is in this state by entering the show running-config privileged EXEC command. To re-enable the interface, enter the interface vlan vlan-id global configuration command, and specify the VLAN ID of the shutdown interface. With the switch in interface configuration mode, enter the no shutdown command.


Step 10 You must now reconfigure the switch. If the system administrator has the backup switch and VLAN configuration files available, you should use those.


Recovering from a Command Switch Failure

This section describes how to recover from a failed command switch. You can configure a redundant command switch group by using the Hot Standby Router Protocol (HSRP). For more information, see "Clustering Switches" and "Configuring HSRP."


Note HSRP is the preferred method for supplying redundancy to a cluster.


If you have not configured a standby command switch, and your command switch loses power or fails in some other way, management contact with the member switches is lost, and you must install a new command switch. However, connectivity between switches that are still connected is not affected, and the member switches forward packets as usual. You can manage the members as standalone switches through the console port or, if they have IP addresses, through the other management interfaces.

You can prepare for a command switch failure by assigning an IP address to a member switch or another switch that is command-capable, making a note of the command-switch password, and cabling your cluster to provide redundant connectivity between the member switches and the replacement command switch. This section describes two solutions for replacing a failed command switch:

Replacing a failed command switch with a cluster member

Replacing a failed command switch with another switch

For information on command-capable switches, refer to the release notes.

Replacing a Failed Command Switch with a Cluster Member

To replace a failed command switch with a command-capable member in the same cluster, follow these steps:


Step 1 Disconnect the command switch from the member switches, and physically remove it from the cluster.

Step 2 Insert the member switch in place of the failed command switch, and duplicate its connections to the cluster members.

Step 3 Start a CLI session on the new command switch.

You can access the CLI by using the console port or, if an IP address has been assigned to the switch, by using Telnet. For details about using the console port, refer to the switch hardware installation guide.

Step 4 At the switch prompt, enter privileged EXEC mode:

Switch> enable 
Switch#

Step 5 Enter the password of the failed command switch.

Step 6 Enter global configuration mode.

Switch# configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.

Step 7 Remove the member switch from the cluster.

Switch(config)# no cluster commander-address 

Step 8 Return to privileged EXEC mode.

Switch(config)# end 
Switch#

Step 9 Use the setup program to configure the switch IP information. This program prompts you for IP address information and passwords. From privileged EXEC mode, enter setup, and press Return.

Switch# setup
         --- System Configuration Dialog ---
Continue with configuration dialog? [yes/no]: y

At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.

Basic management setup configures only enough connectivity
for management of the system, extended setup will ask you
to configure each interface on the system

Would you like to enter basic management setup? [yes/no]: 

Step 10 Enter Y at the first prompt.

The prompts in the setup program vary depending on the member switch you selected to be the command switch:

Continue with configuration dialog? [yes/no]: y

or

Configuring global parameters:

If this prompt does not appear, enter enable, and press Return. Enter setup, and press Return to start the setup program.

Step 11 Respond to the questions in the setup program.

When prompted for the host name, recall that on a command switch, the host name is limited to 28 characters; on a member switch to 31 characters. Do not use -n, where n is a number, as the last characters in a host name for any switch.

When prompted for the Telnet (virtual terminal) password, recall that it can be from 1 to 25 alphanumeric characters, is case sensitive, allows spaces, but ignores leading spaces.

Step 12 When prompted for the enable secret and enable passwords, enter the passwords of the failed command switch again.

Step 13 When prompted, make sure to enable the switch as the cluster command switch, and press Return.

Step 14 When prompted, assign a name to the cluster, and press Return.

The cluster name can be 1 to 31 alphanumeric characters, dashes, or underscores.

Step 15 After the initial configuration displays, verify that the addresses are correct.

Step 16 If the displayed information is correct, enter Y, and press Return.

If this information is not correct, enter N, press Return, and begin again at Step 9.

Step 17 Start your browser, and enter the IP address of the new command switch.

Step 18 From the Cluster menu, select Add to Cluster to display a list of candidate switches to add to the cluster.


Replacing a Failed Command Switch with Another Switch

To replace a failed command switch with a switch that is command-capable but not part of the cluster, follow these steps:


Step 1 Insert the new switch in place of the failed command switch, and duplicate its connections to the cluster members.

Step 2 Start a CLI session on the new command switch.

You can access the CLI by using the console port or, if an IP address has been assigned to the switch, by using Telnet. For details about using the console port, refer to the switch hardware installation guide.

Step 3 At the switch prompt, enter privileged EXEC mode:

Switch> enable 
Switch#

Step 4 Enter the password of the failed command switch.

Step 5 Use the setup program to configure the switch IP information.

This program prompts you for IP address information and passwords. From privileged EXEC mode, enter setup, and press Return.

Switch# setup
         --- System Configuration Dialog ---
Continue with configuration dialog? [yes/no]: y

At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.

Basic management setup configures only enough connectivity
for management of the system, extended setup will ask you
to configure each interface on the system

Would you like to enter basic management setup? [yes/no]: 

Step 6 Enter Y at the first prompt.

The prompts in the setup program vary depending on the switch you selected to be the command switch:

Continue with configuration dialog? [yes/no]: y

or

Configuring global parameters:

If this prompt does not appear, enter enable, and press Return. Enter setup, and press Return to start the setup program.

Step 7 Respond to the questions in the setup program.

When prompted for the host name, recall that on a command switch, the host name is limited to 28 characters. Do not use -n, where n is a number, as the last characters in a host name for any switch.

When prompted for the Telnet (virtual terminal) password, recall that it can be from 1 to 25 alphanumeric characters, is case sensitive, allows spaces, but ignores leading spaces.

Step 8 When prompted for the enable secret and enable passwords, enter the passwords of the failed command switch again.

Step 9 When prompted, make sure to enable the switch as the cluster command switch, and press Return.

Step 10 When prompted, assign a name to the cluster, and press Return.

The cluster name can be 1 to 31 alphanumeric characters, dashes, or underscores.

Step 11 When the initial configuration displays, verify that the addresses are correct.

Step 12 If the displayed information is correct, enter Y, and press Return.

If this information is not correct, enter N, press Return, and begin again at Step 9.

Step 13 Start your browser, and enter the IP address of the new command switch.

Step 14 From the Cluster menu, select Add to Cluster to display a list of candidate switches to add to the cluster.


Recovering from Lost Member Connectivity

Some configurations can prevent the command switch from maintaining contact with member switches. If you are unable to maintain management contact with a member, and the member switch is forwarding packets normally, check for these conflicts:

A member switch (Catalyst 3550, Catalyst 3500 XL, Catalyst 2950, Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900 switch) cannot connect to the command switch through a port that is defined as a network port.

Catalyst 3500 XL, Catalyst 2950, Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900 member switches must connect to the command switch through a port that belongs to the same management VLAN.

A member switch (Catalyst 3550, Catalyst 2950, Catalyst 3500 XL, Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900 switch) connected to the command switch through a secured port can lose connectivity if the port is disabled because of a security violation.

Preventing Autonegotiation Mismatches

The IEEE 802.3AB autonegotiation protocol manages the switch settings for speed (10 Mbps, 100 Mbps, and 1000 Mbps excluding GBIC ports) and duplex (half or full).There are situations when this protocol can incorrectly align these settings, reducing performance. A mismatch occurs under these circumstances:

A manually-set speed or duplex parameter is different from the manually set speed or duplex parameter on the connected port.

A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.

To maximize switch performance and ensure a link, follow one of these guidelines when changing the settings for duplex and speed:

Let both ports autonegotiate both speed and duplex.

Manually set the speed and duplex parameters for the ports on both ends of the connection.


Note If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The speed parameter can adjust itself even if the connected port does not autonegotiate.


GBIC Security and Identification

Cisco-approved Gigabit Interface Converter (GBIC) modules have a serial EEPROM that contains the module serial number, the vendor name and ID, a unique security code, and cyclic redundancy check (CRC). When a GBIC is inserted in the switch, the switch software reads the EEPROM to check the serial number, vendor name and ID, and recompute the security code and CRC. If the serial number, the vendor name or ID, the security code, or CRC is invalid, the switch places the interface in an error-disabled state.


Note If you are using a non-Cisco approved GBIC module, remove the GBIC module from the switch, and replace it with a Cisco-approved module.


After inserting a Cisco-approved GBIC, use the errdisable recovery cause gbic-invalid global configuration command to verify the port status, and enter a time interval for recovering from the error-disabled state. After the elapsed interval, the switch brings the interface out of the error-disabled state and retries the operation. For more information about the errdisable recovery command, refer to the Catalyst 3550 Multilayer Switch Command Reference.

Diagnosing Connectivity Problems

This section describes how to troubleshoot connectivity problems:

Understanding Ping

Executing Ping

Understanding IP Traceroute

Executing IP Traceroute

Understanding Ping

The switch supports IP ping, which you can use to test connectivity to remote hosts. Ping sends an echo request packet to an address and waits for a reply. Ping returns one of these responses:

Normal response—The normal response (hostname is alive) occurs in 1 to 10 seconds, depending on network traffic.

Destination does not respond—If the host does not respond, a no-answer message is returned.

Unknown host—If the host does not exist, an unknown host message is returned.

Destination unreachable—If the default gateway cannot reach the specified network, a destination-unreachable message is returned.

Network or host unreachable—If there is no entry in the route table for the host or network, a network or host unreachable message is returned.

Executing Ping

If you attempt to ping a host in a different IP subnetwork, you must define a static route to the network or have IP routing configured to route between those subnets. For more information, see "Configuring IP Unicast Routing."

IP routing is disabled by default on all switches. If you need to enable or configure IP routing, see "Configuring IP Unicast Routing."

Beginning in privileged EXEC mode, use this command to ping another device on the network from the switch:

Command
Purpose

ping ip host | address

Ping a remote host through IP or by supplying the host name or network address.



Note Though other protocol keywords are available with the ping command, they are not supported in this release.


This example shows how to ping an IP host:

Switch# ping 172.20.52.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echoes to 172.20.52.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
Switch#

Table 34-1 describes the possible ping character output.

Table 34-1 Ping Output Display Characters 

Character
Description

!

Each exclamation point means receipt of a reply.

.

Each period means the network server timed out while waiting for a reply.

U

A destination unreachable error PDU was received.

C

A congestion experienced packet was received.

I

User interrupted test.

?

Unknown packet type.

&

Packet lifetime exceeded.


To terminate a ping session, enter the escape sequence (Ctrl-^ X by default). You enter the default by simultaneously pressing and releasing the Ctrl, Shift, and 6 keys, and then pressing the X key.

Understanding IP Traceroute

You can use IP traceroute to identify the path that packets take through the network on a hop-by-hop basis. The command output displays all network layer (Layer 3) devices, such as routers, that the traffic passes through on the way to the destination.

Your switches can participate as the source or destination of the traceroute privileged EXEC command and might or might not appear as a hop in the traceroute command output. If the switch is the destination of the traceroute, it is displayed as the final destination in the traceroute output. Intermediate switches do not show up in the traceroute output if they are only bridging the packet from one port to another within the same VLAN. However, if the intermediate switch is a multilayer switch that is routing a particular packet, this switch shows up as a hop in the traceroute output.

The traceroute privileged EXEC command uses the Time To Live (TTL) field in the IP header to cause routers and servers to generate specific return messages. Traceroute starts by sending a User Datagram Protocol (UDP) datagram to the destination host with the TTL field set to 1. If a router finds a TTL value of 1 or 0, it drops the datagram and sends back an Internet Control Message Protocol (ICMP) time-to-live-exceeded message to the sender. Traceroute determines the address of the first hop by examining the source address field of the ICMP time-to-live-exceeded message.

To identify the next hop, traceroute sends a UDP packet with a TTL value of 2. The first router decrements the TTL field by 1 and sends the datagram to the next router. The second router sees a TTL value of 1, discards the datagram, and returns the time-to-live-exceeded message to the source. This process continues until the TTL is incremented to a value large enough for the datagram to reach the destination host (or until the maximum TTL is reached).

To determine when a datagram reaches its destination, traceroute sets the UDP destination port number in the datagram to a very large value that the destination host is unlikely to be using. When a host receives a datagram destined to itself containing a destination port number that is unused locally, it sends an ICMP port unreachable error to the source. Because all errors except port unreachable errors come from intermediate hops, the receipt of a port unreachable error means this message was sent by the destination.

Executing IP Traceroute

Beginning in privileged EXEC mode, follow this step to trace the path packets take through the network:

Command
Purpose

traceroute ip host

Trace the path packets take through the network by using IP.



Note Though other protocol keywords are available with the traceroute privileged EXEC command, they are not supported in this release.


This example shows how to perform a traceroute to an IP host:

Switch# traceroute ip 171.9.15.10

Type escape sequence to abort.
Tracing the route to 171.69.115.10

  1 172.2.52.1 0 msec 0 msec 4 msec
  2 172.2.1.203 12 msec 8 msec 0 msec
  3 171.9.16.6 4 msec 0 msec 0 msec
  4 171.9.4.5 0 msec 4 msec 0 msec
  5 171.9.121.34 0 msec 4 msec 4 msec
  6 171.9.15.9 120 msec 132 msec 128 msec
  7 171.9.15.10 132 msec 128 msec 128 msec
Switch#

The display shows the hop count, IP address of the router, and the round-trip time in milliseconds for each of the three probes that are sent.

Table 34-2 Traceroute Output Display Characters 

Character
Description

*

The probe timed out.

?

Unknown packet type.

A

Administratively unreachable. Usually, this output means that an access list is blocking traffic.

H

Host unreachable.

N

Network unreachable.

P

Protocol unreachable.

Q

Source quench.

U

Port unreachable.


To terminate a trace in progress, enter the escape sequence (Ctrl-^ X by default). You enter the default by simultaneously pressing and releasing the Ctrl, Shift, and 6 keys, and then pressing the X key.

Using Debug Commands

This section explains how you use debug commands to diagnose and resolve internetworking problems. It contains this information:

Enabling Debugging on a Specific Feature

Enabling All-System Diagnostics

Redirecting Debug and Error Message Output


Caution Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco technical support staff. It is best to use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use.


Note For complete syntax and usage information for the Catalyst 3550-specific debug commands, refer to the Catalyst 3550 Multilayer Switch Command Reference for this release.


Enabling Debugging on a Specific Feature

All debug commands are entered in privileged EXEC mode, and most debug commands take no arguments. For example, beginning in privileged EXEC mode, enter this command to enable the debugging for Switch Port Analyzer:

Switch# debug span-session

The switch continues to generate output until you enter the no form of the command.

If you enable a debug command and no output is displayed, consider these possibilities:

The switch might not be properly configured to generate the type of traffic you want to monitor. Use the show running-config command to check its configuration.

Even if the switch is properly configured, it might not generate the type of traffic you want to monitor during the particular period that debugging is enabled. Depending on the feature you are debugging, you can use commands such as the TCP/IP ping command to generate network traffic.

To disable debugging of SPAN, enter this command in privileged EXEC mode:

Switch# no debug span-session

Alternately, in privileged EXEC mode, you can enter the undebug form of the command:

Switch# undebug span-session

To display the state of each debugging option, enter this command in privileged EXEC mode:

Switch# show debugging

Enabling All-System Diagnostics

Beginning in privileged EXEC mode, enter this command to enable all-system diagnostics:

Switch# debug all


Caution Because debugging output takes priority over other network traffic, and because the debug all privileged EXEC command generates more output than any other debug command, it can severely diminish switch performance or even render it unusable. In virtually all cases, it is best to use more specific debug commands.

The no debug all privileged EXEC command disables all diagnostic output. Using the no debug all command is a convenient way to ensure that you have not accidentally left any debug commands enabled.

Redirecting Debug and Error Message Output

By default, the network server sends the output from debug commands and system error messages to the console. If you use this default, you can use a virtual terminal connection to monitor debug output instead of connecting to the console port.

Possible destinations include the console, virtual terminals, internal buffer, and UNIX hosts running a syslog server. The syslog format is compatible with 4.3 Berkeley Standard Distribution (BSD) UNIX and its derivatives.


Note Be aware that the debugging destination you use affects system overhead. Logging messages to the console produces very high overhead, whereas logging messages to a virtual terminal produces less overhead. Logging messages to a syslog server produces even less, and logging to an internal buffer produces the least overhead of any method.


For more information about system message logging, see "Configuring System Message Logging."

Using the show forward Command

The output from the show forward privileged EXEC command provides some useful information about the disposition of a packet entering an interface. Depending upon the parameters entered about the packet, the output provides lookup table results, maps and masks used to calculate forwarding destinations, bitmaps, and egress information.


Note For more syntax and usage information for the show forward command, refer to the Catalyst 3550 Multilayer Switch Command Reference for this release.


This is an example of the output from the show forward privileged EXEC command for Fast Ethernet port 8, where VLAN ID, source and destination MAC addresses, and source and destination IP addresses were provided.

Switch# show forward fa0/8 vlan 8 0000.1111.2222 0022.3355.9800 ip 8.8.8.10 4.4.4.33 255
signature:00000007, comparison ind:10, control info:2000941A control map:00000000
vlan:8, vlanid entry:000C0012 00000000 00000000 04620000
vlan:8, vlanid entry:000C0012 00000000 00000000 04620000

lookup  key                                   bk adata    rawoff secoff sec
qos     940808080A04040421 800000000000FF0000 0  00000000 006304 004064  4
acl     940808080A04040421 800000000000FF0000 1  00000082 045408 002016  1
learn   187008000011112222 801008002233559800 0  80010003 002176 002176  0
forw    187008000011112222 801008002233559800 1  40020000 043328 010560  5

bridgeDestMap:  00000000 00000000 0000FFFF FFFFFFC7
vlanMask:       00000000 00000000 0000FFFF FFFFFE7F
portMask:       00000000 00000000 00000000 00000080
sourceMask:     00000000 00000000 00000000 00000000
globalMap:      00000000 00000000 00000000 00000000
globalMask:     00000000 00000000 0002FFFF EFFFFC03
forwMap:        00000000 00000000 00000000 00000100

frame notifies:
src u_dat vlan fl q-map
2   00    8    00 00000000 00000000 00000000 00000100
Egress q 8
signature:00000007, comparison ind:10, control info:2000941A control map:00000000
vlan:8, vlanid entry:000C0012 00000000 00000000 04620000
FastEthernet0/9 vlan 8, dst 0022.3355.9800 src 0000.1111.2222, cos 0x0, dscp 0x0

Much of this information is useful mainly for Technical Support personnel, who have access to detailed information about the switch application-specific integrated circuits (ASICs). However, you can look at the Egress q section to get information about the output interface. There is an egress section for each separate destination port. The important information is in the line containing the name of the output interface, output VLAN ID, and rewritten destination MAC address for the frame. The example shows that the output interface is Fast Ethernet port 9 and the output VLAN is VLAN 8 and provides the rewritten source and destination MAC address for the frame.

If the output interface is a trunk port that needs to transmit multiple copies of the frame on different VLANs (for example, for IP multicast frames), several lines might contain the same output interface name, but different output VLANs. If output security access control lists (ACLs) are present, it is possible that one or more of these Egress q sections will not contain a line listing an output port. This happens when the output ACL denies the packet.

When the CPU is one of the destinations for a packet, a Cpu q section is displayed, followed by a queue name. This name should correspond to one of the queue names in the output from the show controllers cpu-interface privileged EXEC command, where statistics are displayed for the number of packets received at each queue.

This is an example of the Cpu q section display:

Cpu q:100 - routing queue

Using the crashinfo File

The crashinfo file saves information that helps Cisco technical support representatives to debug problems that caused the IOS image to fail (crash). The switch writes the crash information to the console at the time of the failure, and the file is created the next time you boot the IOS image after the failure (instead of while the system is failing).

The information in the file includes the IOS image name and version that failed, a dump of the processor registers, and a stack trace. You can provide this information to the Cisco technical support representative by using the show tech-support privileged EXEC command.

All crashinfo files are kept in this directory on the Flash file system:

flash:/crashinfo/crashinfo_n where n is a sequence number.

Each new crashinfo file that is created uses a sequence number that is larger than any previously-existing sequence number, so the file with the largest sequence number describes the most recent failure. Version numbers are used instead of a timestamp because the Catalyst 3550 switches do not include a real-time clock. You cannot change the name of the file that the system will use when it creates the file. However, after the file is created, you can use the rename privileged EXEC command to rename it, but the contents of the renamed file will not be displayed by the show stacks or the show tech-support privileged EXEC command.

You can display the most recent crashinfo file (that is, the file with the highest sequence number at the end of its filename) by entering the show stacks or the show tech-support privileged EXEC command. You also can access the file by using any command that can copy or display files, such as the more or the copy privileged EXEC command.