Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide, 12.1(22)EA11 and Later
Troubleshooting
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Troubleshooting

Table Of Contents

Troubleshooting

Using Recovery Procedures

Recovering from a Software Failure

Recovering from Lost or Forgotten Passwords on Non-LRE Catalyst 2950 Switches

Recovering from Lost or Forgotten Passwords on Catalyst 2950 LRE Switches

Password Recovery with Password Recovery Enabled

Procedure with Password Recovery Disabled

Recovering from Lost or Forgotten Passwords on Catalyst 2955 Switches

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 and SFP Module Security and Identification

Diagnosing Connectivity Problems

Using Ping

Understanding Ping

Executing Ping

Using Layer 2 Traceroute

Understanding Layer 2 Traceroute

Usage Guidelines

Displaying the Physical Path

Diagnosing LRE Connection Problems

Using Debug Commands

Enabling Debugging on a Specific Feature

Enabling All-System Diagnostics

Redirecting Debug and Error Message Output

Using the debug auto qos Command

Using the show controllers Commands

Using the crashinfo File


Troubleshooting


This chapter describes how to identify and resolve Catalyst 2950 and Catalyst 2955 software problems related to the Cisco IOS software. Depending on the nature of the problem, you can use the command-line interface (CLI), the device manager, or to identify and solve problems. To identify and resolve Cisco Course Wave Division Multiplexer (CWDM) Gigabit Interface Converter (GBIC) problems, you must have the enhanced software image (EI) installed on your non-Long-Reach Ethernet (LRE) Catalyst 2950 switch.


Note For complete syntax and usage information for the commands used in this chapter, see the command reference for this release and the Cisco IOS Command Summary for Cisco IOS Release 12.1.


This chapter consists of these sections:

Using Recovery Procedures

Preventing Autonegotiation Mismatches

GBIC and SFP Module Security and Identification

Diagnosing Connectivity Problems

Diagnosing LRE Connection Problems

Using Debug Commands

Using the show controllers Commands

Using the crashinfo File

Using Recovery Procedures

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

Recovering from a Software Failure

Recovering from Lost or Forgotten Passwords on Non-LRE Catalyst 2950 Switches

Recovering from Lost or Forgotten Passwords on Catalyst 2950 LRE Switches

Recovering from Lost or Forgotten Passwords on Catalyst 2955 Switches

Recovering from a Command Switch Failure

Recovering from Lost Member Connectivity

Recovering from a Software Failure

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 that you are using.

Follow these steps to recover from a software failure:


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 Disconnect the switch power cord.

Step 4 Reconnect the power cord to the switch.

The software image does not load. The switch starts in boot loader mode, which is indicated by the switch# prompt.

Step 5 Use the boot loader to enter commands, and start the transfer.

switch# copy xmodem: flash:image_filename.bin

Step 6 When the Xmodem request appears, use the appropriate command on the terminal-emulation software to start the transfer and to copy the software image to flash memory.


Recovering from Lost or Forgotten Passwords on Non-LRE Catalyst 2950 Switches

Follow these steps if you have forgotten or lost the switch password on a non-LRE Catalyst 2950 switch:


Step 1 Connect a terminal or PC with terminal emulation software to the consoleservice port. For more information, see the switch hardware installation guide.


Note You can configure your switch for Telnet by following the procedure in the "Accessing the CLI" section on page 2-9.


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

Step 3 Unplug the switch power cord.

Step 4 Reconnect the power cord to the switch and, within 15 seconds, press the Mode button while the System LED above port 1X is still flashing green. Continue pressing the Mode button until the System LED turns briefly amber and then solid green; then release the Mode button.

Several lines of information about the software appear, as do instructions:

The system has been interrupted prior to initializing the flash file system. These 
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 consoleservice port.

Step 7 Load any helper files:

switch: load_helper

Step 8 Display the contents of flash memory:

switch: dir flash:

The switch file system appears in the directory.

Step 9 Rename the configuration file to config.text.old.

This file contains the password definition.

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

Step 10 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 11 At the switch prompt, change to privileged EXEC mode:

switch> enable

Step 12 Rename the configuration file to its original name:

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

Step 13 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 use the following normal commands to change the password.

Step 14 Enter global configuration mode:

switch# configure terminal

Step 15 Change the password:

switch(config)# enable secret <password>

or

switch(config)# enable password <password>

Step 16 Return to privileged EXEC mode:

switch(config)# exit 
switch#

Step 17 Write the running configuration to the startup configuration file:

switch# copy running-config startup-config

The new password is now included in the startup configuration.


Recovering from Lost or Forgotten Passwords on Catalyst 2950 LRE Switches

An end user with physical access to the switch can recover from a lost password by interrupting the boot process during power-on and by entering a new password. This is the default configuration for Catalyst 2940Catalyst 2950 LRE switches.


Note A system administrator can disable some of the functionality of the password recovery 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 and password recover has been disabled, a status message shows this during the recovery process.


Follow these steps 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.


Note See the "Connecting the Console Port" and "Starting the Terminal Emulation Software" sections in "Appendix D, Configuring the Switch with the CLI-Based Setup Program."


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

Step 3 Unplug the switch power cord.

Step 4 Reconnect the power cord to the switch and, within 15 seconds, press the Mode button while the System LED above port 1X is still flashing green. Continue pressing the Mode button until the System LED turns briefly amber and then solid green; then release the Mode button.

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

go 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. 

go 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

Follow these steps when the password-recovery is enabled:


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 serviceport.

Step 3 Load any helper files:

switch: load_helper

Step 4 Display the contents of flash memory:

switch: dir flash:

The switch file system appears in the directory.

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 VLAN 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.

Follow these steps when the password-recovery mechanism is disabled:


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 appears in the directory.

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 VLAN 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 Lost or Forgotten Passwords on Catalyst 2955 Switches

The Catalyst 2955 switch boot loader uses break-key detection to stop the automatic boot sequence for the password recovery purpose.


Note The break key character is different for each operating system.

On a SUN work station running UNIX, Ctrl-C is the break key.

On a PC running Windows 2000, Ctrl-Break is the break key.

Cisco TAC has tabulated break keys for most common operating systems and an alternative break key sequence for those terminal emulators that do not support the break keys. See http://www.cisco.com/warp/public/701/61.html#how-to for that list.


Follow these steps if you have forgotten or lost the switch password.


Step 1 Connect a terminal or PC with terminal emulation software to the console port. For more information, see the switch hardware installation guide.


Note You can configure your switch for Telnet by following the procedure in the "Accessing the CLI" section on page 2-9.


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

Step 3 Connect the power cord to the switch, and apply power to the switch.

After the switch performs POST, the switch begins the autoboot process. The boot loader prompts the user for a break key character during the boot-up sequence, as shown in this example:

***** The system will autoboot in 15 seconds ***** 

Send a break key to prevent autobooting. 

Step 4 When the boot loader prompts you, enter the break key.

This example shows the messages that appear on the console after the user enters a break key:

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

After the message appears, the boot loader prompt resumes.

On the Catalyst 2955C-12 and Catalyst 2955S-12 switches, the port 13 LED blinks green, and the port 14 LED is off during the initial appearance of the boot loader prompt. On the Catalyst 2955T-12 switch, the port 1 LED blinks green, and the port 2 LED is off during the initial appearance of the boot loader prompt.

Step 5 Initialize the flash file system:

switch# flash_init

Step 6 If you 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 Display the contents of flash memory as in this example:

switch# dir flash:
Directory of flash:/

The switch file system appears in the directory.

Step 9 Rename the configuration file to config.text.old.

This file contains the password definition.

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

Step 10 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 11 At the switch prompt, change to privileged EXEC mode:

switch> enable

Step 12 Rename the configuration file to its original name:

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

Step 13 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 use these normal commands to change the password.

Step 14 Enter global configuration mode:

switch# configure terminal

Step 15 Change the password:

switch(config)# enable secret <password>

or

switch(config)# enable password <password>

Step 16 Return to privileged EXEC mode:

switch(config)# exit 
switch#

Step 17 Write the running configuration to the startup configuration file:

switch# copy running-config startup-config

The new password is now included in the startup configuration.


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 Chapter 6, "Clustering Switches", and the Getting Started with Cisco Network Assistant, available on Cisco.com.


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 have 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, see 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, see 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 manufacturing default configuration, or set up the switch through the management module.

Step 10 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 11 Enter Y at the first prompt.

The prompts in the setup program vary depending on the member switch that 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 12 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 character 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 13 When prompted for the enable secret and enable passwords, enter the passwords of the failed command switch again.

Step 14 When prompted, make sure to enable the switch as the cluster command switch, and press Return.

Step 15 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 16 After the initial configuration appears, verify that the addresses are correct.

Step 17 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 18 Start your browser, and enter the IP address of the new command switch.

Step 19 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 Disconnect the command switch from the member switches, and physically remove it from the cluster.

Step 2 Insert the new 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, see 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 Use the manufacturing default configuration, or set up the switch through the management module.

Step 7 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 8 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 9 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 character 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 10 When prompted for the enable secret and enable passwords, enter the passwords of the failed command switch again.

Step 11 When prompted, make sure to enable the switch as the cluster command switch, and press Return.

Step 12 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 13 When the initial configuration displays, verify that the addresses are correct.

Step 14 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 15 Start your browser, and enter the IP address of the new command switch.

Step 16 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 (Cisco Systems Intelligent Gigabit Ethernet Switch Module, Catalyst 3550, 3500 XL, 2955, 2950, 2940, 2900 XL, 2820, and 1900) cannot connect to the command switch through a port that is defined as a network port.

Catalyst 3500 XL, 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 (Cisco Systems Intelligent Gigabit Ethernet Switch Module, Catalyst 3550, Catalyst 3500 XL, Catalyst 2950, Catalyst 2940, Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900) 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 and SFP Module Security and Identification

Cisco Course Wave Division Multiplexer (CWDM) Gigabit Interface Converter (GBIC) and small form-factor pluggable (SFP) 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 an CWDM GBIC or SFP module is inserted in the switch, the switch software reads the EEPROM to check the serial number, vendor name and vendor ID, and recompute the security code and CRC. If the serial number, the vendor name or vendor 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 CWDM GBIC or SFP module, remove the GBIC or SFP module from the switch, and replace it with a Cisco module.


After inserting a Cisco or module, 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, see the command reference for this release.

Diagnosing Connectivity Problems

This section describes how to troubleshoot connectivity problems:

Using Ping

Using Layer 2 Traceroute

Using Ping

This section consists of this information:

Understanding Ping

Executing Ping

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.

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 31-1 describes the possible ping character output.

Table 31-1 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 end 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.

Using Layer 2 Traceroute

This section describes this information:

Understanding Layer 2 Traceroute

Usage Guidelines

Displaying the Physical Path

Understanding Layer 2 Traceroute

The Layer 2 traceroute feature allows the switch to identify the physical path that a packet takes from a source device to a destination device. Layer 2 traceroute supports only unicast source and destination MAC addresses. It determines the path by using the MAC address tables of the switches in the path. When the switch detects a device in the path that does not support Layer 2 traceroute, the switch continues to send Layer 2 trace queries and lets them time out.

The switch can only identify the path from the source device to the destination device. It cannot identify the path that a packet takes from source host to the source device or from the destination device to the destination host.

Usage Guidelines

These are the Layer 2 traceroute usage guidelines:

Cisco Discovery Protocol (CDP) must be enabled on all the devices in the network. For Layer 2 traceroute to functional properly, do not disable CDP. If any devices in the physical path are transparent to CDP, the switch cannot identify the path through these devices.


Note For more information about enabling CDP, see Chapter 23, "Configuring CDP."


A switch is reachable from another switch when you can test connectivity by using the ping privileged EXEC command. All switches in the physical path must be reachable from each other.

The maximum number of hops identified in the path is ten.

You can enter the traceroute mac or the traceroute mac ip privileged EXEC command on a switch that is not in the physical path from the source device to the destination device. All switches in the path must be reachable from this switch.

The traceroute mac command output shows the Layer 2 path only when the specified source and destination MAC addresses belong to the same VLAN. If you specify source and destination MAC addresses that belong to different VLANs, the Layer 2 path is not identified, and an error message appears.

If you specify a multicast source or destination MAC address, the path is not identified, and an error message appears.

If the source or destination MAC address belongs to multiple VLANs, you must specify the VLAN to which both the source and destination MAC addresses belong. If the VLAN is not specified, the path is not identified, and an error message appears.

The traceroute mac ip command output shows the Layer 2 path when the specified source and destination IP addresses belong to the same subnet. When you specify the IP addresses, the switch uses Address Resolution Protocol (ARP) to associate the IP addresses with the corresponding MAC addresses and the VLAN IDs.

If an ARP entry exists for the specified IP address, the switch uses the associated MAC address and identifies the physical path.

If an ARP entry does not exist, the switch sends an ARP query and tries to resolve the IP address. If the IP address is not resolved, the path is not identified, and an error message appears.

When multiple devices are attached to one port through hubs (for example, multiple CDP neighbors are detected on a port), the Layer 2 traceroute feature is not supported. When more than one CDP neighbor is detected on a port, the Layer 2 path is not identified, and an error message appears.

This feature is not supported in Token Ring VLANs.

Displaying the Physical Path

You can display physical path that a packet takes from a source device to a destination device by using one of these privileged EXEC commands:

traceroute mac [interface interface-id] {source-mac-address} [interface interface-id] {destination-mac-address} [vlan vlan-id] [detail]

traceroute mac ip {source-ip-address | source-hostname} {destination-ip-address | destination-hostname} [detail]

For more information, see the command reference for this release.

Diagnosing LRE Connection Problems

Table 31-2 lists problems that you might encounter when configuring and monitoring the LRE ports on the Catalyst 2950 LRE switches. For more information about LRE connections, see the "Environmental Guidelines for LRE Links" section on page 12-9.

For switch upgrade and customer premises equipment (CPE) device upgrade troubleshooting information, see the "Upgrading LRE Switch Firmware" section on page 12-23.

Table 31-2 LRE Port Problems 

Problem
Suspected Cause and Suggested Solution

Amber LRE port LED

The switch and CPE device are unable to establish an LRE link using the selected profile.

Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15).

Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters.

Excessive CRC errors on an LRE link

A noisy environment (such as motors and power surges) is causing interference with the LRE link.

Change to a profile that has the interleave feature enabled, such as the LRE-5, LRE-10, LRE-15, LRE-10-1, LRE-10-3, or LRE-10-5 profile.

Change the interleave block size value to a value other than 0.

Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15) to increase the noise margin.

The LRE link length and quality are close to the limit of operation.

Change to a lower profile (for example, LRE-5 instead of LRE-15).

Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters.

High Reed-Solomon error count without CRC errors

The interleave feature is helping Reed-Solomon error correction to function correctly in a noisy environment. This situation means that the system is on the verge of generating CRC errors.

Change to a profile that has the interleaver feature enabled, such as the LRE-5, LRE-10, LRE-15, LRE-10-1, LRE-10-3, or LRE-10-5 profile.

Change the interleave block size value to any value other than 0.

Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15) to increase the noise margin.

The LRE link length and quality are close to the limit of operation.

Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15).

Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters.

Ethernet performance degradation due to excessive network latency

The interleave feature introduces extra latency to increase noise margin.

Adjust upper-layer network protocols to allow for high latency.

Change to a profile with a higher data rate to increase link bandwidth. This decreases the noise margin.

Choose a lower interleave block size value.

Select a low-latency (LL) LRE profile, such as LRE-5LL, LRE-10LL, or LRE-15LL.

Note Use the LL private profiles with care. The LL profiles have the LL feature enabled and the interleaver feature turned off. The LL feature does not delay data transmission, but it makes data more susceptible to interruptions on the LRE link.

All other profiles, public and private, have the interleaver feature enabled and the LL feature disabled. The interleaver feature provides maximum protection against small interruptions on the LRE link but delays data transmission. For more information about the LRE profiles, see the "LRE Links and LRE Profiles" section on page 12-2.

LRE link quality reduced in installations with bundled cables

Cross-talk between the LRE links is causing all links to degrade. Disable unused LRE ports by using the lre shutdown interface configuration command.


Using Debug Commands

This section explains how you use the 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

Using the debug auto qos Command


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 specific debug commands, see the 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 EtherChannel:

Switch# debug etherchannel

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

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

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

Even if the switch is properly configured, it might not generate the type of traffic that 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 EtherChannel, enter this command in privileged EXEC mode:

Switch# no debug etherchannel

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

Switch# undebug etherchannel

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 Chapter 26, "Configuring System Message Logging."

Using the debug auto qos Command

You can use the debug auto qos privileged EXEC command to display quality of service (QoS) commands that are automatically generated when automatic-QoS (auto-QoS) is enabled.

Beginning in privileged EXEC mode, follow these steps to display the QoS commands and enable auto-QoS for voice over IP (VoIP) within a QoS domain:

 
Command
Purpose

Step 1 

debug auto qos

Enable debugging for auto-QoS. When debugging is enabled, the switch displays the QoS commands that are automatically generated when auto-QoS is enabled or disabled.

Step 2 

configure terminal

Enter global configuration mode.

Step 3 

interface interface-id

Specify the interface that is connected to a Cisco IP Phone, and enter interface configuration mode. You also can specify the uplink interface that is connected to another switch or router in the interior of the network.

Step 4 

auto qos voip {cisco-phone | trust}

Enable auto-QoS.

The keywords have these meanings:

cisco-phone—If the interface is connected to a Cisco IP Phone, the QoS labels of incoming packets are trusted only when the Cisco IP phone is detected.

trust—The uplink interface is connected to a trusted switch or router, and the VoIP classification in the ingress packet is trusted.

Step 5 

end

Return to privileged EXEC mode.

Step 6 

show auto qos interface interface-id

Verify your entries.

This command displays the auto-QoS configuration that was initially applied; it does not display any user changes to the configuration that might be in effect.

For more information about auto-QoS, see the "Configuring Auto-QoS" section on page 29-9.

This example shows how to display the QoS commands that are automatically generated when auto-QoS is enabled:

Switch# debug auto qos
AutoQoS debugging is on
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z. 
Switch(config)# interface gigabitethernet0/17
Switch(config-if)# auto qos voip cisco-phone

Using the show controllers Commands

You can display the statistics, configuration, and other information about the Catalyst 2950 LRE switch, the connected CPE devices, and the LRE link. Use the privileged EXEC commands in Table 31-3 to display this information:

Table 31-3 Commands for Displaying LRE and CPE Information

show controllers ethernet-controller interface-id [asic | cpe [port port-id] | phy]

Displays per-interface transmit and receive statistics read from the hardware, the interface internal registers, and the statistics read from LRE and CPE ports.

show controllers lre cpe {identity | mfg | protected | version} [interface-id]

Displays information about the Cisco LRE CPE devices connected to an LRE switch.

show controllers lre

Displays information about the LRE link.

show controllers lre log

Displays the history of the link, configuration, and timer events for a specific LRE interface or for all the LRE switch interfaces.


For more information about the fields in the command output, refer to the switch command reference for this release.

Using the crashinfo File

This feature is available if your switch is running Cisco IOS Release 12.1(11)EA1 or later.

The crashinfo file saves information that helps Cisco technical support representatives to debug problems that caused the software 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 image after the failure (instead of while the system is failing).

The information in the file includes the software image name and version that failed, a dump of the processor registers, and a stack trace. You can give this information to the 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 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 delete crashinfo files by using the delete 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.