• Configuration file has missing or incorrect boot system statement
• Incorrect configuration register value
• Corrupted flash image
• Hardware failure

When the router boots, it looks in the configuration file for a boot system statement. This boot system statement can force the router to boot from another image instead of the IOS in flash. To identify the boot image source, type the show version command and look for the line that identifies the image boot source.

Use the show running-config command and look for a boot system statement near the top of the configuration. If the boot system statement points to an incorrect IOS image, delete the statement using the “no” version of the command.

An incorrect configuration register setting will prevent the IOS from loading from flash. The value in the configuration register tells the router where to get the IOS. This can be confirmed by using the show version command and looking at the last line for the configuration register. The correct value varies from hardware platform to hardware platform. A part of the documentation of the internetwork should be a printed copy of the show version output. If that documentation is not available, there are resources on the Cisco documentation CD or Cisco website to identify the correct configuration register value. Correct this by changing the configuration register in the configuration and saving this as the start-up configuration.

If there is still a problem, the router may have a corrupted flash image file. If this is the case, an error message should be displayed during boot. That message may take one of several forms. Some examples are:

• open: read error...requested 0x4 bytes, got 0x0
• trouble reading device magic number
• boot: cannot open "flash:"
• boot: cannot determine first file name on device "flash:"ú

If the flash image is corrupt, a new IOS should be uploaded into the router.

If none of the above appears to be the problem, the router could have a hardware failure. If this is the case, the Cisco Technical Assistance (TAC) center should be contacted. Although hardware failures are rare, they do occur.

Note: The value of the configuration register is not displayed by either the show running-config or show startup-config commands.

Lab Activity Lab Exercise: Troubleshooting Configuration Register Boot Problems In this lab, the students will check and document the configuration register settings related to the boot method.