iosswrel/ps1835/products_command_reference_ chapter09186a00800ca743.html#1017887
Content 5.1 Router Boot Sequence and Verification 5.1.5 Troubleshooting IOS boot failure In the event that the router does not boot properly, there are several things that could be wrong: 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: 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. Lab Activity e-Lab Activity: Troubleshooting IOS Boot Failure In this lab, the students will check and document the configuration register settings related to the boot method, configure the router to boot from NVRAM, and reload the router.
Content 5.2 Managing the Cisco File System 5.2.1 IOS file system overview Routers and switches depend on software for their operation. The two types of software required are operating systems and configuration. The operating system used in almost all Cisco devices is the Cisco Internetwork Operating System (IOS). The Cisco IOS® is the software that allows the hardware to function as a router or switch. The IOS file is several megabytes. The software a router or switch uses is referred to as the configuration file or the config. The configuration contains the “instructions” that define how the device is to route or switch. A network administrator creates a configuration that defines the desired functionality of the Cisco device. The functions that can be specified by the configuation are the IP addresses of the interfaces, routing protocols, and networks to be advertised. The configuration file typically is a few hundred to a few thousand bytes. Each of the software components is stored in memory as a separate file. These files are also stored in different types of memory. The IOS is stored in a memory area called flash. Flash memory provides non-volatile storage of an IOS that can be used as an operating system at startup. The flash allows the IOS to be upgraded or stores multiple IOS files. In many router architectures, the IOS is copied into and run from Random Access Memory (RAM). A copy of the configuration file is stored in Non-volatile RAM (NVRAM) to be used as a configuration during startup. This is referred to as the “startup config”. The startup configuration is copied into RAM at boot time. This configuration in RAM is the configuration used to operate the router. It is referred to as the “running config”. Beginning with version 12 of the IOS, a single interface to all the file systems that a router uses is provided. This is referred to as the Cisco IOS File System (IFS). The IFS provides a single method to perform all the file system management that a router uses. This would include the flash memory file systems, the network file systems (TFTP, rcp, and FTP), and reading or writing data (such as NVRAM, the running configuration, ROM). The IFS uses a common set of prefixes to specify file system devices. The IFS uses the URL convention to specify files on network devices and the network. The URL convention identifies the location of the configuration files following the colon as [[[//location]/directory]/filename]. The IFS also supports FTP file transfer. Interactive Media Activity Drag and Drop: IOS File System Overview When the student has completed this activity, the student will be able to list the configuration files and their locations.
Content 5.2 Managing the Cisco File System 5.2.2 IOS naming conventions Cisco develops many different versions of the IOS. The IOS supports varied hardware platforms and features. Cisco is also continuously developing and releasing new versions of the IOS. To identify the different versions, Cisco has a naming convention for IOS files. This IOS naming convention uses different fields in the name. Among the fields are the hardware platform identification, the feature set identification, and the numerical release. The first part of the Cisco IOS file name identifies the hardware platform for which this image is designed. The second part of the IOS file name identifies the various features that this file contains. There are many different features to choose from. These features are packaged in "software images". Each feature set contains a specific subset of Cisco IOS features. Examples of feature-set categories are: The third part of the file name indicates the file format. It specifies if the IOS is stored in flash in a compressed format and whether the IOS is relocatable. If the flash image is compressed, the IOS must be expanded during boot as it is copied to RAM. A relocatable image is copied from flash into RAM to run. A non-relocatable image is run directly from flash. The fourth part of the file name identifies the release of the IOS. As Cisco develops newer versions of the IOS, the numerical version number increases. Interactive Media Activity Drag and Drop: IOS Naming