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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:
- 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. 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: - Basic – A basic feature set for
the hardware platform, for example IP and IP/FW
- Plus – A basic feature set plus additional features
such as IP Plus, IP/FW Plus, and Enterprise Plus
- Encryption – The addition of the 56-bit data
encryption feature sets, such as Plus 56, to either a basic or
plus feature set. Examples include IP/ATM PLUS IPSEC 56 or
Enterprise Plus 56. From Cisco IOS Release 12.2 onwards, the
encryption designators are k8/k9:
- k8 – Less than
or equal to 64-bit encryption in IOS version 12.2 and up
- k9 – Greater than 64-bit encryption (on 12.2 and
up)
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