Managing Cisco IOS Software

1
Managing Cisco IOS Software

• Module 5
• CCNA 2 Version 3.0

2
Router Startup Sequence

• Test the router hardware
• Find and load the Cisco IOS software.
• Find and apply configuration statements,
  including protocol functions and interface
  addresses.

3
Loading the Cisco IOS

• Global configuration mode boot system commands
  can be specified to enter fallback sources for
  the router to use in sequence
• No boot system commands in NVRAM?
• system by default uses the Cisco IOS software in
  flash memory
• Flash memory is empty?
• router then attempts to use TFTP to load an IOS
  image from the network

4
Boot System Commands

• 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

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Boot System Commands

• Boot IOS from Flash Memory

Not vulnerable to network failures that can occur
when loading system images from TFTP servers.

• The router will execute the boot system commands
  as needed in the order in which they were
  originally entered into configuration mode.

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Boot System Commands

• Boot IOS from TFTP Server

If flash is corrupted, IOS can be loaded from a
TFTP server
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Boot System Commands
If flash is corrupted and server fails to load
image, final option is ROM
Likely a subset of the Cisco IOS that lacks full
configurations may have an older version if
software has been updated since purchase

• Boot IOS from ROM

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The Configuration Register

• The order in which the router looks for system
  bootstrap information depends on the boot field
  setting in config register
• The configuration register is a 16-bit register
  in NVRAM
• The lowest four bits of the configuration
  register form the boot field

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Changing the Boot Field

• Configuration register setting can be changed
  with the global configuration mode command
• config-register value
• Use a hexadecimal number as the argument for this
  command.
• To ensure that the upper 12 bits are not changed,
  first retrieve the current values of the
  configuration register using the show version
  commandnext slide
• Then use the config-register command, changing
  only the value of the last hexadecimal digit.

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Note Router(config)config-register 0x2100
Router will boot into ROM monitor mode
Note Router(config)config-register 0x2102
Router will look in the flash for boot
system commands
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Identifying Config Register
Show versionat bottom
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• Syntax Description - config-register value
• Value Hexadecimal or decimal value that
  represents the 16-bit configuration register
  value that you want to use the next time the
  router is restarted. The value range is from 0x0
  to 0xFFFF (0 to 65535 in decimal).
• Defaults
• Refer to the documentation for your platform for
  the default configuration register value. For
  many newer platforms, the default is 0x2102,
  which causes the router to boot from Flash memory
  and the Break key to be ignored.

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• Examples
• In the following example, the configuration
  register is set to boot the system image from
  Flash memory
• config-register 0x2102

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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

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Identifying Boot Image Source
IDs boot image source
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The IOS File System

• 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
• Functions that can be specified by the Network
  Administrator in the configuration are
• IP addresses of the interfaces
• routing protocols
• networks to be advertised
• The configuration file typically is a few hundred
  to a few thousand bytes

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Software Components in Memory
Each of the software components are stored in
memory as a separate files also stored in
different types of memory
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File Storage on the Router

• 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
• flash allows the IOS to be upgraded or stores
  multiple IOS files
• In many router architectures, the IOS is copied
  into and run from RAM
• A copy of the configuration file is stored in
  NVRAM to be used as a configuration during
  startup
• Referred to as the startup config
• The startup configuration is copied into RAM at
  boot time
• The configuration in RAM is the configuration
  used to operate the router (referred to as the
  running config)

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Cisco IOS File System (IFS)

• A single interface to all the file systems used
  by the router was implemented with version 12 of
  the IOS
• 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 includes
• the flash memory file systems
• the network file systems (TFTP, rcp, and FTP)
• reading or writing data (such as NVRAM, the
  running configuration, ROM)
• The IFS uses a common set of prefixes to specify
  file system devices

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IOS Naming Convention

• To ID different version, Cisco has a naming
  convention for IOS files
• The IOS naming convention uses different fields
  in the name

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• The first part identifies the hardware platform
• The second part of the IOS file name identifies
  the various features
• Features are packaged in "software images
• The third part of the file name indicates the
  file format
• If the flash image is compressed, the IOS must be
  expanded during boot as it is copied to RAM
• relocatable means image is copied from flash
  into RAM to run
• non-relocatable image is run directly from flash
• The fourth part of the file name identifies the
  release of the IOS

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Managing Configuration Files Using a TFTP Server

• On a Cisco router or switch
• active configuration is in RAM
• default location for the startup configuration is
  NVRAM
• If the configuration is lost, startup
  configuration should be backed up
• One of these backup copies of the configuration
  can be stored on a TFTP server

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Copying a Configuration File to a TFTP Server
The copy running-config tftp Command

• Enter the IP address of TFTP server to store the
  config file

• Enter the name to assign to the configuration
  file or accept the default name

• !!!!!!!!!!!!!! appear while the file is being
  transferred

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Loading backup config from TFTP

• The copy tftp running-config command

• Enter the IP address of TFTP server to store the
  config file

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Managing config files using copy/paste

• Another way to create a backup copy of the config
  is to capture the output of show running-config
  command
• Copy output, paste into text file and save text
  file
• Some editing will be needed

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Managing a Configuration File Using Copy Paste

• Select Transfer
• Select Capture Text
• Specify the name for the text file to capture the
  configuration
• Select Start to start capturing text
• Display the configuration to the screen by
  entering show running-config
• Press the space bar when each "-More -" prompt
  appears
• When the complete configuration has been
  displayed, stop the capture by
• Select Transfer
• Select Capture Text
• Select Stop

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Managing a Configuration File Using Copy Paste

• After the capture is complete, the configuration
  file needs to be edited to remove extra text
• The configuration file can be edited from a text
  editor such as Notepad
• To edit the file from Notepad click on File gt
  Open
• Find the captured file and select it. Click Open.
• The lines that need to be deleted contain
• show running-config
• Building configuration...
• Current configuration
• - More -
• Any lines that appear after the word "End"
• At the end of each of the interface sections add
  the no shutdown command
• Comments may also be added to explain the various
  parts of the configuration. A comment is added by
  beginning a line with an exclamation mark !.

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Restoring a Configuration File Using Hyperterminal

• HyperTerminal can be used to restore a
  configuration. The clean backup of the
  configuration can be copied into the router.
• Enter router global configuration mode.
• From HyperTerminal, click on Transfer gt Send Text
  File.
• Select the name of the file for the saved backup
  configuration.
• The lines of the file will be entered into the
  router as if they were being typed.
• After the configuration is entered, press Ctrl-Z
  key to exit global configuration mode.
• Restore the startup configuration with copy
  running-config startup-config

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Saving a Copy of the Cisco IOS to a TFTP Server

• As the image is erased from flash, a series of
  es will appear to show the erase process

• As each datagram of the IOS image file is
  downloaded, an ! will be displayed. This IOS
  image is several megabytes and may take some
  time.

• NOTE
• Check for enough room in FLASH before upgrading
  the IOS.
• The new flash image will be verified after it is
  copied

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Managing the IOS using Xmodem

• If the IOS image in flash has been erased or
  corrupted, the IOS may need to be restored from
  the ROM monitor mode (ROMmon)
• In many of the Cisco hardware architectures, the
  ROMmon mode is identified from the rommon 1 gt
  prompt
• First, identify why the IOS image did not load
  from flash
• This could be due to a corrupt or missing image
• The flash should be examined with the dir flash
  command.

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• If an image is located that appears to be valid,
  an attempt should be made to boot from that
  image. This is done using boot flash command.
  For example if the image name was
  c2600-is-mz.121-5, the command would be
• rommon 1gtboot flashc2600-is-mz.121-5
• If the router properly boots, examine a couple of
  items to determine why the router booted to the
  ROMmon
• First, use the show version command to check the
  configuration register to ensure that it is
  configured for the default boot sequence. If the
  configuration register value is correct,
• Next use the show startup-config command to see
  if there is a boot system command instructing the
  router to use the IOS for ROM monitor.

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• If the router will not properly boot from the
  image or there is no IOS image, a new IOS will
  need to be downloaded.
• IOS file may be recovered using either Xmodem to
  restore the image through the console, or
  downloading the image using TFTP from the ROMmon
  mode.

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Managing the IOS using Xmodem

• The Xmodem command can be used from the ROMmon
  mode to restore the IOS software image from the
  PC.
• command is xmodem -c image_file_name.
• For example,
• xmodem -c c2600-is-mz.122-10a.bin 
• The -c instructs the Xmodem process to use Cyclic
  Redundancy Check (CRC) for error checking during
  the download.

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• The router will a warning message.
• informs that the bootflash will be erased and
  asks to confirm continuing.
• Now the Xmodem transfer needs to be started from
  the terminal emulator.
• In HyperTerminal, select Transfer gt Send File.
  Then in the Send File popup specify the image
  name/location, select Xmodem as the protocol, and
  start the transfer.
• Once the transfer is complete a message appears
  indicating Download Complete!.
• Before restarting the router, the config register
  needs to be set back to 0x2102. Enter the command
  config-register 0x2102 at the privileged EXEC
  prompt.

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Restoring the IOS from aTFTP Session

• The IOS can also be restored from a TFTP session
• Downloading the image using TFTP from ROMmon is
  the fastest way to restore an IOS image to the
  router
• This is done by setting environmental variables
  and then using the tftpdnld command
• Since the ROMmon has very limited functions, no
  configuration file is loaded during boot
• The router therefore has no IP or interface
  configuration
• The environmental variables provide a minimal
  configuration to allow for the TFTP of the IOS

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• The minimum variables required to use tftpdnld
  are
• IP_ADDRESS The IP address on the LAN interface
• IP_SUBNET_MASK The subnet mask for the LAN
  interface
• DEFAULT_GATEWAY The default gateway for the LAN
  interface
• TFTP_SERVER The IP address of the TFTP server
• TFTP_FILE The IOS filename on the server
• Note All variable names are case sensitive.

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File System Verification

• There are several commands that can be used to
  verify the router file system.
• show version
• show flash

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Show Version Command

• The show version command can be used to
• check the current IOS image
• Check total amount of flash
• identify the source of the IOS image that the
  router used to boot
• display the configuration register
• The boot field setting of the configuration
  register can be examined to determine from where
  the router is to load the IOS
• If these do not agree, there may be a corrupt or
  missing IOS image in flash or there may be boot
  system commands in the startup configuration.

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Show Flash Command

• The show flash command can also be used to verify
  the file system
• This command is used to
• identify IOS image(s) in flash
• Check the amount of flash that is available
• confirm that there is ample space to store a new
  IOS image.

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Managing Cisco IOS Software
THE END

• Module 5
• CCNA 2 Version 3.0