Module 5: Managing Cisco IOS Software

1
Module 5 Managing Cisco IOS Software

• CCNA 2 version 3.0

2
Stages of the router power-on boot sequence

• Test the router hardware.
• Find and load the Cisco IOS software
• IOS is loaded into RAM
• Find and apply configuration statements,
  including protocol functions and interface
  addresses (A valid configuration file is loaded
  from NVRAM if specified by the config register)
• If the router cannot find a valid configuration
  during the startup sequence, the router will
  enter a question driven setup mode
• Routers need, Operating System File
  Configuration File

3
(No Transcript)
4
How a Cisco device locates and loads IOS

• The default source for Cisco IOS software depends
  on the hardware platform, but most commonly the
  router looks to the boot system commands saved in
  NVRAM. (NVRAM stores the startup config file)
• The settings in the configuration register enable
  the following alternatives
• Global configuration mode boot system commands
  can be specified to enter fallback sources for
  the router to use in sequence.
• If NVRAM lacks boot system commands that the
  router can use, the system by default uses the
  Cisco IOS software in flash memory.
• If flash memory is empty, the router then
  attempts to use TFTP to load an IOS image from
  the network.

5
(No Transcript)
6
Using the boot system command

• Flash memory Stores a fully functional IOS
  image. A system image from flash memory can be
  loaded. The advantage is that information stored
  in flash memory is not vulnerable to network
  failures that can occur when loading system
  images from TFTP servers.
• Network server In case flash memory becomes
  corrupted, a system image can be loaded from a
  TFTP server.
• ROM If flash memory is corrupted and the
  network server fails to load the image, booting
  from ROM is the final bootstrap option in
  software. However, the system image in ROM will
  likely be a subset of the Cisco IOS that lacks
  the protocols, features and configurations of the
  full Cisco IOS. Also, if the software has been
  updated since the router was purchased, the
  router may have an older version stored in ROM. 
  

7
Configuration register

• The order in which the router looks for system
  bootstrap information depends on the boot field
  setting in the configuration register.
• The default configuration register setting can be
  changed with the global configuration mode
  command
• Router(config) config-register

8
Configuration register cont.,

• The configuration register is a 16-bit register
  in NVRAM.
• The lowest four bits of the configuration
  register form the boot field.
• The boot field is the part of the configuration
  register that indicates the location of the IOS
• To ensure that the upper 12 bits are not changed,
  first retrieve the current values of the
  configuration register using the show version
  command. Then use the config-register command,
  changing only the value of the last hexadecimal
  digit.

9
Configuration register cont.,

• To enter the ROM monitor mode, set the
  configuration register value to 0xnnn0, where nnn
  represents the previous value of the non-boot
  field digits. This value sets the boot field bits
  to 0000 binary. From ROM monitor, boot the
  operating system manually by using the b command
  at the ROM monitor prompt.
• To configure the system to boot automatically
  from ROM, set the configuration register to
  0xnnn1, where nnn represents the previous value
  of the non-boot field digits. This value sets the
  boot field bits to 0001 binary.
• To configure the system to use the boot system
  commands in NVRAM, set the configuration register
  to any value from 0xnnn2 to 0xnnnF, where nnn
  represents the previous value of the non-boot
  field digits. These values set the boot field
  bits to a value between 0010 and 1111 binary.
  Using boot system commands in NVRAM is the
  default.

10
Note Router(config)config-register 0x2100
Router will boot into ROM monitor mode
Note Router(config)config-register 0x2102
Router will look in the startup
configuration for boot system commands
11
Troubleshooting IOS boot failure

• Possible things that could be wrong
• Configuration file has missing or incorrect boot
  system statement
• Incorrect configuration register value
• Corrupted flash image
• Hardware failure
• 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.

12
Still a problem? The router may have a corrupted
flash image file.

• 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
• Note The value of the configuration register is
  not displayed by either the show running-config
  or show startup-config commands.
• The Cisco Technical Assistance (TAC) center is
  available for hardware failures. Although
  hardware failures are rare, they do occur.

13
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 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.

14
IOS naming conventions
15

• 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.
• 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)

16

• 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.
• 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.

17
Managing configuration files using TFTP

• In a Cisco router or switch, the active
  configuration is in RAM and the default location
  for the startup configuration is NVRAM.
• One of these backup copies of the configuration
  can be stored on a TFTP server. First verify
  connectivity to the TFTP server.
• Enter the command copy running-config tftp.
• The copy command will move configuration files
• At the prompt, enter the IP address of the TFTP
  server to store the configuration file.
• Enter the name to assign to the configuration
  file or accept the default name.
• Confirm the choices by typing yes each time.

18
Loading the backup configuration file from a TFTP
server can restore the router configuration.

• Enter the command copy tftp running-config.
• At the prompt, select a host or network
  configuration file.
• At the system prompt, enter the IP address of the
  TFTP server where the configuration file is
  located.
• At the system prompt, enter the name of the
  configuration file or accept the default name.
• Confirm the configuration filename and the server
  address that the system supplies.

19
Managing configuration files using copy and 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

20
Cleaning up your text file

• 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. Clicking File gt Save
  will save the clean version of the configuration.

21
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.
• Observe any errors.
• After the configuration is entered, press Ctrl-Z
  key to exit global configuration mode.
• Restore the startup configuration with copy
  running-config startup-config.
• To restore a saved copy of the configuration
• Erase the backup configuration file and reboot
  the router

22
Managing IOS images using TFTP

• 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

This command will copy an IOS image from a TFTP
server to a router
23
Managing IOS images 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.
• This first step in this process is to identify
  why the IOS image did not load from flash.
• The flash should be examined with the
• dir flash command.
• ROM monitor mode uses the command
• Rommon1gtboot flashfilename
• to run the IOS image in flash

24
Download using Xmodem from ROMmon

• To restore the IOS through the console, the local
  PC needs to have a copy of the IOS file to
  restore and a terminal emulation program such as
  HyperTerminal.
• The IOS can be restored using the default console
  speed of 9600 bps. The baud rate can be changed
  to 115200 bps to speed up the download.
• The console speed can be changed from ROMmon mode
  using the confreg command. After entering the
  confreg command, the router will prompt for the
  various parameters that can be changed.
• Before restarting the router, the console speed
  needs to be set back to 9600 and the config
  register back to 0x2102. Enter the command
  config-register 0x2102 at the privileged EXEC
  prompt.

25
Environment variables

• 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.

26
Environment variables cont.,

• Note All variable names are case sensitive.
• 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

27
File system verification

• The show version command can be used to check the
  current image and the total amount of RAM, NVRAM
  and Flash memeory in the router.
• It also verifies two other items concerning
  loading the IOS.
• identifies the source (location) of the IOS image
  that the router used to boot
• displays the configuration register.

28
File system verification

• The show flash command can also be used to verify
  the file system.
• This command is used to identify IOS image(s) in
  flash as well as the amount of flash that is
  available.

29
THE

• END