1. Ch. 5 – Managing Cisco IOS Software
CCNA 2 version 3.0
Rick Graziani
Cabrillo College

2. Note to instructors
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Thanks! Rick
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3. Overview Identify the stages of the router boot sequence
Determine how a Cisco device locates and loads the Cisco IOS
Use the boot system command
Identify the configuration register values
Briefly describe the files used by the Cisco IOS and their functions
List the locations on the router of the different file types
Briefly describe the parts of the IOS name
Save and restore configuration files using TFTP and copy-and-paste
Load an IOS image using TFTP
Load an IOS image using XModem
Verify the file system using show commands
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4. Stages of the router power-on boot sequence
Test the router hardware.
Find and load the Cisco IOS software.
Find and apply configuration statements, including protocol functions and interface addresses.
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5. Router Boot Process – At a Glance
1. ROM
1. POST
2. Bootstrap code executed
3. Check Configuration Register value (NVRAM)
0 = ROM Monitor mode
1 = ROM IOS
= startup-config in NVRAM
2. Check for IOS boot system commands in startup-config file (NVRAM)
If boot system commands in startup-config
a. Run boot system commands in order they appear in startup-config to locate the IOS
b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)
3. Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config
a. Flash (sequential)
b. TFTP server (netboot) - The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server.
c. ROM (partial IOS) or keep retrying TFTP depending upon router model
- If no IOS located, get partial IOS version from ROM
4. Locate and load startup-config
a. If startup-config found, copy to running-config
b. If startup-config not found, prompt for setup-mode
c. If setup-mode bypassed, create a “skeleton” default running-config (no startup-config)
1, 2 3 4
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6. 2. Check for IOS boot system commands in startup-config file (NVRAM)
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7. Using the boot system command
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8. Configuration register
Check Configuration Register value (NVRAM)
0 = ROM Monitor mode
1 = ROM IOS
= startup-config in NVRAM
The order in which the router looks for system bootstrap information depends on the boot field setting in the configuration register.
The configuration register is a 16-bit register in NVRAM.
The lowest four bits of the configuration register form the boot field.
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.
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9. show version – Showing the configuration register
Gateway-Router>show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-DO3S-M), Version 12.0(5)T1, RELEASE SOFTWARE (fc 1)
Copyright (c) by cisco Systems, Inc.
Compiled Tue 17-Aug-99 13:18 by cmong
Image text-base: 0x , data-base: 0x80CB67B0
ROM: System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
NoSmo-Gateway uptime is 5 weeks, 3 days, 20 hours, 33 minutes
System returned to ROM by power-on
System restarted at 13:30:22 PST Thu Mar
System image file is "flash:c2600-do3s-mz T1"
cisco 2621 (MPC860) processor (revision 0x102) with 39936K/9216K bytes of memory .
Processor board ID JAB ( )
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version
2 FastEthernet/IEEE interface(s)
4 Serial(sync/async) network interface(s)
32K bytes of non-volatile configuration memory.
--More—
Configuration register is 0x2102
Gateway-Router>
IOS source
configuration register
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10. Modifying the configuration register
Router(config)#config-register value
To change the boot field in the configuration register, follow these guidelines:
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.
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11. Troubleshooting IOS boot failure
What would you do?
How would you begin?
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12. Possible problems
Configuration file has missing or incorrect boot system statement
Incorrect configuration register value
Corrupted flash image
Hardware failure
How would you determine if any of these were the problem?
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13. Troubleshooting
An incorrect boot system command. Use the show running-config command and look for a boot system statement
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 router may have a corrupted flash image file. If this is the case, an error message should be displayed during boot. 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 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
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14. IOS file system overview
startup-config
running-config
IOS
ios
RAM
IOS (running)
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 software a router or switch uses is referred to as the configuration file or the config, running-config and startup-config.
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15. Cisco IOS File System (IFS)
startup-config
IOS
running-config
ios
IOS (running)
RAM
Beginning with version 12.0 of the IOS, a single interface to all the file systems that a router uses is provided, Cisco IOS File System (IFS).
The IFS provides a single method to perform all the file system management that a router uses, including
the flash memory file systems,
the network file systems (TFTP, rcp, and FTP)
reading or writing data (such as NVRAM, the running configuration, ROM).
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16. Cisco IOS File System (IFS)
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.
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17. Preparing for TFTP Be sure you can communicate with the TFTP server.
Know the name of the IOS file you are going to copy from on the router.
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18. Cisco IOS File System (IFS)
copy from-file to-file
system:
nvram:
flash:
running-config
RAM
IOS (running)
startup-config
IOS
ios
copy flash:<filename> tftp:
copy tftp: flash:<filename>
copy tftp: nvram:startup-config
copy nvram:startup-config tftp:
copy tftp: system:running-config
copy system:running-config tftp:
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19. Cisco Traditional Copy Commands
copy from-file to-file
running-config
RAM
IOS (running)
startup-config
IOS
ios
copy flash tftp
copy flash tftp
copy tftp startup-config
copy startup-config tftp
copy tftp running-config
copy running-config tftp
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20. IOS naming conventions
A relocatable image is copied from flash into RAM to run. A non-relocatable image is run directly from flash.
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)
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21. Example
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22. Managing configuration files using TFTP
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23. Managing configuration files using copy and paste
Perform the following to capture the configuration using the text displayed on the HyperTerminal screen to a text file:
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 Stop
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24. Managing IOS images using TFTP
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25. Restoring the IOS image from Flash
If the IOS image in flash has been erased or corrupted, the IOS may need to be restored from the ROM monitor mode (ROMmon).
1. ROM
1. POST
2. Bootstrap code executed
3. Check Configuration Register value (NVRAM)
0 = ROM Monitor mode
1 = ROM IOS
= startup-config in NVRAM
In many of the Cisco hardware architectures, the ROMmon mode is identified from the rommon 1 > prompt.
The flash should be examined with the rommon 1 > dir flash: command.
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.
rommon 1>boot flash:c2600-is-mz.121-5
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26. Restoring the IOS image from Flash
running-config
RAM
IOS (running)
startup-config
IOS
ios
If the router properly boots, determine why the router booted to the ROMmon instead of using IOS from flash.
show version - to check the configuration register to ensure that it is configured for the default boot sequence
show startup-config - to see if there is a boot system command instructing the router to use the IOS for ROM monitor.
If the router will not properly boot from the image or there is no IOS image, a new IOS will need to be downloaded.
The IOS file may be recovered using either:
Xmodem to restore the image through the console
Downloading the image using TFTP from the ROMmon mode.
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27. Download using Xmodem from ROMmon
console
Optional – Modifying the console baud rate to speed-up upload.
Requires rebooting of the router and the terminal session (at 9600) should be terminated and a new session started at bps to match the console speed.
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28. Download using Xmodem from ROMmon
console
The Xmodem command can be used from the ROMmon mode to restore the IOS software image from the PC.
The format of the command is: xmodem -c image_file_name
The -c instructs the Xmodem process to use Cyclic Redundancy Check (CRC) for error checking during the download.
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29. Download using Xmodem from ROMmon
console
The router will prompt not to begin the transfer and present a warning message.
The 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 > Send File.
Then in the Send File popup specify the image name/location, select Xmodem as the protocol, and start the transfer.
During the transfer, the Sending File popup will display the status of the transfer.
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30. Download using Xmodem from ROMmon
Router(config)#config-register 0x2102
Router(config)#line con 0
Router(config-line)#speed 9600
console
Once the transfer is complete a message appears that flash is being erased.
This is followed by the “Download Complete!” message.
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.
While the router is rebooting, the bps terminal session needs to be ended and a 9600 bps session begun.
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31. Download using TFTP from ROMmon
The IOS can also be restored from a TFTP session using the tftpdnld command.
The environmental variables provide a minimal configuration to allow for the TFTP of the IOS.
To set a ROMmon environment variable:
rommon>IP_ADDRESS=
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32. Download using TFTP from ROMmon
Once the variables are set for the IOS download, the tftpdnld command is entered with no arguments.
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33. File system verification
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34. Getting the TFTP Software
TFTP software is available for free for multiple OS’s.
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35. Starting TFTP on Windows
Be sure TFTP is running before copying to or from the TFTP server.
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36. Password Recovery
Step 1 config-register - At the router type the show version command. Record the configuration register setting, which is usually 0x In a real world scenario, If for some reason you cannot log into the router, i.e. someone changed the password, then of course you will not be able to perform this step.
Step 2 – Entering rommon
Within 60 seconds press the Break key (control-break on a PC). You may need to press this more than once. You will then see the following prompt:
System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE
Copyright (c) by cisco Systems
2500 processor with 8192 Kbytes of main memory
Abort at 0x10EA82C (PC)
>
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37. Password Recovery
Step 3 Breaking in - For the 2500 Series routers, after the “>” prompt type o/r 0x42 and press return. (Note, that this is the letter “o,” not the numeral zero.) Then type “i” and press return.
Abort at 0x10EA82C (PC)
> o/r 0x42
> i
o/r 0x42 – This will change the configuration register on the router to ignore the startup-config file during boot-up.
i – This will reboot (reload) the router.
The router will reboot and ask you if you want to go into setup mode. Type no
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38. Password Recovery Step 4 – Recovering the password Router> enable
Router# config t
To recover your previous startup-config file so you do not lose your previous configuration (if needed):
Router# copy startup-config running-config
Set your enable secret password. class is what we always use!.
Router(config)# enable secret class
Change the configuration-register back to its proper value.
Question: What happens the next time you reboot the router if you do not do this?
Router(config)# config-register 0x2102
Router(config)# exit
Copy the running-config with the current privileged password to the startup-config.
Router# copy running-config startup-config
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39. Password Recovery Step 5 – Verify
At the router type the show version command.
The configuration register setting should be 0x2102.
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40. Downloading an IOS
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41. Downloading an IOS
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42. Downloading an IOS
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43. Downloading an IOS
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44. Summary
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45. Ch. 5 – Managing Cisco IOS Software
CCNA 2 version 3.0
Rick Graziani
Cabrillo College