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5.2 Managing the Cisco File
System 5.2.6 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 > prompt.This
first step in this process is to 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. 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
1>boot flash:c2600-is-mz.121-5 If the router properly
boots, then there are a couple of items that need to be
examined to determine why the router booted to the ROMmon
instead of using IOS from flash. 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, 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.
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, or downloading the image using TFTP from
the ROMmon mode. 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.
When prompted “change console baud rate? y/n [n]:” selecting
y will provide a prompt to select the new speed. After
changing the console speed and restarting the router into the
ROMmon mode, the terminal session (at 9600) should be
terminated and a new session started at 115200 bps to match the
console speed. 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. For example, to restore an IOS
image file with the name “c2600-is-mz.122-10a.bin”, type the
command: 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. 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. When the process is
continued, the router will then prompt to start the transfer.
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. Once the transfer is
complete a message appears indicating 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 115200 bps terminal
session needs to be ended and a 9600 bps session begun. Lab
Activity Lab Exercise: Password Recovery Procedures In this
lab, the students will gain access to a router with an unknown
privileged mode (enable) password. Lab Activity Lab
Exercise: Managing IOS Images with ROMmon and Xmodem In this
lab, the students will recover a Cisco 1700 series router using
ROM monitor (ROMmon) (rommon >) due to a missing or corrupt
IOS boot flash image. Web Links Loading and Maintaining
System Images http://www.cisco.com/en/US/products/sw/
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5.2 Managing the Cisco File
System 5.2.7 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. The ROMmon TFTP
transfer works only on the first LAN port so a simple set of IP
parameters are set for this interface. To set a ROMmon
environment variable, the variable name is typed, then the
equal sign (=), and the value for the variable
(VARIABLE_NAME=value). For example, to set the IP address to
10.0.0.1, type IP_ADDRESS=10.0.0.1 at the ROMmon prompt.
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
To check the ROMmon
environment variables, the set command can be used. Once
the variables are set for the IOS download, the
tftpdnld command is entered with no arguments. The
ROMmon will echo the variables and then a confirmation prompt
will appear with a warning that this will erase the flash. As
each datagram of the IOS file is received, a “!” will be
displayed. When the complete IOS file has been received, the
flash will be erased and the new IOS image file written.
Appropriate messages will be displayed as the process is
completed. When the new image is written into flash and the
ROMmon prompt is displayed, the router can be restarted by
typing i. The router should now boot from the new IOS
image in flash. Web Links Loading and Maintaining System
Images http://www.cisco.com/en/US/products/sw/ iosswrel/
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5.2 Managing the Cisco File
System 5.2.8 File system verification There
are several commands that can be used to verify the router file
system. One of those is the show version command. The
show version command can be used to check the current
image and the total amount of flash. It also verifies two other
items concerning loading the IOS. It identifies the source of
the IOS image that the router used to boot and displays 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.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. This command is often
used to confirm that there is ample space to store a new IOS
image. As previously mentioned, the configuration file may
contain boot system commands. These commands can be used to
identify the source of the desired IOS boot image. Multiple
boot system commands may be used to create a fallback sequence