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When a router is stuck in Rommon mode, one of the following | When a router is stuck in Rommon mode, one of the following are the causes. | ||
. Configuration register value. | . Configuration register value. | ||
Revision as of 19:32, 14 May 2010
When a router is stuck in Rommon mode, one of the following are the causes.
. Configuration register value.
. Unable to locate a valid Cisco IOS software image.
. Corrupt Flash image.
Check Configuration Register Settings
If the router is stuck in ROMmon mode, the first setting that should be checked is the value of the configuration register. The first four bits of the configuration register comprise the boot field. The value of the boot field defines the source of a default Cisco IOS® software image that will be used to run the router. If the value of the boot field is 0 (configuration register value of XXX0), on startup the system enters and remains in the ROM monitor mode (rommon>), awaiting a user command to boot the system manually. If your router keeps entering the ROMmon mode each time the system is restarted, it is probably due to the setting of the configuration register. To verify the configured value of the configuration register, use the confreg command as shown below:
rommon 2 > confreg
Configuration Summary enabled are:
load rom after netboot fails
console baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n [n]:
As indicated by the output of the confreg command above, the configuration register is set to a value that forces the router to go into the ROMmon mode each time it is reloaded or power-cycled. To make the router boot automatically from a default Cisco IOS software image, change the configuration register value as shown below: rommon 2 > confreg
Configuration Summary enabled are:
load rom after netboot fails
console baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n [n]: y
enable "diagnostic mode"? y/n [n]:
enable "use net in IP bcast address"? y/n [n]:
disable "load rom after netboot fails"? y/n [n]:
enable "use all zero broadcast"? y/n [n]:
enable "break/abort has effect"? y/n [n]:
enable "ignore system config info"? y/n [n]:
change console baud rate? y/n [n]:
change the boot characteristics? y/n [n]: y
enter to boot:
0 = ROM Monitor 1 = the boot helper image 2-15 = boot system [0]: 2
Configuration Summary enabled are:
load rom after netboot fails
console baud: 9600
boot: image specified by the boot system commands or default to: cisco2-C2600
do you wish to change the configuration? y/n [n]: n
You must reset for new config to take effect.
By doing this, you have changed the configuration register to a value that makes it look for a valid Cisco IOS software image on startup and boot from the same. The router must now be reset.
rommon 3 > reset
The router should now reload with a valid Cisco IOS software image.
Look for a Valid Image in Flash
If the configuration register value is set to make the system boot automatically from a default Cisco IOS software image, and if no break signal is sent during start up, the router should boot normally. However, if the router still enters the ROMmon mode, it is probably because the device is unable to locate a valid Cisco IOS software image. The first thing you need to do then is to look for a valid Cisco IOS software image. To do this, issue the dir <device> command for each available device, and look for a valid Cisco IOS software image. For example, to look for the IOS in the Flash, use the command shown below.
rommon 1 > dir flash:
File size Checksum File name 5358032 bytes (0x51c1d0) 0x7b16 c2600-i-mz.122-10b.bin
rommon 2 >
Note that if the router returns the "bad device name" message, the device specified probably does not exist. The output above indicates that a valid image is indeed present in the Flash. Try to boot from that image using the boot command.
rommon 2 > boot flash:c2600-i-mz.122-10b.bin
program load complete, entry point: 0x80008000, size: 0x51c0dc Self decompressing the image : #################################################
The router should now boot with the Cisco IOS software image specified in the boot command. However, there are times when a valid image does not exist on any of the devices or the image on the Flash might be corrupted. In these cases, a valid image has to be downloaded using Trivial File Transfer Protocol (TFTP) or by using the Xmodem procedure. Both these procedures can be carried out from the ROMmon mode.
Download using TFTP from ROMmon
Step 1 Specify the required variables, for example:
rommon 1> IP_ADDRESS=172.15.19.11 -IP address for the router you are using.
rommon 2> IP_SUBNET_MASK=255.255.255.0 -Subnet mask for the router you are using.
rommon 3> DEFAULT_GATEWAY=172.16.19.1 -Default gateway for the router you are using
(not required if the TFTP server is in the
same subnet as the router).
rommon 4> TFTP_SERVER=172.15.20.10 -IP address of the server from which you want to
download the image file.
rommon 5> TFTP_FILE=/tftpboot/c2600-i-mz -Name of the file that you want to download.
rommon 6>tftpdnld -Starts the process.
IP_ADDRESS=172.15.19.11
IP_SUBNET_MASK=255.255.255.0
DEFAULT_GATEWAY=172.16.19.1
TFTP_SERVER=172.15.20.10
TFTP_FILE=/tftpboot/2600-i-mz
Invoke this command for disaster recovery only.
WARNING: all existing data in all partitions on flash will be lost!
Do you wish to continue? y/n: [n]:
Enter y to download the Cisco IOS software image.
When the process is complete, the ROM monitor mode prompt appears on your screen.
rommon 7>
The router is now ready to boot from the Cisco IOS image. Enter the boot ROM monitor command to reboot the router.
Download using Xmodem from ROMmon
The xmodem command establishes a connection between a console and the router console port for disaster recovery, if both the boot and system images are erased from flash memory.
Step 1 Connect a console to the router's console port.
Step 2 Power up the router. The power-on self-test diagnostics run and the boot ROM searches for a valid boot image and Cisco IOS image in flash memory. If the boot image and Cisco IOS image are not found, the ROM monitor prompt is displayed:
rommon 1>
Step 3 Enter the xmodem command and the name of the source file containing the Cisco IOS image:
rommon 1> xmodem filename
When the source file is found, messages similar to the following appear:
Do not start upload program yet...
File size Checksum File name
2537948 bytes (0x26b9dc) c2600-i-mz.122-10.bin
WARN: This operation will ERASE bootflash. If the xmodem
download to bootflash fails, you will lose any good image
you may already have in bootflash.
Invoke this application only for disaster recovery.
Do you wish to continue? [yes/no]:
Step 4 Enter yes to copy the Cisco IOS image into flash memory. Messages similar to the following appear:
Ready to receive file prog ...
Erasing flash at 0x3000000
program flash location 0x3000000
Transfer complete!
The router is now ready to boot from the Cisco IOS image and need to be reset.