What Is Rommon Mode
Table Of Contents
Perform these steps to configure the router to boot up in ROM monitor mode the next time it is.u upgrade ROMMON, System will reboot after upgrade. 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.
ROM Monitor
The ROM monitor firmware runs when the router is powered up or reset. The firmware helps to initialize the processor hardware and boot the operating system software. You can use the ROM monitor to perform certain configuration tasks, such as recovering a lost password or downloading software over the console port. If there is no Cisco IOS software image loaded on the router, the ROM monitor runs the router.
This appendix contains the following sections:
•Entering the ROM Monitor
•ROM Monitor Commands
•Command Descriptions
•Disaster Recovery with TFTP Download
•Configuration Register
•Console Download
•Debug Commands
•Exiting the ROM Monitor
Entering the ROM Monitor
To use the ROM monitor, you must be using a terminal or PC that is connected to the router over the console port.
Perform these steps to configure the router to boot up in ROM monitor mode the next time it is rebooted.
Purpose | ||
|---|---|---|
Step 1 | enable | Enters privileged EXEC mode. Enter your password if prompted. |
Step 2 | configure terminal | Enters global configuration mode. |
Step 3 | config-reg 0x0 | Resets the configuration register. |
Step 4 | exit | Exits global configuration mode. |
Step 5 | reload | Reboots the router with the new configuration register value. The router remains in ROM monitor and does not boot the Cisco IOS software. As long as the configuration value is 0x0, you must manually boot the operating system from the console. See the boot command in the 'Command Descriptions' section in this appendix. After the router reboots, it is in ROM monitor mode. The number in the prompt increments with each new line. Note In ROM monitor mode, only the Fast Ethernet LAN interface FE0 is enabled and is available for communication, while the other three Fast Ethernet LAN interfaces (FE1, FE2, and FE3) are disabled. After the IOS software boots up, all of the four Fast Ethernet LAN interfaces are enabled. This feature is available if the ROM monitor version that is installed on your router is 12.3(8r)YI6 or later. |
Timesaver Break (system interrupt) is always enabled for 60 seconds after the router reboots, regardless of whether it is set to on or off in the configuration register. During this 60-second window, you can break to the ROM monitor prompt by pressing the Break key.
ROM Monitor Commands
Enter ? or help at the ROM monitor prompt to display a list of available commands and options, as follows:
Commands are case sensitive. You can halt any command by pressing the Break key on a terminal. If you are using a PC, most terminal emulation programs halt a command when you press the Ctrl and the Break keys at the same time. If you are using another type of terminal emulator or terminal emulation software, see the documentation for that product for information on how to send a Break command.
Command Descriptions
Table C-1 describes the most commonly used ROM monitor commands.
Description | |
|---|---|
help or ? | Displays a summary of all available ROM monitor commands. |
-? | Displays information about command syntax; for example: The output for this command is slightly different for the xmodem download command: |
reset or i | Resets and initializes the router, similar to a power up. |
dirdevice: | Lists the files on the named device;for example, flash memory files: |
For more information about the ROM monitor boot commands, see the . | |
b | Boots the first image in flash memory. |
bflash:[filename] | Attempts to boot the image directly from the first partition of flash memory. If you do not enter a filename, this command will boot this first image in flash memory. |
Disaster Recovery with TFTP Download
The standard way to load new software on your router is to use the copy tftp flash privileged EXEC command from the Cisco IOS software command-line interface (CLI). However, if the router is unable to boot Cisco IOS software, you can load new software while in ROM monitor mode.
This section describes how to load a Cisco IOS software image from a remote TFTP server to the router flash memory. Use the tftpdnld command only for disaster recovery, because it erases all existing data in flash memory before downloading a new software image to the router.
TFTP Download Command Variables
This section describes the system variables that can be set in ROM monitor mode and that are used during the TFTP download process. There are both required variables and optional variables.
Download south park the fractured but whole. Note The commands described in this section are case sensitive and must be entered exactly as shown.
Required Variables
These variables must be set with these commands before you use the tftpdnld command:
Command | |
IP address of the router. | IP_ADDRESS= ip_address |
Subnet mask of the router. | IP_SUBNET_MASK=ip_address |
IP address of the default gateway of the router. | DEFAULT_GATEWAY=ip_address |
IP address of the TFTP server from which the software will be downloaded. | TFTP_SERVER=ip_address |
Name of the file that will be downloaded to the router. | TFTP_FILE=filename |
Optional Variables
These variables can be set with these commands before using the tftpdnld command:
Command | |
Configures how the router displays file download progress. 0—No progress is displayed. 1—Exclamation points (!!!) are displayed to indicate file download progress. This is the default setting. 2—Detailed progress is displayed during the file download process; for example: •Initializing interface. •Interface link state up. •ARPing for 1.4.0.1 •ARP reply for 1.4.0.1 received. MAC address 00:00:0c:07:ac:01 | TFTP_VERBOSE=setting |
Number of times the router attempts ARP and TFTP download. The default is 7. | TFTP_RETRY_COUNT=retry_times Adolph coors in the brewing industry pdf download. Oxford University Press. December 12, 2014. History Colorado. |
Length of time, in seconds, before the download process times out. The default is | TFTP_TIMEOUT=time |
Whether or not the router performs a checksum test on the downloaded image: 1—Checksum test is performed. 0—No checksum test is performed. | TFTP_CHECKSUM=setting |
Using the TFTP Download Command
Perform these steps in ROM monitor mode to download a file through TFTP.
Step 1 Use the appropriate commands to enter all the required variables and any optional variables described in preceding sections.
Step 2 Enter the tftpdnld command as follows:
Note The -r variable is optional. Entering this variable downloads and boots the new software but does not save the software to flash memory. You can then use the image that is in flash memory the next time you enter the reload command.
You will see output similar to the following:
Step 3 If you are sure that you want to continue, enter y in response to the question in the output:
The router begins to download the new file.
If you mistakenly entered yes, you can enter Ctrl-C or Break to stop the transfer before the flash memory is erased.
Configuration Register
The virtual configuration register is in nonvolatile RAM (NVRAM) and has the same functionality as other Cisco routers. You can view or modify the virtual configuration register from either the ROM monitor or the operating system software. Within the ROM monitor, you can change the configuration register by entering the register value in hexadecimal format, or by allowing the ROM monitor to prompt you for the setting of each bit.
Changing the Configuration Register Manually
To change the virtual configuration register from the ROM monitor manually, enter the confreg command followed by the new value of the register in hexadecimal format, as shown in the following example:
The value is always interpreted as hexadecimal. The new virtual configuration register value is written into NVRAM but does not take effect until you reset or reboot the router.
Changing the Configuration Register Using Prompts
Entering the confreg command without an argument displays the contents of the virtual configuration register and a prompt to alter the contents by describing the meaning of each bit.
In either case, the new virtual configuration register value is written into NVRAM but does not take effect until you reset or reboot the router.
The following display shows an example of entering the confreg command:
Console Download
You can use console download, a ROM monitor function, to download either a software image or a configuration file over the router console port. After download, the file is either saved to the mini-flash memory module or to main memory for execution (image files only).
Use console download when you do not have access to a TFTP server.
Note If you want to download a software image or a configuration file to the router over the console port, you must use the ROM monitor dnld command.
Note If you are using a PC to download a Cisco IOS image over the router console port at 115,200 bps, ensure that the PC serial port is using a 16550 universal asynchronous transmitter/receiver (UART). If the PC serial port is not using a 16550 UART, we recommend using a speed of 38,400 bps or less when downloading a Cisco IOS image over the console port.
Command Description
The following are the syntax and descriptions for the xmodem console download command:
xmodem [-cyrx]destination_file_name
c | Optional. Performs the download using 16-bit cyclic redundancy check (CRC-16) error checking to validate packets. Default is 8-bit CRC. |
y | Optional. Sets the router to perform the download using Ymodem protocol. The default is Xmodem protocol. The protocols differ as follows: •Xmodem supports a 128-block transfer size. Ymodem supports a 1024-block transfer size. •Ymodem uses CRC-16 error checking to validate each packet. Depending on the device that the software is being downloaded from, this function might not be supported by Xmodem. |
r | Optional. Image is loaded into DRAM for execution. The default is to load the image into flash memory. |
x | Optional. Image is loaded into DRAM without being executed. |
destination_file_name | Name of the system image file or the system configuration file. In order for the router to recognize it, the name of the configuration file must be router_confg. |
Follow these steps to run Xmodem:
Step 1 Move the image file to the local drive where Xmodem will execute.
Step 2 Enter the xmodem command.
Error Reporting
Because the ROM monitor console download uses the console to perform the data transfer, when an error occurs during a data transfer, error messages are only displayed on the console once the data transfer is terminated.
If you have changed the baud rate from the default rate, the error message is followed by a message telling you to restore the terminal to the baud rate specified in the configuration register.
Debug Commands
Most ROM monitor debugging commands are functional only when Cisco IOS software has crashed or is halted. If you enter a debugging command and Cisco IOS crash information is not available, you see the following error message:
The following are ROM monitor debugging commands:
•stack or k—Produces a stack trace; for example:
•context—Displays processor context; for example:
•frame—Displays an individual stack frame.
•sysret—Displays return information from the last booted system image. This information includes the reason for terminating the image, a stack dump of up to eight frames, and, if an exception is involved, the address where the exception occurred; for example:
•meminfo—Displays size in bytes, starting address, available range of main memory, the starting point and size of packet memory, and size of NVRAM; for example:
Exiting the ROM Monitor
You must set the configuration register to a value from 0x2 to 0xF for the router to boot a Cisco IOS image from flash memory upon startup or reloading.
The following example shows how to reset the configuration register and cause the router to boot a Cisco IOS image stored in flash memory:
You must reset or power cycle for new config to take effect:
The router will boot the Cisco IOS image in flash memory. The configuration register will change to 0x2101 the next time the router is reset or power cycled.
Hi,The switch could wind up in ROMmon mode due to these reasons,. A switch reload or crash after the image was corrupted or deleted. The Compact Flash which holds the system image has been removed. The configuration register has been changed incorrectly. The configuration register value of 0x0 always brings the switch to ROMmon mode. The typical configuration register is 0x2102, with the boot system flash command pointing to the system image to load.
The boot variable is incorrect, but a valid image is still presentIn our case, config register is set correctly as 0x2102, I would suggest you to verify the boot variable.1. When the switch gone into rommon, Issue the dir bootflash: command to list the files present in the bootflash, or issue the dir slot0: command to list the files present in the Compact Flash device.rommon 1 dir bootflash:rommon 2 dir slot0:Note: The reason the switch reboots continuously is because the system image file name specified does not exist, but there is a valid file in the bootflash and slot0. Also, the system image file name specified is case sensitive. If it is not specified correctly, it causes a continuous reboot.2. The system is back up, Issue the dir bootflash: command to note the file in the bootflash. Issue the dir slot0: command if you loaded the system file present in the slot0.Issue the show bootvar command to check the current boot variable.example:Switch# show bootvarBOOT variable = bootflash:cat4000-is-mz.121-8a.Ew,1CONFIGFILE variable does not existBOOTLDR variable does not exist3. Remove the existing incorrect boot variable and add the correct one.
Issue the configure terminal command in order to do this.Switch# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Switch(config)# no boot system flash bootflash:cat4000-is-mz.121-8a.EwSwitch(config)# boot system flash bootflash:cat4000-is-mz.121-11b.EWSwitch(config)# end4.
Save the configuration from running to startup, by issuing the write memory command.Switch# write memoryBuilding configuration.Compressed configuration from 4359 bytes to 1730 bytesOK5. Check the boot variable again to make sure it is set properly so that the switch boots up the correct system file on the next rebootRefer:Regards,Aru. Please rate if the post is useful. Hi,The switch could wind up in ROMmon mode due to these reasons,. A switch reload or crash after the image was corrupted or deleted. The Compact Flash which holds the system image has been removed.
The configuration register has been changed incorrectly. The configuration register value of 0x0 always brings the switch to ROMmon mode. The typical configuration register is 0x2102, with the boot system flash command pointing to the system image to load. The boot variable is incorrect, but a valid image is still presentIn our case, config register is set correctly as 0x2102, I would suggest you to verify the boot variable.1. When the switch gone into rommon, Issue the dir bootflash: command to list the files present in the bootflash, or issue the dir slot0: command to list the files present in the Compact Flash device.rommon 1 dir bootflash:rommon 2 dir slot0:Note: The reason the switch reboots continuously is because the system image file name specified does not exist, but there is a valid file in the bootflash and slot0. Also, the system image file name specified is case sensitive. If it is not specified correctly, it causes a continuous reboot.2.
The system is back up, Issue the dir bootflash: command to note the file in the bootflash. Issue the dir slot0: command if you loaded the system file present in the slot0.Issue the show bootvar command to check the current boot variable.example:Switch# show bootvarBOOT variable = bootflash:cat4000-is-mz.121-8a.Ew,1CONFIGFILE variable does not existBOOTLDR variable does not exist3.
Remove the existing incorrect boot variable and add the correct one. Issue the configure terminal command in order to do this.Switch# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Switch(config)# no boot system flash bootflash:cat4000-is-mz.121-8a.EwSwitch(config)# boot system flash bootflash:cat4000-is-mz.121-11b.EWSwitch(config)# end4.
Save the configuration from running to startup, by issuing the write memory command.Switch# write memoryBuilding configuration.Compressed configuration from 4359 bytes to 1730 bytesOK5. Check the boot variable again to make sure it is set properly so that the switch boots up the correct system file on the next rebootRefer:Regards,Aru. Please rate if the post is useful. Hi ArumugamFirst, thanks a lot for your help.I understand that if my image is corrupted or deleted, it will be impossible to start with a 'boot' command from the rommon mode.I have no device available on slot0 and my config-register is 0x2102, so my problem must be an incorrect boot variable.The result of show botvar isSwitch#show bootvarBOOT variable = variable does not existCONFIGFILE variable does not existBOOTLDR variable does not existconfigure-register is 0x2102I think that i will must set my boot variable. If yes, how must i do it?Thanks againMarcelo.