Router Stuck in ROMMON Mode

One time in a project, I worked on Cisco Catalyst 6500 series, it's one of the biggest switches you can find in the market, not to mention very expensive too.

The thing is it was using CatOS instead of IOS, the client only want to use IOS. CatOS is another flavor of Cisco Operating System which uses a set based commands. Meaning when you want to configure something the command usually use "set" as the first command.

So I upgraded the image to IOS, I had to change several switches since they were using quite a lot of those switches.

Then the problem came, one of the switches stuck in the ROMMON mode. It's not showing the normal switch > prompt but only the rommon 1 > prompt.

This is not a serious problem, I only forgot to change back the configuration register value.

You might have experienced this before, or in case you find this problem in the future, lucky you got in this post.

When a router/switch stuck in ROMMON mode, the first thing you need to check is the configuration register value.

The normal operation configuration register value is 0x2102, you can verify the value using the confreg command in the ROMMON prompt, or using show version in the normal prompt.

Here is the output you get if you have no problem with the configuration register:

rommon 1 > confreg


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]:

And this is the output if you have the wrong configuration register:

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]:

With the confreg command, you'll also prompted if you want to change the configuration register value. Type y if you want to change it or type n or press enter if you want to leave it.

If you type y, you'd be taken to a series of questions, just answer no to all but the change the boot characteristics, set the value on the next prompt to 2.

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 or power cycle for new config to take effect

Reset the device using the following command:

rommon 3 > reset

With the above steps, your Cisco device should be running normal again but if it's not, that means the device might unable to find the valid IOS image. This can happen because of mistype or even corrupted image file.

Verify first that you have a valid IOS image using:

rommon 3 > dir flash:
File size Checksum File name
3114612 bytes (0x2f8674) 0x7612 c2600-i-mz.113-9.T

There you can see I have an IOS image c2600-i-mz.113-9.T, then set the device to boot from the image using boot flash: command followed by the name of the IOS image.

rommon 2 > boot flash:c2600-i-mz.122-10b.bin
program load complete, entry point: 0x80008000, size: 0x51c0dc
Self decompressing the image : #################################################
##################################

It will decompress the image and start loading the device normally.

Related to the CCNA exam, the most common question for configuration register is the default value of the confreg which is 0x2102 and the value needed to disregard the content of the NVRAM (for password recovery) which is 0x2142