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Contents

• Router Boots In Rommon Mode
• What Does Rommon Mode Mean
• Cisco 3850 Rommon Mode

Introduction

Jan 09, 2016  Whether you bought your lab gear online or have a switch that's down and can't come up, you need to know the Cisco ROMMON procedure. It's different on different platforms, but the process is.

This page explains how to recover a Cisco 2600 Series Router and a VG200 stuck in ROMmon (rommon# ..> prompt).

Router Boots In Rommon Mode

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

There are no specific prerequisites for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

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. For more information on the software configuration register bit meanings, see Configuring the Software Configuration Register.

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:

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:

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.

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.

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.

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.

Note: There are instances where the system message 'Device does not contain a valid magic number' appears. If this happens, in addition to getting a valid Cisco IOS software image, you might need to reseat the Flash or replace it, if it is damaged.

Download using TFTP from ROMmon

This is the fastest way to re-install a new Cisco IOS software image on the router. Go to Using the tftpdnld Command.

Download using Xmodem from ROMmon

You can also download a new Cisco IOS software version through the console port, using Xmodem. Go to Xmodem Console Download Procedure Using ROMmon.

Related Information

To reset a Cisco router to factory default (removing the startup configuration file), perform these steps:

1.To erase the configuration file, issue the erasenvram: command. Reload the router by issuing the reload command.

2.If this does not solve the problem, attempt to break into ROM Monitor (ROMmon) by issuing the break sequence (usually Ctrl and break from the Hyperterminal) from a console connection.

Refer to: Cisco Standard Break Key Combinations. You should see this ROMmon prompt:

rommon 1>

3.Change the configure register value to ignore the startup configuration by issuing the confreg command, as shown in this example:

What Does Rommon Mode Mean

rommon 2> confreg 0x2142

4.To reload the router, issue the reset command, as shown in this example:

rommon 3> reset

5.After the router boots, issue the enable command at the Router > prompt. The prompt changes to Router#, indicating that the router is now in privileged mode.

6.To enter config mode, issue the config terminal command. You should now see a Router(config)# prompt.

7.To change the configure register to recognize the startup configuration, issue the config-register command, as shown in this example:

Router (config)# config-register 0x2102

To break out of configuration mode, press Cntl and Z. To save the blank configuration, issue the copy-running config-startup config command.

View more Cisco How-To Tutorialshttp://www.BradReese.Com

Cisco 3850 Rommon Mode