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IOS-XR | ROMMON | PART #1

Updated: Nov 17, 2019


The ROM Monitor is a bootstrap program that initializes the hardware and boots the Cisco IOS XR software when you power on or reload a router. A version of the ROM Monitor software exists on each card. If the Cisco IOS XR software cannot boot on a card, the card startup ends in ROM Monitor mode.

During normal operation, users do not see the ROM Monitor prompt or use ROM Monitor mode. ROM Monitor mode is used only in special circumstances, such as reinstalling the entire software set, resetting the router password, or specifying a configuration file to use at startup.


The ROM Monitor software is known by many names. It is sometimes called ROMMON because of the CLI prompt in ROM Monitor mode. The ROM Monitor software is also called the boot software , boot image , or boot helper . Although it is distributed with routers that use the Cisco IOS XR software, ROM Monitor is a separate program from the Cisco IOS XR software. During normal startup, the ROM Monitor initializes the cards, and then control passes to the Cisco IOS XR software. After the Cisco IOS XR software takes over, ROM Monitor is no longer in use.

You can check your classic rommon variable using the command below into your IOS-XR system:

In this case, you can´t edit! it´s only a 'read only' file.


You can check it using the command below:

On the bottom of your screen you can see this message: "classic-rommon-var" [readonly] (...)

If you really want to change your rommon variables, you must need to reboot and use the default method to do this.


Follow these steps to configure the router to boot up in ROM monitor mode the next time it is rebooted.

If there is a standby DSC, the configuration register on the standby DSC is also set to 0x0. When you place the active RP in ROM Monitor mode, the system fails over to the standby RP, which then becomes the active RP. If both RPs need to be in ROM Monitor mode, connect to the new active RP and enter the reload command.


CAUTION: Resetting the configuration register may change the baud rate for the console. The default baud rate is 9600.


A break (system interrupt) is always enabled for 60 seconds after the router reboots, regardless of its setting (on or off) in the configuration register. During this 60-second window, you can break to the ROM monitor prompt by pressing the Control + C.


Enter ? or help at the ROM monitor prompt to display a list of available commands and options. Note: Commands are case sensitive!!


The table below summarizes the commands commonly used in ROM Monitor:

Don't forget to use the "sync" command to save your changes and for some commands we need to reload the equipment to take effect.


Instance #01: Overriding the Base configuration in XR:


Instance #02: Change variables:


Instance #03: Boot the vm image located on the tftp server:




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3 comentarios


Parabéns pelo site, ficou muito bom.

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Thiago Silva
Thiago Silva
19 nov 2019

Muito bom, bem detalhado o procedimento. Layout do site ficou show. Parabéns pela iniciativa e contribuição.

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Excellent post!

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