CHAPTER
5-1
Hardware Installation Guide for the Cisco 4000 Series Integrated Services Router
OL-32185-02
5
ROM Monitor Overview and Basic
Procedures
This chapter provides an overview of ROM Monitor concepts and operations.
This chapter includes the following main topics:
• ROM Monitor Overview, page 5-1
• Access ROM Monitor Mode, page 5-2
• Displaying the Configuration Register Setting, page 5-6
• Environment Variable Settings, page 5-6
• Exiting ROM Monitor Mode, page 5-8
ROM Monitor Overview
The ROM Monitor is a bootstrap program that initializes the hardware and boots the
Cisco IOS XE software when you power on or reload a router. When you connect a terminal to the router
that is in ROM Monitor mode, the ROM Monitor command-line interface (CLI) prompt is displayed.
During normal operation, users do not 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 XE software, ROM
Monitor is a separate program from the Cisco IOS XE software. During normal startup, the ROM
Monitor initializes the router, and then control passes to the Cisco IOS XE software. After the
Cisco IOS XE software takes over, the ROM Monitor is no longer in use.
Environmental Variables and the Configuration Register
Two primary connections exist between ROM Monitor and the Cisco IOS XE software: the ROM
Monitor environment variables and the configuration register.
The ROM Monitor environment variables define the location of the Cisco IOS XE software and describe
how to load it. After the ROM Monitor has initialized the router, it uses the environment variables to
locate and load the Cisco IOS XE software.
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