Cisco Systems ISR4451XK9 manual ROM Monitor Overview and Basic Procedures

C H A P T E R 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

•Entering ROM Monitor Mode, page 5-2

•Displaying the Configuration Register Setting, page 5-5

•Environment Variable Settings, page 5-5

•Exiting ROM Monitor Mode, page 5-7

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 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 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, 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 ROM Monitor has initialized the router, it uses the environment variables to locate and load the Cisco IOS XE software.

The configuration register is a software setting that controls how a card starts up. One of the primary uses of the configuration register is to control whether the card starts in ROM Monitor mode or Administration EXEC mode. The configuration register is set in either ROM Monitor mode or

Hardware Installation Guide for the Cisco 4451-X Integrated Services Router

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