Cisco ASR 9000 Series Configuration Manual page 12

ROM Monitor Overview
Information About ROM Monitor
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.
Understanding the Role of the Route Switch Processor (RSP) Card
The Cisco ASR 9000 Series Router contains series of chassis slots, each of which can hold one of several
types of line cards (LCs). Two slots in the chassis are reserved for route switch processors (RSP) cards that
provide the central point for chassis provisioning and management.
The active RSP for the owner SDR is called the Designated Shelf Controller (DSC). This card performs
system-wide functions. If the active RSP card is placed in ROM Monitor mode, it is no longer running the
Cisco IOS XR software. If a standby RSP card is available, then the standby RSP card resumes router operations.
If both the RSP cards are not available or if the active RSP (previously standby) is also placed in the ROM
Monitor mode, router operations will stop.
Designated Secure Domain Router Shelf Controller (DSDRSC)
When the Designated Secure Domain Router Shelf Controller (DSDRSC) in an SDR is placed in ROM Monitor
mode, the router operations are transferred to the standby DSDRSC (if available). If both the primary and
standby DSDRSCs are in ROM Monitor mode, then the router operations cease because the
Cisco IOS XR software is no longer running.
Accessing ROM Monitor Mode on the RSP Card
In most situations, you interact with the ROM Monitor mode only on the RSP cards. The active RSP card
contains the administration configuration for the entire system and distributes the required software to all the
other nodes in the router. All the tasks in this document describe ROM Monitor mode accessed through the
RSP card for the system.
The line cards have its own ROM Monitor software which can be upgraded using the RSP FPD upgrade
operation, if required.
Environmental Variables and the Configuration Register
Two primary connections exist between ROM Monitor and the Cisco IOS XR software: the ROM Monitor
environment variables and the configuration register.
The ROM Monitor environment variables define the location of the Cisco IOS XR software and describe how
to load it. After ROM Monitor has initialized the card, it uses the environment variables to locate and load
the Cisco IOS XR software. The common environment variables are BOOT, IP_ADDRESS,
DEFAULT_GATEWAY, TFTP_FILE, TURBOBOOT and SUBNET_MASK.
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 Administration EXEC mode as needed.
Typically, you set the configuration register using the Cisco IOS XR software prompt on the active RSP when
you need to use ROM Monitor mode. When the maintenance in ROM Monitor mode is complete, you change
the configuration register so the card reboots with the Cisco IOS XR software.
Cisco ASR 9000 Series Aggregation Services Router ROM Monitor Configuration Guide, Release 5.1.x
4 OL-30420-01