User guide

A-4 Cisco 2500 Series Access Server User Guide
Cisco Internetwork Operating System
The configuration register can be used by system administrators to control some very low
level operations of the access server. When the configuration register is set to specific values
(shown in Table A-2), the access server can be instructed to stop the boot process in any of
the three operating environments. You modify the configuration register value by using the
configuration command config-reg [value].
ROM Monitor
ROM monitor performs the bootstrap process and provides low-level diagnostics. You
cannot use ROM monitor to operate any of the interfaces. You can only access ROM
monitor via the console port. Setting the configuration register value to 0x0 and reloading
causes the access server to operate in the ROM monitor environment. The ROM monitor is
used to recover from system failures, and to recover a lost password.
Boot ROM
Boot ROM is used primarily to modify the Cisco IOS image that is loaded into Flash
memory. Flash memory is read-only when you are running the Cisco IOS software from
Flash memory; boot ROM allows write operations to Flash memory. If you are running in
boot ROM, only a limited subset of the Cisco IOS feature set is available. For example, boot
ROM does not support IP routing or subinterfaces. You can set the configuration register
value to 0x1 and reload to cause the access server to operate in the boot ROM environment.
Timesaver Enter the configuration command ip default-gateway [ipaddress] to tell
Cisco IOS software where to send IP packets when you are running from boot ROM if the
destination address is not directly connected. This command can be left in the configuration
file while you are running from Flash memory because it will be ignored when IP routing
is enabled.
You can modify the Cisco IOS image if you are running in boot ROM by entering the
command copy tftp flash. You can also modify Flash memory while running from Flash
memory by entering the command partition flash or using Flash Load Helper. See the
publication Access and Communication Servers Configuration Guide for more
information.