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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 3 Configuring the Switch for the First Time
Modifying the Supervisor Engine Startup Configuration
Understanding the ROM Monitor
The ROM monitor (ROMMON) is invoked at switch bootup, reset, or when a fatal exception occurs. The
switch enters ROMMON mode if the switch does not find a valid software image, if the NVRAM
configuration is corrupted, or if the configuration register is set to enter ROMMON mode. From
ROMMON mode, you can manually load a software image from bootflash or a flash disk, or you can
boot up from the management interface. ROMMON mode loads a primary image from which you can
configure a secondary image to boot up from a specified source either locally or through the network
using the BOOTLDR environment variable. This variable is described in the “Switch#” section on
page 3-32.
You can also enter ROMMON mode by restarting the switch and then pressing Ctrl-C during the first
five seconds of startup. If you are connected through a terminal server, you can escape to the Telnet
prompt and enter the send break command to enter ROMMON mode.
Note Ctrl-C is always enabled for five seconds after you reboot the switch, regardless of whether the
configuration-register setting has Ctrl-C disabled.
The ROM monitor has these features:
• Power-on confidence test
• Hardware initialization
• Boot capability (manual bootup and autoboot)
• File system (read-only while in ROMMON)
Configuring the Software Configuration Register
The switch uses a 16-bit software configuration register, which allows you to set specific system
parameters. Settings for the software configuration register are preconfigured in NVRAM.
Here are some reasons why you might want to change the software configuration register settings:
• To select a boot source and default boot filename
• To control broadcast addresses
• To set the console terminal baud rate
• To load operating software from flash memory
• To recover a lost password
• To manually boot the system using the boot command at the bootstrap program prompt
• To force an automatic bootup from the system bootstrap software (boot image) or from a default
system image in onboard flash memory, and read any boot system commands that are stored in the
configuration file in NVRAM
Caution To avoid possibly halting the Catalyst 4500 series switch switch, remember that valid configuration
register settings might be combinations of settings and not just the individual settings listed in Table 3-3.
For example, the factory default value of 0x2101 is a combination of settings.
Table 3-3 lists the meaning of each of the software configuration memory bits. Table 3-4 defines the boot
field.