Installation guide

D-2 Cisco 4000 Series Installation Guide
Virtual Configuration Register Settings
Table D-1 Virtual Configuration Bit Meanings
Changing Configuration Register Settings
Some common reasons to modify the value of the virtual configuration register follow:
• Recover a lost password
• Change the console baud rate
• Enable or disable the Break function
• Manually boot the operating system using the b command at the ROM monitor prompt
• Force the router to boot automatically its system image in Flash memory, or boot as per
any boot system commands that are stored in its configuration file in NVRAM
Note If the router finds no boot system commands, it uses the configuration register value
to form a filename from which to boot a default system image stored on a network server.
(See Table D-3.)
Bit No. Hex Meaning
00–03 0x0000–0x000
F
Boot field (see Table D-2)
06 0x0040 Causes system software to ignore nonvolatile memory contents
07 0x0080 OEM bit enabled
08 0x0100 Break disabled
10 0x0400 IP broadcast with all zeros
11–12 0x0800–0x1000 Console line speed
13 0x2000 Boots default ROM software if network boot fails
14 0x4000 IP broadcasts do not have net numbers
15 0x8000 Enables diagnostic messages and ignores NVRAM contents