User guide

Maintaining the Cisco 2500 Series Access Server B-17
Virtual Configuration Register Settings
Virtual Configuration Register Settings
The access server has a 16-bit virtual configuration register, which is written into NVRAM.
You might want to change the virtual configuration register settings for the following
reasons:
• Set and display the configuration register value
• Force the system into the ROM monitor or boot ROM.
• Select a boot source and default boot filename
• Enable or disable the Break function
• Control broadcast addresses
• Set the console terminal baud rate
• Recover a lost password (ignore the NVRAM startup-config)
• Enable booting from a Trivial File Transfer Protocol (TFTP) server
Table B-2 lists the meaning of each of the virtual configuration memory bits and defines
the boot field names.
Caution To avoid confusion and possibly halting the access server, remember that valid
configuration register settings might be combinations of settings and not just the individual
settings listed in Table B-2. For example, the factory default value of 0x2102 is a
combination of settings.
Table B-2 Virtual Configuration Register Bit Meanings
Bit No.
1
Hexadecimal Meaning
00–03 0x0000–0x000F Boot field
06 0x0040 Causes system software to ignore the contents of NVRAM
(startup-config)
07 0x0080 OEM bit is enabled
08 0x0100 Break is disabled
10 0x0400 IP broadcast with all zeros