Installation Manual

4-8
Troubleshooting
Virtual Configuration Register Settings
Maintenance
Virtual Configuration Register Settings
The router 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 configuration file in NVRAM)
■ Enable TFTP server boot
Table 4-3 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 router, remember that valid
configuration register settings might be combinations of settings and not just
the individual settings listed in table 4-3. For example, the factory default value
of 0x2102 is a combination of settings.
Table 4-3. Virtual Configuration Register Bit Meanings
Bit No.
a
a. The factory default value for the configuration register is 0x2102. This value is a combination
of the following: bit 13 = 0x2000, bit 8 = 0x0100, and bits 00 to 03 = 0x0002.
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
11–12 0x0800–0x1000 Console line speed
13 0x2000 Load the boot ROM software if a Flash boot fails five
times
14 0x4000 IP broadcasts do not have network numbers
15 0x8000 Enable diagnostic messages and ignore the contents
of NVRAM
J3138.bk Page 8 Wednesday, March 18, 1998 6:07 PM