2
Changing the Configuration Register Settings
OL-5598-01
About the Configuration Register
Table 1 describes the configuration register bits.
Ta b l e 1 Configuration Register Bit Descriptions
Bit
Number Hexadecimal Meaning
00–03 0x0000–0x000F Boot field. The boot field setting determines whether the router loads an
operating system and where it obtains the system image.
See Table 2 for details.
06 0x0040 Causes the system software to ignore the contents of NVRAM.
07 0x0080 Original Equipment Manufacturer (OEM) bit enabled.
08 0x0100 Controls the console Break key:
•
(Factory default) Setting bit 8 causes the processor to ignore the
console Break key.
•
Clearing bit 8 causes the processor to interpret Break as a command
to force the router into the ROM monitor mode, halting normal
operation.
Break can always be sent in the first 60 seconds while the router is
rebooting, regardless of the configuration register settings.
09 0x0200 This bit controls the system boot:
•
Setting bit 9 causes the system to use the secondary bootstrap.
•
(Factory default) Clearing bit 9 causes the system to boot from flash
memory.
This bit is typically not modified.
10 0x0400 Controls the host portion of the IP broadcast address:
•
Setting bit 10 causes the processer to use all zeros.
•
(Factory default) Clearing bit 10 causes the processor to use all ones.
Bit 10 interacts with bit 14, which controls the network and subnet
portions of the IP broadcast address. See
Table 3 for the combined effects
of bits 10 and 14.
05, 11,
12
0x0020,
0x0800, 0x1000
Controls the console line speed. See Table 4 for the eight available bit
combinations and console line speeds.
Factory default is 9600 baud, where bits 5, 11, and 12 are all zero (clear).
Note
You cannot change the console line speed configuration register
bits from the Cisco IOS command-line interface (CLI). You can,
however, change these bits from the ROM monitor (see
“Using
the ROM Monitor”). Or, instead of changing the configuration
register settings, you can set the console line speed through other
Cisco
IOS commands..
13 0x2000 Determines how the router responds to a network boot failure:
•
Setting bit 13 causes the router to boot the default ROM software
after 6 unsuccessful network boot attempts.
•
(Factory default) Clearing bit 13 causes the router to indefinitely
continue network boot attempts.
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