Cisco Systems Cisco 3600 Changing Configuration Register Settings, Bit Number Hexadecimal Meaning

Appendix C Configuration Register

Changing Configuration Register Settings

Table C-1 Configuration Register Bit Meanings

Bit
Number	Hexadecimal	Meaning
00–03	0x0000-0x000F	Boot field. (See Table C-2.)
06	0x0040	Causes the system software to ignore the contents of
		NVRAM.
07	0x0080	OEM bit enabled.
08	0x0100	Break disabled.
09	0x0200	Causes the system to use the secondary bootstrap.
		This is typically not used (set to 0).
10	0x0400	IP broadcast with all zeros.
5, 11, 12	0x0020,	Console line speed.
	0x0800, 0x1000
13	0x2000	Boots default ROM software if the network boot fails.
14	0x4000	IP broadcasts do not have net numbers.
15	0x8000	Enables diagnostic messages and ignores the contents
		of NVRAM.

Changing Configuration Register Settings

You might want to modify the value in the configuration register to perform the following tasks:

•Recover a lost password

•Change the console data 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 automatically boot its system image in Flash memory, or boot in accordance with any boot system commands stored in the router’s configuration file in NVRAM

You can change the configuration register from either the ROM monitor or the operating system software. To change the configuration register from the ROM monitor, see the “Configuration Register Commands” section on page B-7. To change the configuration register from the system software, do the following:

Step 1 Connect a console terminal to the console port of the router as described in the “Connecting to the

Console Port” section on page 3-44, using the blue RJ-45 to DB-9 console adapter cable.

Note If you have a terminal with a DB-25 port, use an RJ-45 rollover cable and DB-25 adapter. The RJ-45-to-DB-25 adapter (Cisco part number 29-0810-01) can be purchased from Cisco.

For information about cable pinouts, refer to the online document Cisco Modular Access Router Cable Specifications. This document is available online and on the Cisco Documentation CD-ROM.

Cisco 3600 Series Routers Hardware Installation Guide

C-2 OL-2056-05