Specifications

D-1

Cisco 3900 Series, 2900 Series, and 1900 Series Integrated Services Routers Software

OL-21850-01

APPENDIX

Changing the Configuration Register Settings

The following sections describe the 16-bit configuration register in NVRAM in the Cisco 3900 series,

2900 series, and 1900 series integrated services routers (ISRs):

• About the Configuration Register, page D-1

• Changing the Configuration Register Settings, page D-4

• Displaying the Configuration Register Settings, page D-5

• Configuring the Console Line Speed (Cisco IOS CLI), page D-5

About the Configuration Register

The router has a 16-bit configuration register in NVRAM. Each bit has value 1 (on or set) or value 0 (off

or clear), and each bit setting affects the router behavior upon the next reload power cycle.

You can use the configuration register to

• Force the router to boot into the ROM monitor (bootstrap program)

• Select a boot source and default boot filename

• Enable or disable the Break function

• Control broadcast addresses

• Recover a lost password

• Change the console line speed

Table 1 describes the configuration register bits.

Table 1 Configuration Register Bit Descriptions

Bit

Number Hexadecimal Meaning

00–03 0x0000–0x00

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 OEM

bit enabled.