| 5.1 |  | Router Boot Sequence and Verification |
| 5.1.4 |  | Configuration register |

| The order in which the router looks for system bootstrap information depends on the boot field setting in the configuration register. The default configuration register setting can be changed with the global configuration mode command config-register. Use a hexadecimal number as the argument for this command. The configuration register is a 16-bit register in NVRAM. The lowest four bits of the configuration register form the boot field. To ensure that the upper 12 bits are not changed, first retrieve the current values of the configuration register using the show version command. Then use the config-register command, changing only the value of the last hexadecimal digit. To change the boot field in the configuration register, follow these guidelines: To enter the ROM monitor mode, set the configuration register value to 0xnnn0, where nnn represents the previous value of the non-boot field digits. This value sets the boot field bits to 0000 binary. From ROM monitor, boot the operating system manually by using the b command at the ROM monitor prompt. To configure the system to boot automatically from ROM, set the configuration register to 0xnnn1, where nnn represents the previous value of the non-boot field digits. This value sets the boot field bits to 0001 binary. To configure the system to use the boot system commands in NVRAM, set the configuration register to any value from 0xnnn2 to 0xnnnF, where nnn represents the previous value of the non-boot field digits. These values set the boot field bits to a value between 0010 and 1111 binary. Using boot system commands in NVRAM is the default.
| Lab Activity e-Lab Activity: Configuration Register In this lab, the students will learn to change the boot procedure of the router.
| Web Links config-register Global Configuration Command http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_command_reference_ chapter09186a00800ca743.html#1017887