tailieunhanh - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 69

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 69 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 649 Tuesday May 20 2003 2 53 PM Locating and Loading Cisco IOS Software 649 Example 14-3 Booting from ROM Router configure terminal Router config boot system rom Ctrl-Z Router copy running-config startup-config Lab Activity Using the boot system Command In this activity you gather information about the Cisco IOS Image and determine its boot source. You also check the config register settings and document a fallback boot sequence. Configuration Register Values The order in which the router looks for Cisco IOS Software images to load depends on the boot field setting in the configuration register. You can change the default configuration register setting with the global configuration command config-register. Use a hexadecimal number as the argument for this command as shown in Example 14-4. Example 14-4 Chaging the Boot Field Setting in the Configuration Register Router configure terminal Router config config-register 0x10F Ctrl - Z The configuration register is set so that the router examines the startup file in NVRAM for boot system options. The configuration register is a 16-bit register in NVRAM. The lowest 4 bits of the configuration register bits 3 2 1 and 0 form the boot field. To change the boot field and leave all other bits set at their original values follow these guidelines Set the configuration register value to 0x100 if the ROM monitor needs to be entered. This setting is primarily a programmer s environment. Boot the operating system manually from the ROM monitor. Use the b command at the ROM monitor prompt to boot the system. This value sets the boot field bits to 0-0-0-0. Set the configuration register to 0x101 to configure the system to boot automatically from the limited Cisco IOS Software image in ROM. This value sets the boot field bits to 0-0-0-1. Page 650 Tuesday May 27 2003 2 16 PM 650 Chapter 14 Managing Cisco IOS Software Set the configuration register to any value from 0x102 to 0x10F to configure the system to use