Understanding the o/r 0x2142 command In ROM Monitor or during password recovery, what does setting the configuration register to 0x2142 (for example via 'o/r 0x2142') accomplish on a Cisco router?

Introduction / Context:
Password recovery and emergency maintenance sometimes require booting a router without loading the startup-config from NVRAM. Cisco devices use a configuration register that influences boot behavior. Setting it to a special value, commonly 0x2142, instructs the router to ignore NVRAM at next boot, allowing administrators to safely enter and change passwords and other settings.

Given Data / Assumptions:

• You can access ROMMON (ROM Monitor) or otherwise set the configuration register.
• You intend to preserve but temporarily bypass the startup-config.
• The device will be reloaded after the change.

Concept / Approach:

The configuration register's low-order bits control boot behavior. Value 0x2142 tells IOS to ignore the NVRAM startup-config upon boot. After the router boots to default settings, you can copy the saved configuration into running-config, reset passwords, and then restore the register to the normal 0x2102 before saving and reloading.

Step-by-Step Solution:

Verification / Alternative check:

show version displays the current configuration register. After fixes, confirming 0x2102 ensures normal boots will use the startup-config again.

Why Other Options Are Wrong:

• Restarting, entering ROMMON, or viewing a lost password are not the direct effects of 0x2142.
• Forcing ROM image boot is controlled by other config-register bits and boot statements, not strictly 0x2142.

Common Pitfalls:

• Forgetting to revert to 0x2102, causing future boots to ignore configuration.
• Accidentally overwriting the original configuration by saving before copying it into running-config.

Final Answer:

It is used to bypass the configuration in NVRAM.