Resetting a Cisco 2600 router is a critical procedure for network engineers and administrators who need to recover from configuration errors, forgotten passwords, or corrupted IOS images. The Cisco 2600 series, while aging, remains in operation in many legacy environments, making the ability to restore these devices a vital skill. This process involves interacting with the router's bootloader, commonly known as ROM Monitor (ROMMON), to bypass the current configuration and reload the device.
Understanding the Context for a Reset
Before initiating a reset, it is essential to understand precisely why it is necessary. The goal is typically to recover from a specific scenario rather than to perform routine maintenance. These scenarios include situations where the configuration register is misconfigured, preventing the router from loading the correct IOS image or startup configuration. Another common trigger is an unknown or forgotten enable password, which locks administrative access to the device. In some cases, the IOS image itself may be corrupted or deleted, requiring a reload or replacement. A reset via ROMMON effectively returns the device to a state where these fundamental boot processes can be addressed without the interference of the existing software configuration.
Preparation and Physical Access
Unlike a software command executed from a terminal, a reset requires physical interaction with the router. You must have direct console access to the device, typically using a rollover cable connected to a PC with terminal software like PuTTY or Tera Term. Before powering down the device, it is prudent to document any remaining configuration snippets or verify the current IOS version located on the flash memory. Ensure you have the necessary image files ready if the reset process indicates that the router cannot locate a valid IOS. The physical environment should be stable, ensuring the router is plugged into a reliable power source to avoid interruption during the reload sequence.
Initiating the Reset Sequence
The reset is triggered by interrupting the boot process as the router powers on. While the device is receiving power, you must send a break signal or press the interrupt key combination within the first 60 seconds of the boot process. For most Cisco 2600 models, this involves pressing the Ctrl and Break keys on your console terminal keyboard simultaneously. You should look for specific prompts in the terminal window indicating that the router has halted the boot cycle and is waiting for ROMMON commands. Seeing the ">" or "rommon 1 >" prompt confirms that you have successfully broken into the bootloader and can proceed with the configuration change or reload.
Command Syntax and Configuration Register
Once in ROMMON, the primary goal of the reset is to alter the configuration register value. The default value is usually 0x2102, which tells the router to load the startup configuration from NVRAM. To bypass the corrupted configuration, you change this value to 0x2142. This specific hexadecimal value instructs the router to ignore the startup configuration stored in NVRAM during the next boot sequence. To execute this, you type the command config-register 0x2142 at the rommon prompt. After setting this value, you proceed to the final step of rebooting the device using the reset or boot command.
Post-Reset Configuration and Verification
After the router completes the reset and reloads, it will boot as if it has never been configured. You will typically be greeted with the initial setup dialog or a prompt indicating that there is no startup configuration present. At this point, the device is unlocked, and you can regain administrative access. The immediate priority is to restore basic connectivity and verify the integrity of the IOS image. You should check the current configuration register to ensure it has been set correctly and then reload the device again to return it to the normal operating state (0x2102). This second reload ensures the router boots normally using the restored or new configuration.
