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• power back on a router after power off for a while
• there is lightning strike around
• unprotected power outlet (i.e. no UPS)
• after configuring a router, you reload the router
• after installing new IOS image, you reload the router to let the new IOS image become active
• you implemented a wrong config register value
First step to take is to verify whether the router actually lost configuration. In order to do so, you might want to check the config register value to verify if it is 0x2102 (the default) or else. When the config register value is not set as 0x2102, then the router might act differently than the default.
Following is an example. Let's say the router config register value is set to 0x2142. By having such value, the router will never load saved configuration every time the router boots up from either power up, power cycle, or reload command. The router ignores the saved configuration and instead boots up using default (blank) configuration.
Such abnormal behavior is typically unwanted at any time. To avoid, you need to set the value back to the 0x2102.
To find out what the current router config register value is, you can simply do a "show version" from the CLI prompt and look at the last line.
To set the value back to 0x2102 (default value), one way of doing it is via the CLI with following commands
If for some reason the router goes to ROMMON mode, you can issue the 0x2102 value with following command
When the router has 0x2102 config register value, the router will act as factory recommended (Cisco recommended) including loading the current configuration after reload or power cycle.
When you are in luck, there is one possibility is that the router still has the configuration even though the router does not boot the configuration. This situation applies when the router configuration prior reload or prior power loss is saved (by issuing "copy running-config startup-config" or "write memory" prior).
Configuration Register Setting Descriptions
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