No matter for an end-user or a company, you may hope your new bought router to benefit you best; thus, it’s necessary to restore the router to factory settings. Now, there are the simple but practical tips for resetting Cisco routers:
1. To erase the configuration file, issue the erase nvram: command.
Reload the router by issuing the reload command.
2. If this does not solve the problem, attempt to break into ROM Monitor (ROMmon) by issuing the break sequence (usually Ctrl and break from the Hyperterminal) from a console connection.
You should see this ROMmon prompt:
3. Change the configure register value to ignore the startup configuration by issuing the confreg command, as shown in this example:
rommon 2> confreg 0×2142
4. To reload the router, issue the reset command, as shown in this example:
rommon 3> reset
5. After the router boots, issue the enable command at the Router > prompt.
The prompt changes to Router#, indicating that the router is now in privileged mode.
6. To enter config mode, issue the config terminal command.
You should now see a Router(config)# prompt.
7. To change the configure register to recognize the startup configuration, issue the config-register command, as shown in this example:
Router (config)# config-register 0×2102
To break out of configuration mode, press Ctrl and Z.
To save the blank configuration, issue the copy-running config-startup config command.
These tips on resetting to factory default setting are suitable for all Cisco routers.
Note: The configurations below are stored in ROMMON, and cannot be reset to Factory Default Settings by the write erase or config-register 0×2142 commands.
memory-size iomem <not default>
Verify if you are resetting successfully
Use this information to ensure whether your router has been returned to the factory defaults or not.
show running-config—Used to verify that the previous running configuration has been erased. The user should be left with a skeleton configuration. For example, there should be no IP addresses configured under any interface on the router.
show version—Used to verify that the configuration register is set to the default value of 0×2102.
The material is referred from: networkequipment.net/2012/02/10/how-to-reset-a-cisco-router-to-factory-settings/
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