If you have built a home lab (or are running really ancient hardware in production), you may find yourself in need of resetting the password configured on a 2500 series router. Depending on the router platform, the syntax is different. Here's how to do it on a 2500:
1. Reboot the router and send a break sequence to enter ROMMON mode. Break sequences can be sent using a Ctrl+Break key combination, or if you are on a system that doesn't have a break sequence, try using your terminal software to send a break sequence.
2. (optional) Type the letter O and hit enter. Record the existing setting, it's most likely 0x2102.
3. To reset the configuration register and have the router bypass the startup-config, type the following:
To boot the router, type the letter i and hit enter.