Standard Break Key Sequence Combinations During Password Recovery

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Introduction

This document provides standard break key sequence combinations for the most common operating systems, and some tips on how to troubleshoot problems.

The Electronic Industries Association RS-232 logic level uses +3 to +25 volts to signify a Space (Logic 0) and -3 to -25 volts for a Mark (logic 1). A break signal is when the data line remains in the space condition for a specified duration, usually 100 ms to 1/2 second. All characters begin with a start bit and end with a stop bit (and also a parity bit or two). The level condition of the start and stop bits is always opposite. So, no character combination can look like the break signal. A break signal enables you to access a ROM Monitor on Cisco IOS® devices when a password recovery is necessary.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Standard Break Key Combinations

Tips to Troubleshoot

• Problems that you encounter during password recovery often occur because you are not sure about what the break key sequence is for the (non-Cisco) software you use. For software not listed in the table, and for additional information, refer to the documentation of the individual software packages.



• The auxiliary (AUX) port is not active during the boot sequence of a router. Therefore, it is no use if you send a break through the AUX port. You need to have connection to the console port, and have these settings:
  
  9600 baud rate
  
  No parity
  
  8 data bits
  
  1 stop bit
  
  No flow control


• Some versions of Windows NT have hyperterminal software that cannot send the correct break key signal. Visit http://www.hilgraeve.com/htpe/index.html for an upgrade of the hyperterminal software.

How to Simulate a Break Key Sequence

Break key sequence simulation is useful if your terminal emulator does not support the break key, or if a bug does not allow your terminal emulator to send the correct signal.

Note: The hyperterminal under Windows NT had this behavior in the past.

Complete these steps to simulate a break key sequence:

1. Connect to the router with these terminal settings:
   
       1200 baud rate
       No parity
       8 data bits
       1 stop bit
       No flow control
   You no longer see any output on your screen, and this is normal.


2. Power cycle (switch off and then on) the router and press the SPACEBAR for 10-15 seconds in order to generate a signal similar to the break sequence.
3. Disconnect your terminal, and reconnect with a 9600 baud rate. You enter the ROM Monitor mode.

If all these methods fail to properly send a break, retry the procedures from a different terminal or PC platform.

I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. Achieving your CCNA certification is much more than just memorizing Cisco exam material. It is having the real world knowledge to configure your Cisco equipment and be able to methodically troubleshoot Cisco issues. So I encourage you to continue in your studies for your CCNA exam certification.