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Learn how to fix the problem of Python scripts getting stuck while exiting configuration mode on Cisco IOS devices using `telnetlib`.
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Resolving Telnet Exit Issues in Python Scripts for Cisco IOS Devices

When automating network devices using Python, many programmers encounter common pitfalls associated with telnet connections. One such issue arises when trying to exit configuration mode on Cisco IOS devices. This guide aims to identify this problem and provide a clear solution for those using Python's telnetlib library.

Understanding the Problem

You may have successfully written a script to configure a Cisco Multilayer switch in GNS3, but face frustration when the script fails to exit configuration mode. During execution, commands such as exit or end are sent to the device, but the process gets stuck, requiring you to manually clear the session.

Here's a brief outline of the symptoms:

Successfully executing configuration commands like int loop 2 and ip address 1.1.1.2 255.255.255.255.

The script hangs when attempting to exit configuration mode using exit or end.

The last exit or end command is problematic as it is removing the initial letter 'e'.

The Solution: Encoding Exit Commands

The root of the issue lies in how commands are sent over the telnet connection. The commands issued by the script must be properly encoded to prevent unexpected behavior. The solution is quite simple. You need to use Python’s string encoding capabilities when writing the exit command to the telnet connection.

Correcting the Exit Command

Instead of writing the command directly, you should encode it properly using str.encode(). Here’s the change that should be made in your script:

Before

[[See Video to Reveal this Text or Code Snippet]]

After

[[See Video to Reveal this Text or Code Snippet]]

By making this adjustment, your script should correctly interpret the exit or end command without altering the string.

Revised Code Snippet

Here's how your modified telnet script will look after implementing this change:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In conclusion, resolving the telnet exit issue when automating network configurations with Python can be achieved through proper string encoding. By utilizing the str.encode() method, you can ensure that your exit commands function as intended without hanging or altering characters.

By following the guidelines in this guide, you should find your Python script working successfully, allowing for seamless exits from configuration mode on your Cisco IOS devices.

For anyone facing similar challenges, this simple fix can save time and reduce frustrations during network programming.