Fixing VT-x/EPT and KVM Issues in GNS3 VM: A Complete Troubleshooting Guide

GNS3 is a powerful network simulation tool but running it smoothly on a virtual machine (VM) often requires hardware virtualization support, such as VT-x/EPT for Intel processors or AMD-V/RVI for AMD processors. If these features are not properly enabled, you may encounter errors preventing GNS3 VM from running KVM acceleration, leading to poor performance or failed startups. This guide will walk you through the common causes of VT-x/EPT and KVM issues in GNS3 VM and provide step-by-step solutions to resolve them. The image below depicts the first error you're likely to encounter when you launch the GNS3 software after installation.

This issue arises due to incorrect virtualization settings or conflicts with Windows features like Hyper-V. A quick workaround is to disable the Intel VT-x/EPT option in the VM settings. However, after doing so, you may encounter another error when importing appliances, which is related to the Kernel-based Virtual Machine (KVM). The specific error code may vary depending on the operation being performed.

At this stage, you might feel frustrated and consider relying solely on Cisco Packet Tracer for your tasks. However, the following steps will resolve these issues and ensure GNS3 runs smoothly on your computer. 

Step 1

Click the Start Menu button and search for "Turn Windows features on or off." Once the window opens, scroll through the list and uncheck the following options:

• Hyper-V
• Virtual Machine Platform
• Windows Hypervisor Platform

After unchecking these options, click "OK." You will be prompted to restart your computer to apply the changes. However, before restarting, there's one more setting to adjust in Windows Security to prevent further conflicts

Step 2
Click the Start Menu button again and search for Windows Security and select Device Security.

In the Device Security section, locate and click on Core Isolation details. There, you'll find the Memory Integrity toggle, simply toggle it off as shown in the images below.

You'll be prompted to restart your PC after this step. Once your system has fully booted, open the VMware Workstation app, go to Edit Virtual Machine Settings, and confirm that the Intel VT-x/EPT option is enabled, as shown below.

By now, GNS3 should function without errors. Keep in mind that the software consumes a significant amount of memory due to custom appliances, so having at least 16GB of RAM is recommended for optimal performance.

If you encounter any issues not covered in this guide, feel free to leave a comment below. Attaching a screenshot of the error will greatly help with troubleshooting.

Credits: Donfaruk19