2 Setting Up a GNS3 Environment

Mathew J. Heath Van Horn, PhD

I’ve been teaching networking principles for many years. In my experience, one of the biggest obstacles to learning about networks and related applications is the lack of a lab for learners to practice. Graphical Network Simulator 3 (GNS3) solves many of those problems. GNS3 uses few hardware resources and can emulate complex networks using authentic images. Students no longer require access to a dedicated lab or to spend money on cloud architectures. GNS3 can be installed and used on most laptops on the market. A faster processor and more RAM on the host machine will improve the GNS3 experience, which applies to any application.

This installation is based on Windows 11, and you will need to install Oracle VirtualBox. Oracle provides detailed instructions for installing VirtualBox, which will not be repeated here.

Installing the optional extension pack can be helpful, but it is limited to personal use only, not commercial or enterprise use. A few of the features used are:

  • USB2/3 support
  • Webcam passthrough
  • PXE Boot
  • Some VM displays are better when the extension pack is used

Note: VirtualBox now splits VM settings into basic and expert modes. Most of this textbook requires expert mode.

Phase 0 – Professional Alignment

Enterprise networks are designed, tested, and maintained in virtual environments before changes are deployed to production systems. In this chapter, you will build the virtual lab environment that supports the hands-on exercises throughout this book while developing foundational skills used by network administrators, systems administrators, and cybersecurity professionals.

DCWF

The knowledge and skills developed in this chapter align with the following Department of Defense Cyber Workforce Framework (DCWF) work roles:

  • 511 – Network Operations Specialist
  • 531 – Systems Administrator
  • 451 – System Security Analyst

NICE Work Roles

This chapter supports competencies associated with the following NICE Workforce Framework for Cybersecurity work roles:

  • Network Operations Specialist
  • Systems Administrator
  • Cyber Defense Infrastructure Support Specialist

Professional Skills

By completing this chapter, you will begin developing the ability to:

  • Install and configure enterprise network simulation software.
  • Deploy and manage virtualization platforms that support enterprise networking.
  • Configure host and guest networking to support virtual lab environments.
  • Verify communication between virtual devices and the host operating system.
  • Troubleshoot software installation, virtualization, and network connectivity issues.
  • Prepare a repeatable laboratory environment for enterprise networking and cybersecurity exercises.

What you’ll be able to do

After completing this chapter, you should be able to:

  • Install GNS3 and Oracle VirtualBox on a supported operating system.
  • Configure the GNS3 virtual machine and supporting software components.
  • Import and configure the appliances required for subsequent laboratory exercises.
  • Verify connectivity between the host operating system and the virtual networking environment.
  • Troubleshoot common installation, configuration, and connectivity problems.
  • Prepare a fully operational lab environment for use throughout the remaining chapters.

Learning Objectives

  • Create a working GNS3 Learning Environment on a PC or laptop

Prerequisites

Deliverables

  • None – This is for student needs

Resources

contributors and testers

  • Kyle Wheaton, Cybersecurity Student, ERAU-Prescott

Phase I – Install GNS3 Environment

There are two parts to GNS3: the GNS3 Working Environment and the GNS3 Virtual Machine (VM). This phase covers the installation of the GNS3 environment.

The GNS3 Workspace
Figure 14 – GNS3 Workspace
  1. Navigate to the GNS3 website

    NOTE: There is an experimental version of GNS3 (version 3.x.x). At the time of this writing, it is unstable. Stay within GNS3 versions 2.x.x and everything should work fine.

  2. Click on the Free Download button
  3. Select Windows and then Download 
  4. Create your GNS3 Community Account as prompted, log in, and then return to the download page

    NOTE: As of 30 May 2026, no one has reported spam from this registration.

  5. Run the installer you downloaded and accept the default options. Not all systems reported these prompts, but if you are prompted:
      • Permit uBridge to run as root to capture packets
      • Do not accept the free offers
      • Do NOT start GNS automatically! Doing so can distract new learners due to the expected errors that will pop up

Phase II – Install the GNS3  VM (Virtual Machine)

This is where you will install the GNS3 VM. Remember, the GNS3 Working Environment and the GNS3 VM must be the same version.

  1. Navigate to the GNS3 VM download page
  2. Select the image for VirtualBox
  3. Extract (unzip) the .zip file

    NOTE: We recommend using 7-Zip because we encounter fewer errors when unzipping files than with the Windows built-in unzipping program.

    NOTE: You may get two errors while unzipping the file, and it will show 99% completion. This happens on occasion and does not affect the extracted file.

  4. Start Oracle VirtualBox Manager
  5. Select File → Import Appliance → Import
    Depiction of the menu items to click on.
    Figure 1 – Import appliance
  6. Click the folder and navigate to the .ova file (“GNS3 VM.ova”) you downloaded and unzipped. In this example, our .ova file is named “GNS3 VM.ova”
    Select the GNS3 VM file
    Figure 1.1 – Select the GNS3 VM file
  7. Select the .ova file and click on Open
    Depiction of the menu items to click on.
    Figure 2 – Importing GNS3 VM
  8. Click Finish
    Importing the GNS3 VM appliance
    Figure 3 – Importing the GNS3 VM appliance
  9. Adjust the network settings of the GNS3 VM by selecting the VM and then selecting settings
    Clicking on settings in VirtualBox
    Figure 5 – Clicking on settings in VirtualBox
  10. In the network settings, under Network Adapter 1, select the name of the host-only adapter drop-down arrow. YES, even if the correct name is already in the box. Just do it, and click OK. If you don’t do this, you will get a network error when you start the virtual machine
    Selecting the network adapter
    Figure 6 – Selecting the network adapter

    NOTE: If no Host-only adapter is available, your VirtualBox version may need to be updated or reinstalled. If the VM still does not launch properly, open Device Manager -> Network adapters -> VirtualBox Host-Only Ethernet Adapter -> Disable Device. Wait about 10 seconds, then re-enable the device and restart VirtualBox.

  11. Finally, start the GNS3 VM you installed to ensure it runs properly. This is a very lightweight version of Linux
    GNS3 VM running
    Figure 7 – GNS3 VM running
  12. Stop the GNS3 VM

Phase III – Configure GNS3

Now, we will configure the GNS3 working environment for first-time use. You may encounter many errors when it first starts. This is normal because the GNS3 default Windows settings use VMWare, and we are using VirtualBox.  If you mess up the configuration, you can always re-run the setup wizard by navigating to the GNS3 toolbar and clicking on Help –> Setup Wizard.

  1. Launch GNS3

    NOTE: Sometimes, VPNs can interfere with GNS3’s proper operation. It is recommended that they be disabled before launching GNS3.

    NOTE: You may see the prompt “uBridge requires root permissions to interact with network interfaces.” Say YES. This allows you to connect GNS3 with the actual network if desired.

    NOTE: Sometimes, GNS3 asks you to name a new project. If so, pick any name and click OK.

  2. Next, choose how to run your GNS3 network simulations by selecting Run appliances in a virtual machine
    Depiction of the menu items to click on.
    Figure 8 – GNS3 working environment setup wizard
  3. Accept the defaults for the Local Server Configuration and click Next
    Depiction of the menu items to click on.
    Figure 9 – GNS3 Setup Wizard – Local Server Configuration
  4. You should get a successful message. Click Next
    Depiction of the menu items to click on.
    Figure 10 – GNS3 Setup Wizard – Local Server Status
  5. The Windows GNS3 default setting is to use VMWare, so you will get an error. Select OK and choose VirtualBox
    GNS3 Error message
    Figure 11 – GNS3 error, cannot find GNS3 VM in VMWare
  6. When you change the radio button, the GNS3 VM you imported and started in VirtualBox earlier should auto-populate. Use the default settings and click Next
    Depiction of the menu items to click on.
    Figure 12 – GNS3 VM Setup Wizard Changing to VirtualBox
  7. Then select Finish
    Depiction of the menu items to click on.
    Figure 13 – Finish Setup Wizard
  8. In a minute or two, you should have a screen like the one in Figure 14. The windows are adjustable, but the window to take note of is the “Servers Summary.” You should see your bare-metal machine (in Figure 14, it is Dr. HVH) and the GNS3 VM, which shows green lights and details on how many resources are being used. If the server indicator light is still grey, power off the GNS3 VM and restart the GNS3 Working Environment
    Depiction of the menu items to click on.
    Figure 14 – this is what your screen should look like after finishing the Setup Wizard

     

Phase IV Final note – Disabling KVM

Depending on your bare-metal machine’s hardware, you may see an error indicating that KVM acceleration cannot be used. Turn off KVM support in the gns3_server.conf by adding enable_kvm = false to the [Qemu] section. Follow the steps below.

NOTE: If your routers and switches never seem to boot up (indicating throttling and appearing as lines of code streaming upward), you must follow these steps to disable KVM.

  1. Start the GNS3 VM in VirtualBox
  2. Use the cursor keys to navigate to configure
    Depiction of the menu items to click on.
    Figure 15 – Disabling Qemu settings in the GNS VM
  3. Add the following lines to the bottom: [Qemu] enable_kvm = false
    Depiction of the menu items to click on.
    Figure 16 – Disabling Qemu for the GNS3 VM
  4. Press <ctrl> O  to write out the file (e.g. save the file)
  5. Accept the path by pressing <enter>
  6. Press <ctrl> X to exit
  7. Restart the GNS3 VM

NOTE: The GNS3 VM controls all non-VM devices. As you complete labs, you will add many routers and switches. If your routers and switches start lagging, you may want to increase the cores and RAM of the GNS3 VM.

Career Connection

Virtual laboratory environments are an essential part of modern IT operations. Network engineers, systems administrators, cybersecurity analysts, and cloud professionals routinely use tools such as GNS3 and virtualization platforms to design, validate, troubleshoot, and document network solutions before implementing them in production. The skills developed in this chapter establish the foundation for safely building, testing, and maintaining enterprise networks throughout your career.

End of Lab

Feedback email
Figure 00 – Contact us via prmaster@erau.edu

License

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Mastering Enterprise Networks 3e Copyright © 2024 by Mathew J. Heath Van Horn is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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