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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 networks and associated applications is the lack of a lab for learners to play. 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 better processor and more RAM on the host machine will improve the GNS3 experience, which is valid with every application.

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

Testers:

  • TBD

Phase I – Install GNS3 Environment

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

Picture of the GNS3 Workspace
Figure 14 – GNS3 Workspace
  1. Navigate to GNS3 at https://www.gns3.com/
  2. Click on the Free Download button
  3. Select Windows or Linux as appropriate, and then Download
  4. Create your GNS3 Community Account as prompted, login, and then return to the download page

    NOTE: As of 22 Jan 2025, No one has reported spam from this registration.

  5. Run the installer you downloaded and accept the default options. If 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 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 at https://www.gns3.com/software/download-vm
  2. Select the image for VirtualBox
  3. Extract (unzip) the .zip file

    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. Download and launch https://www.virtualbox.org/wiki/Downloads
  5. Select File → Import Appliance → Import
    Depiction of the menu items to click on.
    Figure 1 – Import appliance
  6. Navigate to the .ova file (“GNS3 VM.ova”) you downloaded and unzipped. In this example, our .ova file is named “GNS3 VM.ova”
  7. Select the .ova file and click on “Open”
    Depiction of the menu items to click on.
    Figure 2 – Importing GNS3 VM
  8. Click Next
    Depiction of the menu items to click on.
    Figure 3 – Importing an appliance
  9. Click Finish to accept the default appliance settings
    Depiction of the menu items to click on.
    Figure 4 – Appliance settings in VirtualBox
  10. Adjust the network settings of the GNS3 VM by selecting the VM and then selecting settings
    Depiction of the menu items to click on.
    Figure 5 – Clicking on settings in VirtualBox
  11. 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
    Depiction of the menu items to click on.
    Figure 6 – Selecting the network adapter in VirtualBox

    NOTE: If no Host-only adapter is available, your VirtualBox version may need to be updated or reinstalled. If the VM still will not launch properly, then open Device Manager -> Network adapaters -> Virtualbox Host-Only Ethernet Adapter -> Disable Device. Re-enable the device again and restart VirtualBox.

  12. Finally, start the GNS3 VM you installed to ensure it runs properly. This is a very lightweight version of Linux
    Depiction of the menu items to click on.
    Figure 7 – GNS3 VM settings
  13. 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 settings use VMWare, and we are using VirtualBox. Alternatively, VMware is now free for personal use, but at the time the book was written, the free version did not function with GNS3. We are trying to keep things free for learners to learn and not make them spend money.

Also, if you mess up the configuration, you can always re-run the setup wizard. On the GNS3 toolbar, click Help –> Setup Wizard.

  1. Launch GNS3

    NOTE: Sometimes, VPNs will interfere with GNS3’s correct functioning. 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 GNS3 default setting is to use VMWare by default so you will get an error. Select OK and choose VirtualBox
    Depiction of the menu items to click on.
    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. 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 show green lights and details of 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
  9. When you start GNS3, it can take a minute or two while the GNS3 VM launches. The indicator will remain grey until it is fully running

Phase IV Final note – Disabling KVM

Depending on the hardware of your bare-metal machine, you may get an error stating 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.

  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
End of Lab

 

License

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Mastering Enterprise Networks 2e 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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