Installing a GNS3 Server on Ubuntu

Now that I finally have some free time, I am starting to build out my homelab. One of the first tools that I am building is a GNS3 server that runs on an Ubuntu VM in Proxmox.

Table of contents

Version Info

• Proxmox: 9.1.4
• GNS3 Server: 2.2.55

This guide walks through setting up a GNS3 Server inside an Ubuntu Server VM running on Proxmox. This approach keeps GNS3 isolated, enables better performance with nested virtualization, and works well for home labs and remote access setups.

1. Create an Ubuntu Server VM on Proxmox

Download Ubuntu Server ISO

Download an Ubuntu Server install image from the official Ubuntu website (for example, Ubuntu 22.04 LTS).

Upload the ISO to Proxmox

You can upload the ISO either through the Proxmox Web GUI or via secure copy (scp).

Option A: Proxmox Web GUI

1. Expand your Proxmox node in the left navigation pane
2. Click on the local storage
3. Open the ISO Images tab
4. Click Upload and select the Ubuntu Server ISO

Option B: Secure Copy (scp)

From your local machine, copy the ISO to the Proxmox ISO directory:

scp ubuntu-22.04.5-live-server-amd64.iso root@192.168.0.123:/var/lib/vz/template/iso/

Create the Virtual Machine

In the Proxmox web interface:

1. Click Create VM
2. Select the uploaded Ubuntu ISO as the installation media
3. Allocate resources appropriate for GNS3

Recommended minimums:

• Memory: 8 GB RAM
• Storage: 32 GB

Enable Nested Virtualization

During VM creation, when you reach the CPU configuration step:

• Enable Nested Virtualization
• Set nested-virt = on under Extra CPU Flags

This is required for running virtualized network appliances inside GNS3.

2. Install Ubuntu Server

1. Boot the VM
2. Open the console from the Proxmox UI
3. Follow the Ubuntu Server installer prompts

Once installation completes:

1. Shut down the VM
2. Start it again

This ensures the installation media is detached and the system boots from disk.

3. Install the GNS3 Server

After logging into the VM, install the GNS3 server using the official installation script.

Run the Installation Script

As root, run:

cd /tmp
curl https://raw.githubusercontent.com/GNS3/gns3-server/master/scripts/remote-install.sh > gns3-remote-install.sh
bash gns3-remote-install.sh --with-iou --with-i386-repository

Notes

• The --with-iou option enables IOU support
• The --with-i386-repository option is required for some legacy images
• The --with-openvpn option is not used here, since this setup assumes access from a trusted home network

4. Verify the GNS3 Server

Check that the GNS3 service is running:

systemctl status gns3

If running correctly:

• The server listens on port 3080 by default
• It is reachable at the VM’s IP address

To confirm the listening port:

sudo ss -tulnp | grep gns3

5. Add the Remote Server to GNS3

On your local machine, open GNS3 and configure the remote server:

1. Go to Edit → Preferences → Server
2. Uncheck Enable local server
3. Enter the VM’s IP address in the Host field
4. Enter the credentials for the GNS3 server

Default credentials:

• Username: gns3
• Password: gns3

Apply the changes and restart GNS3 if prompted.

Future

• Integrating the server with Tailscale or VPN access
• Automating VM creation with Terraform or Ansible