GNS3 Overview

GNS3 is a network emulation software used to simulate, design and test network topologies of varying degrees of complexity.

• It lets you create topologies by dragging different types of devices on a canvas and connecting them with virtual cables.
• It uses Dynamips to emulate a subset of Cisco devices such as switches and routers
• It integrates with QEMU (Quick Emulator), allowing you to virtualize your own custom devices such as servers and PCs.
• It integrates with Wireshark letting you capture and inspect live traffic data moving across your virtual cables
• You can connect your virtual network topologies to real physical network equipment, enabling you to test your virtual networks under real world conditions.

GNS3 has two parts: a client (the GUI your interact with) and a server responsible for running the simulations. The server can run either on your local machine or on a remote server for enhanced performance.

On Linux, GNS3 server runs natively on your machine. On Windows and macOS it runs inside a virtual machine called GNS3 VM, which needs a hypervisor to host it.

Windows11 | macOS
  └── hypervisor (Hyper-V, VMware, or VirtualBox)
        └── GNS3 VM
            └── emulated devices

Because the emulated devices are virtual machines running inside another virtual machine, the hypervisor must support nested virtualization. Without it, devices still run but performance takes a big hit, which makes multi-device topologies practically unusable.