GNS3

GNS3, short for Graphical Network Simulator-3, is a cross-platform open-source network emulation software that enables the design, testing, and demonstration of complex networks. It combines emulation engines such as Dynamips for Cisco IOS, as well as QEMU, VirtualBox, and Docker to run real operating-system images inside a simulated network. The software provides a graphical user interface to build topologies by dragging devices onto a canvas, connecting them with links, and configuring devices through consoles and startup scripts. A GNS3 project consists of devices, links, and per-device configurations, and can be run locally or on a remote server.

GNS3 supports a wide range of devices, including Cisco routers and switches via IOS images, as well as devices from other vendors that provide supported virtual images. It enables multi-vendor labs, WAN simulations, and edge-network topologies. Real-time features include packet capture with Wireshark, performance statistics, and direct console access. The platform integrates with virtualization and container technologies such as VMware, VirtualBox, and Docker, enabling hybrid lab environments. GNS3 runs on Windows, macOS, and Linux, and uses a client-server architecture: the GUI communicates with a background GNS3 server that orchestrates the emulation engines.

Typical use cases include network certification practice, protocol testing, and lab automation for networking professionals and students. The project is open-source and maintained by a community of developers, with optional paid training and support provided by third-party organizations. GNS3 remains widely used in education, IT labs, and professional preparation for networking certifications.