GNS3 helps you build graphic models of computer networks, and simulate networks of different levels of complexity. This program can be used by students that are trying to get various certifications, but also by network engineers and other professionals. It comes as an open-source solution that runs on all popular Windows versions.
GNS3 comes with a lot of comprehensive documentation regarding its features and tools, as well as their functionality. Moreover, its graphical user-interface was designed in such way that you will not feel the need to further customize it. The main window of the program allows you to drag network components (various routers, firewalls, switches, guests, etc.) and drop them on the working area. You are afterward enabled to create different connections between them, while taking into consideration the network standards, of course. GNS3 supports link types like: Ethernet, GigaEthernet, ATM, FastEthernet, POS, Manual, Serial, etc.
GNS3 comes with additional components that are specific to network simulations. It enables you to install tools like: Dynamips, VirtualBox, Qemu, Dynagen, etc. Therefore, any user that is into this complex field of computing can use GNS3 for simulating various network models.