GNS3

GNS3 is a graphical network simulation software that allows users to design, configure, and test complex network topologies in a virtual environment. It works by combining real Cisco IOS images or open-source network operating systems with virtual machines to emulate hardware behavior, enabling engineers to build lab environments without the need for physical equipment. It uses a drag-and-drop interface that facilitates the creation and troubleshooting of routed and switched networks, making it a standard tool for study, certification preparation, and proof-of-concept testing.