: The most reliable method is purchasing a personal license for Cisco Modeling Labs . Once purchased, you can download the refplat.iso file containing IOSv-L2 , IOSv , ASAv , and Nexus images to import into GNS3.
Start GNS3 and the GNS3 VM
These are Linux-based virtual images. They are significantly more stable, support more modern features (like advanced switching and API calls), and are the current standard for professional network simulation. Installation and Configuration cisco switch ios image download for gns3 install