The original cisco IOS image files of routers, switches, and firewalls, which can be used to create a network with gns3 and get the feel of working with real router. for more information for how to use and install visit gns3

once it is installed all you need is the ios files which are original cisco ios here to work on without setting up a costly lab for ccna, ccnp, ccsp, ccvp, ccie.