Cisco intellectual property laws strictly prohibit the public distribution, sharing, or downloading of IOS image files from unauthorized third-party websites. To obtain legal, official Cisco software images for lab testing, you must use one of the following methods:
In many cases, the best approach is to use GNS3 for some devices and connect it to a real physical switch or router via your computer's network interfaces, creating a hybrid lab for ultimate flexibility.
Browse to and select the downloaded cisco-vios-l2.gns3a file.
Before you search for a file, you must understand what you are looking for.
Cisco IOS Software, Catalyst 4500 L3 Switch Software...