Mastering the is a rite of passage for network professionals. By obtaining a legitimate IOS image, correctly setting Idle-PC values, and allocating proper memory, you can build complex routing labs that mirror real-world enterprise networks.
For those who find legacy Dynamips images unstable, modern GNS3 labs often use images. These are official virtual images provided by Cisco: cisco 2811 ios image gns3 download for 19