I started using GNS3 early in its development and took to it like a duck to water. From the beginning I could see it was going to be an invaluable networking tool. I’ve used it to get hands-on experience with operating systems such as Cisco IOS, Junos OS, and Arista, as well as to pass quite a few network certification exams. To this day, I use it on a regular basis to test router configurations before deploying real equipment to the field. The Book of GNS3 is my way of sharing this great resource with other networking professionals, like you.