When I was a systems and network engineer I used a VMWare and GNS3 lab a lot for labbing out network scenarios and testing configs. These days as a Red Teamer

When I was a systems and network engineer I used a VMWare and GNS3 lab a lot for labbing out network scenarios and testing configs. These days as a Red Teamer I use VMWare for setting up vulnerable virtual machines and entire Active Directory environments to lab out attack scenarios. Anything that needs to be on the public Internet, like a test vulnerability scanner, probably goes on AWS instead.