I use VMWare Workstation Pro to run a product called Eve-NG. It's a Linux OS piece that you can either run on bare metal or a hypervisor. So I run the latter.
You can used it to load Cisco, HPE Aruba, Fortigate, pFsense, Mikrotik etc Switch, Router, Firewall images so you don't have to literally deal with a 6 foot tall rack full of hardware. You just run their images in an emulated environment.
The nested operation comes from the fact that you can spin up Eve-NG, create a directory for the switch, router, firewall you want to play with and simply copy the image to said directory and Eve-NG will pass through the virtualization layers needed so you are only running one instance in VMWare Player. Makes is easier to backup, snapshot etc...