Series Post 2, Setting up the Gateway Virtual Machine, a virtual router
If we have a lab and we want to keep it separate from rest of our environment, we need a gateway. You can do this with a linux VM, another physical router, or several other options. For our lab, we decided to use Microsoft Windows Server to be our gateway. After setting this up, looking back, it would have been easier to setup the DC first, so I'd recommend doing that, then setting this up.
LAN 1: DHCP (External Network)
LAN 2: Static IP (Internal Lab Network) 192.168.1.1
Once that finishes, you can go ahead and setup the "Router" feature.
This is probably the easiest server you'll be setting up. If you run into any issue, don't worry, go ahead and setup the DC. Once you setup the DC, you need to remember to come back to the GATEWAY and join it to the domain.