Hi,
Gateway address is the IP address your virtual server will use to connect to the internet.
For a computer to work in a network and be able to access computers outside of that network you need at least one gateway.
Your other questions appear to have to do with you trying to configure a domain controller as a virtual machine which you also ask about here:
DHCP Authorization Issue: 20070
My advice would be to scrap your current virtual machine, find yourself a simple step by step guide, for example this is a first hit when I search:
https://social.technet.microsoft.com/wiki/contents/articles/12370.windows-server-2012-set-up-your-fi...
or perhaps this one is better:
http://social.technet.microsoft.com/wiki/contents/articles/20834.windows-2012-r2-active-directory-in...
Then follow those steps and see if you can figure it out then and yes you will have to give your VM a static IP address before starting the wizards.
--
Wil
| Author of Vimalin. The virtual machine Backup app for VMware Fusion, VMware Workstation and Player |
| More info at
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@wilva