My AD Name in our small Company is vbsi.com, it NATs Internet and has an Valid IP Set on it's Server. Client Pings goes out of local IP Range

Hi

I have a small network at my company with 50 clients, and one AD Server which runs DNS, DHCP and Internet Sharing via NAT, my DHCP IP Range is 172.17.2.1 to 172.17.2.100.

My AD Domain Name is: vbsi.com

The AD Server has an valid IP and it shares Internet via Windows Server NAT Services.

My Problem is when I ping Some client like myComputer.vbsi.com It's Result an Valid Internet IP like 208.91.197.27

in place of 172.17.2.20 for example, and all client pings returns this result.

what is the problem? I should not use VBSI.com on my local Network? If I use it I should not Set Valid IP and Internet Sharing On It's Server? ...