Open Command Prompt and type repadmin /showrepl . If you see "Successful," your DCs are officially talking.
Now that the new server is a DC, change its Preferred DNS to 127.0.0.1 (itself) and set the Alternate DNS to your first DC. Pro-Tip: The "Forgotten Step" Open Command Prompt and type repadmin /showrepl
A DC is a lighthouse; it can't move. Assign a static IP and set the Preferred DNS to the IP of your existing DC. Open Command Prompt and type repadmin /showrepl
