I recently added a DC to an existing domain that had two existing DCs. I created a second site in AD sites and services, added the new server to the new site and shipped the server to the 2nd location. The sites are connected by VPN. I can ping servers by IP address across the VPN but not by name. DCDIAG /test:DNS passes at both sites. repadmin /replsum fails error 1722 "The RPC server is unavailable" when replicating across the VPN. Local replication between the two original DCs has 0 errors. repadmin /syncall runs with no errors.