We have a single domain that had 2 sites for over 3yrs connected via ISA Server 2006 VPN. DC1 and DC2 have been replicating without issues. We added a 3rd site with ISA Server 2006 VPN and all three sites can communicate with each others servers without issues. Just last week we put in a new server in site 3 to be a DC. Created the site in ADSS and then ran a DCPROMO on DC3. DC3 is getting updates from both DC1 and DC2, but neither DC1 or DC2 get any updates from DC3. We have AD integrated DNS and there is an A record in DNS at all three sites and DC1 and DC2 can ping DC3. From DC1 and DC2 you can view SYSVOL and Netlogon Shares. But in site 3 on DC1 and DC2 the NTDS connection will not populate for site 3. DCDIAG on DC3 shows no errors. If I try to manually create a connection in ADSS for site 3 on DC1 or DC2 to DC3 I get either the directory property can't be found in cache when I check the topology or if I manually add a connection to site 3 and then replicate I get an RPC server is unavailable. Not sure what to check next. I think it is a DNS issue somewhere on DC1 and DC2. But DC3 is getting the replication of users/computers/ etc in AD from DC1 and DC2 just not the other way.