Add new DC with DNS on a Mulitple DC with DNS servers

Currently have 6 Domain Controllers and all 6 DC are running DNS server. (1 Primary DC with DNS and 5 sub-DC with DNS). I have just promoted a new Domain Controller and I need to know how to setup/add the DNS server on it. Each DC will use its own DNS as a Primary DNS and it will use the other DNS as a Secondary DNS. Please provide links or instructions on how to setup/add the DNS on this new DC on a multiple DC with a multiple DNS serves.

1. Suggests network connectivity issues.

Are you using Forwarders? Or Root Hints (the default)?

What rules are in place to allow this server to make queries on the Internet (will need Outbound UDP Port 53 at the very least)?

2. RPC connectivity. Check it can resolve the name of the target server and check Firewalls if there are any between the servers.

3. Suggests Firewalls again, this one is problem 1 again.