Which tool should you use?

This question doesn’t tell us if DC2 already exists or not. Dcpromo will only work if DC2 is a member server and is being promoted to a domain controller.

Dsmgmt has the ability to control replication of application directory partitions. Dsmgmt is installed with active directory binaries. Steps to add DC2 as a replication partner would be as follows:

dsmgmt
partition management
connections
connect to server DC2
quit
add nc replica dc=app1,dc=contoso,dc=com DC2.contoso.com
list nc replica dc=app1,dc=contoso,dc=com
quit
quit

It was interesting to note that when I created a new partition to test this, the partition was instantly replicated to the existing domain controllers within the domain. I assumed that I would have to manually add each one as replication partners. To verify the ability to add a replication partner, I first did a “remove nc replica”.

Reference is http://technet.microsoft.com/en-us/library/cc730970(v=ws.10).aspx

It is interesting to note that the example included with the reference uses ntdsutil, even though the page is for dsmgmt. I was also unable to execute the “activate instance ntds” portion of the example. I added another application directory partition using the exact steps listed with the ntdsutil and had the same results as when using the dsmgmt command.