The following error occurred during the attempt to contact the domain controlled DC01: The RPC server is unavailable This condition may be caused by the DNS lookup problem
closed as not a real question by MDMarra, Greg Askew, Dennis Kaarsemaker, Ward, Jacob Apr 7 '13 at 15:48
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. If this question can be reworded to fit the rules in the help center, please edit the question.
The replication connection is attempting this process:
Failures that happen after this point yield a different error.
By far the most common problem is that the DNS server used by the source DC can't resolve the destination DC for some reason. Once this is fixed, things start working.
Less common is the IP connection getting blocked in some way. Perhaps there is a firewall between the two points and it is blocking the wrong ports. The list of ports that need to be open between domain controllers is quite extensive, so if this is being done, much care needs to be taken to it right.
Sometimes the firewall on the destination DC is blocking the connection. This is a very unusual thing, but does need looking at.
SMB connection failures mean the network path is completely clear, but something at the Windows level is broken. This is high-mojo, and there are no generic steps to fix it.