I'm trying to connect to an OPC Server on an Application Station with a DC role, across a firewall but when using OPC Watchit I get the error "The RPC server is unavailable". I can RDP to the machine without issue and I have 4 other OPC Clients connected successfully on this side of the firewall. This connection had been working successfully prior to assigning the DC role to the APPs station. Am I missing something that should be obvious. The user credentials are fine and have been confirmed on both the client and server machines, although the functionality of the DC machine prevents me from creating a local username.
OPC and DC role don't really mix well - generally. When an OPC client connects to the OPC Server it will be connecting using the context of the active user. That user needs to have access to the DCOM infrastructure of the App Station. And here you problem starts - not unless the OPC Remote is a member of the domain then generally can't do this.
Say the client can be made to connect to the server by bending all the rules then callback kicks in. Callback security assumes the security context of DeltaV OPC Server - generally DeltaVAdmin. So the server will need to have access to the client to push updates - another challenge for DC role.
Best practices for DeltaV OPC Server - don't use it on a domain controller unless all machines connecting it is a domain member or domain trust is established.