By default, AD replication via remote procedure calls (RPCs) takes place dynamically over an available port via the RPC Endpoint Mapper using port 135 (the same as Microsoft Exchange). An administrator may override this functionality and specify the port that all replication traffic passes through, thereby locking down the port.
To set a specific port, perform the following steps:
Because some routers filter packets, administrators should confirm that they don't filter out any intermediate network devices or software that filters packets between domain controllers.