Created an environment with the only one database on it (caserv) and the database name on this server is the same as on the other physical server.
However, when I tried to create dsource it give me the following error: Error: Detected two Oracle databases with the same unique name "caserv".
Error Code: exception.oracle.environment.unique_name.conflict
According to Oracle's documentation, a db_unique_name must be globally unique (see for example: http://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams056.htm). When we discover a database, we record the db_unique_name of the database, whether or not it is ever linked as a dSource. When linking, we check whether we already have discovered a database with the same unique name, and as you have seen, we will not link a database that has a non-unique db_unique_name.
Duplicate db_unique_names within an Oracle infrastructure can cause unpredictable and difficult to diagnose issues with RMAN and DataGuard. Since we utilize RMAN in linking a dSource, we avoid these issues by preventing linking of a database with a duplicate db_unique_name.
As the error suggests, changing the db_unique_name of one of the databases will allow you to link them.