Duplicate From Active Database Errors : ORA-17629 and ORA-17627: ORA-12154: Tns:Could Not Resolve

Duplicate From Active Database Errors : ORA-17629 and ORA-17627: ORA-12154: Tns:Could Not Resolve

The duplicate database from active failed with the following errors : 

ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-12154: TNS:could not resolve the connect identifier specified
ORA-17629: Cannot connect to the remote database server

Cause 1:

For Active Duplication you need to connect to the target and Auxiliary DB using net service name ,even if you are running RMAN at the Auxiliary DB.
The net service name to connect to the Auxiliary DB should also be configured at the target Database.

In the tnsnames.ora on the machine of the TARGET database, there are 2 services created to connect to auxiliary database that have the same "service name" but "different" configuration.

Possible Cause 2:

Mismatch of Parameters DEFAULT_DOMAIN and DB_DOMAIN

db_domain=PROD.world         # init.ora
default_domain=PROD.WORLD    # sqlnet.ora

# DEFAULT_DOMAIN defined on sqlnet.ora is 'case' sensitive and when defined must match
   DB_DOMAIN initialization parameter

Solution:

1. To be sure that the tnsnames.ora file of each machine (machine where is the source database and machine where is the auxiliary database) has the service name to connect to auxiliary database.

2. Verify that there are not duplicate service_name with different configuration in the tnsnames.ora file.