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NNL-00020:

warning: no TNSNAMES.ORA file and no preferred name servers in SQLNET.ORA
Cause: The control program was unable to find a TNSNAMES.ORA file and was unable to find a default name server in SQLNET.ORA. The control program will operate in this state, but will be unable to resolve any names until a default server has been set, and that server must be set using its raw TNS address.
Action: The control program's SQLNET.ORA file must exist in the correct system-specific location, and must be readable by the control program. The file must contain a names.preferred_servers entry with valid name server addresses. The first server in the preferred-server list must be running, and there must be network connectivity between the control program and that server. Alternatively, a TNSNAMES.ORA file with valid name server information must exist in the correct system-specific location.