MS-SQL DB LINK does not work in ORACLE12C RAC

1. ORACLE PROUDCTS : ORACLE DATABASE 12C ENTERPRISE 

2. VERSION : 12.1.0.2.0 - 64bit 

3 os : AIX-UNIX6.1 

4. MS-SQL connect program :dg4msql

5. run sql : select * from "IDX"@DG4MSQL5T

i dont't know why this sql could not work in ORACLE

could you send solution about this issue?

sql> select * from "IDX"@DG4MSQL5T

ORA-28500: connection from ORACLE to a non-Oracle system returned this message:

[DataDirect][ODBC lib] Data source name not found and do default driver specified {IM002}

ORA-02063: preceding 2 lines from DG4MSQL5T