In all replications, the source database must be an Oracle database. Therefore, two-way replication with MS SQL Server is not supported. ODBC connection is used to connect to MS SQL, thus DSN (Data Source Name) with the same name must be setup by the system administrator on both source and target systems.
If both source and target databases are running on Windows platform then DSN (Data Source Name) with the same name are required on source and target machine. But if source is Linux then DNS is only required on Windows target machine.
Currently, no DDL replication is supported for MS SQL
Windows to Windows Oracle to MSSQL replication is a beta feature and it will be fully supported in next release.