If you are having problems establishing a connection across a network, you can use debugging options at both the client and the server to diagnose problems. On the database server, you use the -z option. The startup information appears in the database server messages window: you can use the -o option to log the results to an output file.

See -z dbeng12/dbsrv12 server option and -o dbeng12/dbsrv12 server option.