Communication Primary database to Standby database

Hello ,

Before I aske my question I would like to describe the environment we plan to configure (Linux hosts, Oracle database Enterprise Edition release 12.2):

=> host 01: Primary database db01

=> host 02: physical cascading Standby database db02

=> host 03: physical cascaded Standby database  db03

In this scenario only the current Standby database will ship the redologs to host 03. That means that the parameter REDO_ROUTES of the DataGuard configuration have to be setup like this

=> db01 (LOCAL:db02)(db02:db03)

=> db02 (LOCAL:db01)(db01:db03)

For all databases the port 1521 will be used.

That means that only db01 and db02 are supposed to change their roles (primary/standby) and that db03 should always be a standby database. This is the planned  configuration. When connecting to host 03 on which the cascaded Standby database is configured it should not be possible to connect backwards to the databases on host 01 and host 02 (e.g. with sqlplus "user"/"password"