Explanation
You can set up a single IPSec VPN with a simple layout that you might use for a proof of concept (POC).

Explanation/Reference: https://docs.cloud.oracle.com/en-us/iaas/Content/Block/Concepts/blockvolumebackups.htm

Explanation
Customer and Oracle's responsibilities can be divided into the following areas:
Physical Security: Oracle is responsible for protecting the global infrastructure that runs all of the services offered in Oracle Cloud Infrastructure. This infrastructure consists of the hardware, software, networking, and facilities that run Oracle Cloud Infrastructure services.
Identity and Access Management (IAM): As with all Oracle cloud services, you should protect your cloud access credentials and set up individual user accounts. You are responsible for managing and reviewing access for your own employee accounts and for all activities that occur under your tenancy. Oracle is responsible for providing effective IAM services such as identity management, authentication, authorization, and auditing.
Workload Security: You are responsible for protecting and securing the operating system and application layers of your compute instances from attacks and compromises. This protection includes patching applications and operating systems, operating system configuration, and protection against malware and network attacks. Oracle is responsible for providing secure images that are hardened and have the latest patches. Also, Oracle makes it simple for you to bring the same third-party security solutions that you use today.
Data Classification and Compliance: You are responsible for correctly classifying and labeling your data and meeting any compliance obligations. Also, you are responsible for auditing your solutions to ensure that they meet your compliance obligations.
Host Infrastructure Security: You are responsible for securely configuring and managing your compute (virtual hosts, containers), storage (object, local storage, block volumes), and platform (database configuration) services. Oracle has a shared responsibility with you to ensure that the service is optimally configured and secured. This responsibility includes hypervisor security and the configuration of the permissions and network access controls required to ensure that hosts can communicate correctly and that devices are able to attach or mount the correct storage devices.
Network Security: You are responsible for securely configuring network elements such as virtual networking, load balancing, DNS, and gateways. Oracle is responsible for providing a secure network infrastructure.
Client and Endpoint Protection: Your enterprise uses various hardware and software systems, such as mobile devices and browsers, to access your cloud resources. You are responsible for securing all clients and endpoints that you allow to access Oracle Cloud Infrastructure services.

Explanation/Reference: https://www.oracle.com/a/ocom/docs/oracle-database-exadata-cloud-service-ds.pdf