This image shows the connectivity options for accessing resources from outside Oracle Cloud:

• From your on-premises data center, you can connect to a VCN through a dynamic routing gateway (DRG), by using private Oracle Cloud Infrastructure FastConnect circuits, or encrypted IPSec VPN connections, or both.
• From the public internet, you can connect to a VCN through an internet gateway. Use Oracle Cloud Infrastructure Web Application Firewall for proactive threat detection. Protection against DDoS attacks is built into the Oracle Cloud Infrastructure DNS service.