Explanation
References: https://docs.cloud.oracle.com/en-us/iaas/Content/Network/Concepts/fastconnectoverview.htm You use a DRG when connecting your existing on-premises network to your virtual cloud network (VCN) with one (or both) of these:
IPSec VPN
Oracle Cloud Infrastructure FastConnect
You also use a DRG when peering a VCN with a VCN in a different region:
Remote VCN Peering (Across Regions)