By default, the primary VNIC of an instance in a subnet has one primary private IP address. A private IP can have an optional public IP assigned to it if it resides in a public subnet. The explanation is that a private IP address is an IPv4 address that is assigned to a VNIC and belongs to the CIDR block of the VCN or subnet. By default, the primary VNIC of an instance in a subnet has one primary private IP address, which is automatically assigned by OCI and cannot be changed. However, you can also assign secondary private IP addresses to a VNIC, either manually or automatically, up to a maximum of 31 per VNIC. A private IP address can have an optional public IP address assigned to it, which allows the instance to communicate with the internet. A public IP address can be either ephemeral or reserved, depending on whether you want to keep it after stopping or terminating the instance. A private IP address can only have a public IP address assigned to it if it resides in a public subnet, which means that the subnet's route table has a route rule that directs traffic to the internet gateway.