What is true of the relationship between a primary VNIC and a secondary VNIC in OCI?

The relationship between a primary VNIC and a secondary VNIC in Oracle Cloud Infrastructure (OCI) is characterized by specific networking rules and functionality. The choice stating that all VNICs must be in the same availability domain is correct because, within OCI, a virtual network interface card (VNIC) is tied directly to the instance it is associated with, and instances themselves are located in specific availability domains.

Availability domains are distinct, isolated locations within a region that provide high availability and fault tolerance. Although multiple VNICs can exist within a single instance, they must inherently operate within the same availability domain where that instance resides. Therefore, having all VNICs in the same availability domain ensures that they can communicate effectively, leveraging the OCI networking architecture.

Regarding the other options, the functionality and limits associated with public IP addresses, cross-VCN relationships, and IP address limitations of secondary VNICs do not accurately portray the capabilities and requirements of OCI networking. Understanding these aspects is essential for effectively managing network configurations in OCI.