Which two reasons could prevent vNet peering in Azure?

A primary reason preventing vNet peering in Azure is that the two virtual networks (vNets) have overlapping IP addresses. When two vNets share the same IP address space, it results in routing conflicts, making it impossible for Azure to distinguish between the addresses when routing traffic. This overlap complicates connectivity since packets meant for one vNet may inadvertently be routed to the other, causing significant challenges in communication and management. By ensuring that the IP address ranges for each vNet are unique, Azure enables seamless and effective communication without the risk of overlapping routes.

While issues related to subscriptions, regions, or IP address types may affect connectivity in other ways, they do not directly prevent vNet peering like overlapping IP addresses do. For instance, while vNets can be in different subscriptions and still peer as long as they are under the same Azure Active Directory, overlapping IP spaces remain a critical and non-negotiable barrier to successful peering.