What must be done for a server to communicate with an ArcGIS Enterprise portal?

For a server to successfully communicate with an ArcGIS Enterprise portal, it is essential to register the server with the portal. This registration process establishes a trusted relationship between the portal and the server, enabling them to exchange information and allows the server to be recognized as an entity that can provide services, such as web maps and layers.

When the server is registered with the portal, it gains access to the portal's resources and functionalities. This process typically includes specifying the server's URL, which allows the portal to directly communicate with the server for publishing content, managing users, and performing administrative tasks. This step is foundational as it ensures that the server is part of the overall ArcGIS Enterprise architecture, facilitating collaboration and resource sharing.

The other options would not achieve the necessary communication setup. For instance, resetting the server or upgrading the operating system would not inherently establish the portal-server relationship required for effective interaction. Installing additional hardware might improve performance or capacity but does not address the communication setup between the server and the portal. Thus, registering the server is the critical step needed for enabling communication with the ArcGIS Enterprise portal.