Why is a domain controller essential in a network?

A domain controller plays a crucial role in a network, primarily by controlling domain access and blocking unauthorized access. It acts as a centralized server that manages the security and permissions for all users within the domain. By authenticating users, the domain controller ensures that only authorized personnel can access sensitive information and resources. This process helps maintain the integrity of the network and protects against potential security breaches.

Moreover, the domain controller simplifies user management by enabling administrators to create and enforce policies, manage user accounts and permissions, and apply security settings uniformly across the network. This centralized control is essential for both operational efficiency and security compliance, making the domain controller a vital component of a secure and well-managed network environment.

The other options, while they may contribute to network functionality in different contexts, do not accurately describe the primary role of a domain controller. For instance, improving network speed and performance or providing internet connectivity are not functions specific to a domain controller. Instead, those tasks might be handled by other network equipment or services. Storing document files for users is also not a function of a domain controller, as file storage is typically managed through specialized servers or cloud services.