What is the most viable action for reducing excessive activity related to domain controllers in a network?

Installing a global catalog server in one of the domain controllers at the remote site is effective for reducing excessive activity related to domain controllers because it enhances the efficiency of directory queries within that site. A global catalog server holds a partial replica of every object in the directory forest, which allows users to access important information without having to contact all domain controllers across the network for the full details. This setup reduces the load on the main domain controllers and minimizes unnecessary traffic, leading to faster response times and optimal performance.

Increasing the number of domain controllers might seem beneficial, but it does not directly address excessive activity and can potentially increase network traffic if not managed properly. Limiting user access to domain controllers could improve security but might not alleviate performance issues if legitimate processes are still causing high traffic. Upgrading the bandwidth of the network could help if there’s congestion, but it doesn't inherently manage how many queries or processes are hitting the domain controllers. Thus, installing a global catalog server serves as a targeted solution to manage and distribute load effectively.