Final answer:
The most effective tool for ensuring common configuration, no rogue software, and up-to-date patches for all workstations is a Virtual Desktop Environment (VDE).
Step-by-step explanation:
If you are concerned with ensuring all workstations at a large company have a common configuration, do not contain rogue software installations, and all patches are kept up to date, the most effective tool among the options provided would be VDE, which stands for Virtual Desktop Environment.
A VDE allows for centralized management of desktops, ensuring that each user's workstation is consistent with the company's standards. With VDE, you can manage software installations, enforce security policies, and ensure that all systems receive the necessary updates and patches in a timely and uniform manner. VPN, DNS, and HTTP would not provide the functionality required for this specific task of standardizing and securing workstation configurations.