What solution can an Information Security Officer implement to provide independent functionality for separate departmental networks?

Providing each department with a virtual firewall is the best solution for ensuring independent functionality for separate departmental networks. Virtual firewalls allow different departments to have their own configurations and policies applied without requiring separate physical devices. This setup is often more efficient, as it reduces hardware costs and resource expenditure while still maintaining strong security measures tailored to each department's specific needs.

Virtual firewalls can be managed centrally, providing ease of administration while still allowing for customization pertinent to each department's requirements. This method enables departments to operate independently, effectively isolating network traffic and enhancing security while remaining flexible concerning scaling.

The other options may involve more complex setups or additional costs. Using a single physical firewall with multiple configurations might create potential security risks if any misconfiguration occurs and could limit the individual departmental needs. Installing additional hardware firewalls for each department can be prohibitively expensive and may also complicate management. Utilizing cloud-based firewall services is effective but may not provide the same level of immediate control and configurability that virtual firewalls would afford in a local network context.