What should a system administrator use to separate departmental networks effectively?

Using a VLAN, or Virtual Local Area Network, is an effective method for separating departmental networks. VLANs allow for the segmentation of a single physical network into multiple logical networks, which means that devices on different VLANs cannot communicate directly with one another unless routed. This segmentation enhances security and reduces broadcast traffic, as each VLAN operates as its own distinct network.

For instance, in a corporate environment, separating finance, HR, and IT departments into their own VLANs can help restrict access to sensitive data and ensure that network traffic is managed efficiently. Additionally, VLANs can improve performance by limiting broadcast domains, leading to faster and more reliable network communications.

Other options, such as VPN, while useful for secure communications over public networks, do not segment networks. VNC, a remote desktop protocol, is not designed for network segmentation, and VM refers to a virtual machine, which is a technique used to run multiple operating systems on a single physical server rather than managing network segmentation. Thus, VLAN is the most appropriate choice for effectively separating departmental networks.