Which VLAN assignment method is least commonly used in network design?

The least commonly used VLAN assignment method in network design is based on access device type. This method assigns VLANs depending on the type of device that connects to the network, such as PCs, printers, or servers. While it can be useful for straightforward scenarios, it is not typically used in more complex network designs, where factors like service requirements and security are prioritized.

In contrast, methods based on geographical location, service design, and security system requirements are often favored because they provide a clear structure for managing traffic, ensuring performance, and adhering to security protocols. Utilizing geographical location helps in organizing and managing VLANs according to physical site layouts, which can simplify network management. Service design aligns VLANs with specific services or applications that may require distinct bandwidth or quality of service, and security requirements are integral in modern network designs to ensure that sensitive data is protected and segregated effectively. Thus, while VLAN assignment based on access device type has its applications, it tends to be less flexible and comprehensive compared to these other methods, which makes it less commonly used in contemporary network designs.