Virtual LANs (VLANs) are a fundamental networking technology used to logically segment a physical Layer 2 network into multiple distinct broadcast domains. This allows network administrators to group devices together based on function or department, regardless of their physical location. By creating these separate logical networks on a single physical switch, VLANs eliminate the need to purchase and manage multiple physical switches for segmentation, thereby reducing hardware costs and simplifying network management. Traffic between VLANs requires a Layer 3 device, such as a router, to be forwarded.

B. Assigning multiple IP addresses to a device is a function of the host's operating system and network stack, not a feature provided by VLANs.

C. VLANs can simplify network design, but communication between them requires inter-VLAN routing, which can add complexity. This is a consequence, not an advantage.

D. VLANs segment and isolate traffic into different broadcast domains; they do not prevent all network traffic. They control the flow of traffic at Layer 2.

1. Juniper Networks. (2023). Understanding VLANs on EX Series Switches. TechLibrary. Retrieved from https://www.juniper.net/documentation/us/en/software/junos/vlan/topics/concept/vlans-ex-series-understanding.html. (See the "Benefits of VLANs" section

which states

"VLANs enable you to logically group devices and to partition your network... without having to run new cables or make major changes in your current network infrastructure.")

2. Juniper Networks. (2023). Junos OS for EX Series Switches

Release 23.4R1. "VLANs Overview". Retrieved from https://www.juniper.net/documentation/us/en/software/junos/vlan/topics/concept/vlan-ex-series-overview.html. (This document explains that VLANs are "a collection of network nodes that are grouped together in a single broadcast domain... independent of their physical location.")