Define a VLAN, distinguish between access and trunk ports, and explain how Spanning Tree Protocol (STP) prevents loops.

• A. VLANs segment broadcast domains; access ports carry a single VLAN; trunk ports carry multiple VLANs using 802.1Q; STP detects/blocks loops to prevent broadcast storms.
• B. VLANs segment broadcast domains.
• C. VLANs group devices by MAC address; access ports carry multiple VLANs; trunk ports carry one VLAN only.
• D. VLANs are used for routing between subnets; STP creates loops for redundancy.

Answer: (B)

VLANs segment broadcast domains, meaning they keep broadcast traffic within the devices that share the same VLAN and prevent it from reaching devices in other VLANs. This is the fundamental function that defines what a VLAN does on a switch network.

To implement multiple logical networks on the same physical switch, consider how ports are used. An access port attaches to a single VLAN and sends and receives frames untagged, which are then associated with that VLAN. A trunk port, on the other hand, carries traffic for several VLANs on one link and uses tagging (typically 802.1Q) to identify which VLAN each frame belongs to. Spanning Tree Protocol prevents loops by ensuring there’s only one active path between switches; it does this by electing a root bridge and blocking redundant links so that the network avoids broadcast storms.

Together, these ideas explain how VLANs isolate traffic, how ports handle VLAN membership, and how the network stays loop-free. Some statements describe VLANs incorrectly, such as grouping devices by MAC addresses (VLANs are defined by logical segmentation, not by MAC) or routing between subnets (VLANs are a Layer 2 construct, with inter-VLAN routing handled at Layer 3).