Virtual LANs (VLANs) are a network segmentation technique that allows a single physical network to be logically divided into multiple isolated broadcast domains. This division is achieved by assigning specific switch ports to different VLANs, creating distinct communication groups within the same physical infrastructure. Devices within the same VLAN can communicate with each other as if they are on the same network, even if they are physically located on different switches or network segments. VLANs enhance network security, improve performance, and simplify network management by logically organizing devices based on their functions or departmental affiliations.

​

Trunking, on the other hand, is a method for facilitating communication between switches and routers while preserving VLAN information. Trunk links are connections between networking devices that carry traffic for multiple VLANs simultaneously. By tagging each frame with VLAN information, trunking allows for the transfer of data across different VLANs over the same physical link. Common trunking protocols include IEEE 802.1Q, which inserts a VLAN tag into the Ethernet frame, and ISL (Inter-Switch Link), a Cisco proprietary protocol. Trunking is particularly valuable in scenarios where VLANs span multiple switches, ensuring that VLAN information is maintained as data traverses the network.