Virtual LAN
lastmod 2023-03-18created 2016-05-066 edits
In a computer network, a single layer 2 network can be partitioned to create multiple distinct broadcast domains; once separated this way, packets can move between them only through one or more routers. Such a domain is called a virtual LAN, also written as Virtual Local Area Network, Virtual LAN, or simply VLAN.
It is usually performed on switch or router equipment. Simpler devices support partitioning only at the port level, so sharing VLANs across devices requires dedicated cabling for each VLAN. More sophisticated devices mark packets by adding tags, so that a single interconnect (trunk) can be used to carry data for multiple VLANs.
Physically replicating the function of a VLAN would require a separate, parallel network cable and equipment separated from the main network. However, unlike physically separated networks, VLANs share bandwidth, so VLAN trunks require link aggregation and QoS prioritization.
Using VLANs to group host computers with common requirements regardless of their physical location can greatly simplify network design. A VLAN has the same characteristics as a physical local area network (LAN), with the difference that end stations can be grouped together more easily even if they are not on the same network switch. VLAN membership can be configured through software instead of physically relocating devices or connections. Most enterprise networks today use the concept of virtual LANs. Without VLANs, a switch considers all interfaces on the switch to be in the same broadcast domain.