VLAN

[2][3] In this context, virtual refers to a physical object recreated and altered by additional logic, within the local area network.

Because VLAN membership can be configured through software, this can greatly simplify network design and deployment.

Without VLANs, grouping hosts according to their resource needs the labor of relocating nodes or rewiring data links.

VLANs allow devices that must be kept separate to share the cabling of a physical network and yet be prevented from directly interacting with one another.

Simpler equipment might partition only each physical port (if even that), in which case each VLAN runs over a dedicated network cable.

Without VLAN capability, users are assigned to networks based on geography and are limited by physical topologies and distances.

By using VLANs, one can control traffic patterns and react quickly to employee or equipment relocations.

VLANs provide the flexibility to adapt to changes in network requirements and allow for simplified administration.

Quality of service schemes can optimize traffic on trunk links for real-time (e.g. VoIP) or low-latency requirements (e.g. SAN).

This limited the total bandwidth of an Ethernet network to 10 Mbit/s and the maximum distance between nodes to a few hundred feet.

In the process, he independently reinvented transparent bridging, the technique used in modern Ethernet switches.

To help alleviate this problem, Sincoskie invented VLANs by adding a tag to each Ethernet frame.

In this scheme, each switch could be assigned to handle frames of a single color, and ignore the rest.

[9] This was extended with IEEE 802.1ad to allow nested VLAN tags in service of provider bridging.

Early network designers often segmented physical LANs with the aim of reducing the size of the Ethernet collision domain—thus improving performance.

Remote management of the switch requires that the administrative functions be associated with one or more of the configured VLANs.

(Note that the term 'trunk' is also used for what Cisco calls "channels" : Link Aggregation or Port Trunking).

Switches typically have no built-in method to indicate VLAN to port associations to someone working in a wiring closet.

It is necessary for a technician to either have administrative access to the device to view its configuration, or for VLAN port assignment charts or diagrams to be kept next to the switches in each wiring closet.

Prior to the introduction of the 802.1Q standard, several proprietary protocols existed, such as Cisco Inter-Switch Link (ISL) and 3Com's Virtual LAN Trunk (VLT).

This internal tagging allows IEEE 802.1Q to work on both access and trunk links using standard Ethernet hardware.

If the user changes ports and needs access to the same VLAN, the network administrator must manually make a port-to-VLAN assignment for the new connection.

With a VLAN Management Policy Server (VMPS), an administrator can assign switch ports to VLANs dynamically based on information such as the source MAC address of the device connected to the port or the username used to log onto that device.