The IEEE 802.1Q networking standard lays down the specifications for VLANs (Virtual Local Area Networks or Virtual LANs) on an IEEE 802.3 Ethernet network. The standard is generally referred as Dot1Q. VLANs are a logical group of computers that appear to be on the same LAN irrespective of the configuration of the underlying physical network. Network administrators partition the networks to match the functional requirements of the VLANs so that each VLAN comprise of a subset of ports on a single or multiple switches or bridges. This allows computers and devices in a VLAN to communicate in the simulated environment as if it is a separate LAN.
IEEE 802.1Q standard outlines the methods by which VLAN tags can be added to Ethernet frames, so that the frame can identify the VLAN to which it is destined to.
When a frame moves into a VLAN-enabled section of an Ethernet network, the tag is added to denote the VLAN membership. A frame can be within only one VLAN at a time.
IEEE 802.1Q also lays down the procedures that bridges and switches needs to adopt to manage VLAN tagged Ethernet frames.
Additionally, the standard can also define a quality-of-service (QoS) prioritization scheme as well as Generic Attribute Registration Protocol.
The main fields of a frame of classic Ethernet are −