VLAN (Virtual Local Area Network) is a virtual local area network. With its help, it is possible to combine several networks. This allows you to create additional virtual networks to existing physical network devices.

The principle of operation

The main purpose of using VLANs is to create a number of subnets to separate multiple devices within the framework of a single switch. This separation is often required in organizations where there is a need to subnetwork several departments, for example, human resources, accounting, IT department. Ethernet frames are isolated from each other. This separation is useful primarily for the data security of a single department.

Each Ethernet frame in the subtitle should contain a tag, thanks to which the common switch determines who exactly owns a particular subnet. Four-byte tags must include 2 required fields:

  1. TPID with information about the protocol;
  2. A TCI with control information, which is divided into several block fields:
    • PCP with priority traffic indication;
    • CFI with MAC address formats;
    • The VID with the virtual network ID.
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