VLANtunnisteita

VLANtunnisteitä, known in English as VLAN tags or 802.1Q tags, are a method for identifying and segmenting virtual local area networks (VLANs) within a switched Ethernet network. These tags are inserted into the Ethernet frame header, specifically in the IEEE 802.1Q standard. This tagging allows network devices, such as switches and routers, to distinguish between different VLANs on the same physical network infrastructure.

A VLAN tag consists of several fields, including a Tag Protocol Identifier (TPID), a Priority code point (PCP) for Quality of Service (QoS) prioritization, a Drop Eligible Indicator (DEI), and the VLAN Identifier (VID). The VID is the crucial part, a 12-bit number that can uniquely identify up to 4096 VLANs. When an Ethernet frame traverses a network that uses VLANs, a switch adds a VLAN tag to frames entering a trunk port. Devices on the other end of the trunk port then use this tag to determine which VLAN the frame belongs to and how to handle it.

The primary purpose of VLAN tagging is to enable network segmentation. By assigning different VIDs to different groups of devices or network segments, administrators can isolate broadcast traffic, improve security by preventing unauthorized access between segments, and optimize network performance. For instance, a company might use one VLAN for its finance department and another for its sales department, even if they share the same physical switches. This prevents broadcast storms within one department from affecting the other and allows for granular control over traffic flow. VLAN tagging is a fundamental technology for modern, scalable, and secure network designs.