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How VLANs work
A VLAN is identified on network switches by a VLAN ID. Each port on a switch can have one or more VLAN IDs assigned to it and will land in a default VLAN if no other one is assigned. Each VLAN provides data-link access to all hosts connected to switch ports configured with its VLAN ID.

A VLAN ID is translated to a VLAN tag, a 12-bit field in the header data of every Ethernet frame sent to that VLAN. Because a tag is 12 bits long, up to 4,096 VLANs can be defined per switching domain. VLAN tagging is defined by IEEE in the 802.1Q standard.

When an Ethernet frame is received from an attached host, it has no VLAN tag. The switch adds the VLAN tag. In a static VLAN, the switch inserts the tag associated with the ingress port's VLAN ID. In a dynamic VLAN, it inserts the tag associated with that device's ID or the type of traffic it generates.

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