Trunking
Carrying traffic for multiple VLANs over a single switch link using 802.1Q tagging.
Trunking uses IEEE 802.1Q to insert a 4-byte tag into each Ethernet frame, identifying its VLAN, so one physical link between two switches — or a switch and a router — can carry many VLANs at once. The native VLAN is the exception: its frames travel untagged, so both ends must share the same native VLAN ID or traffic is misassigned. Do not confuse a trunk with an access port, which belongs to one VLAN and strips tagging. VLAN 1 is the default native VLAN on Cisco-style switches, and leaving it so is a known security concern.
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