The type of VLAN used to designate which traffic is untagged when crossing a trunk port is called the Native VLAN. Key points about Native VLAN:
- When a switch receives untagged frames (frames without VLAN tags) on a trunk link, it associates them with the Native VLAN.
- The Native VLAN handles all untagged traffic across a trunk port.
- By default, VLAN 1 is the Native VLAN unless it is changed to another VLAN.
- Both ends of the trunk link must have the same Native VLAN ID configured.
- It is considered best practice for security reasons to change the Native VLAN from default VLAN 1 to a different, unused VLAN to prevent potential VLAN hopping attacks.
In summary, untagged traffic on a trunk is carried in the Native VLAN.
