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Routing & Switching · Foundational

Native VLAN

The VLAN whose frames are sent untagged across an 802.1Q trunk, VLAN 1 by default on Cisco.

Definition

Both ends of a trunk must agree on the native VLAN; mismatches merge two VLANs and are reported by CDP. Best practice is to set the native VLAN to an unused VLAN or tag it (vlan dot1q tag native) to mitigate double-tagging attacks.

Example

switchport trunk native vlan 999

Exam tip

CDP logs '%CDP-4-NATIVE_VLAN_MISMATCH' when the two ends differ.

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