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Routing & Switching · Foundational

Allowed VLAN List

The set of VLANs permitted to traverse a trunk, all VLANs (1-4094) by default on Cisco.

Definition

Restricting the allowed list limits broadcast scope and STP instances. Use add, remove, except or none keywords to modify it. A VLAN missing from the allowed list on either side will not pass traffic across the trunk.

Example

switchport trunk allowed vlan add 50

Exam tip

show interfaces trunk lists allowed, active and forwarding VLANs; check all three when traffic fails.

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