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Routing & Switching · Foundational

Trunk Port

A switch port that carries multiple VLANs over one link, identifying them with 802.1Q tags.

Definition

Trunks interconnect switches, routers (router-on-a-stick), and hypervisors. All VLANs are allowed by default on Cisco trunks; the allowed list should be pruned. Frames in the native VLAN cross untagged. Junos calls this interface-mode trunk.

Example

switchport mode trunk / switchport trunk allowed vlan 10,20,30

Exam tip

'switchport trunk allowed vlan 40' replaces the list; use 'add' to append. A classic outage-causing trap.

Don't confuse it with

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