Trunking (802.1Q)

Trunking carries traffic from multiple VLANs over one link using VLAN tags.

Updated: 2026-03-05

Definition

A trunk link carries traffic for multiple VLANs between switches (or to a router/L3 switch) using VLAN tagging (802.1Q).

Trunks keep VLAN separation while allowing VLANs to span multiple switches.

Key points

802.1Q adds VLAN tags to frames
Native VLAN is untagged (be careful with mismatches)
Used between switches and to routers (router-on-a-stick)

Common mistakes

Native VLAN mismatch causing traffic leaks or connectivity issues.
Allowing all VLANs on trunks instead of limiting to required VLANs.

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Cisco CCNA (200-301)

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