Also known as: trunk, IEEE 802.1Q trunk, dot1q trunk
Quick Definition
A switch port configured to carry traffic for multiple VLANs using 802.1Q tags.
A trunk port carries frames from multiple VLANs simultaneously by adding 802.1Q tags to each frame. The tag contains a 12-bit VLAN ID (0–4095), allowing switches and routers to identify which VLAN each frame belongs to. Trunk links are typically used between switches, and between a switch and a router performing inter-VLAN routing. Trunk ports can be configured manually or negotiated using DTP.
interface GigabitEthernet0/1 switchport mode trunk switchport trunk allowed vlan 10,20,30 switchport trunk native vlan 99
Frames on the native VLAN are NOT tagged on trunk links (they pass untagged). This creates a VLAN hopping vulnerability if the native VLAN matches a data VLAN. Always set the native VLAN to an unused VLAN.
A logical segmentation of a switch network into separate broadcast domains.
A switch port assigned to a single VLAN, connecting end devices such as PCs and printers.
The VLAN whose frames pass untagged on a trunk link — VLAN 1 by default.
A Cisco proprietary protocol that automatically negotiates trunk formation between switches.
A trunk port carries frames from multiple VLANs simultaneously by adding 802.1Q tags to each frame. The tag contains a 12-bit VLAN ID (0–4095), allowing switches and routers to identify which VLAN each frame belongs to. Trunk links are typically used between switches, and between a switch and a router performing inter-VLAN routing. Trunk ports can be configured manually or negotiated using DTP.
Frames on the native VLAN are NOT tagged on trunk links (they pass untagged). This creates a VLAN hopping vulnerability if the native VLAN matches a data VLAN. Always set the native VLAN to an unused VLAN.
Trunk Port falls under the VLANs domain of the 200-301 exam. Understanding it in context with related terms like vlan and access-port is essential for answering scenario-based questions correctly.