Configuring VLAN Trunk Example

By | 9th November 2015

How to Configure a Trunk Port.

To configure a switch port as a trunk link, use the switchport mode trunk command. This command puts the interface into permanent trunking mode and negotiates to convert the neighboring switch or links into trunk links.

Note: A trunk port is a port that is configured to carry traffic for all the VLANs on a switched network,
Trunk ports mark frames traffic with unique identifying tags – either 802.1Q tags or Inter-Switch Link (ISL) tags as they move between switches.

Let’s use the topology below for a demo.

The VLANs 10, 20, and 30 will support the management, IT, and Sales computers, PC1, PC2, and PC3. The F0/1 port on switch S1 will be configured as a trunk port and will forward traffic for VLANs 10, 20, and 30.

trunk port config

Configuration example:

SW1#config t

SW1(config)#interface fa0/1

SW1(config-if)#switchport mode trunk



Fa0/1 is a native VLAN which is a default VLAN and is normally used to manage switches. But converting it to trunk mode is an added security!. However, you can change or modify a native VLAN. This I  said earlier is added security.

Use the following command to move or assign another switch port as native VLAN:

SW1#config t

SW1(config)#interface fa0/1

SW1(config-if)#switchport trunk native vlan 20


Use the show interface fa0/1 or show running-config command to verify the trunk has been configured or not.

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Managing VLAN  a VTP enabled network

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