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.

Lets use the topology below foe a it 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

SW1(config-if)#end

Note:

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

SW1(config-if)#end

The show interface fa0/1 or show running-config command reveals that the trunk has been configured or not.

How To Configure Switch Security

VLAN Trunking

VLAN Switchport Membership mode

VLAN Configuration on Cisco Switch

Troubleshoot VTP configuration

Native VLAN mismatches

Troubleshoot VLAN and Trunks

Managing VLAN  a VTP enabled network

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