Introduction:

VLANs provide an effective way to segment networks and separate traffic for various purposes, such as security or performance optimization. To maintain VLAN separation across multiple switches, 802.1Q VLAN tagging is employed. This article explains the purpose of 802.1Q VLAN tagging and how it enables traffic separation across trunk links, along with configuration examples.

Purpose of 802.1Q VLAN Tagging:

The primary purpose of 802.1Q VLAN tagging is to encapsulate Ethernet frames with VLAN identifiers (tags), allowing traffic from different VLANs to be separated and transmitted over a single trunk link between switches. By adding a VLAN tag to the frame header, switches can identify the VLAN membership of each frame and forward it accordingly, ensuring proper traffic separation and maintaining VLAN integrity across the network.

Configuration Example:

To configure an 802.1Q trunk link on a Cisco switch, use the following commands:

1. Enter global configuration mode:

Switch# configure terminal

2. Enter the interface configuration mode for the desired port:

Switch(config)# interface [INTERFACE_TYPE] [INTERFACE_NUMBER]

3. Set the interface to trunk mode:

Switch(config-if)# switchport mode trunk

4. Enable 802.1Q encapsulation on the trunk link:

Switch(config-if)# switchport trunk encapsulation dot1q

5. (Optional) Configure allowed VLANs on the trunk link:

Switch(config-if)# switchport trunk allowed vlan [VLAN_LIST]

6. Save the configuration:

Switch(config-if)# end
Switch# write memory

Conclusion:

802.1Q VLAN tagging is an essential aspect of VLAN implementation in networks spanning multiple switches. By encapsulating Ethernet frames with VLAN tags and configuring trunk links, network administrators can maintain traffic separation and VLAN integrity, contributing to a secure and efficient network infrastructure.