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Understanding Dot1q VLAN Tagging

If you are a network security engineer, you must be aware of the importance of VLANs in network segmentation. But have you ever wondered how these VLANs are created, identified, and managed?

This is where Dot1q VLAN tagging comes into play.

In this blog post, we will delve deep into the concept of Dot1q VLAN tagging and understand its working mechanism.

What is Dot1q VLAN Tagging?

Dot1q VLAN tagging is a standardized method of identifying and managing VLANs in a network. It is a part of IEEE 802.1Q standard that defines the method of VLAN tagging in Ethernet frames. By adding a tag to the Ethernet frame, Dot1q VLAN tagging enables switches to identify and segregate traffic from different VLANs.

Definition and Purpose

Dot1q VLAN tagging allows network administrators to divide a LAN into multiple VLANs and manage them efficiently. Each VLAN is assigned a unique VLAN ID that enables switches to separate VLAN traffic from other VLANs. The VLAN ID is added to the Ethernet frame as a tag, which helps switches to forward traffic to the respective VLAN ports.

The purpose of Dot1q VLAN tagging is to provide network administrators with a more robust and scalable method of network segmentation than traditional LAN segmentation methods. With VLAN tagging, network administrators can create logical network segments that are isolated from each other, even though they are physically connected to the same network.

How Does Dot1q VLAN Tagging Work?

Now that we have understood the basics of Dot1q VLAN tagging, let's dive deeper into its working mechanism.

Tagging Process and Layer 2 Switching

When a switch receives an Ethernet frame, it checks whether the frame has a VLAN tag or not. If the frame does not have a VLAN tag, the switch forwards the frame to all the ports in the same VLAN as the source port. On the other hand, if the frame has a VLAN tag, the switch looks into the VLAN ID in the tag and forwards the frame to the respective VLAN port.

For example, suppose a switch receives an Ethernet frame from VLAN 10. The switch adds a VLAN tag with the VLAN ID of 10 to the frame and forwards it to the respective VLAN port. When the frame reaches the destination switch, the switch checks the VLAN tag and forwards the frame to the destination port in VLAN 10.

Layer 2 switching plays a vital role in the working of Dot1q VLAN tagging. Layer 2 switches perform the function of VLAN tagging and forwarding based on the VLAN ID in the Ethernet frame tag. Layer 2 switches also maintain the VLAN database, which includes VLAN IDs, port assignments, and other VLAN-related information.


In conclusion, Dot1q VLAN tagging is a crucial aspect of network segmentation that enables network administrators to create logical network segments and manage them efficiently.

Understanding the working mechanism of Dot1q VLAN tagging can help network security engineers design and implement secure VLAN-based networks.

If you want to learn more about VLAN tagging and network security, you can check out Orhan Ergun's Layer 2 course on layer 2 networking.

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Stanley Arvey

I am a certified network engineer with over 10 years of experience in the field. I have a deep understanding of networking and IT security, and I am always looking for new challenges.

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