I've been reading up on network segmentation and the use of VLANs to enhance security and network management. However, I'm still a bit unclear about the concept of VLAN tagging. Can someone please explain what VLAN tagging is and how it works in the context of network segmentation? Also, are there any best practices or common pitfalls to be aware of when implementing VLAN tagging in a network?

2 Answers 2


VLAN tagging is a way to label network traffic so switches can identify which Virtual Local Area Network (VLAN) a packet belongs to. It's crucial for network segmentation, improving security, and optimizing network management.

Here's a quick rundown:

Ethernet Frames: When devices communicate in an Ethernet network, they exchange data in frames. VLAN tagging adds a tag to these frames, typically in the 802.1Q format, to indicate the VLAN.

Switch Configuration: To use VLAN tagging, configure your switches. Specify which ports are part of specific VLANs and define each VLAN's ID. The VLAN ID goes into the frame's tag.

Isolation and Segmentation: Switches examine the VLAN ID in the tag. They only forward frames to ports belonging to the same VLAN, keeping traffic separate. This enhances security and network organization.

Best Practices:

Document your VLAN setup for clarity. Implement access controls and firewalls for security. Regularly review and adjust your VLANs. Common Pitfalls:

Misconfiguration can cause traffic leaks or isolation problems. Don't create too many VLANs; it complicates management. Monitor VLAN traffic to spot issues. Hope this clears things up! Feel free to ask if you need more details.


VLANs logically divide switches into separate, unconnected switches. Frames in one VLAN cannot be sent to an interface for a different VLAN. In order to connect to a device that communicates with multiple VLANs (routers, switches, etc.), there needs to be a method to distinguish which frames belong to which VLANs so that the frames can remain separate for each VLAN.

To accomplish that, ethernet was extended to insert a tag into the ethernet header (Cisco originally did this with an encapsulation of the frame, but the industry decided on inserting tags into frame headers). The tags are inserted into the frame headers on links that carry multiple VLANs. You can have one VLAN that is not tagged, and it is distinguished from the other VLANS on the link by not having a tag, and it is called the native VLAN.

Access interfaces that go to end-devices (PCs, printers, etc., which do not normally support VLANs) are assigned to a particular VLAN, and they do not insert tags into the frame headers. Trunk links are links that carry multiple VLANs frames, and frames are tagged on trunk links (with the possible exception of a native VLAN).

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