Understanding 802.1Q Trunking – A Core Concept in Networking

Hey everyone 👋

This is my first post here, and I’m really happy to join the DEV community — great to see so many people sharing knowledge here.

I’ve been working on networking projects lately and wanted to share one of the most essential CCNA concepts: 802.1Q Trunking.

When you configure VLANs, you quickly notice that each VLAN is isolated to a single switch.

But what happens when you want VLANs to communicate across multiple switches?

That’s exactly where 802.1Q comes in.

What is 802.1Q Trunking

802.1Q Trunking is an IEEE standard that allows multiple VLANs to travel over a single physical link.

Each Ethernet frame is tagged with a VLAN ID, letting the receiving switch know which VLAN the frame belongs to.

This makes it possible for VLANs to extend beyond a single switch, connecting entire networks logically.

Example topology

Below is a simple diagram showing two switches connected by a trunk link.

Notice how VLAN 10 and VLAN 20 can communicate between SW1 and SW2 using 802.1Q tagging.

Key takeaways

• Access ports handle traffic for one VLAN only.
• Trunk ports carry traffic for several VLANs using 802.1Q tags.
• The native VLAN stays untagged by default.

It’s a fundamental mechanism for VLAN communication across a network.

If you’d like to go deeper with diagrams and configuration examples, I wrote a detailed explanation for learners, it’s totally free to read:

👉 802.1Q Trunking Explained (Free Guide)

Thanks for reading.

I’m new here, so feel free to share your feedback or tips for improving future posts.

Comments

[Dorian Alary]

Great articles!

[Elwin Berrar]

thank!