Networking 5 things

4 Things About VLANs You Must Know

4 things about VLANs that your switch is secretly doing…

Lesson notes

Key points

1. Logical, not physical: A VLAN splits one physical switch into several separate logical networks.
2. Its own broadcast domain: Broadcasts from one VLAN never reach devices in a different VLAN.
3. Trunks carry tags: Trunk links use IEEE 802.1Q tags to say which VLAN each frame belongs to.
4. Routers join them: To talk between VLANs, you need a router or a layer 3 switch.

Takeaway: Each VLAN is its own broadcast domain; routing connects them.

Quick check: What device is needed for traffic to pass between two VLANs?

A layer 2 hub
A repeater
A router or layer 3 switch

VLANs are separate networks, so inter-VLAN traffic must be routed at layer 3.

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