VLAN (Virtual LAN)

A VLAN (Virtual LAN) partitions a physical switch network into several independent Layer 2 networks. Devices in different VLANs cannot talk directly; traffic between them must pass through a router or Layer 3 switch.

Why it matters

VLANs let you separate guests, staff, servers and IoT devices on shared hardware, shrinking broadcast domains and enabling firewall policy between groups. Frames on a trunk link carry an IEEE 802.1Q tag with a VLAN ID from 1 to 4094 so the receiving switch knows which VLAN they belong to.

Example

VLAN 10  staff    10.0.10.0/24
VLAN 20  guests   10.0.20.0/24
VLAN 30  cameras  10.0.30.0/24

A guest laptop on VLAN 20 cannot reach a camera on VLAN 30 unless the router explicitly allows it.

Common mistakes

• Assuming VLANs alone are a complete security boundary without inter-VLAN firewall rules.
• Mismatched native or allowed VLANs on a trunk, which silently drops traffic.
• Reusing the same subnet in two VLANs.

Related

• Network switch
• Subnet
• Broadcast
• LAN

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