What Is a VLAN? Definition and Configuration

What Is a VLAN? Definition, Operation, and Configuration

April 15, 2026·2 min read·250 words

A VLAN (Virtual LAN) is a logical network within a physical network that separates traffic without requiring additional hardware. The 802.1Q standard uses a 4 bytes tag in the Ethernet header. A maximum of 4094 VLANs are supported. VLANs are an essential building block of enterprise network segmentation.

Why Use VLANs?

Separate broadcast domains (one broadcast domain per VLAN)
Security: isolation between departments and user groups (finance, IT, guests)
Flexibility: users can join the correct VLAN regardless of the switch port
Efficiency: no separate cabling required
Policies: QoS, ACL, inter-VLAN routing

Port Modes

Access: 1 VLAN, untagged, for an endpoint (PC, IP phone)
Trunk: multiple tagged VLANs, for inter-switch links
Hybrid: mixed mode (Juniper)
Native VLAN: untagged VLAN on a trunk (VLAN 1 by default)

Basic Cisco Configuration

vlan 10 ; name DATA
interface Gi1/0/1 ; switchport mode access ; switchport access vlan 10
interface Gi1/0/48 ; switchport mode trunk ; switchport trunk allowed vlan 10,20,30

Common VLANs

VLAN 10: DATA (business workstations)
VLAN 20: VOICE (IP telephony)
VLAN 30: WIFI-GUEST
VLAN 40: PRINT
VLAN 50: CAM (cameras)
VLAN 99: MGMT

VLAN Security

VLAN hopping: prevent it with a dedicated, blocked native VLAN
Port security: limit the number of MAC addresses
DHCP snooping + DAI: anti-spoofing protection
Private VLAN: intra-VLAN isolation

Beyond 4094

QinQ (802.1ad): VLAN-in-VLAN, Metro Ethernet
VXLAN: 16M VNI, L2 overlay over L3
The 2026 standard for data centers

Order from OPTINOC

Campus VLAN design + 802.1Q trunking + inter-VLAN routing. Cisco, Aruba, Juniper, FortiSwitch. Quotes within 48h.

Frequently Asked Questions

Combien de VLANs peut-on créer sur un switch ?

Le standard 802.1Q supporte jusqu'à 4 094 VLANs (IDs 1 à 4094, le VLAN 1 étant le VLAN par défaut). En pratique, la plupart des switches d'entreprise supportent 1 000 à 4 000 VLANs actifs simultanément. Pour aller au-delà, il faut passer à VXLAN qui supporte 16 millions d'identifiants.

Quelle est la différence entre un VLAN et un sous-réseau ?

Un VLAN opère en couche 2 (liaison de données) et isole le trafic Ethernet. Un sous-réseau opère en couche 3 (réseau) et segmente les adresses IP. En pratique, on associe généralement un VLAN à un sous-réseau IP : VLAN 10 = 10.10.10.0/24, VLAN 20 = 10.20.20.0/24.

Faut-il un switch manageable pour les VLANs ?

Oui, les VLANs nécessitent un switch manageable (Layer 2 minimum). Les switches non manageables n'ont pas de notion de VLAN. Tous les switches Cisco Catalyst, Juniper EX, HPE Aruba CX et FortiSwitch proposés par OPTINOC supportent les VLANs.