How to Configure VLANs on a Cisco Catalyst Switch
VLANs (Virtual LANs) segment a single physical switch into multiple logical networks. This guide covers creating VLANs, assigning access ports, and configuring 802.1Q trunks on Cisco Catalyst switches.
What You Need
- Cisco Catalyst switch (2960-X, 9300, 3850, etc.)
- Console or SSH access
Step-by-Step Instructions
Step 1: Create the VLAN
configure terminal vlan 10 name Data vlan 20 name Voice vlan 30 name Guest exit
Step 2: Assign access port to a VLAN
interface GigabitEthernet1/0/1 switchport mode access switchport access vlan 10 exit
Step 3: Configure a trunk port (uplink)
interface GigabitEthernet1/0/48 switchport mode trunk switchport trunk allowed vlan 10,20,30 switchport trunk native vlan 1 exit
Step 4: Add voice VLAN to access port
interface GigabitEthernet1/0/2 switchport mode access switchport access vlan 10 switchport voice vlan 20 exit ! VoIP phone tags voice traffic on VLAN 20, PC traffic stays on VLAN 10.
Step 5: Verify VLAN configuration
show vlan brief show interfaces switchport show interfaces trunk
Frequently Asked Questions
What is the native VLAN?
On a trunk port, the native VLAN is the VLAN whose traffic is sent untagged (no 802.1Q tag). Default is VLAN 1. Best practice: change native VLAN to an unused VLAN ID to prevent VLAN hopping attacks.
Can I have the same VLAN ID on different switches?
Yes — VLAN IDs are switch-local. The same VLAN 10 exists independently on each switch. To connect them, configure trunk links with VLAN 10 in the allowed list.
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