Zyxel Switch - Configure Voice VLAN to Improve Voice Traffic Quality

Voice traffic is highly sensitive to delay, jitter, and packet loss. Zyxel Voice VLAN helps improve call quality by automatically placing IP phone traffic into a dedicated VLAN while assigning it a higher 802.1p priority. This ensures that voice packets receive preferential treatment over regular data traffic, helping maintain stable and clear VoIP communication even when the network is under load.

In this example, Voice VLAN 100 is used with 802.1p priority 6. The configuration demonstrates how to identify IP phones by their OUI (MAC address prefix), automatically assign them to the Voice VLAN, and verify the configuration using port mirroring and Wireshark.

Note: The IP addresses and subnet masks shown in this article are example values. Replace them with those used in your own network. 

Network Topology

The example topology consists of:

• An IP Phone connected to Switch-1 (XS3800-28).
• A PC connected to Switch-1.
• Switch-1 connected to Switch-2 (GS2220-50HP).
• Voice traffic is carried through VLAN 100, while management remains on VLAN 1.

Step 1 – Configure the Voice VLAN

Before enabling Voice VLAN, create VLAN 100 on both switches.

Ensure that:

• VLAN 100 exists on both Switch-1 and Switch-2.
• VLAN 100 is allowed across the inter-switch link (trunk).
• Devices assigned to VLAN 100 can communicate between both switches.

Step 2 – Configure Voice VLAN

Navigate to:

Menu → Switching → VLAN → Voice VLAN Setup → Voice VLAN Global Setup

Configure:

• Voice VLAN: 100
• Priority: 6

Click Add.

The configured priority (802.1p CoS) marks voice packets so that switches can prioritize them over normal data traffic.

Configure the Voice VLAN OUI

Next, configure the OUI (Organizationally Unique Identifier) used to recognize supported IP phones.

Navigate to:

Menu → Switching → VLAN → Voice VLAN Setup → Voice VLAN OUI Setup

Configure:

• OUI Address: 00:15:65:93:81:54
• OUI Mask: ff:ff:ff:00:00:00
• Description: IP Phone

Click Add (or Apply, depending on the firmware version).

Note: With this configuration, the switch automatically recognizes devices whose MAC addresses match the specified OUI and assigns their traffic to the configured Voice VLAN.

Step 3 – Configure Port Mirroring (Verification)

To verify that Voice VLAN is working correctly, configure port mirroring.

Navigate to:

Menu → Switching → Mirroring → Mirroring

Configure the following:

• Active: Enabled
• Monitor Port: Port connected to the monitoring PC
• Mirrored Port: Port connected to the IP Phone (Port 2 in this example)
• Direction: Both

Click Apply.

Port mirroring allows Wireshark to capture all traffic passing through the selected switch port for verification.

Step 4 – Verify the Configuration

Connect the monitoring PC to the configured monitor port.

Open Wireshark and apply the following display filter:

arp || igmp

Next:

1. Log in to Switch-2.

2. Navigate to:

   Menu → Management → Diagnostic → Ping Test

3. Ping the IP Phone.

The ping should complete successfully.

(Insert improved Wireshark screenshot here.)

Inspect the captured packets in Wireshark.

The Ethernet frame should show:

• 802.1Q VLAN ID: 100
• 802.1p Priority: 6

This confirms that the switch has correctly identified the IP phone, assigned it to the configured Voice VLAN, and applied the configured QoS priority.

Result

After completing the configuration:

• IP phones are automatically detected using their OUI.
• Voice traffic is automatically assigned to Voice VLAN 100.
• Voice packets receive 802.1p priority 6.
• Voice and data traffic remain logically separated.
• Wireshark confirms that VLAN tagging and QoS priority are applied correctly.

This configuration improves VoIP performance by ensuring that voice traffic receives higher forwarding priority throughout the Zyxel switching infrastructure.