Troubleshooting for Voice VLAN and Auto VoIP

Updated 06-26-2024 07:44:49 AM 3277
This Article Applies to: 







This article describes the Voice VLAN and Auto VoIP functions on Omada switches and provides simple steps to do a troubleshooting when problems like IP Phones unable to go online or bad experience during calls happen.


  • Omada Smart, L2+ and L3 swithes


IP phones are now widely used. To ensure call quality, it is necessary to prioritize voice traffic. Omada switches supports Voice VLAN or Auto VoIP, which can be configured to ensure a stable connection and a good user experience during calls.

This article briefly describes the scenarios for Voice VLAN and Auto VoIP, and then provides detailed troubleshooting steps for common issues.

Voice VLAN and Auto VoIP are used in different scenarios based on the capabilities of IP phones to handle VLAN-tagged packets.

  • Voice VLAN: Voice VLAN is used in scenarios where IP phones cannot handle packets with VLAN tags and cannot send or receive packets with VLAN tags. Meanwhile, the configuration for Voice VLAN is fixed and suitable for IP phones that cannot handle VLAN-tagged packets. By matching the OUI, switches can add VLAN tags and 802.1p priority to the packets sent by the IP phones.
  • Auto VoIP: Auto VoIP is suitable for scenarios where IP phones can handle VLAN-tagged packets and can both receive and send packets with VLAN tags. It utilizes LLDP-MED (Link Layer Discovery Protocol-Media Endpoint Discovery) to negotiate with the IP phones and actively configure the settings. IP phones are required to add the corresponding VLAN tags or priority tags as per the customer's requirements when sending out packets.

Troubleshooting steps

Step 1. Check the type of IP phone and verify the configuration method

Check the type of IP phone

Refer to the product brochure or datasheet to determine if the IP phone can handle VLAN-tagged packets. Check if it claims to support the 802.1Q standard or VLAN configuration. If no related information is not mentioned in the promotional materials or datasheet, or if you are unsure about the support, search online or consult the technical support of the IP phone manufacturer. When contacting technical support, ask about the product's support for the 802.1Q standard and VLAN configuration.

Verify the configuration method

After you have confirmed whether the IP phone can handle VLAN-tagged packets, check if you have selected the correct configuration method. As mentioned earlier, if the IP phone cannot handle VLAN-tagged packets, configure Voice VLAN to add tags to the packets. If the IP phone can handle VLAN-tagged packets, configure Auto VoIP to ensure that the IP phone sends out the tagged packets.

If the IP phone cannot handle VALN-tagged packets, continue to Case 1. If the IP phone can handle VLAN-tagged packets, skip to Case 2.

Case 1: Checking Voice VLAN configuration for an IP phone that cannot handle VLAN-tagged packets

IP phone registration failed, that is, the traffic of the IP phone is not added with VLAN tags and enters the dedicated voice VLAN. Follow these steps:

Step 1. Check the global configuration of Voice VLAN

Go to the Voice VLAN page, check if a VLAN is specified as the dedicated voice VLAN. Make sure this VLAN has been created as an 802.1Q VLAN before designating it as a voice VLAN. Check if the VLAN has been pre-configured and ensure that IP phone servers and other related devices are also on this VLAN to ensure IP phone service.

Step 2. Verify if the ports are added to the Voice VLAN

After selecting the Voice VLAN, the ports connected to the IP phones should be added to this VLAN. If the port is only connected to an IP phone and does not need to forward other traffic, you can untag the port and add it to this VLAN and configure its PVID (Port VLAN ID) as the VLAN ID of the Voice VLAN. If there are other devices, such as PCs or APs, connected to the port in addition to the IP phone, then tag the port and add it to the voice VLAN.

Step 3. Check if Voice VLAN is enabled on the ports

After adding the port to the Voice VLAN, go to the Voice VLAN's Port Config page and verify if Voice VLAN is enabled for the port. Normally, the Operational Status should be Active as shown in the figure below.

Step 4. Verify if the OUI (Organizationally Unique Identifier) of the IP phone brand is in the OUI Config List of the Voice VLAN page

If the OUI of the IP phone is in the OUI Config List of the Voice VLAN page, the traffic from the IP phone will not be forwarded to the Voice VLAN. Omada switches come with preconfigured OUIs for common IP phone brands. If the phone brand is not listed, manually add it. On the OUI Config page, click Add to manually add the OUI, as shown in the figure below.

Step 5. Check the priority configuration of the Voice VLAN

After verifying the VLAN configuration, the IP phones should be registered and available for use. If you experience issues such as call quality degradation, jitter, or noise during the call, check the priority configuration of the Voice VLAN. On the Voice VLAN's Global Config page, the priority can be set from 0 to 7, with 0 being the lowest priority and 7 being the highest. If there are consistent call quality issues despite no physical line issues, you can change the priority level to ensure timely forwarding of voice traffic and improve call quality. The default priority for voice traffic is 5 but can be manually increased, as shown in the figure below.

Case 2: Checking Auto VoIP configuration for an IP phone that handle VLAN-tagged packets

Auto VoIP uses the information carried in LLDP-MED packets for negotiation to allow the IP phone can send packets with specified tags as per the customer’s requirements. Therefore, first check LLDP-MED configuration, and then check other Auto VoIP related parameters.

Step 1. Check if LLDP and LLDP-MED are enabled and functioning normally

Go to the L2 FEATURES-LLDP-LLDP Config page, and enable LLDP globally. LLDP for a port is usually enabled by default.

Go to the LLDP-MED Config page, go to the Port Config section, and set the LLDP-MED Status of the corresponding port to Enabled. This will initiate LLDP-MED negotiation with the neighboring device.

In the Neighbor Info section on the LLDP-MED Config page, you can click the port to check if it has obtained the information from the neighboring device.

Step 2. Check if Auto VoIP is enabled globally and if the VLAN configured for voice traffic in the network is correct

Ensure that Auto VoIP is enabled globally.

Check the port parameters. If the IP phone is not registering properly, it is likely due to incorrect VLAN configuration. Unlike Voice VLAN, Auto VoIP does not directly assign a dedicated Voice VLAN and configure 802.1p priority globally. Instead, each port has individual configurations. Determine the VLAN in which the IP phone server is and add the port connected to the IP phone to this VLAN.

Step 3. Check the port mode for Auto VoIP

As shown in the figure below, each port can be configured with parameters such as Interface Mode, Value, CoS Override Mode, and DSCP Value.

In most cases, both the VLAN and its forwarding priority for voice traffic should be specified simultaneously, the Interface Mode should be set to VLAN ID mode to specify the VLAN. This VLAN should be the same as the VLAN configured for the IP phone server. If the IP phone is not registering properly, check if the VLAN ID configuration is correct.

After verifying the VLAN settings, the IP phones should be registered and available for use. If you experience issues such as call quality degradation, jitter, or noise during the call, check the priority settings after confirming that there are no physical link quality issues.

Step 4. Check if the priority for Auto VoIP is correct and reasonable

Because 802.1p priority is not specified in the VLAN ID mode, DSCP Value is configured to control the forwarding priority for voice traffic. The DSCP priority ranges from 0 to 63, which is similar to the 802.1p priority. The larger the number, the higher the priority.

For CoS Override Mode, it is recommended to choose Disabled. In this mode, the switch will forward the voice traffic based on the DSCP priority configured for the port. The default DSCP priority for voice traffic should be in the range of 40-47, corresponding to TC-5 forwarding queue. If you experience poor call quality during network congestion, increase the priority level. If the CoS Override Mode is set to Enabled, the switch will disregard the configured DSCP priority and directly forward voice traffic in the default TC-5 queue, so it is not recommended.


Till here, we have introduced a simple process of troubleshooting for Voice VLAN and Auto VoIP. If the issues persist, please contact TP-Link Support or the IP phone vendor for further assistance.

Get to know more details of each function and configuration please go to Download Center to download the manual of your product.

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