Article ID:5861
Introduction
The Voice Virtual Local Area Network (VLAN) is used when traffic from Voice over Internet Protocol (VoIP) equipment is assigned to a specific VLAN that is made up of voice devices such as IP phones, Voice over Internet Protocol (VoIP) endpoints, and voice systems. The switch can automatically detect and add port members to the Voice VLAN, and assign the configured Quality of Service (QoS) to packets from the Voice VLAN. If the voice devices are in different Voice VLANs, IP routers are needed to provide communication.
The Voice VLAN feature permits the switch ports to carry voice traffic with Layer 3 IP precedence and Layer 2 class of service (CoS) values from an IP phone. Based on IEEE 802.1p CoS, the switch supports QoS which uses classification and scheduling to send network traffic from the switch. You can configure the Cisco IP phone to forward traffic with an IEEE 802.1p priority, and configure the switch to trust or override the traffic priority assigned by an IP phone.
Configuring Voice VLANs ensures that the VoIP devices will not have to contend directly with the broadcasts, data, and other traffic from other VLANs which could cause delays when delivering the traffic. Voice VLANs generally make the network configuration simple by marking the packets for QoS and which are assigned higher priority.
In the scenario below, the ports on the switch that are connected to the IP Phones are configured with Voice VLAN settings.
The switch supports two dynamic Voice VLAN modes: Telephony Organization Unique Identifier (OUI) mode and Auto Voice VLAN mode. The two modes affect how Voice VLAN and/or Voice VLAN port memberships are configured. The two modes are mutually exclusive to each other.
- Telephony OUI — In Telephony OUI mode, the Voice VLAN must be a manually-configured VLAN, and cannot be the default VLAN. When the device is in Telephony OUI mode and a port is manually configured as a candidate to join the Voice VLAN, the device dynamically adds the port to the Voice VLAN if it receives a packet with a source MAC address matching to one of the configured telephony OUIs. An OUI is the first three bytes of an Ethernet MAC address. To configure the Voice VLAN Telephony OUI settings on your switch through the CLI, click here.
- Auto Voice VLAN — In Auto Voice VLAN mode, the Voice VLAN can be either the default Voice VLAN, manually configured, or learned from external devices such as UC3xx or UC5xx, and from switches that advertise Voice VLAN in Cisco Discovery Protocol (CDP) or Voice VLAN Discovery Protocol (VSDP). VSDP is a Cisco-defined protocol for voice service discovery. Unlike Telephony OUI mode that detects voice devices based on telephony OUI, Auto Voice VLAN mode depends on Auto Smartport to dynamically add the ports to the Voice VLAN. If enabled, Auto Smartport adds a port to the Voice VLAN if it detects an attaching device to the port that advertises itself as a phone or media end points through CDP and/or LLDP-MED.
Voice VLAN Triggers
When the Dynamic Voice VLAN mode is Auto Voice VLAN, Auto Voice VLAN becomes operational only if one or more triggers occur. Possible triggers are static voice VLAN configuration, voice VLAN information received in neighbor CDP advertisement, and voice VLAN information received in the VSDP. If desired, you can activate Auto Voice VLAN immediately without waiting for a trigger.
When Auto Smartport is enabled, depending on Auto Voice VLAN mode, Auto Smartport is enabled when Auto Voice VLAN becomes operational. If desired, you can make Auto Smartport independent of Auto Voice VLAN.
Note: The defaults and the voice VLAN triggers are designed to have no effect on installations without a voice VLAN or on switches that have already been configured. You can manually disable and enable Auto Voice VLAN and/or Auto Smartport to fit your deployment if needed.
Auto Voice VLAN
Auto Voice VLAN is responsible in maintaining the voice VLAN, but depends on Auto Smartport to maintain the voice VLAN port memberships. Auto Voice VLAN performs the following functions when it is in operation:
- It discovers voice VLAN information in CDP advertisements from directly connected neighbor devices.
- If multiple neighbor switches and/or routers, such as Cisco Unified Communication (UC) devices, are advertising their voice VLAN, the voice VLAN from the device with the lowest MAC address is used.
Note: If connecting the device to a Cisco UC device, you may need to configure the port on the UC device using the switchport voice vlan command to ensure the UC device advertises its voice VLAN in CDP at the port.
- It synchronizes the voice VLAN-related parameters with other Auto Voice VLAN-enabled switches, using VSDP. The device always configures itself with the voice VLAN from the highest priority source it is aware of. The priority is based on the source type and MAC address of the source providing the voice VLAN information. Source type priority from high to low are static VLAN configuration, CDP advertisement, and default configuration based on changed default VLAN, and default voice VLAN. A numeric low MAC address is of higher priority than a numeric high MAC address.
- It maintains the voice VLAN until a new voice VLAN from a higher priority source is discovered or until the Auto Voice VLAN is restarted by the user. When restarted, the device resets the voice VLAN to the default voice VLAN and restarts the Auto Voice VLAN discovery.
- When a new voice VLAN is configured or discovered, the device automatically creates it, and replaces all the port memberships of the existing voice VLAN to the new voice VLAN. This may interrupt or terminate existing voice sessions, which is expected when network topology is altered.
Note: The device can synchronize with VSDP-capable switches in the same management VLAN and in the directly connected IP subnets configured at the device.
Auto Smartport works with CDP and/or LLDP to maintain the port memberships of the voice VLAN when voice end-points are detected from the ports:
- When CDP and LLDP are enabled, the device sends out CDP and LLDP packets periodically to advertise the voice VLAN to the voice endpoints to use.
- When a device attaching to a port advertises itself as a voice endpoint through CDP and/or LLDP, the Auto Smartport automatically adds the port to the voice VLAN by applying the corresponding Smartport macro to the port (if there are no other devices from the port advertising a conflicting or superior capability). If a device advertises itself as a phone, the default Smartport macro is phone. If a device advertises itself as a phone and host or phone and bridge, the default Smartport macro is IP Phone + Desktop.
Voice VLAN QoS
Voice VLAN can propagate the CoS/802.1p and Differentiated Services Code Point (DSCP) settings by using Link Layer Discovery Protocol-Media Endpoint Discovery (LLDP-MED) Network policies. The LLDP-MED is set by default to response with the Voice QoS setting if an appliance sends LLDP-MED packets. MED-supported devices must send their voice traffic with the same CoS/802.1p and DSCP values, as received with the LLDP-MED response.
You can disable the automatic update between Voice VLAN and LLDP-MED and use your own network policies.
Working with the OUI mode, the device can additionally configure the mapping and remarking (CoS/802.1p) of the voice traffic based on the OUI.
By default, all interfaces are CoS/802.1p trusted. The device applies the quality of service based on the CoS/802.1p value found in the voice stream. In Auto Voice VLAN, you can override the value of the voice streams using advanced QoS. For Telephony OUI voice streams, you can override the quality of service and optionally remark the 802.1p of the voice streams by specifying the desired CoS/802.1p values and using the remarking option under Telephony OUI.
Voice VLAN Constraints
The following constraints exist:
- Only one Voice VLAN is supported.
- A VLAN that is defined as a Voice VLAN cannot be removed.
Objective
To manually configure the Auto Voice VLAN settings on your switch, follow this workflow:
- Create a VLAN. For instructions on how to create VLANs using the Command Line Interface (CLI), click here.
- Configure Voice VLAN properties.
- Configure Dynamic Auto Voice VLAN Settings.
- (Optional) Configure LLDP or CDP settings. To configure LLDP using the CLI-based instructions, click here. To configure CDP settings, click here.
- Configure Smartports settings. For instructions, click here.
Note: By default, CDP, LLDP, LLDP-MED, auto Smartport mode, and basic QoS with trusted DSCP are all enabled. All ports are members of default VLAN 1, which is the default Voice VLAN.
This article provides instructions on how to configure Voice VLAN Properties on a switch through the Command Line Interface (CLI).
Note: In this scenario, a switch with pre-configured Voice VLAN Telephony OUI settings is being configured with Auto Voice VLAN settings.
Applicable Devices
- Sx350 Series
- SG350X Series
- Sx500 Series
- Sx550X Series
Software Version
- 2.3.0.130
Configure Auto Voice VLAN Properties
Display Voice VLAN Settings
Step 1. To display the voice vlan local information about the Voice VLAN local configuration, enter the following:
SG350X#show voice vlan local
Note: In this example, the current Voice VLAN type is Telephony OUI.
Step 2. (Optional) To display the Voice VLAN status for all interfaces or for a specific interface if the Voice VLAN type is OUI, enter the following:
The options are:
- type oui — Common and OUI-voice-VLAN specific parameters are displayed.
- interface-id — (Optional) Specifies an Ethernet port ID.
- detailed — (Optional) Displays information for non-present ports in addition to present ports.
Note: In this example, the information on the OUI-enabled Voice VLAN is displayed.
You should now have successfully displayed the current Voice VLAN settings on your switch through the CLI.
Configure Voice VLAN Properties
The default VLAN of the switch is VLAN 1 which cannot act as the Voice VLAN. However, if there is no other configured VLAN, VLAN 1 can be assigned to Voice VLAN.
Note: To know how to configure VLAN settings on your switch through the CLI, click here for instructions.
Step 1. Log in to the switch console. The default username and password is cisco/cisco. If you have configured a new username or password, enter the credentials instead.
Note: To learn how to access an SMB switch CLI through SSH or Telnet, click here.
Note: The commands may vary depending on the exact model of your switch. In this example, the SG350X switch is accessed through Telnet.
Step 2. From the Privileged EXEC mode of the switch, enter the Global Configuration mode by entering the following:
SG350X#configure
Step 3. In the Global Configuration mode, enter the Interface Configuration context by entering the following:
SG350X(config)#voice vlan id [vlan-id]
- vlan-id — Specifies the Voice VLAN. The range is from one up to 4094.
Note: In this example, Voice VLAN 40 is being configured.
Step 4. Press Y on your keyboard to continue.
Step 5. To specify a value of VPT (802.1p VLAN priority tag) that will be advertised by LLDP in the Network Policy TLV, enter the following:
SG350X(config)#voice vlan vpt [vpt-value]
- vpt-value — The VPT value to be advertised (range 0-7).
Step 6. Press Y on your keyboard to continue.
Step 7. To specify a value of DSCP that will be advertised by LLDP in the Network Policy TLV, enter the following:
SG350X(config)#voice vlan dscp [dscp-value]
Step 8. Press Y on your keyboard to continue.
Configure Dynamic Auto Voice VLAN Settings
Manually re-configuring the voice VLAN ID, CoS/802.1p, and/or DSCP from their default values results in a static voice VLAN, which has higher priority than auto voice VLAN that was learned from external sources.
Note: If the device is currently in Telephony OUI mode, you must disable it before you can configure Auto Voice VLAN.
Step 9. To change the administrative state from OUI-enabled to auto-enabled (or auto-triggered), you must first set the administrative state to disabled by entering the following:
SG350X(config)#voice vlan state [disabled]
- disable — Disable Auto Voice Vlan or Telephony OUI.
Step 10. Press Y on your keyboard to continue.
Step 11. To enable Auto Voice VLAN, enter the following:
SG350X(config)#voice vlan state [auto-enabled]
- auto-enabled — The operational state is auto-enabled.
Step 12. (Optional) To configure the voice VLAN be enabled by a trigger, enter the following:
SG350X(config)#voice vlan state [auto-triggered]
Note: In this example, auto-triggered is enabled. When the device detects a Voice VLAN advertisement, Auto Voice VLAN is activated. The operational state is auto-enabled only if one of the following occurs:
- A static local configured voice VLAN ID, CoS/802.1p, and/or DSCP that is not factory default is configured.
- A CDP voice VLAN advertisement is received from a neighboring CDP device that is not a device of the same family as the current device.
- A VSDP message was received from a neighbor switch. VSDP is a Cisco Small Business proprietary protocol for SF and SG series managed switches.
- In all other cases the operational state is disabled.
Step 13. (Optional) To restart the Voice VLAN discovery process on all Auto Voice VLAN-enabled switches in the VLAN by removing all externally learned voice VLAN attributes and resetting the voice VLAN to the default voice VLAN, enter the following:
SG350X(config)#voice vlan refresh
Step 14. Enter the exit command to go back to the Privileged EXEC mode:
SG350X(config)#exit
You should now have successfully configured the Auto Voice VLAN settings on your switch through the CLI.
Display Voice VLAN Settings
Step 1. To display the Voice VLAN status for all interfaces or for a specific interface if the Voice VLAN type is auto, enter the following:
SG350X#show voice vlan type auto [interface-id | detailed]
The options are:
- type auto — Common and Auto Voice VLAN-specific parameters are displayed.
- interface-id — (Optional) Specifies an Ethernet port ID.
- detailed — (Optional) Displays information for non-present ports in addition to present ports.
Note: In this example, the information on the auto-enabled Voice VLAN is displayed.
Step 2. (Optional) To display the voice vlan local information about the Voice VLAN local configuration, enter the following:
SG350X#show voice vlan local
Step 3. (Optional) In the Privileged EXEC mode of the switch, save the configured settings to the startup configuration file by entering the following:
SG350X#copy running-config startup-config
Step 4. (Optional) Press Y for Yes or N for No on your keyboard once the Overwrite file [startup-config].... prompt appears.
You should now have displayed the Auto Voice VLAN configuration settings on your switch through the CLI.