Auto Voice VLAN, Auto Smartports, CDP, and LLDP
Defaults
By factory defaults, CDP, LLDP, and LLDP-MED on the switch are enabled, manual Smartport mode is enabled, Basic QoS with trusted DSCP is enabled, and all ports are members of default VLAN 1, which is also the default Voice VLAN.
In addition, Dynamic Voice VLAN mode is the default to Auto Voice VLAN with enabling based on trigger, and Auto Smartport is the default to be enabled depending on Auto Voice VLAN.
Voice VLAN Triggers
When Dynamic Voice VLAN mode is Auto Voice VLAN enabled based on trigger, it means Auto Voice VLAN will become 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 Voice VLAN Discovery Protocol (VSDP). If desired, an administrator can make Auto Voice VLAN mode operate immediately without waiting for a trigger.
When Auto Smartport is enabled depending on Auto Voice VLAN mode, it means Auto Smartport will be enabled when Auto Voice VLAN becomes operational. If desired, an administrator can enabled Auto Smartport independent of Auto Voice VLAN.
NOTE The default configuration list here applies to switches whose firmware version supports Auto Voice VLAN out of the box. It also applies to unconfigured switches that have been upgraded to the firmware version that supports Auto Voice VLAN.
NOTE The defaults and the voice VLAN triggers are designed to have no affect on any installations without a voice VLAN, and 200 and 300 series switches that have already been configured. You may 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 to maintain 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 UC devices, are advertising their voice VLAN, the voice VLAN from the device with the lowest MAC address is used.
NOTE If connecting the switch 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 Voice Service Discovery Protocol (VSDP). The switch 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, 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 high priority source is discovered or until the Auto Voice VLAN is restarted by the administrator. When restarted, the switch resets the voice VLAN to the default voice VLAN and restarts the Auto Voice VLAN discovery.
- When a new voice VLAN is configured/discovered, the switch 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 If the switch is in Layer 2 mode, it can synchronize with only VSDP capable switches in the same management VLAN. If the switch is in layer 3 mode, it can synchronize with VSDP capable switches that are in the directly-connected IP subnets configured at the switch.
Auto Smartport works with CDP/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 switch 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 is 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 phone+desktop.