Voice VLAN allows configuring a port to provide QoS to voice and data traffic in a scenario where a terminal is connected to an IP phone which is in turn connected to the port on the switch. The IP phone bridges the data traffic from the terminal into the switch port. Any voice traffic from the IP phone is also sent to the same port with no differentiation. Therefore it is in the administrator’s interest to provide different QoS to the voice traffic and the data traffic by placing the voice traffic on a different VLAN from the data traffic.
This can be achieved by configuring a voice VLAN on the desired switch port using LLDP-MED TLVs. Media Endpoint Discovery (MED) TLVs allow the switch to apply certain policies by informing the remote media device to configure itself using different TLV.
In this use-case scenario we employ the use of the network policy TLV, which is defined as per TIA-TR41. The network policy TLV can be used to inform a specific VLAN to use for an application stream.
The OS allows the user to configure the VLAN for voice traffic. In the following figure, the user configures a voice VLAN of 25 and the switch port has a PVID of 50. Therefore all the voice traffic is switched onto VLAN 25 and the untagged packets from the terminal are switched into VLAN 50.
To configure LLDP-MED TLV, run the following:
switch (config) # interface ethernet 1/4
switch (config interface ethernet 1/4) # lldp med-tlv-select media-capabilities
switch (config interface ethernet 1/4) # lldp med-tlv-select network-policy
switch (config interface ethernet 1/4) # lldp med-tlv-select all
To verify LLDP-MED TLV configuration, run the following:
switch (config) # show lldp interface
TLV flags:
PD: port-description, SN: sys-name, SD: sys-description, SC: sys-capabilities, MA: management-address
ETS-C: ETS-Configuration, ETS-R: ETS-Recommendation, AP: Application Priority, PFC: Priority Flow Control
CEE: Converged Enhanced Ethernet DCBX version
MED-CAP: Media Capabilities
MED-NWP: MED-Network Policy
Interface Receive Transmit TLVs
-----------------------------------------------------------------------------------------
Eth1/1 Enabled Enabled PD, SD
Eth1/2 Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R
Eth1/3 Disabled Disabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R, MED-NWP
Eth1/4 Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R, MED-CAP, MED-NWP
Eth1/5 Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R
Eth1/6 Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R
...
switch (config) # show lldp interface ethernet 1/4
TLV flags:
PD: port-description, SN: sys-name, SD: sys-description, SC: sys-capabilities, MA: management-address
ETS-C: ETS-Configuration, ETS-R: ETS-Recommendation, AP: Application Priority, PFC: Priority Flow Control
CEE: Converged Enhanced Ethernet DCBX version
MED-CAP: Media Capabilities
MED-NWP: MED-Network Policy
Interface Receive Transmit TLVs
-----------------------------------------------------------------------------------------
Eth1/4 Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R, MED-CAP, MED-NWP.
switch (config) # show lldp interface ethernet 1/4 med-cap
Media Capabilities:
LLDP-MED Capab : Yes
Network Policy : Yes
Location Id : No
Ext Power MDI-PSE: No
Ext Power MDI-PD : No
Network Policy:
Application Type : 1 (Voice)
VLAN Id : 11
L2 Priority : 0
DSCP Value : 0
To configure voice VLAN, take the following steps:
Create a VLAN.
switch(config) # vlan200switch(config vlan200) # exitswitch(config) #Set the interface mode to be hybrid.
switch(config) #interfaceethernet1/4switchport mode hybridswitch(config) #interfaceethernet1/4switchport hybrid allowed-vlan200Assign the VLAN to the interface.
switch(config) #interfaceethernet1/4switchport voice vlan200(Optional) Change the PVID of the port so that untagged packets go to a different VLAN than the default.
switch(config)# vlan300switch(config vlan300)# exitswitch(config)#interfaceethernet1/4switchport access vlan300Verify the configuration.
switch(config)# showinterfaceswitchport Interface Mode Access vlan Allowed vlans --------------------------------------------------------------------------------- Eth1/1access1Eth1/2access1Eth1/3access1Eth1/4hybrid300200Eth1/5access1...switch(config)# show lldpinterfaceethernet1/4TLV flags: PD: port-description, SN: sys-name, SD: sys-description, SC: sys-capabilities, MA: management-address ETS-C: ETS-Configuration, ETS-R: ETS-Recommendation, AP: Application Priority, PFC: Priority Flow Control CEE: Converged Enhanced Ethernet DCBX version MED-CAP: Media Capabilities MED-NWP: MED-Network Policy Interface Receive Transmit TLVs ---------------------------------------------------------------------------------------- Eth1/4Enabled Enabled PD, SN, SD, SC, MA, PFC, AP, ETS-C, ETS-R, MED-CAP, MED-NWPswitch(config)# show lldpinterfaceethernet1/4med-cap Media Capabilities: LLDP-MED Capab : Yes Network Policy : Yes Location Id : No Ext Power MDI-PSE: No Ext Power MDI-PD : No Network Policy: Application Type :1(Voice) VLAN Id :200L2 Priority :0DSCP Value :0
To remove voice VLAN and LLDP-MED TLV, take the following steps:
Remove the voice VLAN from the interface.
switch(config)# nointerfaceethernet1/4switchport voice vlanDisable the MED TLV from the interface.
switch(config)#interfaceethernet1/4lldp med-tlv-select none
LLDP MED cannot be enabled on a router port interface and vice versa (i.e. a port that has LLDP MED enabled cannot be configured as a router port interface).
LLDP MED cannot be enabled on a LAG and vice versa (i.e. a port that has LLDP MED enabled cannot be configured as a LAG).
If switchport is in trunk, dot1q-tunnel, or dcbx-access, configuring either the TLV or Voice VLAN gives a warning message.