A voice VLAN is a VLAN ( virtual local area network) that is specifically allocated for the user’s voice data as we all know the VoIP traffic is very sensitive and VOIP traffic can deal with the delay, Bandwidth congestion, etc. The reason we need Voice VLAN is to prioritize that traffic after separating them. Once you will separate the voice traffic in your network then you can prioritize your voice traffic and It ensures the quality of voice traffic by improving its transmission priority of it when transmitted with other traffic. That is to say, when other services (data, video, etc.) are transmitted simultaneously, voice service will be prioritized and transmitted with a higher forwarding priority.
How Does Voice VLAN Work?
To prioritize the voice traffic, we need to identify them.
Voice VLAN can identify voice data streams in two ways. One is by identifying the source MAC addresses of the received packets (MAC address-based mode), and the other is by identifying the VLAN tags of the received packets (VLAN-based mode).
There are 2 ways we can install our VOIP phones in our network.
- We can connect our Phones to a switch port and from phone to PC.
- We can connect our phone and PC to two different ports of a switch.
The second is one is not recommended because we have to use an additional port in the switch .as we have 3 ports available in the phone we can connect our PC to the phone directly.
Let’s say according to the above diagram our phone and PC are connected.
Behind the scenes, we have a trunk between our switch and IP phone. The port on the IP phone that connects to the computer is an access port. The IP phone will forward all traffic from the computer to the switch untagged, traffic from the IP phone itself will be tagged. The only two VLANs that are allowed though, are the access and voice VLANs.
Voice VLAN Configuration.
Let’s configure a switch port where we use VLAN 50 for the DATA and VLAN 25 for our IP phone.
First, we have to create the two VLANs:
SW1(config)#vlan 50 SW1(config-vlan)#name DATA SW1(config-vlan)#exit SW1(config)#vlan 25 SW1(config-vlan)#name VOIP SW1(config-vlan)#exit
Now, let’s configure the port with respective Data and Voice Vlans.
SW1(config)#interface fa0/1 SW1(config-if)#switchport mode access SW1(config-if)#switchport access vlan 50 SW1(config-if)#switchport voice vlan 25 SW1(config-if)#exit
Now let’s Verify the configuration by using switchport command .
SW1#show interfaces fa 0/1 switchport Name: fa0/1 Switchport: Enabled Administrative Mode: static access Operational Mode: static access Administrative Trunking Encapsulation: negotiate Operational Trunking Encapsulation: native Negotiation of Trunking: Off Access Mode VLAN: 50 (DATA) Trunking Native Mode VLAN: 1 (default) Administrative Native VLAN tagging: enabled Voice VLAN: 25 (VOIP) Administrative private-vlan host-association: none Administrative private-vlan mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk Native VLAN tagging: enabled Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk associations: none Administrative private-vlan trunk mappings: none Operational private-vlan: none Trunking VLANs Enabled: ALL Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs Allowed: ALL Protected: false Unknown unicast blocked: disabled Unknown multicast blocked: disabled Appliance trust: none
Another thing is very important to understand that, When we configure the voice vLAN on switch port it will show us as non-trunking but in reality its a trunk .Now lets verify.
SW1#show interfaces fa0/1 trunk Port Mode Encapsulation Status Native vlan Fa0/1 off negotiate not-trunking 1 Port Vlans allowed on trunk Fa0/1 25-50 Port Vlans allowed and active in management domain Fa0/1 25-50 Port Vlans in spanning tree forwarding state and not pruned Fa0/1 25-50
Above we see that VLAN 25 and 50 are allowed on this interface. Although it shows up as non-trunking . in reality, it is a trunk.