Voice and Data using an Access port and the Auxiliary VLANs

And so, we’ve finally come to the primary purpose of this article – to describe the specific problems that are solved by the Auxiliary VLANs feature. Namely, the problem serves as an answer to the following question (note: illustration is identical to the one above): voice job

Voice VLAN – Auxiliary VLAN – One Port for two VLANs

In situations where only one physical port is available on your switch, how do you accept and receive Voice and Data traffic on one switchport while still keeping them in independent VLANs?

The solution:

First, use the VOIP phone’s built in switch – connect the PC to the phone, and the “LAN” port of the phone to the wall jack (which subsequently leads to the switchport).

Second, use the Auxillary VLAN configuration to accept the tagged voice traffic from the VOIP phone, and untagged traffic from the PC:

Spanning tree has an optimization known as Portfast which speeds up how quickly an access port is enabled.

Spanning tree also has an optimization known as BPDU guard which also (by default) only applies to access ports.

Port Security (by default) only applies to access ports.

There are other optimizations that exist for access ports that are tailored to ports facing network clients — like PC’s and VOIP phones.

If the interface facing your VOIP phone and PC is configured as a trunk port, it will not be able to take advantage of the optimizations which exist for access ports.

Of course, for each of these optimizations there are manual overrides that can be applied, but it increases the complexity of the network configuration. Besides, there is a much simpler solution to using a Trunk port for Voice and Data VLANs on a single port, and that solution is what this article has been building towards.

The more optimal solution is to use the Auxiliary VLAN feature (also known as the Voice VLAN).

With this configuration, traffic arriving on the single available switchport will still be accepted in two different VLANs on your network. Allowing you to separate Voice and Data traffic, despite it arriving on the same physical switchport.