I’ve had three conversations in the past week or so around whether a voice VLAN is required or recommended for use with Skype for Business. Let’s take a quick look at where the concept of voice VLANs came from, what they can do for you, and whether you need them for your SfB deployment.
The idea of a voice VLAN first came about when the only IP endpoint for you IP PBX was a phone on their desk. The phones generally needed a specific DHCP configuration, and if the phones were in their own VLAN this was easier to do. QoS was implemented as 802.1p at the layer 2 (switch) level, and it was much easier to simply say “this voice VLAN gets a priority of 5”. Some switches would use Cisco Discovery Protocol (CDP) or Link-Layer Discovery Protocol (LLDP) to automatically put a device that said it was a phone into the voice VLAN. Much of this early IP telephony was done with voice guys coming from a traditional TDM PBX environment. The world of IP was new to them, so anything that made their lives easier and more automatic was welcomed by not only the voice guys, but also by any IT guys who had to work with them.
Raise your hand if you ever had to explain IP subnetting to your voice guys new to IP, and try to sort out for them why the IP telephone system vendor was blabbering on about Class A subnet masks and VLAN 0. Thankfully for me, my voice guys were smarter than your average bear and quickly picked up some good habits vs the drivel in the phone vendor manuals. (Thanks Brian and Willy!)
The curious thing is that at no point did anything actually require a voice VLAN. They just made life a lot easier and more “automagic”. You could deploy a perfectly good VoIP solution without using voice VLANs.
Fast forward to today, when we talk about Unified Communications instead of IP telephony. We now have soft clients, room systems, and mobile clients. In additional to voice, we have modalities like video, web conferencing and screen sharing, all from the same client. We’ve also got BYOD and Cloud technologies to add excitement to the mix.
Having your desk phones into a voice VLAN doesn’t provide any benefit to you when you’re conferencing from a PC, or watching a PowerPoint on your iPhone in the lunchroom while you wait for the coffee to finish brewing. A good number of your users might not even have a desk phone, opting instead for a headset and soft client.
One scenario where a voice VLAN does make some sense, is when you’re doing a large-scale deployment and the number of phones you are adding outstrips the number of available IP addresses on your existing subnets. In this case, it may make sense to create a new VLAN for the phones. I say “may” as you might also have a requirement to use IP subnets for location determination for emergency calling. Overlaying a single voice VLAN to cover your site may not be suitable – you may have to deploy multiple voice VLANs to provide the location granularity required. It may make more sense to simply further partition your network into general purpose user VLANs.
Do I recommend voice VLANs? No. I think they’re a thing of the past. They add complexity to your network, increase your administration, and affect only a very small number of your UC endpoints. For those endpoints that they do affect, they do not offer any benefits that can be provided via other means, and often those other means will need to be in place for other endpoint types and other modalities.