QoS implementation in a mixed-vendor enviroment

[Gustav92]

Consider the following escenario: a small enterprise network. One fortigate, 3 cisco 3560 multilayer switches, and several (around 8 or so) cheaper L2 switches (TP-link and Dlink). All users are connected to the L2 switches, which in turn are connected to the multilayer ones. There's a VM running Issabel, several IP phones distributed between the different departments. The network is really messy, I was recently hired to redesign it, using only the available infraestructure, meaning we probably won't buy any new switches/routers/anything, at least not anytime soon. My biggest concern is the voip service, nearly all users report a very deficient experience when using the ip phones. I was thinking maybe I could implement QoS policies. The cheap L2 switches supposedly support 802.1p priority tagging. My question is, is this feature useful in any way? Will the cisco 3560 be able to see/use this tag? How can I use it?

[Joseph W. Doherty · Accepted solution]

"The cheap L2 switches supposedly support 802.1p priority tagging. My question is, is this feature useful in any way?"

Maybe. (Personally I avoid using L2 CoS and manage QoS at L3 using the IP ToS tag.)

"Will the cisco 3560 be able to see/use this tag?"

It can.

"How can I use it?"

You might be able to mark VoIP frames with a different ("better") CoS marking (usually CoS 5 for VoIP bearer frames) and prioritize those frames (and perhaps packets) over other non-VoIP traffic. (NB: The 3560 should also be able to set a IP ToS marking based on a L2 frame marking. [Your VoIP equipment might also be able to set L2 CoS and/or L3 ToS.])

[Gustav92]

I didn't see this answer earlier, don't know why I didn't get a notification. Thank you very much.