CoS values have no inherent significance. In and of themselves, a CoS value does not bestow any importance to a frame. The IOS does not see a frame with a CoS of 5 and somehow automatically give it more importance over a frame it sees with a CoS of 2. The diffferentiation between the handling of traffic occurs when the traffic is scheduled.
For example, a 3550 switch has 4 egress queues, and by default WRR is configured to service each queue equally; they all have the same weight. So, unless we change the weighting on the queues and direct the more important traffic to the "heavier" queue, all traffic will be handled the same. In other words, the actual CoS value in and of itself is meaningless. So, I could tag, say, VoIP traffic with a CoS of only 1, but as long as I direct that traffic to a heavily weighted queue, or a priority queue (queue 4 on the 3550), that is fine.
Is all this correct? If not, where exactly is my understanding wrong?
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Yes and no. Actual preference for particular CoS (or L2 ToS) markings depends on device configuration. You're correct, that in itself, CoS tags mean nothing and many default device configurations won't treat the traffic differently but when devices do treat differently, often there are expectations about the importance of different markings, so I would recommend not marking traffic in such a way that becomes a problem later on.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...