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QoS Settings & other issues

Hi we have the following qos settings running on our core switches 355012T

mls qos trust dscp

wrr-queue bandwidth 5 80 15 1

wrr-queue cos-map 1 0

wrr-queue cos-map 2 3 4

wrr-queue cos-map 3 1 2

wrr-queue cos-map 4 5 6 7

priority-queue out

my concern is that when the links get busy we are experiencing real slow downs for the data network. Would increasing the allocation for cos 0 help?

My guess is no as the voice will always be serviced 1st.

Also we wish to tag some of our important vlan's with higher cos settings. How could we achieve this?


Cisco Employee

Re: QoS Settings & other issues


There are no absolute QoS settings, because your network usage will change as applications are changing. Also be aware, that the queueing settings only come into the picture, if the link is overloaded. Only then your config will allocate resources to application classes. If there is no overload condition, then everything will be sent with wirespeed. To make a suggestion to set the parameters in your environment to different values, one would need to understand your traffic mix, application requirements, duration of overload conditions, etc. A lot of information usually not available; and even if: would it be the same tomorrow?

So my suggestion is to start with what you have and to continuously monitor your network. Watch out for drops on interfaces, average load during peak hours over time and - depending on the device capabilities - QoS related counters. Only act, if there are indications that you experience issues for some important applications or your projected traffic load will be above link speed in forseeable future. In the latter case adding more bandwidth is for sure the best approach, better than finetuning queueing parameters.

For your last question: you can assign a default cos value to an access port other than 0. This will allow you to classify important traffic at the entry to your network.

Hope this helps! Please use the rating system.

Regards, Martin

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