Unanswered Question
Apr 3rd, 2007

Hi all, can anyone tell me when using cos/qos, is the cos value actually first set in the pc or phone etc that sends the packet, then you just tell the switch to trust what cos value the pc etc is sending, then you use qos to provide the policy to the cos value you have told the switch to trust ?

I have this problem too.
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kamal-learn Wed, 04/04/2007 - 00:04


-QOS quality of service is a paradigm , a set of rules to prioritize packet..

-COS is class of services ,values are from 0..7 deal with the Layer 2.

-some operating systems allow you to change the value of the TOS(type of services) of your packets .(may be with some software this values can be automatically mapped to to dscp layer 3.)

- suppose you changed these TOS values on your PC,then the packets sent after hitting the layer 2 device ie a switch on your network ,in their way to a layer 3 device, the switch will act depending on your config made using QOS commands , if the switch is configured to trust them the QOS command will take care of them and forward them according to the policy, if not the tos of your packet gonna be ignored and may be another values at layer 3 DSCP will be assigned to them in the marking process after the classification then these values gonna be mapped to COS at layer 2 when the hit another layer 2 device and so on...

PLS do rate if it does help.

carl_townshend Wed, 04/04/2007 - 06:17

can you give me an example of this config on a switch, explaing what each line means, for example if we had a voice phone plugged in.


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