QoS - Clarification

Unanswered Question
Jun 14th, 2007

L2 switchport is trust the device. Then, will L2 switch use the dscp value to classify the traffic or the cos value ?

I have this problem too.
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Aaron Harrison Fri, 06/15/2007 - 04:31


You set the switchports (depending on hardware and software versions) like so:

mls qos trust dscp (to use DSCP to classify)

mls qos trust cos (to trust CoS)

If you have the port set up to conditionally trust the cisco-phone, then it uses CoS and can optionally instruct the phone to mark down PC-port traffic.



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Steven Holl Tue, 06/19/2007 - 13:34

L2 switchports won't look at DSCP values since DSCP is a L3 header. CoS tags are only carried through on trunk links. L3 switchports won't trust DSCP, and you need to trust it with the 'mls qos trust' commands recommended above.


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