From: robbie (robbie@packetized.org)
Date: Tue Oct 26 2004 - 21:48:11 GMT-3
From how I read the explanations, I understand it to mean that if the
switch is configured to trust-cos on that port, that it marks the packet
with an internal-DSCP value based on the CoS, whatever the CoS may be.
The internal-DSCP value is derived from a 'qos map' of some sort,
whether it's 'mls qos dscp-mutation' or some other map.
Having said that, if your question is 'does the cos-to-dscp map operate
on the frame prior to the dscp-mutation map changing the internal dscp
value of the frame?' then I believe that the answer is no, because you
have to have trust 'mls qos trust dscp' configured on the interface
instead of 'mls qos trust cos'.
I think my understanding of it is right - someone confirm/deny?
cheers,
robbie
(ps: 'cisco catalyst qos: quality of service in campus networks' is a
great book on the subject)
Edwards, Andrew M wrote:
> I haven't been able to drum up a clear answer in my mind on this one...
>
> If I set a port to trust cos, I know that the default COS (or 0) is
> applied to unmarked traffic. What I don't know is if the switchport
> marks the IP packet with the DSCP value to the cos-to-dscp map?
>
> Or, is the DSCP mapping just another way the switch could filter/act on
> the packet?
>
> Any help with this is appreciated.
>
> andy
>
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