Re: QOS Trust Boundry

From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Wed Jan 14 2009 - 09:40:05 ARST

Pavel,
I hope nobody gets tested at this level of detail, but it IS possible to
have COS markings between the PC and the phone, and cisco has commands
to instruct the switch on the phone to either remark or trust those
markings. The phone has no interest, AFAIK, in the DSCP markings and
those will pass through no matter what.

-Carlos

Pavel Bykov @ 8/01/2009 20:26 -0200 dixit:
> Rookie, to answer your question:
> Yes, you can do it. From testing, service policy takes precedence over port
> settings. E.G. you can have "trust cos" on the port and "trust dscp" only
> for some packets that match a class
>
> P.S.: Beware of the cofusion that arises from port trust state.
> Only CoS is reset to 0. But no CoS is coming from PC, since there is no
> 802.1p field. Only voice VLAN has that.
> DSCP is not reset to 0 directly, only indirectly when the "trust mode" is
> "trust cos"
> I.E.: PC sends DSCP EF, port receives it and does not have any COS, so there
> is nothing to reset. It uses the default port CoS, which as you can see is
> 0. It then plugs that 0 into internal DSCP mapping table to find out CoS and
> DSCP values, and set them accordingly... but, there is a catch. DSCP Reqrite
> has to be ON for it to set DSCP to something else.
>
>
> On Thu, Jan 8, 2009 at 9:30 PM, Rookie Ccie <rookie.ccie@gmail.com> wrote:
>
>> Dear Experts,
>>
>> If I enable cat qos trust boundary feature on a 3560 using *mls qos trust
>> device cisco-phone* command and enable an inbound policy map (to match
>> specific PC traffic) on the same interface, what will be the behaviour ?
>>
>> Rgds
>>
>>
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-- 
Carlos G Mendioroz  <tron@huapi.ba.ar>  LW7 EQI  Argentina

Blogs and organic groups at http://www.ccie.net

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