Re: 3650 COS/DSCP to queue mapping

I did cos 3 + cos override on pc1 side and trust dscp on pc2 side.
I can't do a show mls qos maps now but I set up a dscp24 to cos5 mapping.

On Tue, Sep 4, 2012 at 3:30 PM, marc edwards <renorider_at_gmail.com> wrote:

> Can either of you do a sh mls qos maps? Also, please show access
> interfaces config. My hunch is that the dscp-cos map hasn't been changed to
> refelect dscp 24 as cos 05. I am also curious to see if you have trusted
> cos or dscp on access. That will change things.
>
> Regards,
>
> Marc
>
>
> On Tue, Sep 4, 2012 at 8:23 AM, ccie99999 <ccie99999_at_gmail.com> wrote:
>
>> I've labbed this (cos3->dscp24->cos5) and I see I receive cos3 on the
>> second pc as well as dscp24.
>>
>> pc1(vlan1) - sw - pc2(vlan2)
>>
>> (I do trust cos on pc2 interface side).
>>
>> I guess it's fine I see dscp24.. don't understand why I see cos3.
>>
>> thanks
>>
>>
>> On Tue, Sep 4, 2012 at 12:33 PM, gp <gs4me2me_at_gmail.com> wrote:
>>
>> > Hi Joe,
>> >
>> > I tried lab what you wrote, and not have result that I expected. So I
>> have
>> > one question; in your opinion what cos value will have frame when leave
>> > switch: cos 3 or cos 5?
>> >
>> > I had cos 3, that confuse me.
>> >
>> > Thanks
>> >
>> >
>> > -----Original Message-----
>> > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>> > Joe
>> > Astorino
>> > Sent: Thursday, August 30, 2012 6:34 PM
>> > To: Anthony Sequeira
>> > Cc: Matt Eason; Cisco certification
>> > Subject: Re: 3650 COS/DSCP to queue mapping
>> >
>> > Hi Matt,
>> >
>> > Anthony answered your question simply and correctly, but I just wanted
>> to
>> > add some things that helped me understand this. Like Anthony said,
>> > whatever
>> > you trust is basically how the switch determines the queue at a high
>> level,
>> > but at a deeper level there are a few different mappings going on.
>> Let's
>> > assume you trust CoS. You would have:
>> >
>> > - CoS to DSCP mapping INTERNAL to the switch
>> > - DSCP to CoS mapping INTERNAL to the switch
>> > - CoS to output queue mapping
>> >
>> > The point I am making is that even though a frame comes in with a
>> > particular
>> > CoS value, that value COULD change internally based on the internal
>> > COS-DSCP
>> > and DSCP-COS, and the frame COULD be queued based on the value derived
>> from
>> > the internal mappings and not on the original value. Let's look at some
>> > example output for a second
>> >
>> > Here are some mapping tables for cos-dscp, dscp-cos and cos-output-q on
>> a
>> > 3750 switch. Note these are probably not default values because this is
>> a
>> > production switch.
>> >
>> > Here is the COS to DSCP mapping:
>> >
>> > switch#sh mls qos maps cos-dscp
>> > Cos-dscp map:
>> > cos: 0 1 2 3 4 5 6 7
>> > --------------------------------
>> > dscp: 0 8 16 24 32 40 48 56
>> >
>> > Here is the DSCP to CoS mapping
>> >
>> > switch#sh mls qos map dscp-cos
>> > Dscp-cos map:
>> > d1 : d2 0 1 2 3 4 5 6 7 8 9
>> > ---------------------------------------
>> > 0 : 00 00 00 00 00 00 00 00 01 01
>> > 1 : 01 01 01 01 01 01 02 02 02 02
>> > 2 : 02 02 02 02 03 03 03 03 03 03
>> > 3 : 03 03 04 04 04 04 04 04 04 04
>> > 4 : 05 05 05 05 05 05 05 05 06 06
>> > 5 : 06 06 06 06 06 06 07 07 07 07
>> > 6 : 07 07 07 07
>> >
>> > Finally, here is the CoS to output queue mapping
>> >
>> > switch#sh mls qos map cos-output-q
>> > Cos-outputq-threshold map:
>> > cos: 0 1 2 3 4 5 6 7
>> > ------------------------------------
>> > queue-threshold: 2-1 2-1 3-1 3-1 4-1 1-1 4-1 4-1
>> >
>> >
>> > Let's just look at CoS 3 for example. We see that CoS 3 is mapped to
>> DSCP
>> > 24. In turn DSCP 24 is mapped right back to CoS 3 in the DSCP to COS
>> > mapping. In turn, CoS 3 is put into output queue 3, threshold 1.
>> > Fine. So in this case, it comes in as CoS 3 and is queued based on CoS
>> 3
>> > because we trust CoS and because the DSCP-COS mapping is sort of
>> "synced".
>> > But...what if you went in and mucked with the DSCP-COS mapping
>> internally
>> > such that DSCP 24 was no longer mapped back to CoS 3? What if it was
>> > re-mapped to CoS 5 ?
>> >
>> > So you COULD have the frame come in as CoS 3 ...internally we go CoS 3
>> > --> DSCP 24, then DSCP 24 to CoS 5 then queued based on CoS 5
>> >
>> > These are intricate details, but when you are studying for the lab, I
>> think
>> > it is important to get to the dirty details! Best of luck and I hope
>> this
>> > helps you out.
>> >
>> >
>> >
>> > On Thu, Aug 30, 2012 at 10:45 AM, Anthony Sequeira
>> > <terry.francona_at_gmail.com> wrote:
>> > > Hi Matt!
>> > >
>> > > What an AWESOME question. While the documentation does not make it
>> > > clear, the value that you trust on ingress, in your example, CoS, is
>> > > the marking that is used in the appropriate default queue mapping
>> > > table on the egress port.
>> > >
>> > > Anthony Sequeira, CCIE, CCSI, VCP
>> > > http://www.stormwind.com
>> > > Twitter: @compsolv
>> > > Facebook: http://www.facebook.com/compsolv
>> > >
>> > >
>> > >
>> > > On 8/29/12 9:11 PM, "Matt Eason" <matt.d.eason_at_gmail.com> wrote:
>> > >
>> > >>Hi Guys,
>> > >>
>> > >>
>> > >>
>> > >>Can you help clarify the following. If I have a switchport configured
>> > >>on a
>> > >>3560 to trust CoS inbound, that cos value is then mapped to an
>> > >>internal DSCP value via the COS>DSCP map. That s fine.
>> > >>
>> > >>
>> > >>
>> > >>Does this switch then determine the output queue from the original CoS
>> > >>value or the internal DSCP value which was assigned by the switch? I
>> > >>see both a DSCP>Output queue map and a COS>Output queue map exists.
>> > >>
>> > >>
>> > >>
>> > >>Thanks,
>> > >>
>> > >>
>> > >>
>> > >>Matt
>> > >>
>> > >>
>> > >>Blogs and organic groups at http://www.ccie.net
>> > >>
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>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> >
>> >
>> >
>> > --
>> > Regards,
>> >
>> > Joe Astorino
>> > CCIE #24347
>> > http://astorinonetworks.com
>> >
>> > "He not busy being born is busy dying" - Dylan
>> >
>> >
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Received on Tue Sep 04 2012 - 15:31:52 ART