Re: 3650 COS/DSCP to queue mapping

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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> >
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>
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Received on Tue Sep 04 2012 - 08:30:06 ART