Re: MLS QOS

Marc,
switch don't do "correlation" in any of the meanings of that word I
know. If you trust COS, then the incoming COS value is used to derive
the internal DSCP. If you trust DSCOm then incoming DSCP value is used
instead.

Is it hard for me to offer "evidence" of that in written form. What you
need to see it is to generate frames with different markings and see
what happen.
Medianet QoS docs may help showing it:

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND_40/QoSCampus_40.html#wp1098549

-Carlos

marc edwards @ 26/05/2012 12:36 -0300 dixit:
> /This is the whole point of the previous question! If you use "trust
> DSCP" then the switch will indeed use DSCP and not COS./
> /
> /
> Carlos, if trusting DSCP, the switch will use it's mappings to correlate
> the packet's DSCP value to the frame's COS value. Switches deal with
> frames, hense the use of COS. Please show me evidence that supports
> otherwise.
>
> Marc
>
> On Sat, May 26, 2012 at 8:25 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>> wrote:
>
> marc edwards @ 26/05/2012 11:55 -0300 dixit:
>
> 1) doesn't matter because the switch will use it's mappings to
> take dscp
> value and convert to associated cos more importantly the
> mappings have
> to be adjusted. either command is good but I would also add a
> 'switchpot
> voice vlan XX' putting the phone into another network and 'mls
> qos trust
> device cisco-phone'. These commands will put cisco phones on another
> vlan and use macros to ensure .1p is set up properly.
>
>
> It does matter.
> It is how you tell the switch to decide which marking is for good,
> and ignore the other. cos-to-dscp is only used if you decide to
> trust COS, otherwise the DSCP goes straight into internal DSCP.
> dscp-to-cos is used on output to create the L2 marking if needed.
>
> But you also can use trust extend, which instructs the phone
> (switch) to remark PC's packets (or should I say frames) with a
> given COS. That is the remarking that I was referring to.
>
>
> 2) The Cisco phones will most likely mark both but switch will
> only use
> CoS. The DSCP values are adjusted based on the internal switch
> mappings.
> This mapping is not ideal left to default values and is
> typically fixed
> manually. I don't know why cisco just didn't make it default.
> ... This
> command : 'mls qos map cos-dscp 0 8 16 24 32 46 48 56' is used
> in global
> config to map EF (IP precedence 5) to the dscp value 46.
>
>
> What do you mean by "switch will only use COS" ?? This is the whole
> point of the previous question! If you use "trust DSCP" then the
> switch will indeed use DSCP and not COS.
>
> The mapping is older than DSCP, at least older than any DSCP usage
> standarization, I would guess.
>
> -Carlos
>
>
> You are taking the right steps for Catalyst QoS good luck!
>
> HTH
>
> Marc
>
> On Sat, May 26, 2012 at 5:04 AM, Carlos Mendioroz
> <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>
> <mailto:tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>> wrote:
>
> COS fpr sure.
> Phones mark COS & DSCP but only remark COS, so if you want
> tp extend the
> trust border, you have tp trust COS.
> -Carlos
>
> --
> Carlos Mendioroz <tron_at_acm.org <mailto:tron_at_acm.org>
> <mailto:tron_at_acm.org <mailto:tron_at_acm.org>>>
>
>
> -----Original message-----
> From: Vincent Tay <vtay.75_at_gmail.com
> <mailto:vtay.75_at_gmail.com> <mailto:vtay.75_at_gmail.com
> <mailto:vtay.75_at_gmail.com>>>
> To: "Ccielab_at_groupstudy.com <mailto:Ccielab_at_groupstudy.com>
> <mailto:Ccielab_at_groupstudy.com <mailto:Ccielab_at_groupstudy.com>__>"
> <ccielab_at_groupstudy.com <mailto:ccielab_at_groupstudy.com>
> <mailto:ccielab_at_groupstudy.com <mailto:ccielab_at_groupstudy.com>__>>
> Sent: Sat, 26 May 2012, 05:36:38 GMT+00:00
> Subject: MLS QOS
>
> Hi all,
>
> I got the below questions to clarify.
>
> 1) When a cisco VoIP phone is connected to a switchport,
> which is
> better?
> mls qos trust dscp or mls qos trust cos?
>
> 2) The cisco phone will mark cos or dscp value or both? If
> mls qos trust
> cos is use, must i map the cos 5 to dscp 46 manually?
>
> Regards
> Vincent Tay
>
>
> Blogs and organic groups at http://www.ccie.net
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>
>
>
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>> LW7
> EQI Argentina
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net