Fair enough. Maybe I am reading into the process too much and getting
confused. This is the diagram I was initially referencing. That command
below is outlined in it as well.
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12
.2_20_se/configuration/guide/swqos.html#wp1023954
On Sat, May 26, 2012 at 9:59 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:
> All the red marked text (for the list sake, the between asterisk in the
> DSCP paragraph) applies to non IP packets. Sure, non IP packets do not have
> DSCP to be looked at. But that's the exception, not the rule.
>
> -Carlos
>
> marc edwards @ 26/05/2012 13:55 -0300 dixit:
>
>> This is a good reference diagram for the process:
>>
>> Step 3
>>
>>
>>
>> *mls qos trust* [*cos* |*dscp* | *ip-precedence*]
>>
>>
>>
>>
>> Configure the port trust state.
>>
>> By default, the port is not trusted. If no keyword is specified, the
>> default is*dscp*.
>>
>>
>> The keywords have these meanings:
>>
>> *cos*Classifies an ingress packet by using the packet CoS value. For
>>
>> an untagged packet, the port default CoS value is used. The default port
>> CoS value is 0.
>>
>> *dscp*Classifies an ingress packet by using the packet DSCP value. For
>>
>> a non-IP packet, the packet CoS value is used if the packet is tagged;
>> for an untagged packet, the default port CoS is used. Internally, *the
>> switch maps the CoS value to a DSCP value by using the CoS-to-DSCP map*.
>>
>> *ip-precedence*Classifies an ingress packet by using the packet
>>
>> IP-precedence value. For a non-IP packet, the packet CoS value is used
>> if the packet is tagged; for an untagged packet, the default port CoS is
>> used. Internally, the switch maps the CoS value to a DSCP value by using
>> the CoS-to-DSCP map.
>>
>>
>> On Sat, May 26, 2012 at 9:22 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar
>> <mailto:tron_at_huapi.ba.ar>> wrote:
>>
>> 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<http://www.cisco.com/en
/US/__docs/solutions/Enterprise/WAN___and_MAN/QoS_SRND_40/QoSCampus___40.html
#wp1098549>
>>
>> <http://www.cisco.com/en/US/**docs/solutions/Enterprise/WAN_**
>>
and_MAN/QoS_SRND_40/QoSCampus_**40.html#wp1098549<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>
>> <mailto: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>>
>> <mailto: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>>
>> <mailto: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>>
>> <mailto: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**>__>
>> <mailto: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**
>> >__>
>> <mailto: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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>>
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>>
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<http://www.groupstudy.com/__**list/CCIELab.html<http://www.groupstudy.com/__
list/CCIELab.html>
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/CCIELab.html>
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>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar
>> <mailto:tron_at_huapi.ba.ar> <mailto:tron_at_huapi.ba.ar
>>
>> <mailto:tron_at_huapi.ba.ar>>> LW7
>> EQI Argentina
>>
>>
>>
>> --
>> 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
Received on Sat May 26 2012 - 10:10:23 ART
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