Re: mls qos map policed-dscp

It will NOT happen by just entering mls qos trust dscp. You need to
configure the map manually.

On Sat, May 2, 2009 at 8:25 PM, Bryan Bartik <bbartik_at_ipexpert.com> wrote:

> Narbik,
>
> What do you mean "unless you change the mapping." There are default maps
> that will make the COS when you trust DSCP. I have tried it! :-)
>
>
> Bryan Bartik
> CCIE #23707, CCNP
> Sr. Support Engineer - IPexpert, Inc.
> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>
> On Sat, May 2, 2009 at 8:06 PM, Narbik Kocharians <narbikk_at_gmail.com>wrote:
>
>> *if I have interface with just mls qos trust dscp, if port receives packet
>>
>>
>> with for example DSCP 46, does it remark also COS field when it sends
>> packet
>> to anoter switch over trunk.*
>> *NO,* it does NOT, when you enter "mls qos trust dscp", it ONLY trusts the
>> DSCP value and it has NOTHING to do with CoS. UNLESS YOU change the
>> mapping.
>> That was your question and this is your answer. If in doubt, please try
>> it,
>> IOS WILL ALWAYS TELL YOU THE TRUTH.
>>
>> *Does mls qos map policed-dscp remark DSCP and COS field or just DSCP?*
>>
>> *NO,* it does NOT touch COS field at all. Unless its configured to do so.
>>
>> This is without twisting word around.
>> On Sat, May 2, 2009 at 1:40 PM, Petr Lapukhov
>> <petr_at_internetworkexpert.com>wrote:
>>
>> > Hi,
>> >
>> > In general, Catalyst switches implement "synchronous" marking logic:
>> > i.e. all potential
>> > QoS labels (L3,L2) are kept synchronized using the DSCP-to-CoS,
>> > CoS-to-DSCP and IP Prec-to-CoS
>> > global mapping tables. This is pretty natural if you think of
>> > "uniform" QoS marking model.
>> > In some cases it is possible to modify just one QoS marking point,
>> > keeping the other intact.
>> >
>> > See below for more details.
>> >
>> > > Does mls qos map policed-dscp remark DSCP and COS field or just DSCP?
>> >
>> > Yes, CoS is modified according to the DSCP-to-CoS mapping table (in
>> > both 3550 and 3560).
>> > You may avoid CoS modification while policing in the 3550 model by
>> > using the configuration
>> > similar to the following:
>> >
>> > mls qos cos policy-map
>> > !
>> > policy-map POLICE_INBOUND
>> > class ICMP
>> > trust dscp
>> > set cos 2
>> > police 64000 16000 exceed-action policed-dscp-transmit
>> >
>> > Here you trust DSCP values and set CoS at the same time. Setting CoS
>> > directly in policy-map in only
>> > possible in the 3550 model when enabled by the special global-mode
>> > command. The 3560 does
>> > not provide such flexibility, and most of the time it is not needed.
>> >
>> > > if I have interface with just mls qos trust dscp, if port receives
>> packet
>> > > with for example DSCP 46, does it remark also COS field when it sends
>> > packet
>> > > to anoter switch over trunk.
>> >
>> > Yes, by default CoS is modified according to the DSCP to CoS mapping
>> table.
>> > In the 3550 model you may avoid this behavior by enabling special CoS
>> > pass-thru mode:
>> >
>> > interface FastEthernet 0/4
>> > mls qos trust dscp pass-through cos
>> >
>> > (there is symmetric DSCP pass-thru mode, configured using the command
>> > "mls qos trust cos pass-through dscp")
>> >
>> > In the 3560 model, it is not possible to disable CoS rewrite. More
>> > than that, you have to set
>> > CoS values for non-IP packets by using the "set dscp" command, as there
>> is
>> > no "set cos" commad. Still, you can disable DSCP rewriting while
>> trusting
>> > CoS
>> > (mls qos trust cos) by entering the global command "no mls qos rewrite
>> ip
>> > dscp"
>> >
>> > HTH,
>> > --
>> > Petr Lapukhov, CCIE #16379 (R&S/Security/SP/Voice)
>> > petr_at_INE.com
>> >
>> > Internetwork Expert, Inc.
>> > http://www.INE.com <http://www.ine.com/> <http://www.ine.com/>
>> > Toll Free: 877-224-8987
>> > Outside US: 775-826-4344
>> >
>> > >
>> > >
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>> > >
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>> >
>>
>>
>> --
>> Narbik Kocharians
>> CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>> www.MicronicsTraining.com <http://www.micronicstraining.com/>
>> www.Net-Workbooks.com <http://www.net-workbooks.com/>
>> Sr. Technical Instructor
>>
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>>
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>
>
> --
>
>

-- 
Narbik Kocharians
CCSI#30832, CCIE# 12410 (R&S, SP, Security)
www.MicronicsTraining.com
www.Net-Workbooks.com
Sr. Technical Instructor
Blogs and organic groups at http://www.ccie.net