From: Raghav Bhargava (raghavbhargava12@gmail.com)
Date: Tue Jan 20 2009 - 02:25:56 ARST
Hi Pavel,
So where does DSCP Transparent mode comes into picture. I agree with your steps.
Please shed some more light as it is becoming interesting now..
thanks
/raghav
On Mon, Jan 19, 2009 at 8:14 PM, Pavel Bykov <slidersv@gmail.com> wrote:
> Darby:
> *Cat3560(config-if)# mls qos trust [cos | dscp ] does the same thing per
> interface*
>
> No, I don't think it does. This command sets the trust mode. Here is my
> understanding of it with quick example with trust CoS and DSCP rewrite
> (without complicating thing too much).
>
> 1.
> Trust setting: Trust CoS
> DSCP rewrite setting: OFF
> Incoming Packet: Cos = 0, DSCP = 46
>
> Packet comes in, CoS > DSCP map is 0 > 0. Internally, CoS is 0, DSCP is also
> 0. Queue is selected based on that. Packet is placed into a Queue with CoS
> 0, but since rewrite was off, DSCP was left the same at 46.
> Output Packet: CoS = 0, DSCP = 46
>
> 2.
> Trust setting: Trust CoS
> DSCP rewrite setting: ON
> Incoming Packet: Cos = 0, DSCP = 46
>
> Packet comes in, CoS > DSCP map is 0 > 0. Internally, CoS is 0, DSCP is also
> 0. Queue is selected based on that. Packet is placed into a Queue with CoS
> 0.
> Since rewrite is on, DSCP is set to calculated value, i.e. 0
> Output Packet: CoS = 0, DSCP = 0
>
> 3.
> Trust setting: Trust DSCP
> DSCP rewrite setting: OFF
> Incoming Packet: Cos = 0, DSCP = 40
>
> Packet comes in, DSCP > Internal DSCP map is used, where 40 maps to 46.
> Queue is selected based on that. Packet is placed into a Queue with CoS,
> that is calculated from DSCP > CoS map, where 46 maps to 5. Notice, 46 is
> used for calculation.
> But since rewrite is off, 40 is left in the header. DSCP is not set to
> calculated value.
> Output Packet: CoS = 0, DSCP = 40
>
> 4.
> Trust setting: NO TRUST (default)
> DSCP rewrite setting: OFF
> Incoming Packet: Cos = 0, DSCP = 46
>
> Packet comes in, CoS > DSCP map is 0 > 0. Internally, CoS is 0, DSCP is also
> 0. Queue is selected based on that. Packet is placed into a Queue with CoS
> 0.
> Since rewrite was off, DSCP was left the same at 46.
> Output Packet: CoS = 0, DSCP = 46
>
>
>
> On Tue, Jan 20, 2009 at 12:33 AM, Darby Weaver <ccie.weaver@gmail.com>
> wrote:
>>
>> *DSCP Transparency *
>>
>> *DSCP Transparency is a Cat3560 feature.*
>>
>> Global command that is disabled by default. If DSCP transparency is
>> enabled
>> by using the no mls qos rewrite ip dscp command, the switch does not
>> modify
>> the DSCP field in the incoming packet, and the DSCP field in the outgoing
>> packet is the same as that in the incoming packet.
>>
>> Cat3560(config)# mls qos rewrite ip dscp
>>
>> disable DSCP transparency to allow switch to modify DSCP values based on
>> trust or ACL
>>
>> -OR-
>>
>> Cat3560(config)# no mls qos rewrite ip dscp
>>
>> Cat3560(config-if)# mls qos trust [cos | dscp ] does the same thing per
>> interface
>>
>> *Passthrough Option is a 3550 Feature:*
>>
>> Cat3550(config-if)# mls qos trust [cos | dscp] pass-through [ dscp | cos]
>>
>> Forces Cat to treat CoS and DSCP independently. So, it trusts one and
>> doesn't change the other marked as pass-through.
>>
>>
>>
>> On 1/19/09, Raghav Bhargava <raghavbhargava12@gmail.com> wrote:
>> >
>> > HI experts,
>> >
>> > I am not able to understand to the DSCP Transparency Mode in QOS. Can
>> > anyone shed some light on it.
>> > I am studying it from the Configuration Guide of Catalyst 3560.
>> >
>> > --
>> > Warm Regards
>> > Raghav
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
>> > _______________________________________________________________________
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>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>>
>>
>>
>>
>>
>>
>>
>
>
>
> --
> Pavel Bykov
> ----------------
> Don't forget to help stopping the braindumps, use of which reduces value of
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>
-- Warm Regards RaghavBlogs and organic groups at http://www.ccie.net
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