Re: QOS

From: Raghav Bhargava (raghavbhargava12@gmail.com)
Date: Tue Jan 20 2009 - 03:20:02 ARST

I got it ...Thanks Pavel....

/raghav

On Mon, Jan 19, 2009 at 9:10 PM, Pavel Bykov <slidersv@gmail.com> wrote:
> Visit any ISP and you'll see a ton of those.
> E.G. Transparently transporting DSCP of your customer's IP traffic without
> modifying it in your L2 network, be it local access, metro connections
> before tunnels, etc.
> Not changing markings in packet and creating identical PHBs can be an
> advantage. A lot of it is design decision and it really depends in what are
> you QoSing.
> Unless traffic it's XinQ (which is anything from QinQ to QinQinQinQ...) then
> transparancy is an important thing to consider.
>
>
> On Tue, Jan 20, 2009 at 6:00 AM, Raghav Bhargava
> <raghavbhargava12@gmail.com> wrote:
>>
>> I got it .. thanks everyone.. One last question what is the scenario
>> where we use it.
>>
>> thanks
>> /raghav
>>
>> On Mon, Jan 19, 2009 at 8:56 PM, Pavel Bykov <slidersv@gmail.com> wrote:
>> > When DSCP rewrite is off, that is the "transparancy mode".
>> >
>> >
>> > http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_46_se/configuration/guide/swqos.html#wp1331378
>> >
>> > Here is excerpt from Cisco to support my claims:
>> >
>> > !!!!!!!!!!!!!!! Begin Cisco.com Quote !!!!!!!!!!!!!!!
>> > In Cisco IOS Release 12.2(25)SE or later, the switch supports the DSCP
>> > transparency feature. It affects only the DSCP field of a packet at
>> > egress.
>> > By default, DSCP transparency is disabled. The switch modifies the DSCP
>> > field in an incoming packet, and the DSCP field in the outgoing packet
>> > is
>> > based on the quality of service (QoS) configuration, including the port
>> > trust setting, policing and marking, and the DSCP-to-DSCP mutation map.
>> >
>> > 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.
>> >
>> > Regardless of the DSCP transparency configuration, the switch modifies
>> > the
>> > internal DSCP value of the packet, which the switch uses to generate a
>> > class
>> > of service (CoS) value that represents the priority of the traffic. The
>> > switch also uses the internal DSCP value to select an egress queue and
>> > threshold.
>> >
>> > !!!!!!!!!!!!!!! End Cisco.com Quote !!!!!!!!!!!!!!!
>> >
>> > On Tue, Jan 20, 2009 at 5:25 AM, Raghav Bhargava
>> > <raghavbhargava12@gmail.com> wrote:
>> >>
>> >> 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
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> > _______________________________________________________________________
>> >> >> > Subscription information may be found at:
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>> >> >>
>> >> >>
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>> >> >>
>> >> >>
>> >> >> _______________________________________________________________________
>> >> >> Subscription information may be found at:
>> >> >> http://www.groupstudy.com/list/CCIELab.html
>> >> >>
>> >> >>
>> >> >>
>> >> >>
>> >> >>
>> >> >>
>> >> >>
>> >> >
>> >> >
>> >> >
>> >> > --
>> >> > Pavel Bykov
>> >> > ----------------
>> >> > Don't forget to help stopping the braindumps, use of which reduces
>> >> > value
>> >> > of
>> >> > your certifications. Sign the petition at
>> >> > http://www.stopbraindumps.com/
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> Warm Regards
>> >> Raghav
>> >
>> >
>> >
>> > --
>> > Pavel Bykov
>> > ----------------
>> > Don't forget to help stopping the braindumps, use of which reduces value
>> > of
>> > your certifications. Sign the petition at http://www.stopbraindumps.com/
>> >
>>
>>
>>
>> --
>> Warm Regards
>> Raghav
>
>
>
> --
> Pavel Bykov
> ----------------
> Don't forget to help stopping the braindumps, use of which reduces value of
> your certifications. Sign the petition at http://www.stopbraindumps.com/
> 

-- 
Warm Regards
Raghav

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