Re: QoS quiz

Well, according to the docs shaping uses FIFO by default which can be
changed to either WFQ or any queuing under nested service-policy.

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6558/white_paper_c11-481499.html

Default Queuing Implementation for the Shape Feature

When you configure the shape command in a class, the default queuing
behavior for the shape queue is FIFO instead of WFQ. You can configure
the bandwidth, fair-queue, or service-policy commands in shape class to
achieve different queuing behaviors.

I can test it in our prof of concept lab but I am quite sure it will
play out exactly that way or else it would be quite a miss by Cisco :-)

Cheers,
A.

On 6/20/2011 9:57 PM, Carlos G Mendioroz wrote:
> Alexei,
> what you describe is what would happen with only one policy at the port,
> which is not the case. When you have parent/child, you basically
> "create" a serial setup where the parent output becomes the child input.
>
> The parent is doing shapping for ALL traffic without classification.
> And it's a FIFO queue. So when it kicks in (rate above shape rate) you
> start delaying all traffic.
>
> Don't take my word, test it. May be there's some way to make it work,
> but I don't know it!
>
> -Carlos
>
> Alexei Monastyrnyi @ 20/06/2011 05:23 -0300 dixit:
>> Carlos
>> I don't think this is the case.
>>
>> In case of shaping buffer not empty the packet which is about to
>> egress would go into scheduler and based on its marking it would be
>> placed into the right queue, in you case in either LLQ or the
>> class-default one. Now if it is a voice packet scheduled for LLQ it
>> will egress as soon as it can regardless of class-default queue being
>> full or not (well, up to the priority XYZ value, where it will be
>> policed, and we are not taking serialization into account here as all
>> is happening at FE speed).
>>
>> So I reckon your voice traffic should be just fine. I may be missing
>> something so please correct me if I am wring.
>>
>> Cheers
>> A.
>>
>>
>> On 6/18/2011 8:35 AM, Carlos G Mendioroz wrote:
>>> The problem with this configuration, which AFAIK is "by the book",
>>> is that it does not protect the Voip stream.
>>>
>>> If you have a data stream that is going over your shape rate,
>>> the shape buffer will be full and your voip traffic has to cross it!
>>> (Read, you will have jitter at best, lost packets more than likely)
>>>
>>> -Carlos
>>>
>>> David Prall @ 17/06/2011 18:49 -0300 dixit:
>>>> Carlos,
>>>> So I would do:
>>>> Class-map match-all voice
>>>> Match protocol rtp
>>>> Match dscp ef
>>>> Policy-map child
>>>> Class voice
>>>> Priority percent 25
>>>> Class class-default
>>>> Bandwidth remaining percent 100
>>>> Set dscp 0
>>>>
>>>> David
>>>>
>>>> --
>>>> http://dcp.dcptech.com
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Carlos G Mendioroz [mailto:tron_at_huapi.ba.ar]
>>>>> Sent: Friday, June 17, 2011 5:40 PM
>>>>> To: David Prall
>>>>> Cc: 'Cisco certification'
>>>>> Subject: Re: QoS quiz
>>>>>
>>>>> Right.
>>>>> This is *one* thing I left out. All traffic should be marked.
>>>>> -Carlos
>>>>>
>>>>> David Prall @ 17/06/2011 18:31 -0300 dixit:
>>>>>> You are matching on RTP, is all RTP already marked EF? You are using
>>>>> shape
>>>>>> average to provide artificial back-pressure at 2Mbps. You have
>>>>> provided for
>>>>>> 500Kbps within the 2Mbps so you will be fine as long as the carrier
>>>>> is
>>>>>> providing priority for the RTP traffic, if they are providing
>>>>> priority for
>>>>>> EF then you need to confirm that the application is setting EF or
>>>>> remark the
>>>>>> traffic on your own to EF. You also need to confirm that the traffic
>>>>> that is
>>>>>> not RTP, is not marked EF, otherwise the SP will put it into
>>>>>> their EF
>>>>> queue
>>>>>> along with your RTP EF traffic, so remarking the class-default to 0
>>>>> may help
>>>>>> here.
>>>>>>
>>>>>> David
>>>>>>
>>>>>> --
>>>>>> http://dcp.dcptech.com
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On
>>>>>>> Behalf
>>>>> Of
>>>>>>> Carlos G Mendioroz
>>>>>>> Sent: Friday, June 17, 2011 5:05 PM
>>>>>>> To: Cisco certification
>>>>>>> Subject: QoS quiz
>>>>>>>
>>>>>>> Easy one, I would think.
>>>>>>>
>>>>>>> Say you have a wan link provided over metro (i.e. access rate is
>>>>> well
>>>>>>> over your contracted BW) and you want to apply QoS to protect your
>>>>>>> Voip.
>>>>>>>
>>>>>>> You have 2Mbps contract, 25% limit on EF marked traffic.
>>>>>>>
>>>>>>> Will this config do the right thing (i.e. protect your voip traffic
>>>>>>> from jitter caused by your data) ?
>>>>>>>
>>>>>>> class-map voice
>>>>>>> match protocol rtp
>>>>>>>
>>>>>>> policy-map child
>>>>>>> class voice
>>>>>>> priority 500
>>>>>>> class class-default
>>>>>>> bandwidth remaining percent 100
>>>>>>>
>>>>>>> policy-map parent
>>>>>>> class class-default
>>>>>>> shape average 2000000
>>>>>>> service-policy child
>>>>>>>
>>>>>>> inferface fastEthernet0/0
>>>>>>> service-policy output parent
>>>>>>>
>>>>>>> --
>>>>>>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>>>>>>
>>>>>>>
>>>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>>>
>>>>>>>
>>>>> _______________________________________________________________________
>>>>>
>>>>>>> Subscription information may be found at:
>>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>> --
>>>>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina

Blogs and organic groups at http://www.ccie.net
Received on Mon Jun 20 2011 - 22:23:33 ART