Re: shape on 3560

Addition of PQ on Cats completely messes things up for other queues
and understanding what happens in them.

Even without PQ in the mix, Carlos raises a valid question. Alas, one
which is impossible to answer.

He's right in saying that shaped queues get a priority in comparison
to shared. However, this priority is only reflected in the bandwidth
allocation part. They carve up the total available bandwidth. Whatever
is left for allocation after shaped queues is carved up by shared
queues.

Now, when it comes to dequeueing part, this is when things are truly
interesting. Carlos mentioned a case when the whole port is
oversubscribed and suggested how the queues will be used. I agree and
very much disagree with what he wrote. The problem is - it all depends
on several things a) time interval; b) number of packets in each
queue; c) size of each individual packet.

Remember the old CIR = Bc / Tc formula. Well, it still applies. We can
only send so many bytes in each time interval to satisfy to total
transmission rate.

Now, what happens when we oversubscribe the port *and* the queues.
Will packet be transmitted if there are available tokens in the
bucket, but not enough to send the packet? In, for example CQ, the
answer is yes. in CBWFQ and HQF, the answer is no. How about SRR?
Cisco doesn't document this (at least I couldn't find it), but this is
important. Now, what happens if, for example, we run out of bytes in
an interval to send due to dequeueing method used... Where does the
next interval start? Q1, or the next queue where the previous interval
stopped? Again, something Cisco doesn't document, but is rather
important.

Analyzing QoS is immensely fun topic to me. I think it's an essence of
networking, but I'll stop now :-). I have some wonderful sequoia trees
to see!

--
Marko Milivojevic - CCIE #18427
Senior Technical Instructor - IPexpert
FREE CCIE training: http://bit.ly/vLecture
Mailto: markom_at_ipexpert.com
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On Sun, Aug 7, 2011 at 12:04, Paul Negron <negron.paul_at_gmail.com> wrote:
> I agree with Marko on this one.
>
> The Delay cannot be verified to be 40/30/30 since you cannot measure how
> many packets from the Priority Q are actually being serviced in relation to
> the WFQ scheduler that only spits out one packet at a time.
>
> Also, what delay are you referencing for a 40/30/30 share. Queuing delay
> only?
>
> What about CPU, Serialization which change pending the packet size. Sure,
> Serialization delay is almost non-existent with Ethernet designs but it is
> still there. Thus, you cannot guarantee effective throughput.
>
> Paul
>
> --
> Paul Negron
> CCIE# 14856 CCSI# 22752
> Senior Technical Instructor
>
>
>
>> From: gp <gs4me2me_at_gmail.com>
>> Reply-To: gp <gs4me2me_at_gmail.com>
>> Date: Sun, 7 Aug 2011 20:16:40 +0200
>> To: 'Carlos G Mendioroz' <tron_at_huapi.ba.ar>, 'Marko Milivojevic'
>> <markom_at_ipexpert.com>
>> Cc: <ccielab_at_groupstudy.com>
>> Subject: RE: shape on 3560
>>
>> So queue which is shaped has guaranteed bandwidth in relation to shared
>> queues?
>>
>> Gp
>>
>>
>> -----Original Message-----
>> From: Carlos G Mendioroz [mailto:tron_at_huapi.ba.ar]
>> Sent: Sunday, August 07, 2011 8:05 PM
>> To: Marko Milivojevic
>> Cc: gp; <ccielab_at_groupstudy.com>
>> Subject: Re: shape on 3560
>>
>> Marko,
>> you say that all queues have guaranteed BW but not delay.
>> I don't fully understand that.
>>
>> Are you saying that the delay for a packet of some class is not bounded?
>> If not, delay is also guaranteed.
>>
>> If you have 3 queues, one with 50Mb shape and the other two 1/3 the BW
>> on a 100 Mb link, anything below congestion (and below 50Mb) will be
>> just served, but if the 3 queues try to get 40Mb, what will be the
>> effective throughput of each ?
>> I would say 40/30/30.
>>
>> -Carlos
>>
>> Marko Milivojevic @ 07/08/2011 14:22 -0300 dixit:
>>> All queues are guaranteed bandwidth, but not the delay. SRR is round-robin
>>> alghoritm. Shaped queues are assigned bandwidth first and whatever remains is
>>> used by shared queues, but servicing the data in queues is always equal
>>> between all the queues.
>>>
>>> When you enable PQ, Q1 is serviced until empty and only then Q2-4 are
>>> processed according to the SRR configuration and remaining bandwidth in the
>>> time interval.
>>>
>>> --
>>> Marko Milivojevic - CCIE #18427
>>> Senior Technical Instructor - IPexpert
>>>
>>> Free CCIE Training: http://bit.ly/vLecture
>>>
>>> Mailto: markom_at_ipexpert.com
>>> Telephone: +1.810.326.1444
>>> Community: http://www.ipexpert.com/communities
>>>
>>> :: Sent from my phone. Apologies for errors and brevity. ::
>>>
>>>
>>> On Aug 7, 2011, at 2:42, "gp" <gs4me2me_at_gmail.com> wrote:
>>>
>>>> I read somewhere that shaped queue is processed before shared. Unfortunately
>>>> cannot find it:)
>>>>
>>>> Is it possible to guaranteed some traffic bandwidth to be processed before
>>>> other with limit in task that it cannot be mapped in priority queue because
>>>> some other traffic more important is mapped to priority queue?
>>>>
>>>> For example:
>>>> Q1 - traffic X - priority
>>>> Q2 - traffic XY - less important than traffic X, more important than traffic
>>>> XYZ
>>>> Q3&Q4 - traffic XYZ
>>>>
>>>>
>>>> Regards,
>>>> Gp
>>>>
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: Marko Milivojevic [mailto:markom_at_ipexpert.com]
>>>> Sent: Saturday, August 06, 2011 10:46 PM
>>>> To: gp
>>>> Cc: ccielab_at_groupstudy.com
>>>> Subject: Re: shape on 3560
>>>>
>>>> Sharing and shaping has nothing to do with priority queueing. I.e.
>>>> shaped traffic is not processed before shared - it's only limited to
>>>> certain percentage of the traffic, while shared queues are simply
>>>> guaranteed a minimum.
>>>>
>>>> You can configure shaping as a percentage of negotiated speed, of
>>>> course. By default 100% of interface bandwidth (negotiated speed) is
>>>> available for all queues. If you want to limit Q2 to say, 33% you can
>>>> configure it as "srr-queue bandwidth shape 0 3 0 0". However, if you
>>>> want to limit it to say 5 Mb/s REGARDLESS of the negotiated speed,
>>>> this cannot be done on 3560, as this is a policing and policing is not
>>>> available in the outbound direction on 3560.
>>>>
>>>> --
>>>> Marko Milivojevic - CCIE #18427
>>>> Senior Technical Instructor - IPexpert
>>>>
>>>> FREE CCIE training: http://bit.ly/vLecture
>>>>
>>>> Mailto: markom_at_ipexpert.com
>>>> Telephone: +1.810.326.1444
>>>> Web: http://www.ipexpert.com/
>>>>
>>>> On Sat, Aug 6, 2011 at 13:19, gp <gs4me2me_at_gmail.com> wrote:
>>>>> Thank you Marko for explanation, it helps.
>>>>>
>>>>> What confusing me if I have a task to guaranteed some traffic for example
>>>>> 10Mbps on giga interface on switch, and I cannot use priority queue, so I
>>>>> want to send that traffic before packet in shared queue in way to put it in
>>>>> shaped queue which will be served before shared queues.
>>>>>
>>>>> The problem is that I donb t know what type of interface will be connected
>>>>> to my switch (1Gbps or 100M) and that is value from which will be
>>>>> calculated value for shaping on particular queue.
>>>>>
>>>>> For example:
>>>>> Negotiated speed = 1Gbps
>>>>> Srr-queue bandwidth shape 0 100 0 0
>>>>> Queue 2 will be shaped to 100Mbps
>>>>>
>>>>> Negotiated speed = 100Mbps
>>>>> Srr-queue bandwidth shape 0 100 0 0
>>>>> Queue 2 will be shaped to 10Mbps
>>>>>
>>>>> In other way as I understand there is no way to hard code shape value
>>>>> regarding to negotiated speed?
>>>>>
>>>>> Regards,
>>>>> Gp
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: Marko Milivojevic [mailto:markom_at_ipexpert.com]
>>>>> Sent: Saturday, August 06, 2011 7:42 PM
>>>>> To: gp
>>>>> Cc: ccielab_at_groupstudy.com
>>>>> Subject: Re: shape on 3560
>>>>>
>>>>> It will be using the bandwidth available to the SRR.
>>>>>
>>>>> Cat2#sh mls qos interface fa0/18 queueing
>>>>> FastEthernet0/18
>>>>> Egress Priority Queue : disabled
>>>>> Shaped queue weights (absolute) : B 25 0 0 0
>>>>> Shared queue weights B : B 25 25 25 25
>>>>> The port bandwidth limit : 100 B (Operational Bandwidth:100.0) <<<<<<<
>>>>> The port is mapped to qset : 1
>>>>>
>>>>> See the "port bandwidth limit" line - that's the BW available to the
>>>>> SRR. It is derived from the negotiated speed by default, but can be
>>>>> limited using "srr-queue bandwidth limit" command on the interface.
>>>>>
>>>>> Now, let's see if configured bandwidth influences this in any way:
>>>>>
>>>>> interface FastEthernet0/18
>>>>> bandwidth 50000
>>>>> !
>>>>>
>>>>> Cat2(config-if)#do sh mls qos int fa0/18 qu
>>>>> FastEthernet0/18
>>>>> Egress Priority Queue : disabled
>>>>> Shaped queue weights (absolute) : B 25 0 0 0
>>>>> Shared queue weights B : B 25 25 25 25
>>>>> The port bandwidth limit : 100 B (Operational Bandwidth:100.0)
>>>>> The port is mapped to qset : 1
>>>>>
>>>>> Doesn't look like it does. If I change the bandwidth limit.
>>>>>
>>>>> interface FastEthernet0/18
>>>>> bandwidth 50000
>>>>> srr-queue bandwidth limit 25
>>>>> !
>>>>>
>>>>> Cat2(config-if)#do sh mls qos int fa0/18 qu
>>>>> FastEthernet0/18
>>>>> Egress Priority Queue : disabled
>>>>> Shaped queue weights (absolute) : B 25 0 0 0
>>>>> Shared queue weights B : B 25 25 25 25
>>>>> The port bandwidth limit : 25 B (Operational Bandwidth:27.28)
>>>>> The port is mapped to qset : 1
>>>>>
>>>>> Whenever in doubt - ask IOS :-)
>>>>>
>>>>> --
>>>>> Marko Milivojevic - CCIE #18427
>>>>> Senior Technical Instructor - IPexpert
>>>>>
>>>>> FREE CCIE training: http://bit.ly/vLecture
>>>>>
>>>>> Mailto: markom_at_ipexpert.com
>>>>> Telephone: +1.810.326.1444
>>>>> Web: http://www.ipexpert.com/
>>>>>
>>>>> On Sat, Aug 6, 2011 at 01:18, gp <gs4me2me_at_gmail.com> wrote:
>>>>>> Hello experts,
>>>>>>
>>>>>>
>>>>>>
>>>>>> When doing shaping on 3560 interface does reference bandwidth is
>>>>>> configured
>>>>>> bandwidth with bandwidth command or negotiated speed?
>>>>>>
>>>>>>
>>>>>>
>>>>>> For example the switch port is connected on Fast Ethernet router interface
>>>>>> and I configured bandwidth 1000000 on switch port.
>>>>>>
>>>>>> With srr-queue bandwidth shape 0 100 0 0, will queue 2 be shaped on 10 or
>>>>>> 1
>>>>>> Mbps?
>>>>>>
>>>>>>
>>>>>>
>>>>>> Thank you!
>>>>>>
>>>>>>
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>>
>> --
>> Carlos G Mendioroz B <tron_at_huapi.ba.ar> B LW7 EQI B Argentina
>>
>>
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