02-19-2011 09:00 AM - last edited on 01-19-2023 02:14 AM by Translator
Hello,
Am I correctly understand that 2 commands
shape peak 64000
and
shape average 128000
have the same meaning?
Do anybody know for what purpose Cisco implemented Peak Shaping?
Solved! Go to Solution.
02-20-2011 03:37 AM - last edited on 01-19-2023 02:27 AM by Translator
Hello,
Personally, I would not say that
shape peak 64000
and
shape average 128000
yield the same results. It has been correctly explained that the
shape peak
shapes at a higher rate because every Tc, there are Bc+Be tokens replenished into the token bucket, and thus, the overall traffic rate is
Real Shaping Rate = Configured Rate x (1 + Be/Bc)
This Real Shaping Rate of the
shape peak
can never be exceeded because you can never send more than Bc+Be bytes in an interval of Tc. Indeed, with default settings, Bc=Be, and thus the Real Shaping Rate is doubled. The
shape peak
essentially allows you to use both the committed and excess rate every Tc interval, and you therefore get sustained CIR+EIR rate.
The
shape average
replenishes only Bc tokens per Tc interval. Thus, the
shape average 128000
allows you for sustained rate of 128 kbps. However, after a longer period of low activity, when you accumulate enough excess tokens, you can actually burst up to the Bc+Be rate. Again, with the default settings, Bc=Be and thus the bursting would go up to 256 kbps.
Therefore, the
shape peak 64000
and
shape average 128000
are not equal. The
peak
will shape consistently to 128 kbps, never more, and it will allow to consistently send traffic in excess of the CIR. The
average
will shape the traffic to 128 kbps, along with allowing bursts up to 256 kbps after periods of no or low activity. Clearly, the bursting in
average
would in this case exceed even the PIR configured by your provider.
Best regards,
Peter
02-19-2011 09:58 AM
Sorry for not answering your question directly but google is your friend here. There are lots of link with exmaples and explanations.
Regards,
Ian
02-19-2011 03:38 PM - last edited on 01-19-2023 02:20 AM by Translator
Hi Kondratev,
Yes technically they yield the same..
shape peak 64000
actually has a sending rate of 128000 because the Bc=Be. so
shape average 128000
is the same as
shape peak 64000
Now, to answer why and where
shape peak
can be used
For eg:
If the SP sells you a link with PIR=128000 and CIR=64000, then you cannot use the
shape average 128000
You have to use
shape peak 64000
If the SP sells you a link with PIR=CIR=128000 then you can use either
shape average 128000
or
shape peak 64000
however i recommend
shape average
in this case.
HTH,
Regards,
Please rate if helpful
02-20-2011 01:48 AM - last edited on 01-19-2023 02:21 AM by Translator
Hi Kishore,
I don't understand why I can't use average shaping if SP sells me a link with PIR=128000 and CIR=64000?
I think I can use
shape average 128000
in this case. Am I right?
02-20-2011 02:53 AM
Hi Kondratev,
kondratev wrote:
Hi Kishore,
I don't understand why I can't use average shaping if SP sells me a link with PIR=128000 and CIR=64000?
I think I can use 'shape average 128000' in this case. Am I right?
you can use it but remember that the CIR is still 64000 and SP will police it at their end and start dropping packets during congestion and limit your traffic to 64000 and you will have retransmissions and latency. They will let you burst up to the PIR once you accumulate enough tokens when using the shape average
Please see the below link which will provide you some good info about how the SP's sell PIR etc.
http://blog.ine.com/2008/08/26/understanding-the-shape-peak-command/
HTH
Regards,
Please rate if helpful
02-20-2011 03:37 AM - last edited on 01-19-2023 02:27 AM by Translator
Hello,
Personally, I would not say that
shape peak 64000
and
shape average 128000
yield the same results. It has been correctly explained that the
shape peak
shapes at a higher rate because every Tc, there are Bc+Be tokens replenished into the token bucket, and thus, the overall traffic rate is
Real Shaping Rate = Configured Rate x (1 + Be/Bc)
This Real Shaping Rate of the
shape peak
can never be exceeded because you can never send more than Bc+Be bytes in an interval of Tc. Indeed, with default settings, Bc=Be, and thus the Real Shaping Rate is doubled. The
shape peak
essentially allows you to use both the committed and excess rate every Tc interval, and you therefore get sustained CIR+EIR rate.
The
shape average
replenishes only Bc tokens per Tc interval. Thus, the
shape average 128000
allows you for sustained rate of 128 kbps. However, after a longer period of low activity, when you accumulate enough excess tokens, you can actually burst up to the Bc+Be rate. Again, with the default settings, Bc=Be and thus the bursting would go up to 256 kbps.
Therefore, the
shape peak 64000
and
shape average 128000
are not equal. The
peak
will shape consistently to 128 kbps, never more, and it will allow to consistently send traffic in excess of the CIR. The
average
will shape the traffic to 128 kbps, along with allowing bursts up to 256 kbps after periods of no or low activity. Clearly, the bursting in
average
would in this case exceed even the PIR configured by your provider.
Best regards,
Peter
02-20-2011 12:30 PM
Thank you, Peter!
You explanation is very clear!
05-24-2011 06:35 PM - last edited on 01-19-2023 02:30 AM by Translator
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
Therefore, the shape peak 64000 and shape average 128000 are not equal. The peak will shape consistently to 128 kbps, never more, and it will allow to consistently send traffic in excess of the CIR. The average will shape the traffic to 128 kbps, along with allowing bursts up to 256 kbps after periods of no or low activity. Clearly, the bursting in average would in this case exceed even the PIR configured by your provider.
Shape peak 64000
will shape consistently to 128 Kbps?
Shape average 128000
will allow bursts up to 256000?
My understanding, for most shapers (or policers) was peak allowed bursting (using Be) but sustained would still be what's provided by Bc. Researched this a bit and found http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a00800a3a25.shtml#tokenrefreshrate, which notes Bc tokens replenishment per Tc. Similar info here: http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qcpolts.html#wp6991.
This is something that would be interesting to try in a lab; one method I've found to fully confirm how a Cisco feature works (at least for a specific IOS version and platform).
05-25-2011 01:50 PM - last edited on 01-19-2023 02:37 AM by Translator
Hello Kondratev.
They do not have the same meaning.
shape peak 64000
simply means you are shaping around a CIR of 64000. If you leave this command as is, then you will have a
peak
information rate of 128kbps, but this is best effort and will only be available when there is no congestion in the ISP cloud.
the command is
shape peak
bc be In the above case 64000 is the CIR.
Based on an agreement with your service provider, the CIR provides you with how many bits you can send per 1 second.
By default this 1 second is divided into 8 intervals. That is .125 seconds per interval. The bc is simply how much traffic you can send per interval based on the CIR. The bc in this case is simply the CIR divided by the number of intervals (8). You can change the bc value if you want.
be is equal to bc if you dont configure it. be is the excess burst used to calculate the
peak
information rate.
PIR = CIR x [1 + (be/bc)] --- Since by default bc is equal to be that means by default PIR = CIR x 2
So in the above scenario, the
peak
information rate would be 128kbps (CIR x 2)
sometimes a service provider offers you 2 rates for sending traffic. In this case, they will offer you a
peak
information rate (PIR) and a committed information rate (CIR). The CIR is a guaranteed traffic rate under the agreement. The PIR is best effort, no guarantee. The service provider will allow you to send traffic at rates up to PIR, but only guarantees CIR rate in case of network congestion.
so
shape peak 64000
guarantees a CIR of 64000 and offers best effort PIR of 128000 when there is no congestion in the ISP cloud.
while
shape average 128000
offers a guarantee of 128000bps.
Of course if the ISP guarantees you 128000bps in your agreement and they honor their agreement, then
shape peak 64000
would work with no issue because you will be able to send traffic at
peak
rate all the time. But if the ISP is not honoring their agreement of 128000, your router will drop its rate to 64000bps when there is congestion and in this case the misconfiguration will be costly.
pls rate if it helps!
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide