From: maureen schaar (maureen.schaar@gmail.com)
Date: Thu Mar 29 2007 - 08:34:44 ART
Thanks Stefaan! It's perfectly clear now.
Have a nice day.
Maureen
On 3/29/07, Stefaan Vander Rasieren <svanderr@cisco.com> wrote:
>
> Hi Maureen,
>
> Very interesting questions, indeed. Let me split my comment in 2.
>
> 1) shape peak vs shape average :
> I think this link explains it pretty briefly :
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t2/clsbsshp.htm#wp1019894
>
> When you configure 'shape average <cir> <bc> <be>', your CIR will not
> change regardless what you configure for bc or be. bc and be parameters
> dimension a token bucket, which is the model used for traffic shaping. bc
> is the size of the token bucket and be is the extra size you allow the
> bucket to grow (i.e. by using leftover tokens not used before). On average
> you always shape to CIR.
>
> When you configure 'shape peak <cir> <bc> <be>', your CIR will change
> depending on the be parameter based on the following formula :
> peak rate = CIR(1+Be/Bc). So, if you configure be=0, then your peak rate
> (=actual cir) will = the configured CIR. In essence this configuration
> actually implements the same as a 'shape average' with be always =0. I do
> not believe this configure is often used as the actual CIR is not the one
> you configure and often leads to confusion. As someone said on the list, it
> was intended for users to allow to send at higher rates than the guaranteed
> CIR provided by ISPs, but in reality, if the ISP polices your traffic, it
> can even have an adverse effect.
>
>
> 2) CBWFQ and CBshaping :
>
> There are 2 ways one can configure CBshaping together with CBWFQ. You can
> configure both features (bandwidth and shape command) under the same class
> in the policy-map config, like this :
>
> policy-map test
> class test
> bandwidth percent 30
> shape average 40000000
>
> interface GigabitEthernet0/0
> <snip>
> service-policy output test
>
> Here you guarantee a minimum bandwidth for class test of 30% of the
> interface bandwidth and put an upper limit of bandwidth usage for this class
> to 40M. This is a working and supported config.
>
> The second possible config is when using hierarchical policy-maps. Sample
> config like this :
>
> policy-map child
> class test
> bandwidth percent 30
> policy-map parent
> class class-default
> shape average 40000000
> service-policy child
>
> Here you are guaranteeing 30% of the shaper bandwidth (40M) to class test.
> In this scenario you are actually modeling the shaper queues in the child
> policy-map.
>
> Hope this helps,
>
> Stef
>
> maureen schaar wrote:
> I do believe shape peak can send no more that 512 Kbps and not 1024,
> whereas shape average can send no more than 256 Kbps (but still the
> counters in show policy map int disturb me).
>
> The example you quoted from the doccd:
>
> bandwidth 300
> shape peak 512000
>
> brings me to another issue regarding parent and child policy maps. If
> you were to use this configuration with a bandwidth percent instead
> of an absolute value, you would have to use a hierarchical policy-map
> and the configuration above would not work. I have labbed it up and
> put the results below.
>
> Doccd reference:
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hqos_c/part20/ch10/qsbcbts.htm#wp1046398
>
> Quote/
> If you want to use CBWFQ with the Class-Based Traffic Shaping
> mechanism, the following conditions must be met:
>
> A secondary-level (child) policy map must be created. This
> secondary-level (child) policy map is then used to configure CBWFQ by
> enabling the bandwidth command.
>
> Traffic shaping must be configured in the primary-level (parent) policy
> map.
>
> Note CBWFQ is supported in both the primary-level (parent) policy map
> and the secondary-level (child) policy map. However, to use CBWFQ at
> the secondary-level (child) policy map, traffic shaping must be
> configured in the primary-level (parent) policy map.
> /Unquote
>
> Now the last note sounds like a contradiction to me with the first
> bullet. If I want to use cbwfq and shaping, do I have to create a
> parent and child policy? We will test what happens.
>
> In that analogy, this configuration would be false:
>
> policy-map SHAPE
> class class-default
> shape average 100000
> bandwidth percent 80 --> this is not 80% from the shaped rate, but
> 80% of the interface bandwidth
>
> Now if I apply this policy-map, I get an error saying I am crossing
> the max-reserved (75%) limit:
> W2R5(config-if)#service-policy output PARENT
> I/f Serial1/0 class class-default requested bandwidth 80%, available only
> 75%
>
> This is pointing out that you are not using the shaped rate, but the
> interface bandwidth.
>
> So I changed the bandwidth percent to 60, to see what happened:
>
> W2R5#sh policy-map int
> Serial1/0
>
> Service-policy output: PARENT
>
> Class-map: class-default (match-any)
> 1 packets, 63 bytes
> 5 minute offered rate 0 bps, drop rate 0 bps
> Match: any
> Traffic Shaping
> Target/Average Byte Sustain Excess Interval Increment
> Rate Limit bits/int bits/int (ms) (bytes)
> 100000/100000 2000 8000 8000 80 1000
>
> Adapt Queue Packets Bytes Packets Bytes Shaping
> Active Depth Delayed Delayed Active
> - 0 1 63 0 0 no
> Queueing
> Output Queue: Conversation 41
> Bandwidth 60 (%)
> Bandwidth 76 (kbps)Max Threshold 64 (packets)
> (pkts matched/bytes matched) 1/63
> (depth/total drops/no-buffer drops) 0/0/0
>
> --> NOTE: As I suspected: you are allocating 60% of the interface
> bandwidth (12800) not of the shaped rate!
>
> If I turn this into a parent/child situation, this happens:
>
> policy-map child
> class class-default
> bandwidth percent 80 --> this is 80% from the shaped rate
> policy-map SHAPE
> class class-default
> shape average 1000000
> service-policy child
>
> W2R5#sh policy-map int
> Serial1/0
>
> Service-policy output: PARENT
>
> Class-map: class-default (match-any)
> 25 packets, 721 bytes
> 5 minute offered rate 0 bps, drop rate 0 bps
> Match: any
> Traffic Shaping
> Target/Average Byte Sustain Excess Interval Increment
> Rate Limit bits/int bits/int (ms) (bytes)
> 100000/100000 2000 8000 8000 80 1000
>
> Adapt Queue Packets Bytes Packets Bytes Shaping
> Active Depth Delayed Delayed Active
> - 0 9 513 0 0 no
>
> Service-policy : child
>
> Class-map: class-default (match-any)
> 25 packets, 721 bytes
> 5 minute offered rate 0 bps, drop rate 0 bps
> Match: any
> Queueing
> Output Queue: Conversation 25
> Bandwidth 80 (%)
> Bandwidth 80 (kbps)Max Threshold 64 (packets)
> (pkts matched/bytes matched) 0/0
> (depth/total drops/no-buffer drops) 0/0/0
>
> Now I see that 80% of the shaped rate is allocated to the child policy-map.
>
> FINAL QUESTION: does anyone think you have to use a hierarchical
> policy-map also when using an absolute value for bandwidth? I still
> don't quite get it with the mentioned contradiction in the doccd.
>
>
> Thanks for all your help so far!
>
> Maureen
>
> On 3/29/07, Gary <liguoyi8@gmail.com> wrote:
>
>
>
>
>
> This link is from Cisco DocCD
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hqos_r/qos_s1h.htm#wp1085303
>
> The following example uses peak rate shaping to ensure a bandwidth of 300
> kbps but allow throughput up to 512 kbps if enough bandwidth is available
> on
> the interface:
> bandwidth 300
>
>
> shape peak 512000
>
> If "shape peak 512000" is used, the throughput should be up to 2x512k =
> 1024k. So is it an error here?
> If in the lab, question asks to "allow throughput up to 512 kbps", which
> one
> is correct?
> shape average 512000
> or
> shape peak 512000?
>
>
>
> ________________________________
> From: Blastmor [mailto:alextols@gmail.com]
> Sent: Thursday, March 29, 2007 2:32 PM
> To: Gary
> Cc: maureen schaar; Cisco certification
> Subject: Re: shape average vs shape peak
>
>
> Shape peak is rather useless now.
>
> The case when you can use it, for instance, is when provider allows you to
> burst but you are warned that your traffic can be dropped at any time (when
> ISP is congested) --> so you can use it when your traffic is
> "steady" for jitter and losses(FTP, SMTP and so on)
>
> HTH
>
>
> 2007/3/29, Gary <liguoyi8@gmail.com>:
> > I am confused by average & peak too.
> > According to DocCD, the syntax is : shape peak cir
> > By default be=bc. So the target rate is two times cir.
> > So when should we use "shape peak" and when should we use "shape
> average"?
> >
> >
>
>
> SY, Alexey
>
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