QoS Settings to Match SP Policer

[Chuan Liu]

Hi,

My SP has an ingress policer specifying 100mbps CIR and 256kbps Bc.

When I try to configure a shaper to match this requirement, I cannot specify a Bc value smaller than 400000, as the Tc cannot be less than 4ms. For example,

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OFFICE-01(config-pmap-c)#policy-map policy-map QoS-Outbound-100M

 OFFICE-01(config-pmap-c)#class class-default

  OFFICE-01(config-pmap-c)#shaper average 100000000 265000

Shaping Interval is 3 milliseconds. Intervals below 4 milliseconds rejected.

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If I use the  minimum Bc value of 400000bps, traffic might be dropped by the SP. Any workaround? The major application in the network is http.

Thanks.

Larry

[Akash Agrawal]

Hi Larry,

In shaper, Tc can not be configured for value lesser than 4ms. Better you ask your SP to modify the ingress service-policy. (that can easily be done). Also check with SP, what formula they are using to calculate Bc. They are setting Bc very low and with HTTP, we expect bursty traffic and need some larger Bc value.

Regards,

Akash
 

[Chuan Liu]

Thanks for the comment.

I got back from my SP that they provide the wrong number. 256kbps  is the Be value, not the Bc.

Best regards.

larry

[Joseph W. Doherty]

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Posting

Ah, well your provider should be able to also provide Bc and both may be in bytes.  Knowing both would allow you to configure your shaper to match their policer.

[Joseph W. Doherty · Accepted solution]

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

Bc isn't a per second value, it's a quantity of bits or bytes.

Also, Bc might be given in bytes, so double check whether your ISP's value is 256 KBytes or Kbits.

[Sunil Bhadauria · Accepted solution]

Hello Larry ,

I tried provided policer configuration in lab device : 

CIR = 100000000 bps

Bc = 256000 bps = 32000bytes

when i tried this configuration device corrected confirm burst to 50000 bytes :

#Conform burst size increased to 50000

which also leads to Tc = 50000 * 8 / 100000000 = 4ms 

So I am wondering how did provider achieved such low Bc . Are you sure it is not 256000 bytes , as confirm burst is configured in bytes .

Hope this helps .

Regards

Sunil Bhadauria