What does "shape average percent" mean in the QOS policy

Answered Question
Jan 4th, 2010
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I am working at a client site that is an MPLS customer.  The customer has an MPLS circuit that runs between their Main HQ and their Disaster Recovery site.  I have been asked to analyze and report as well on the way the Qos Policy is written, and to provide any recommendations on how they can improve performance.

There is a statement within the Qos Policy as it exists at each end on the 3825 routers.  The statement is called "shape average percent".  Here is the policy from one side:


policy-map QoS

  class COS2_traffic

   set dscp af31

    shape average percent 12

    bandwidth percent 13

  class COS3_traffic

    set dscp af21

     shape average percent 27

     bandwidth percent 28

     random detect dscp-based

  class class-default

     fair-queue

      random detect


What does this statement mean and how is it different than the the "bandwidth percent" statement?


Thanks

Kevin

Correct Answer by Jon Marshall about 7 years 2 months ago

k-melton wrote:


I am working at a client site that is an MPLS customer.  The customer has an MPLS circuit that runs between their Main HQ and their Disaster Recovery site.  I have been asked to analyze and report as well on the way the Qos Policy is written, and to provide any recommendations on how they can improve performance.

There is a statement within the Qos Policy as it exists at each end on the 3825 routers.  The statement is called "shape average percent".  Here is the policy from one side:


policy-map QoS

  class COS2_traffic

   set dscp af31

    shape average percent 12

    bandwidth percent 13

  class COS3_traffic

    set dscp af21

     shape average percent 27

     bandwidth percent 28

     random detect dscp-based

  class class-default

     fair-queue

      random detect


What does this statement mean and how is it different than the the "bandwidth percent" statement?


Thanks

Kevin


Kevin


The bandwidth percent is a minimum bandwidth guarantee so if there is spare bandwidth that can be used from other classes it will be used.

The shape average percent is a maximum bandwidth guarantee so any packets above that bandwidth will be queued and sent when there is spare bandwidth within that class.


So they are doing 2 fundamentally different things.


Jon

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Correct Answer
Jon Marshall Mon, 01/04/2010 - 07:59
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k-melton wrote:


I am working at a client site that is an MPLS customer.  The customer has an MPLS circuit that runs between their Main HQ and their Disaster Recovery site.  I have been asked to analyze and report as well on the way the Qos Policy is written, and to provide any recommendations on how they can improve performance.

There is a statement within the Qos Policy as it exists at each end on the 3825 routers.  The statement is called "shape average percent".  Here is the policy from one side:


policy-map QoS

  class COS2_traffic

   set dscp af31

    shape average percent 12

    bandwidth percent 13

  class COS3_traffic

    set dscp af21

     shape average percent 27

     bandwidth percent 28

     random detect dscp-based

  class class-default

     fair-queue

      random detect


What does this statement mean and how is it different than the the "bandwidth percent" statement?


Thanks

Kevin


Kevin


The bandwidth percent is a minimum bandwidth guarantee so if there is spare bandwidth that can be used from other classes it will be used.

The shape average percent is a maximum bandwidth guarantee so any packets above that bandwidth will be queued and sent when there is spare bandwidth within that class.


So they are doing 2 fundamentally different things.


Jon

Santosh Shetty Tue, 06/19/2012 - 20:28
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I have a query, in above example how these command workd together



shape average percent 27                 << is this 27% of total BW available?

bandwidht percent 28                     


As per the above explanation it's look like Min BW allocated is 28% and Maximum 27%. Should it not be Min BW value lower than Max BW value?

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